EP4158801A1 - Polarization-diversity optical power supply - Google Patents

Abstract

Provided is an optical communication system comprising a polarization-diversity optical power supply capable of supplying light over a non-polarization-maintaining optical fiber to a polarization-sensitive modulation device. In an example embodiment, the polarization-diversity optical power supply operates to accommodate random polarization fluctuations within the non-polarization-maintaining optical fiber and enables an equal-power split at a passive polarization splitter preceding the polarization-sensitive modulation device.

Description

POLARIZATION-DIVERSITY OPTICAL POWER SUPPLY

CROSS-REFERENCE TO RELATED APPLICATION

[1] This application is a continuation-in-part of and claims priority to U.S. patent application 16/888,890, filed on June 1, 2020, the entire content of which is herein incorporated by reference. This application claims priority to U.S. provisional patent application 63/145,368, filed on February 3, 2021, the entire content of which is herein incorporated by reference. BACKGROUND

Field

[2] Various example embodiments relate to optical communication equipment and, more specifically but not exclusively, to optical power supplies. Description of the Related Art

[3] This section introduces aspects that can help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. [4] As the input/output (I/O) capacities of electronic processing chips increase, electrical signals may not provide sufficient I/O capacity across the limited size of a practically viable electronic chip package. A feasible alternative can be to interconnect electronic chip packages using optical signals, which can typically be delivered with a much higher I/O capacity per unit area compared to electrical I/Os.

SUMMARY

[5] Disclosed herein are various embodiments of an optical communication system comprising a polarization-diversity optical power supply capable of supplying light over a non-polarization-maintaining optical fiber to a polarization-sensitive modulation device.

In an example embodiment, the polarization-diversity optical power supply operates to accommodate random polarization fluctuations within the non-polarization-maintaining optical fiber and enables an equal-power split at a passive polarization splitter preceding the polarization-sensitive modulation device.

[6] According to one embodiment, provided is an apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising an optical power supply that comprises: a light source and an electronic controller connected to the light source to cause the light source to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; and a polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively.

[7] In some embodiments of the above apparatus, the electronic controller is configured to cause the first light output and the second light output to be mutually time/frequency orthogonal.

[8] In some embodiments of any of the above apparatus, a degree to which the first light output and the second light output are time/frequency orthogonal is greater than 0 8

[9] In some embodiments of any of the above apparatus, the degree is greater than 0.9. [10] In some embodiments of any of the above apparatus, the degree is greater than

0.99.

[11] In some embodiments of any of the above apparatus, the first light output comprises a first continuous-wave optical field at the first optical frequency, and the second light output comprises a second continuous-wave optical field at the second optical frequency. [12] In some embodiments of any of the above apparatus, a difference between the first optical frequency and the second optical frequency is greater than five times the symbol rate.

[13] In some embodiments of any of the above apparatus, a difference between the first optical frequency and the second optical frequency is approximately an integer multiple of the symbol rate. [14] In some embodiments of any of the above apparatus, the first light output comprises a first optical pulse train of a first period, and the second light output comprises a second optical pulse train of the first period.

[15] In some embodiments of any of the above apparatus, pulses of the first and second optical pulse trains have a same intensity waveform.

[16] In some embodiments of any of the above apparatus, pulses of the first and second optical pulse trains have different respective intensity waveforms.

[17] In some embodiments of any of the above apparatus, the first and second optical pulse trains are phase-locked with respect to one another. [18] In some embodiments of any of the above apparatus, centers of pulses of the first optical pulse train are temporally aligned with centers of corresponding pulses of the second optical pulse train.

[19] In some embodiments of any of the above apparatus, centers of pulses of the first optical pulse train are temporally offset from centers of corresponding pulses of the second optical pulse train by a nonzero time shift.

[20] In some embodiments of any of the above apparatus, the nonzero time shift is smaller than one half the first period.

[21] In some embodiments of any of the above apparatus, the nonzero time shift is smaller than one quarter of the first period. [22] In some embodiments of any of the above apparatus, the difference between the first optical frequency and the second optical frequency is twice the pulse repetition rate. [23] In some embodiments of any of the above apparatus, the difference between the first optical frequency and the second optical frequency is three times the pulse repetition rate. [24] In some embodiments of any of the above apparatus, a spectrum of the first pulse train has two first optical frequency tones; and a spectrum of the second pulse train has two second optical frequency tones different from the two first optical frequency tones.

[25] In some embodiments of any of the above apparatus, the first and second optical frequency tones are equi distantly spaced by an integer multiple of the symbol rate. [26] In some embodiments of any of the above apparatus, the integer multiple is two. [27] In some embodiments of any of the above apparatus, the electronic controller is further configured to imprint first control information on the first light output of the light source and second control information on the second light output of the light source.

[28] In some embodiments of any of the above apparatus, the first control information is identical to the second control information.

[29] In some embodiments of any of the above apparatus, the electronic controller imprints the first and second control information using one or more of: an intensity, a phase, a frequency, and a polarization of the first light output and the second light output.

[30] In some embodiments of any of the above apparatus, the light source comprises a first CW laser oscillating at the first optical frequency, and a second CW laser oscillating at the second optical frequency.

[31] In some embodiments of any of the above apparatus, the electronic controller is configured to control the first CW laser and the second CW laser to controllably set a frequency difference between the first and second optical frequencies. [32] In some embodiments of any of the above apparatus, the polarization combiner comprises one or more of: a polarization beam combiner, a polarization-maintaining optical power combiner, and a polarization-maintaining wavelength multiplexer.

[33] In some embodiments of any of the above apparatus, the light source comprises a CW laser and an optical modulator optically connected to the CW laser, the optical modulator configured to generate a first modulation tone at the first optical frequency.

[34] In some embodiments of any of the above apparatus, the electronic controller is configured to control an optical frequency of the first modulation tone.

[35] In some embodiments of any of the above apparatus, the optical modulator is further configured to generate a second modulation tone at the second optical frequency. [36] In some embodiments of any of the above apparatus, the light source comprises an optical amplitude modulator configured to generate an optical pulse train.

[37] In some embodiments of any of the above apparatus, the light source comprises a pulsed laser configured to generate an optical pulse train.

[38] In some embodiments of any of the above apparatus, the light source comprises an optical delay element configured to delay the first light output with respect to the second light output. [39] In some embodiments of any of the above apparatus, the optical power supply comprises an optical dispersion-compensating element.

[40] In some embodiments of any of the above apparatus, the light source comprises a polarization-diversity in-phase/quadrature modulator. [41] In some embodiments of any of the above apparatus: the polarization-diversity in phase/quadrature modulator is configured to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization; wherein frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization are equal to one another; and wherein frequency spacing between a tone in the first polarization and a tone in the second polarization is an integer multiple of said equal frequency spacing.

[42] In some embodiments of any of the above apparatus, the phase difference between the two tones in the first polarization is equal to the phase difference between the two tones in the second polarization. [43] In some embodiments of any of the above apparatus, the apparatus further comprises an optical transmit module optically end-connected to the output port of the polarization combiner via one or more sections of optical fiber, the transmit module comprising: a polarization splitter having an input port thereof optically connected to an end of one of the sections of the optical fiber to receive light of the optical output; a first optical data modulator connected to a first output of the polarization splitter; and a second optical data modulator connected to a second output of the polarization splitter.

[44] In some embodiments of any of the above apparatus, at least one of the first and second optical data modulators is configured to modulate received light at the symbol rate.

[45] In some embodiments of any of the above apparatus, at least one of the one or more sections of the optical fiber is non-polarization-maintaining.

[46] In some embodiments of any of the above apparatus, the optical fiber is at least one meter long.

[47] In some embodiments of any of the above apparatus, the optical fiber is at least ten meters long. [48] According to another embodiment, provided is an apparatus comprising an optical transmitter that comprises: a passive polarization splitter having an optical input port and first and second optical output ports, the optical input port being optically connected to receive an optical input signal having first and second polarization components, the first polarization component carrying light of a first optical frequency, the second polarization component carrying light of a second optical frequency different from the first optical frequency, the first and second polarization components being mutually orthogonal and jointly undergoing a state-of-polarization change during a time interval, the passive polarization splitter causing light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causing light of a second fixed polarization to be directed from the optical input port to the second optical output port, the first and second fixed polarizations being orthogonal to one another, the state-of- polarization change causing respective spectral compositions of the lights directed to the first and second optical ports to change during said time interval; and a first optical modulator connected to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal.

[49] In some embodiments of the above apparatus, the optical transmitter further comprises a second optical modulator connected to the second optical output port and configured to modulate the light of the second fixed polarization received therefrom in response to a second data signal.

[50] In some embodiments of any of the above apparatus, the first and second optical modulators are connected to transmit the respective modulated lights through different respective optical fibers.

[51] In some embodiments of any of the above apparatus: at some times of said time interval, the first optical modulator receives from the first output port the first optical frequency but not the second optical frequency; and at some other times of said time interval, the first optical modulator receives from the first output port the second optical frequency but not the first optical frequency.

[52] In some embodiments of any of the above apparatus, at yet some other times of said time interval, the first optical modulator receives from the first output port a mix of the first and second optical frequencies.

[53] In some embodiments of any of the above apparatus, the optical input port is optically connected to receive the optical input signal from a proximate end of a section of optical fiber, the optical fiber including at least one section that is non-polarization- maintaining. [54] In some embodiments of any of the above apparatus, the state-of-polarization change is due to time-varying polarization rotation in said at least one section.

[55] In some embodiments of any of the above apparatus, the time-varying polarization rotation is random. [56] In some embodiments of any of the above apparatus, the optical transmitter further comprises an optical power supply optically connected to apply the optical input signal through the optical fiber to the passive polarization splitter.

[57] In some embodiments of any of the above apparatus, the optical power supply comprises: a light source and an electronic controller connected to the light source to cause the light source to generate a first light output having the first optical frequency and a second light output having the second optical frequency, each of the first and second light outputs being steady during said time interval; and a polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output that is coupled into the optical fiber to cause the optical input port of the polarization splitter to receive the optical input signal.

[58] In some embodiments of any of the above apparatus, the first optical modulator is a polarization-sensitive device designed to modulate optical signals having the first fixed polarization. [59] In some embodiments of any of the above apparatus, the first optical modulator is unsuitable for modulating optical signals having the second fixed polarization.

[60] In some embodiments of any of the above apparatus, the second optical modulator is a polarization-sensitive device designed to modulate optical signals having the second fixed polarization. [61] In some embodiments of any of the above apparatus, the second optical modulator is unsuitable for modulating optical signals having the first fixed polarization.

[62] In some embodiments of any of the above apparatus, the difference between the first optical frequency and the second optical frequency can be Af the symbol rate can be Rs, and Af can be within ±10% of Rs. [63] In some embodiments of any of the above apparatus, the apparatus can include: a transmit module that includes at least one optical modulator configured to modulate the optical output signal from the output port of the polarization combiner; and an optical fiber that includes one or more sections of non-polarization-maintaining fiber. The optical fiber can be optically coupled between the output port of the polarization combiner and the transmit module, and the optical fiber can be configured to transmit the optical output signal from the output port of the polarization combiner to the transmit module. [64] In some embodiments of any of the above apparatus, the optical fiber between the transmit module and the polarization combiner can be at least one meter long.

[65] In some embodiments of any of the above apparatus, the optical fiber between the transmit module and the polarization combiner can be at least ten meters long.

[66] In some embodiments of any of the above apparatus, the transmit module can include: a passive polarization splitter having an optical input port and first and second optical output ports, the optical input port being optically connected to receive the optical input signal from the optical power supply having first and second polarization components, the first polarization component carrying light of the first optical frequency, and the second polarization component carrying light of the second optical frequency. The first and second polarization components can be mutually orthogonal and jointly undergo a state-of-polarization change during a time interval, the passive polarization splitter can cause light of a first fixed polarization to be directed from the optical input port to the first optical output port and also cause light of a second fixed polarization to be directed from the optical input port to the second optical output port. The first and second fixed polarizations can be orthogonal to one another, the state-of-polarization change can cause respective spectral compositions of the lights directed to the first and second optical ports to change during the time interval. The transmit module can include a first optical modulator optically coupled to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal. [67] In some embodiments of any of the above apparatus, the optical transmitter can include a second optical modulator optically coupled to the second optical output port and configured to modulate the light of the second fixed polarization received therefrom in response to a second data signal.

[68] In some embodiments of any of the above apparatus, the first and second optical modulators can be optically connected to transmit the respective modulated lights through different respective optical fibers. [69] In some embodiments of any of the above apparatus, at some times of the time interval, the first optical modulator can receive from the first output port the first optical frequency but not the second optical frequency; and at some other times of the time interval, the first optical modulator can receive from the first output port the second optical frequency but not the first optical frequency.

[70] In some embodiments of any of the above apparatus, at yet some other times of the time interval the first optical modulator can receive from the first output port a mix of the first and second optical frequencies.

[71] In some embodiments of any of the above apparatus, the polarization combiner can include at least one of a polarization beam combiner, a polarization-maintaining optical power combiner, or a polarization-maintaining wavelength multiplexer.

[72] In some embodiments of any of the above apparatus, the apparatus can include a chromatic-dispersion-compensating optical element that is configured to pre-disperse the optical output signal from the polarization combiner. [73] In some embodiments of any of the above apparatus, the light source can include: a first laser that is configured to generate first polarized light that has the first optical frequency. The first polarized light can form the first light output of the light source. The light source can include a second laser that is configured to generate second polarized light that has the second optical frequency. The second polarized light can form the second light output of the light source.

[74] In some embodiments of any of the above apparatus, the light source can include: a laser that is configured to generate first polarized light that has the first optical frequency; and an optical splitter that is configured to receive the first polarized light and output a first portion of the first polarized light and a second portion of the first polarized light. The first portion can form the first light output of the light source. The second portion can be transmitted to a frequency shifter that is configured to frequency-shift the second portion to generate a frequency-shifted second portion that has the second optical frequency, and the frequency-shifted second portion can form the second light output of the light source.

[75] In some embodiments of any of the above apparatus, the light source can include: a laser that is configured to generate first light; a modulator that is configured to split the first light into a first spectral tone and a second spectral tone, and generate second light that includes the first and second spectral tones; and a frequency splitter that is configured to frequency-split the second light into a first portion and a second portion. The first portion can include the first spectral tone, and the second portion can include the second spectral tone. The first portion can form the first light output of the light source, and the second portion can form the second light output of the light source. [76] In some embodiments of any of the above apparatus, the light source can include: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a first optical modulator configured to modulate the first polarized light to generate first modulated polarized light; and a second optical modulator configured to modulate the second polarized light to generate second modulated polarized light. The first modulated polarized light can form the first light output of the light source, and the second modulated polarized light can form the second light output of the light source.

[77] In some embodiments of any of the above apparatus, the light source can include an optical delay element configured to delay the second modulated polarized light before the second modulated polarized light is polarization-combined with the first modulated polarized light.

[78] In some embodiments of any of the above apparatus, the light source can include a signal generator configured to generate electrical signals for driving the first and second optical modulators. The first laser, the first modulator, and the signal generator can be configured to generate the first modulated polarized light as a first optical pulse train. The second laser, the second modulator, and the signal generator can be configured to generate the second modulated polarized light as a second optical pulse train.

[79] In some embodiments of any of the above apparatus, the light source can include a signal generator configured to generate electrical signals for driving the first and second optical modulators. The first laser, the first modulator, the second modulator, and the signal generator can be configured to generate the first and second modulated polarized light as dispersion pre-distorted optical signals.

[80] In some embodiments of any of the above apparatus, the first and second modulators can be configured to modulate time stamps onto the first and second modulated polarized light.

[81] In some embodiments of any of the above apparatus, the light source can include: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a second polarization combiner configured to polarization-combine the first polarized light and the second polarized light to generate first combined light; an optical modulator configured to modulate the first combined light to generate a modulated combined light; and a splitter to split the modulated combined light into a first portion and a second portion. The first portion can form the first light output of the light source, and the second portion can form the second light output of the light source.

[82] In some embodiments of any of the above apparatus, the light source can include an optical delay element configured to delay the second portion before the second portion is polarization-combined with the first portion by the polarization combiner.

[83] In another general aspect, an apparatus for communicating optical signals modulated at a symbol rate includes: an optical power supply that includes: a laser; an electronic controller electrically coupled to the laser and configured to cause the laser to generate a first polarized light output having a first optical frequency; and an optical splitter that is configured to receive the first polarized light and output a first portion of the first polarized light and a second portion of the first polarized light. The optical power supply includes a frequency shifter that is configured to frequency-shift the second portion to generate a frequency-shifted second portion that has a second optical frequency different from the first optical frequency. Each of the first portion and the frequency-shifted second portion is steady during a time interval that is significantly longer than one over the symbol rate. The optical power supply includes a polarization combiner configured to receive the first portion and the frequency-shifted second portion. The polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the frequency-shifted second portion, respectively.

[84] In another general aspect, an apparatus for communicating optical signals modulated at a symbol rate includes: an optical power supply that includes: a laser that is configured to generate first light; and a modulator that is configured to split the first light into a first spectral tone and a second spectral tone, and generate second light that includes the first and second spectral tones. The optical power supply includes a frequency splitter that is configured to frequency-split the second light into a first portion and a second portion. The first portion includes the first spectral tone, and the second portion includes the second spectral tone, and each of the first portion and the second portion is steady during a time interval that is significantly longer than one over the symbol rate. The optical power supply includes a polarization combiner configured to receive the first portion and the second portion. The polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the second portion, respectively.

[85] In another general aspect, an apparatus for communicating optical signals modulated at a symbol rate includes: an optical power supply that includes: a first laser that is configured to emit first polarized light at a first wavelength; and a second laser that is configured to emit second polarized light at a second wavelength. The optical power supply includes a first optical modulator configured to modulate the first polarized light to generate first modulated polarized light; and a second optical modulator configured to modulate the second polarized light to generate second modulated polarized light. Each of the first modulated polarized light and the second modulated polarized light is steady during a time interval that is significantly longer than one over the symbol rate. The optical power supply includes a polarization combiner configured to receive the first modulated polarized light and the second modulated polarized light. The polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first modulated polarized light and the second modulated polarized light, respectively.

[86] Implementations can include one or more of the following features. The optical power supply can include an optical delay element configured to delay the second modulated polarized light before the second modulated polarized light is polarization- combined with the first modulated polarized light.

[87] In another general aspect, an apparatus for communicating optical signals modulated at a symbol rate includes: an optical power supply that includes: a first laser that is configured to emit first polarized light at a first wavelength; and a second laser that is configured to emit second polarized light at a second wavelength. The optical power supply includes a first polarization combiner configured to polarization-combine the first polarized light and the second polarized light to generate first combined light; and an optical modulator configured to modulate the first combined light to generate a modulated combined light. The optical power supply includes a splitter to split the modulated combined light into a first portion and a second portion, and each of the first modulated polarized light and the second modulated polarized light is steady during a time interval that is significantly longer than one over the symbol rate. The optical power supply includes a polarization combiner configured to receive the first portion and the second portion. The polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the second portion, respectively.

[88] Implementations can include one or more of the following features. The optical power supply can include an optical delay element configured to delay the second portion before the second portion is polarization-combined with the first portion by the polarization combiner. [89] In another general aspect, a method of communicating optical signals modulated at a symbol rate includes: generating a first light output having a first optical frequency; and generating a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; and polarization- combining the first and second light outputs and generating an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first and second light outputs, respectively. The method includes propagating the optical output signal through an optical fiber that includes one or more sections of non- polarization-maintaining fiber to a transmit module that includes at least one optical modulator configured to modulate the optical output signal.

[90] Implementations can include one or more of the following features. The method can include configuring the first light output and the second light output to be mutually time/frequency orthogonal.

[91] Generating the first light output can include generating a first continuous-wave optical field at the first optical frequency, and generating the second light output can include generating a second continuous-wave optical field at the second optical frequency. [92] A difference between the first optical frequency and the second optical frequency can be approximately an integer multiple of the symbol rate.

[93] Generating the first light output can include generating a first optical pulse train having a first period, and generating the second light output can include generating a second optical pulse train having a second period.

[94] The method can include temporally aligning centers of pulses of the first optical pulse train with centers of corresponding pulses of the second optical pulse train.

[95] The method can include temporally offsetting centers of pulses of the first optical pulse train from centers of corresponding pulses of the second optical pulse train by a nonzero time shift.

[96] Generating a first optical pulse train can include generating a first optical pulse train having a spectrum that includes two first optical frequency tones. Generating a second optical pulse train can include generating a second optical pulse train having a spectrum that includes two second optical frequency tones different from the two first optical frequency tones.

[97] The method can include imprinting first control information on the first light output and second control information on the second light output.

[98] The method can include using a polarization-diversity in-phase/quadrature modulator to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization.

[99] Frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization can be equal to each another.

[100] Frequency spacing between a tone in the first polarization and a tone in the second polarization can be an integer multiple of the frequency spacing between the two tones in the first polarization.

[101] The method can include splitting the optical output signal into a first portion and a second portion; modulating the first portion with first data to generate a first modulated optical signal; and modulating the second portion with second data to generate a second modulated optical signal. [102] In another general aspect, a system includes: an optical power supply that includes: a first light source and an electronic controller connected to the light source to cause the light source to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over a symbol rate. The optical power supply includes a first polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, a first optical output signal in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively.

[103] Implementations can include one or more of the following features. The system can include a first data processing apparatus that includes: a first housing, a first data processor disposed in the first housing, and a first co-packaged optical module that is configured to convert output electrical signals from the first data processor to output optical signals that are provided to a first optical fiber cable optically coupled to the first data processing apparatus. The optical power supply can be configured to provide the first optical output signal to the first co-packaged optical module through a first optical link.

[104] The optical power supply can include: a second light source configured to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate. The optical power supply can include a second polarization combiner connected to receive the first and second light outputs of the second light source at different respective input ports thereof, the second polarization combiner being configured to generate, at an output port thereof, a second optical output signal in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively. The system can include a second data processing apparatus that includes: a second housing, a second data processor disposed in the second housing, and a second co-packaged optical module that is configured to convert output electrical signals from the second data processor to output optical signals that are provided to a second optical fiber cable optically coupled to the second data processing apparatus, the first and second optical fiber cables are either the same cable or different cables. The optical power supply can be configured to provide the second optical output signal to the second co-packaged optical module through a second optical link. [105] The first co-packaged optical module can include a transmit module that includes at least one optical modulator configured to modulate the first optical output signal from the output port of the polarization combiner. The first optical link can include one or more sections of non-polarization-maintaining fiber. The first optical link can be optically coupled between the output port of the polarization combiner and the transmit module, and the first optical link can be configured to transmit the first optical output signal from the output port of the polarization combiner to the transmit module.

[106] The system can include a distributed data processing system, the first data processing apparatus can include a data server, the data server can include a circuit board on which the first data processor is mounted, the circuit board can be positioned relative to the housing such that a first main surface of the circuit board is at an angle relative to a bottom panel of the housing, and the angle can be in a range from 45° to 90°.

[107] The circuit board can be positioned parallel to the front panel.

[108] The first data processor can include at least one of a network switch, a central processor unit, a graphics processor unit, a tensor processing unit, a neural network processor, an artificial intelligence accelerator, a digital signal processor, a microcontroller, or an application specific integrated circuit (ASIC).

[109] The first co-packaged optical module can include a first photonic integrated circuit, a first optical connector part that is configured to be removably coupled to a second optical connector part that is attached to the first optical fiber cable, and an optical power supply connector that is connected to the first optical link to receive supply light from the optical power supply.

[110] The first optical output signal can be modulated with synchronization information, the first co-packaged optical module can include an optical splitter that splits the supply light and provides a first portion of the supply light to a receiver that is configured to extract the synchronization information.

[111] The first co-packaged optical module can include an optical splitter that splits the supply light and provides a first portion of the supply light to an optoelectronic modulator that is configured to modulate onto the first portion of the supply light the output electrical signals from the first data processor to generate modulated light, in which the modulated light is output through the first optical fiber cable. [112] The first co-packaged optical module can be electrically coupled to the first circuit board using electrical contacts that include at least one of spring-loaded elements, compression interposers, or land-grid arrays.

[113] The system can include: a transmit module that includes at least one optical modulator configured to modulate the optical output signal from the output port of the polarization combiner; and an optical fiber that includes one or more sections of non- polarization-maintaining fiber. The optical fiber can be optically coupled between the output port of the polarization combiner and the transmit module, and the optical fiber can be configured to transmit the optical output signal from the output port of the polarization combiner to the transmit module.

[114] The system can include an optical cable assembly that includes the first optical link. The optical cable assembly can include: a first optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a second optical fiber connector including an optical power supply fiber port. The optical power supply fiber port of the first optical fiber connector can be optically coupled to the optical power supply fiber port of the second optical fiber connector. The first optical fiber connector can be configured to be optically coupled to the first co-packaged optical module. The second optical fiber connector can be configured to be optically coupled to the optical power supply to receive the first optical output signal from the output port. [115] The optical cable assembly can include a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the second optical fiber connector.

[116] The system can include an optical cable assembly that includes the first optical link and the second optical link. The optical cable assembly can include: a first optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a second optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a third optical fiber connector including a first optical power supply fiber port and a second optical power supply fiber port. The optical power supply fiber port of the first optical fiber connector can be optically coupled to the first optical power supply fiber port of the third optical fiber connector, and the optical power supply fiber port of the second optical fiber connector can be optically coupled to the second optical power supply fiber port of the third optical fiber connector. The first optical fiber connector can be configured to be optically coupled to the first co-packaged optical module, the second optical fiber connector can be configured to be optically coupled to the second co-packaged optical module, and the third optical fiber connector can be configured to be optically coupled to the optical power supply. [117] The optical cable assembly can include a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the third optical fiber connector.

[118] The optical cable assembly can include a second optical fiber optically coupled to the optical power supply fiber port of the second optical fiber connector and the second optical power supply fiber port of the third optical fiber connector.

[119] The optical cable assembly can include a third optical fiber optically coupled to the transmitter fiber port of the first optical fiber connector and the receiver fiber port of the second optical fiber connector.

[120] The optical cable assembly can include a fourth optical fiber optically coupled to the receiver fiber port of the first optical fiber connector and the transmitter fiber port of the second optical fiber connector.

[121] The optical cable assembly can include an optical fiber guide module including a first port, a second port, and a third port. The first optical fiber can extend through the first and third ports, the second optical fiber can extend through the second and third ports, the third optical fiber can extend through the first and second ports, and the fourth optical fiber can extend through the first and second ports.

[122] The first, third, and fourth optical fibers can extend from the first port of the optical fiber guide module to the first optical fiber connector.

[123] The second, third, and fourth optical fibers can extend from the second port of the optical fiber guide module to the second optical fiber connector.

[124] The first and second optical fibers can extend from the third port of the optical fiber guide module to the third optical fiber connector.

[125] The optical fiber guide module can be configured to restrict bending of the optical fibers that pass through the optical fiber guide module such that each optical fiber within the optical fiber guide module has a bending radius greater than a predetermined value to prevent excess optical light loss or damage to the optical fiber due to bending.

[126] The first co-packaged optical module can include a first photonic integrated circuit optically coupled to the first optical fiber connector and configured to receive the power supply light from the first light source through the optical power supply fiber port of the first optical fiber connector.

[127] The first photonic integrated circuit can be configured to modulate the power supply light to generate a first modulated optical signal, and transmit the first modulated optical signal to the transmitter fiber port of the first optical fiber connector.

[128] The second co-packaged optical module can include a second photonic integrated circuit optically coupled to the second optical fiber connector and configured to receive the power supply light from the second light source through the optical power supply fiber port of the second optical fiber connector.

[129] The second photonic integrated circuit can be configured to modulate the power supply light to generate a second modulated optical signal, and transmit the second modulated optical signal to the transmitter fiber port of the second optical fiber connector.

[130] The first photonic integrated circuit can be configured to, through the receiver fiber port of the first optical fiber connector, receive the second modulated optical signal transmitted from the second photonic integrated circuit.

[131] The second photonic integrated circuit can be configured to, through the receiver fiber port of the second optical fiber connector, receive the first modulated optical signal transmitted from the first photonic integrated circuit. [132] The optical power supply can be optically coupled to the third optical fiber connector and configured to provide a first sequence of optical frame templates to the first optical power supply fiber port and a second sequence of optical frame templates to the second optical power supply fiber port.

[133] The first co-packaged optical module can include a first photonic integrated circuit optically coupled to the first optical fiber connector and configured to receive the first sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the first optical fiber connector.

[134] The first photonic integrated circuit can be configured to modulate the first sequence of optical frame templates to generate a first sequence of loaded optical frames, and transmit the first sequence of loaded optical frames to the transmitter fiber port of the first optical fiber connector.

[135] The second co-packaged optical module can include a second photonic integrated circuit optically coupled to the second optical fiber connector and configured to receive the second sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the second optical fiber connector.

[136] The second photonic integrated circuit can be configured to modulate the second sequence of optical frame templates to generate a second sequence of loaded optical frames, and transmit the second sequence of loaded optical frames to the transmitter fiber port of the second optical fiber connector.

[137] The first photonic integrated circuit can be configured to, through the receiver fiber port of the first optical fiber connector, receive the second sequence of loaded optical frames transmitted from the second photonic integrated circuit.

[138] The second photonic integrated circuit can be configured to, through the receiver fiber port of the second optical fiber connector, receive the first sequence of loaded optical frames transmitted from the first photonic integrated circuit.

[139] In another general aspect, a system includes: a first data processing apparatus including a first optical transmitter that includes: a passive polarization splitter having an optical input port and first and second optical output ports. The optical input port is optically connected to receive an optical input signal having first and second polarization components, the first polarization component carries light of a first optical frequency, and the second polarization component carries light of a second optical frequency different from the first optical frequency. The first and second polarization components are mutually orthogonal and jointly undergo a state-of-polarization change during a time interval. The passive polarization splitter causes light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causes light of a second fixed polarization to be directed from the optical input port to the second optical output port. The first and second fixed polarizations are orthogonal to one another. The state-of-polarization change causes respective spectral compositions of the lights directed to the first and second optical ports to change during said time interval. The first data processing apparatus includes a first optical modulator connected to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal. The apparatus includes a first optical link optically connected between the optical input port and an optical power supply that provides the optical input signal.

[140] Implementations can include one or more of the following features. The first data processing apparatus can include a first housing, and the first optical transmitter can be disposed in the first housing. The system can include: a second data processing apparatus that includes a second housing, and a second optical transmitter disposed in the second housing. The system can include a second optical link optically connected between the second optical transmitter and the optical power supply.

[141] The first optical link can include one or more sections of non-polarization- maintaining fiber. The first optical link can be optically coupled between the output port of the polarization combiner and the transmit module, and the first optical link can be configured to transmit the first optical output signal from the output port of the polarization combiner to the transmit module.

[142] The first data processing apparatus can include a circuit board on which a first photonic integrated circuit is mounted, the first optical transmitter can be part of the first photonic integrated circuit, the circuit board can be positioned relative to the housing such that a first main surface of the circuit board is at an angle relative to a bottom panel of the housing, and the angle can be in a range from 45° to 90°.

[143] The circuit board can be positioned parallel to a front panel of the housing.

[144] The first data processing apparatus can include a first data processor that is configured to provide the first data signal, and the first data processor can include at least one of a network switch, a central processor unit, a graphics processor unit, a tensor processing unit, a neural network processor, an artificial intelligence accelerator, a digital signal processor, a microcontroller, or an application specific integrated circuit (ASIC).

[145] The system can include an optical cable assembly that includes the first optical link. The optical cable assembly can include: a first optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a second optical fiber connector including an optical power supply fiber port. The optical power supply fiber port of the first optical fiber connector can be optically coupled to the optical power supply fiber port of the second optical fiber connector. The first optical fiber connector can be configured to be optically coupled to the first data processing apparatus. The second optical fiber connector can be configured to be optically coupled to the optical power supply.

[146] The optical cable assembly can include a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the optical power supply fiber port of the second optical fiber connector.

[147] The system can include an optical cable assembly that includes the first optical link and the second optical link. The optical cable assembly can include: a first optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a second optical fiber connector including an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a third optical fiber connector including a first optical power supply fiber port and a second optical power supply fiber port. The optical power supply fiber port of the first optical fiber connector can be optically coupled to the first optical power supply fiber port of the third optical fiber connector, and the optical power supply fiber port of the second optical fiber connector can be optically coupled to the second optical power supply fiber port of the third optical fiber connector. The first optical fiber connector can be configured to be optically coupled to the first data processing apparatus, the second optical fiber connector can be configured to be optically coupled to the second data processing apparatus, and the third optical fiber connector can be configured to be optically coupled to the optical power supply.

[148] The optical cable assembly can include a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the third optical fiber connector.

[149] The optical cable assembly can include a second optical fiber optically coupled to the optical power supply fiber port of the second optical fiber connector and the second optical power supply fiber port of the third optical fiber connector.

[150] The optical cable assembly can include a third optical fiber optically coupled to the transmitter fiber port of the first optical fiber connector and the receiver fiber port of the second optical fiber connector. [151] The optical cable assembly can include a fourth optical fiber optically coupled to the receiver fiber port of the first optical fiber connector and the transmitter fiber port of the second optical fiber connector.

[152] The optical cable assembly can include an optical fiber guide module including a first port, a second port, and a third port. The first optical fiber can extend through the first and third ports, the second optical fiber can extend through the second and third ports, the third optical fiber can extend through the first and second ports, and the fourth optical fiber can extend through the first and second ports. [153] The first, third, and fourth optical fibers can extend from the first port of the optical fiber guide module to the first optical fiber connector.

[154] The second, third, and fourth optical fibers can extend from the second port of the optical fiber guide module to the second optical fiber connector. [155] The first and second optical fibers can extend from the third port of the optical fiber guide module to the third optical fiber connector.

[156] The optical fiber guide module can be configured to restrict bending of the optical fibers that pass through the optical fiber guide module such that each optical fiber within the optical fiber guide module has a bending radius greater than a predetermined value to prevent excess optical light loss or damage to the optical fiber due to bending.

[157] The first optical transmitter can be configured to receive power supply light from the optical power supply through the optical power supply fiber port of the first optical fiber connector, modulate the light of the first fixed polarization in response to the first data signal to generate a first modulated optical signal, and transmit the first modulated optical signal to the transmitter fiber port of the first optical fiber connector.

[158] The second optical transmitter can be configured to receive power supply light from the optical power supply through the optical power supply fiber port of the second optical fiber connector, modulate the power supply light to generate a second modulated optical signal, and transmit the second modulated optical signal to the transmitter fiber port of the second optical fiber connector.

[159] The system can include the optical power supply. The optical power supply can be optically coupled to the third optical fiber connector and configured to provide a first sequence of optical frame templates to the first optical power supply fiber port and a second sequence of optical frame templates to the second optical power supply fiber port. [160] The first optical transmitter can be configured to receive the first sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the first optical fiber connector.

[161] The first optical transmitter can be configured to modulate the first sequence of optical frame templates in response to the first data signal to generate a first sequence of loaded optical frames, and transmit the first sequence of loaded optical frames to the transmitter fiber port of the first optical fiber connector.

[162] The second optical transmitter can be configured to receive the second sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the second optical fiber connector.

[163] The second optical transmitter can be configured to modulate the second sequence of optical frame templates to generate a second sequence of loaded optical frames, and transmit the second sequence of loaded optical frames to the transmitter fiber port of the second optical fiber connector.

[164] The first data processing apparatus can be configured to, through the receiver fiber port of the first optical fiber connector, receive the second sequence of loaded optical frames transmitted from the second photonic integrated circuit. [165] The second data processing apparatus can be configured to, through the receiver fiber port of the second optical fiber connector, receive the first sequence of loaded optical frames transmitted from the first photonic integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS [166] Other aspects, features, and benefits of various disclosed embodiments will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which:

[167] FIG. 1 shows a block diagram of an optical communication system in which at least some embodiments can be practiced; [168] FIG. 2 shows a block diagram of an optical power supply module that can be used in the optical communication system of FIG. 1 according to an example embodiment;

[169] FIGs. 3A-3E illustrate some features of the light generated by an optical power supply in the optical communication system of FIG. 1 according to some embodiments;

[170] FIGs. 4A-4F illustrate optical power supplies, one or more of which can be used in the optical communication system of FIG. 1 according to some embodiments;

[171] FIG. 5 shows a block diagram of an example distributed optical transmitter of the optical communication system of FIG. 1 employing an optical power supply module of FIG. 2 according to an embodiment;

[172] FIG. 6 shows a block diagram of an optical transmitter that can be used in the optical communication system of FIG. 1 according to an embodiment; [173] FIGs. 7A-7D graphically show some example use cases illustrating polarization- rotation independent optical-power splitting that can be implemented in the optical communication system of FIG. 1 according to some embodiments; and

[174] FIG. 8 graphically illustrates some signals used/generated in the optical transmitter of FIG. 5 and the corresponding electrical signals recovered by a corresponding optical receiver according to an example embodiment.

[175] FIGS. 9 to 13A are diagrams of examples of optical communications systems.

[176] FIG. 13B is a diagram of an example of an optical cable assembly used in the optical communication system of FIG. 13A.

[177] FIG. 13C is an enlarged diagram of the optical cable assembly of FIG. 13B.

[178] FIG. 13D is an enlarged diagram of the upper portion of the optical cable assembly of FIG. 13B.

[179] FIG. 13E is an enlarged diagram of the lower portion of the optical cable assembly of FIG. 13B.

[180] FIGS. 14 and 15A are diagrams of examples of optical communication systems.

[181] FIG. 15B is a diagram of an example of an optical cable assembly.

[182] FIG. 15C is an enlarged diagram of the optical cable assembly of FIG. 15B.

[183] FIG. 15D is an enlarged diagram of the upper portion of the optical cable assembly of FIG. 15B.

[184] FIG. 15E is an enlarged diagram of the lower portion of the optical cable assembly of FIG. 15B.

[185] FIGS. 16 and 17A are diagrams of examples of optical communication systems.

[186] FIG. 17B is a diagram of an example of an optical cable assembly.

[187] FIG. 17C is an enlarged diagram of the optical cable assembly of FIG. 17B.

[188] FIGS. 18 to 20B are diagrams of examples of data processing systems.

DETAILED DESCRIPTION

[189] At least some embodiments can benefit from the use of a light source configured to supply pulsed light for local optical modulation and/or as a clock reference within a corresponding island of synchronicity, e.g., as disclosed in U.S. patent application 16/847,705, filed on April 14, 2020, which is incorporated herein by reference in its entirety. [190] Emerging optical interconnects aim to co-package and even co-integrate optical transponders with electronic processing chips, which necessitates transponder solutions that consume relatively low power and that are sufficiently robust against significant temperature variations as can be found within an electronic processing chip package. Of significant interest are massively spatially parallel optical interconnect solutions that multiplex information onto relatively few wavelengths and use a relatively large number of parallel spatial paths for chip-to-chip interconnection. In such systems, it can be beneficial to place the light source outside the package housing the corresponding photonic and electronic processing chips, and to connect the light source to the package via one or more optical fibers. In some such systems, the light source can be placed at a separate location optically connected to the package by, e.g., by at least one meter of optical fiber.

[191] In some such systems, at least some photonic components within the package can be polarization sensitive, i.e., can only accept or can only properly process light of a certain polarization state. For example, a one-dimensional vertical grating coupler, which can serve as a coupling interface to the optical fiber connecting the light source to the package, can only couple light of one particular polarization from the fiber to the photonic processing chip while rejecting, deflecting, or dissipating other light. In another example, an optical modulator integrated within a package can effectively modulate only light in one particular polarization state. In such systems, it can therefore be beneficial to connect the light source with the corresponding electronic and photonic processing chips using polarization-maintaining optical fiber (PMF). However, some systems employing PMF may be more difficult and/or more expensive to manufacture than systems employing standard, non-polarization-maintaining optical fiber (SF), e.g., because PMF may be more expensive than SF, and PMF may require rotationally aligned optical fiber connections. SF, however, may not preserve the polarization state of the light upon its transmission from the light source to the package housing.

[192] Some systems that use SF to connect the light source with a photonic chip can therefore require either an active optical polarization control mechanism or a polarization- diversity setup. In some such systems, polarization diversity can be implemented by doubling the number of data modulators within the package, e.g., as disclosed in U.S. Patent No. 5,654,818, which is incorporated herein by reference in its entirety. In some such systems, polarization diversity can be implemented by using more-complex optical data modulator structures, e.g., a 4-port optical modulator disclosed in U.S. Patent No. 10,222,676, which is incorporated herein by reference in its entirety.

[193] U.S. Patent Nos. 6,959,152 and 7,106,970, which are incorporated herein by reference in their entirety, disclose some systems configured to use temporally interleaved and orthogonally polarized trains of optical pulses at the same optical wavelength.

However, such temporal interleaving can lead to a significant timing jitter and/or pulse broadening at the modulator due to random polarization rotations within the corresponding SF.

[194] At least some of the above-indicated problems in the state of the art can be addressed by the use of various embodiments employing a polarization-diversity optical power supply, e.g., as outlined in this specification. For example, a need for PMF can beneficially be circumvented.

[195] FIG. 1 shows a block diagram of a communication system 100 in which at least some embodiments can be practiced. As shown, system 100 comprises nodes lOli-lOle, which in some embodiments can each comprise one or more of: optical communication devices, electronic and/or optical switching devices, electronic and/or optical routing devices, network control devices, traffic control devices, synchronization devices, computing devices, and data storage devices. Nodes lOli-lOU can be suitably interconnected by optical fiber links 102i-102i2 establishing communication paths between the communication devices within the nodes. System 100 can also comprise one or more optical power supply modules 103 producing one or more light supply outputs.

[196] As used herein, a “light supply” or “supplied light” is light intended for use as a modulation carrier in one or more of the optical communication devices of the nodes lOli- 1016 whose complex optical field amplitude is “steady.” Herein, light is referred to as being “steady” either if said light comprises one or more continuous-wave (CW) optical fields or if said light comprises one or more optical pulse trains of period 7} (where pulse repetition rate Ri = 1/77), each of the pulse trains having a substantially constant respective optical-pulse amplitude and a substantially constant respective optical-pulse duration over a time interval that is significantly longer (e.g., at least by a factor of 100) than the duration Ts of a modulation symbol used for optical communication in system 100. (Hereafter, Rs = 1/77 is referred to as the modulation symbol rate.) [197] As used herein, light is called “continuous-wave (CW)” if the complex amplitude of the optical field of said light is approximately (e.g., to within ±20%) constant over a duration Tew that is much longer than a minimum characteristic duration used by communication signals within system 100. In some embodiments, light can be referred to as being CW light if the complex amplitude of the optical field of said light is approximately constant over at least 100 times the duration Ts of a modulation symbol, i.e., Tcw³ 100 Ts. In some embodiments, light can be referred to as being CW light if the complex amplitude of the optical field of said light is approximately constant over a at least Tcw³ 1000 Ts. In some embodiments, the term “continuous-wave” (or CW) can also be applicable to an optical field affected by random noise, random drifts, or small analog dither modulations using one or more sinewave dither tones at frequencies much lower than Rs, e.g., at frequencies smaller than /C/1000, as long as the effect of noise, drift, or dither is not so strong as to induce optical intensity variations, e.g., exceeding ±20% of the average optical intensity within a duration Tew. [198] As used herein, the phrase an “optical pulse train of period TG refers to an optical field whose optical intensity waveform 1(f) = |//o(/)|² is periodic with the time period Ti. In some embodiments, the complex amplitude Eo(t) of the optical field of an optical pulse train can be periodic with an integer multiple of 7}, i.e., with a period of n Ti, where n = 1, 2, 3, ... . [199] As used herein, the term “periodic” refers to a waveform characterized by a parameter or feature (or a change of a parameter or feature) that is repeated every time period T within a duration of time T_D, where T_D is significantly larger than T, e.g., T_D >

100 T. In some cases, the term “periodic” can also be applicable to a waveform affected by random noise, random drifts, or small analog dither modulations using one or more sinewave dither tones at frequencies much lower than 1 IT, e.g., at frequencies smaller than 1/(1000 7), as long as the effect of noise, drift, or dither is not so strong as to obscure (e.g., make substantially undetectable) the waveform periodicity.

[200] In some embodiments, a light supply can also comprise control information.

Control information can be used by other network elements of system 100, e.g., as described in the above-cited U.S. Patent Application No. 16/847,705. As used herein, the term “control information” refers to information imprinted by optical power supply module 130 onto one or more light supplies for the purpose of controlling, managing, and/or monitoring one or more network elements of system 100, and/or for facilitating various synchronization operations within one or more network elements of system 100. In some embodiments, control information can comprise one or more of: a clock frequency, a clock phase, a synchronization time stamp, a frame delimiter, a frame counter, status information, a heartbeat signal, and a command that can be used to control the behavior of other network elements, such as a master/slave assignment or a reset command.

[201] For illustration purposes, only one such optical power supply module 103 is shown in FIG. 1. A person of ordinary skill in the art will understand that some embodiments can have more than one optical power supply module 103 appropriately distributed over system 100 and that such multiple optical power supply modules can be synchronized, e.g., using some of the techniques disclosed in the above-cited U.S. Patent Application No. 16/847,705.

[202] Some end-to-end communication paths can pass through an optical power supply module 103 (e.g., see the communication path between nodes IOI2 and 101b). For example, the communication path between nodes IOI2 and 101b can be jointly established by optical fiber links 1027 and 102s, whereby light supplied by optical power supply module 103 is multiplexed onto optical fiber links 1027 and 102s.

[203] Some end-to-end communication paths can pass through one or more optical multiplexing units 104 (e.g., see the communication path between nodes IOI2 and lOle). For example, the communication path between nodes IOI2 and lOle can be jointly established by optical fiber links 102io and 102n. Multiplexing unit 104 is also connected, through link 102₉, to receive light supplied by optical power supply module 103 and, as such, can be operated to multiplex said received light supply onto optical fiber links 102io and 102n. [204] Some end-to-end communication paths can pass through one or more optical switching units 105 (e.g., see the communication path between nodes lOli and IOI4). For example, the communication path between nodes lOli and IOI4 can be jointly established by optical fiber links 102₃ and 102i2, whereby light from optical fiber links 102₃ and 1024 is either statically or dynamically directed to optical fiber link 102i2. [205] As used herein, the term “network element” refers to any element that generates, modulates, processes, or receives light within system 100 for the purpose of communication. Example network elements include a node 101, an optical power supply module 103, an optical multiplexing unit 104, and an optical switching unit 105.

[206] Some light supply distribution paths can pass through one or more network elements. For example, optical power supply module 103 can supply light to node 1014 via optical fiber links 1027, 1024, and 102i2, letting the supply light pass through network elements IOI2 and 105.

[207] FIG. 2 shows a block diagram of an optical power supply 290 that can be used as part of optical power supply module 103 to create a light supply for use in system 100 according to an example embodiment. Optical power supply 290 comprises: (i) a light source 200 possessing two light outputs 212 and 222, each in a single state of polarization; (ii) an electronic controller 230 configured to control light source 200 such as to establish time/frequency orthogonality between light output 212 and light output 222; and a polarization combiner 240 configured to multiplex light outputs 212 and 222 onto two orthogonal polarization states at its output 242. [208] Herein, a “polarization combiner” is an optical device having two input ports (e.g., connected to 212 and 222) and at least one output port (e.g. 242) and configured to multiplex light in a first polarization state at its first input port onto a first polarization state of light on one of its output ports, and light in a second polarization state at its second input port onto a second polarization state of light on the same output port, the second polarization state at output port 242 being approximately orthogonal to the first polarization state at output port 242. In some embodiments, the two orthogonal polarization states at output port 242 can be horizontally and vertically linearly polarized, respectively. In some other embodiments, the two orthogonal polarization states at output port 242 can be left-handed and right-handed circularly polarized, respectively. In some other embodiments, the two orthogonal polarization states at output port 242 can be relatively orthogonally, elliptically polarized states. In some embodiments, the polarization states at input ports 212 and 222 can be identical. In some other embodiments, the polarization states at input ports 212 and 222 can be orthogonal. In some embodiments, polarization combiner 240 can include polarization-sensitive optical elements, e.g., be implemented as a polarization beam combiner. In some other embodiments, polarization combiner 240 may not include any polarization-sensitive elements, e.g., be implemented as a polarization-maintaining optical power combiner or as a polarization-maintaining wavelength multiplexer.

[209] The concept of “polarization state” is graphically illustrated in FIG. 7A. For example, light in a linear polarization state can be represented by a complex electrical field vector

E(t) = E₀(t ) exp(j2n ft) e_x,

(1) wherein the unit vector e_x can maintain its direction along a linear Cartesian axis (e.g., the x-axis as defined with respect to the fixed coordinate system of light source 200) to an accuracy of, e.g., within ±20 degrees over a relatively long duration, e.g., about one hour. In some embodiments, the unit vector e_x can maintain its direction along a linear Cartesian axis to within an accuracy of, e.g., ±20 degrees for the duration of typical normal operation of optical power supply 290. In the above expression, Eo(t) is the constant or time-varying complex amplitude of the complex electrical field vector, /is the optical frequency, t denotes the time variable and j = V— 1. In another example, a circular polarization state can be represented by a complex electrical field vector

(2) wherein the unit vector e_y is orthogonal to e_x and both unit vectors maintain their directions along two orthogonal linear Cartesian axis to within an accuracy of, e.g., ±20 degrees over a relatively long duration of, e.g., about one hour. As used herein, the term “polarized light” denotes light in some well defined polarization state.

[210] As used herein, two optical fields are said to be “time/frequency orthogonal” if the degree of orthogonality h of the two optical fields’ complex amplitudes E_\{t) and Ei{t), defined as

(3) is close to 1, e.g., has a value between 0.8 and 1. Herein, the integration time interval [/, t + 7] represents the time interval during which time/frequency orthogonality is to be determined. If at least one of the optical fields E_\{t) and Ei{f) has a non-periodic complex amplitude, the integration time interval is chosen to be long compared to a characteristic time duration within system 100, for example, duration T can be chosen to be at least 10 times a duration Ts of a modulation symbol, at least 10 times a duration of an information packet, or at least 10 times a duration of an optical frame template. If both optical fields have periodic complex amplitudes E_\{t) or //?(/) with period T, then the time duration T can be chosen as the duration over which the above integrals are being taken. In some embodiments, two fields can be called time/frequency orthogonal if h is greater than 0 8

In some embodiments two fields can be called time/frequency orthogonal if 77 is greater than 0.9. In some embodiments two fields can be called time/frequency orthogonal if h is greater than 0.99. The degree of orthogonality h can also be expressed in the frequency domain as h = 1- 1 Iϋ S (/)¾^* ( ) d/ 1²/(Cϋΐ i? C ) 1² d/ /"J¾(/0I²<V)

(4)

[211] From the above two definitions (see Eqs. (3) and (4)), it can be seen that two optical fields are time-frequency orthogonal, e.g., if they are: (i) spectrally disjoint, i.e., if the spectral contents of the two fields are primarily located at mutually exclusive optical frequencies; and/or (ii) temporally disjoint, i.e., the complex amplitudes of the two optical fields differ from zero primarily at mutually exclusive times. In some embodiments, two optical fields can be time/frequency orthogonal if they overlap both in time and in frequency, provided that their degree of orthogonality is close to 1, e.g., as indicated by the example values/ranges of h mentioned above.

[212] In some embodiments, light source 200 produces light of different respective optical center frequencies for light outputs 212 and 222. As used herein, the term “optical center frequency” refers to the center of mass of the power spectral density of an optical field. In some embodiments, controller 230 can operate to control the optical frequency separation of light outputs 212 and 222 generated by light source 200, e.g., the difference between the two light sources’ optical center frequencies.

[213] In some embodiments, light source 200 can operate to generate two continuous- wave (CW) light outputs .

[214] In some embodiments, light source 200 can be configured to let light outputs 212 and 222 comprise optical pulse trains of approximately (e.g., to within ±1%) the same period Ti. In some embodiments, the shape of the optical pulses of the pulse train on light output 212 can differ from the shape of the optical pulses of the pulse train on light output 222. In some embodiments, the shape of the optical pulses of the pulse train on light output 212 can be approximately the same as the shape of the optical pulses of the pulse train on light output 222. In some embodiments, controller 230 can be configured to phase-lock said optical pulse trains with respect to one another. In some embodiments, controller 230 can be configured to synchronize said optical pulse trains such that the centers of the optical pulses on light output 212 are temporally aligned with the centers of the pulses on light output 222. As used herein, the term “center of a pulse” refers to a time corresponding to the center of mass of a pulse’s intensity waveform. In some embodiments, controller 230 can be configured to synchronize said optical pulse trains such that the centers of the optical pulses on light output 212 are temporally offset from the centers of the pulses on light output 222 by a fixed amount AT. In some embodiments, AT < Til 2. In some embodiments, AT < Ti / 4.

[215] In some embodiments, controller 230 can invoke light outputs 212 and 222 to carry control information. Control information can be used by other network elements of system 100, e.g., as described in the above-cited U.S. Patent Application No. 16/847,705. As used herein, the term “control information” refers to information imprinted by optical power supply 290 onto one or both of light outputs 212 and 222 (e.g., equally or unequally) for the purpose of controlling, managing, and/or monitoring one or more network elements of system 100, and/or for facilitating various synchronization operations within one or more network elements of system 100. In some embodiments, control information can comprise one or more of: a clock frequency, a clock phase, a synchronization time stamp, a frame delimiter, a frame counter, status information, a heartbeat signal, and a command that can be used to control the behavior of other network elements, such as a master/slave assignment or a reset command. Different types of control information can be imprinted equally or unequally onto both light outputs 212 and 222 using different features thereof. For example, some types of control information can be imprinted using any suitable data modulation equally or unequally imprinted on both light outputs 212 and 222. In various embodiments, control information can be imprinted using an approximately equal change of intensity, phase, frequency, or polarization of light 212 and 222 [216] FIGs. 3A-3E illustrate various features of light outputs 212 and 222 of optical power supply 290 according to some embodiments. FIG. 3A illustrates intensity -versus- time plots of some embodiments of light outputs 212 and 222. In these particular embodiments, light outputs 212 and 222 can be CW at different optical frequencies fi = c/l 1 and f_å= Pk , respectively, where li and l? are the wavelengths associated with optical frequencies f_\ and fi and c is the speed of light in the medium in which the wavelengths are being measured. [217] FIG. 3B illustrates the optical power-spectral densities (PSDs) of light outputs 212 and 222 In some embodiments, the optical frequency difference Af = J/_1-/₂I between light output 212 and light output 222 can be significantly larger than the symbol rate Rs used for communication by a transmitter of node 101 that receives light for modulation from optical power supply 290, i.e., Af » Rs. In some embodiments, Af > 2 Rs. In some other embodiments, Af > 5 Rs. In some other embodiments, the frequency difference Af can be chosen to be approximately (e.g., to within ±10%) an integer multiple of Rs, i.e., Af~ n Rs, with n = 1, 2, 3, ... . In some embodiments, Af ~ Rs. In some embodiments, Af~ 2 Rs_. [218] FIG. 3C shows intensity-versus-time plots of light outputs 212 and 222 for some example embodiments. In these embodiments, light outputs 212 and 222 can, each on a different respective optical center frequency fi ¹ fi, carry an optical pulse train of period Ti and pulse duration Tp. In some embodiments, Tp can be defined as the full-width-at-half height of a pulse’s optical intensity waveform. In other embodiments, Tp can be defined as the reciprocal of the 3-dB bandwidth of the optical pulse spectrum. In some embodiments, Tp can be approximately equal to one half of the pulse train period Ti, i.e., Tp ~ Til 2. In some embodiments, the pulse train of light output 212 can be temporally offset by an amount of time AT relative to the pulse train of light output 222. In some embodiments, the temporal offset AT can be larger than 1.5 times the full-width-at-half-height of the pulses constituting the pulse trains. In some other embodiments, the temporal offset AT can be larger than 2 times the full-width-at-half-height of the pulses constituting the pulse trains. In some embodiments, the temporal offset can be significantly smaller than Til 2.

In some embodiments, the two pulse trains can be temporally aligned, i.e., AT ~ 0. In some embodiments, temporal alignment can imply AT < Tp /10. In some embodiments, temporal alignment can imply AT < Tp /100. In some embodiments, temporal alignment can imply AT < Ti HO. In some embodiments, temporal alignment can imply AT < Til 100. [219] FIGs. 3D and 3E illustrate optical spectra of light outputs 212 and 222 according to some example embodiments. In some embodiments, the frequency separation Af= fi -fi\ can be significantly larger than the pulse repetition rate Ri = l/Ti, i.e., Af » Rp In some other embodiments, Af > 5 R . In some other embodiments, the frequency difference Af can be chosen to be approximately (e.g., to within ±10%) an integer multiple of R , i.e., Af ~ n R , with n = 2, 3, 4, ... . In some embodiments, Af~ 2 R. In some embodiments, Af ~ 3 R. In some embodiments, visualized in FIG. 3E, the complex amplitude of light output 212 and light output 222 can each have a sinusoidal time dependence of period R / 2, i.e., the spectra of light output 212 and light output 222 each comprise two tones spaced by R . The resulting temporal intensity waveforms are therefore proportional to sin²( R t ) for the corresponding pulse trains at light outputs 212 and 222. In various embodiments, the center frequencies of light outputs 212 and 222 can be spaced by 2 R , i.e., the four tones jointly making up light outputs 212 and 222 are all spaced by R In various embodiments, the optical phase difference between spectrally adjacent tones is constant, e.g., the phase difference between the tone at frequency f R / 2 and the tone at frequency f + R / 2 is the same as the phase difference between the tone at frequency f R ! 2 and the tone at frequency f + R 12 Such a constant phase progression can ensure that the temporal skew between pulse trains at light outputs 212 and 222 is approximately zero, e.g., AT= 0. In some embodiments, the tone at frequency f + R / 2 and the tone at frequency f R ! 2 can also have the same phase difference as the phase difference between the tone at frequency f R / 2 and the tone at frequency f + R / 2.

[220] FIGs. 4A-4F illustrate various embodiments of optical power supply 290. Various embodiments corresponding to FIGs. 4A-4C implement some of the schemes described above in reference to FIGs. 3A-3B. In the example embodiment shown in FIG. 4A, two CW laser sources 410 and 420 operate to emit polarized light (i.e., light in respective specific polarization states) at different respective wavelengths li and l? that can be optically amplified using polarization-maintaining optical amplifiers 413 and 423. The two sources of CW light can be polarization-combined using optical polarization combiner 440, configured to combine polarized light on its two input ports 412 and 422 onto two orthogonal polarization states at its output port 441. Spectral characteristics of optical polarization combiner 440 are such that light of both wavelengths li and l? can be passed through with little attenuation. In some embodiments, polarization combiner 440 can be a polarization beam combiner. In some other embodiments, polarization combiner 440 can be a polarization-maintaining optical power combiner. In yet some other embodiments, polarization combiner 440 can be a polarization-maintaining wavelength multiplexer. Polarization combiner 440 can be followed by a polarization-independent optical amplifier 443. Lasers 410 and 420 can be wavelength-controlled by a wavelength controller 430.

[221] In the embodiment of optical power supply 290 shown in FIG. 4B, CW laser source 410 at wavelength li can be free-running or can be wavelength-locked by a wavelength controller 431 and configured to emit polarized light. Light generated by laser source 410 can be amplified by polarization-maintaining optical amplifier 413 before being split by an optical splitter 414. In some embodiments, optical splitter 414 can be a polarization- maintaining optical power splitter. In some other embodiments, optical splitter 414 can be a polarization beam splitter configured to split polarized light incident on its input 415 into two orthogonally polarized parts at its two outputs 416 and 426. In some embodiments, optical splitter 414 can be a linear polarization splitter oriented at 45 degrees relative to the linear polarization state of the incident laser light on its input 415. A portion 416 of the split light at wavelength li can be passed directly to combiner 440, while a portion 426 of the split light can be frequency-shifted using an optical frequency shifter 424, driven by, e.g., a sinusoidal electrical reference signal 432. In some embodiments, frequency shifter

424 includes one of: an acousto-optic modulator, a single-sideband modulator, and a Mach-Zehnder modulator. In some embodiments, frequency shifter 424 can be followed by an optional optical bandpass filter 425 that can pass only one of the several tones that can be generated by the upstream frequency shifter 424. An additional optical amplifier 423 can be used to compensate for optical losses. Frequency-shifted light at port 422 can be polarization-combined with frequency un-shifted light at port 412 in combiner 440.

[222] In the embodiment of optical power supply 290 shown in FIG. 4C, CW laser source 410 can be free-running or wavelength-controlled by wavelength controller 431. The output of laser source 410 can be modulated by an optical modulator 417 driven by an electrical signal generator 433. Modulator 417 can be configured to split a CW optical field at its input into two spectral tones at its output. For example, modulator 417 can be a Mach-Zehnder modulator biased at its transmission null and driven by a sinusoidal electrical signal whose amplitude is substantially smaller than the modulator’s half-wave voltage and whose period is T. This mode of operation is known to suppress the incoming CW tone at optical frequency /o and to produce two spectral tones at /i_,2 =/o ± / at the modulator output. The two tones constituting an optical field 418 can be frequency-split by an optical frequency splitter 419 into portions 416 and 426. In some embodiments, optical frequency splitter 419 can be implemented using an optical (de)interleaver.

Portions 416 and 426 can then be polarization-orthogonally combined using combiner 440. In some embodiments, modulator 417 can further be configured to imprint control information on optical field 418. For example, modulator 417 can be configured to periodically extinguish light of optical field 418 for a brief amount of time. In some embodiments, modulator 417 can be configured to extinguish light of optical field 418 for a duration of 2 Ts once per period of duration 1000 Ts. In some embodiments, modulator 417 can be configured to modulate a time stamp onto light 418 for a duration of 10 Ts once per period of duration 10000 Ts. [223] Various embodiments shown in FIGs. 4D-4F implement some of the schemes described above in reference to FIGs. 3C-3E. In the embodiment of optical power supply 290 shown in FIG. 4D, two laser sources 410 and 420 can emit polarized light at different wavelengths li and %2. In some embodiments, wavelengths li and l? and/or their difference can be controlled by wavelength controller 430. In some embodiments, lasers 410 and 420 can emit CW light. In some other embodiments, light emitted by one or both of lasers 410 and 420 can comprise an optical pulse train. In some embodiments, light emitted by lasers 410 and 420 can be modulated using optical modulators 417 and 427, driven by respective electrical signals generated by signal generator 433. In some embodiments, laser 410 and modulator 417, as well as laser 420 and modulator 427, together with signal generator 433, can be configured such that modulated optical fields 456 and 457 each comprise an optical pulse train with period Ti. In various embodiments, modulators 417 and 427 can be electro-absorption modulators, ring modulators, Mach- Zehnder modulators, or in-phase/quadrature (IQ) modulators. In some embodiments, modulators 417 and 427 and signal generator 433 can be configured to generate optical fields 456 and 457 that are periodically modulated in both amplitude and phase, including chirped and arbitrarily pre-distorted optical fields, e.g., dispersion pre-distorted optical fields. In some embodiments, the functionalities of light generation and modulation provided by laser 410 and modulators 417 as well as by laser 420 and modulators 427 can each be implemented using a single direct-modulated laser or a mode-locked laser. In some embodiments, the output of modulator 427 can be delayed by an optical delay element 419. In some embodiments, delay element 419 can be implemented using a length of optical fiber. In some other embodiments, delay element 419 can be a lumped free- space optical delay element. In some embodiments, the delay AT imposed by delay element 419 onto optical pulse train 457 relative to optical pulse train 456 can be less than half the period of the optical pulse train, i.e., AT < Ti/2. In some other embodiments, the delay imposed by delay element 419 onto optical pulse train 457 relative to optical pulse train 456 can be less than half the period of the optical pulse train modulo an integer multiple of 7}, i.e., AT + k Ti, with k = ±1, ±2, ±3, .... In some embodiments, individual pulses of optical pulse trains 456 and 457 can have substantially similar intensity waveforms. In some other embodiments, individual pulses of optical pulse trains 456 and 457 can have different intensity waveforms. Optical pulse trains 456 and 457 can be polarization-combined using combiner 440, configured to combine light on its two input ports onto orthogonal polarizations at its output port. In some embodiments, a chromatic- dispersion-compensating optical element 470 can pre-disperse polarization-multiplexed optical pulse trains. In some embodiments, chromatic-dispersion-compensating optical element 470 can be a grating-based or an etalon-based optical dispersion compensator. In some other embodiments, chromatic-dispersion-compensating optical element 470 can be implemented using a length of dispersion-compensating optical fiber. In some embodiments, modulators 417 and 427 can further be configured to imprint control information on optical pulse trains 456 and 457. For example, modulators 417 and 427 can be configured to periodically extinguish light 456 and 457 for a brief amount of time. In some embodiments, modulators 417 and 427 can be configured to extinguish light 456 and 457 for a duration of 2 Ts once per period of duration 1000 Ts. In some embodiments, modulators 417 and 427 can be configured to modulate a time stamp onto light 456 and 457 for a duration of 10 Ts once per period of duration 10000 Ts.

[224] In the embodiment of optical power supply 290 shown in FIG. 4E, two laser sources 410 and 420 can emit polarized light at different respective wavelengths li and ki_¬ ln some embodiments, wavelengths li and li and/or their difference can be controlled by wavelength controller 430. Light generated by laser 410 and laser 420 can be combined by a polarization-maintaining optical combiner 428. In some embodiments, polarization- maintaining optical combiner 428 can be a polarization-maintaining optical power combiner. In some embodiments, polarization-maintaining optical combiner 428 can be a polarization-maintaining optical wavelength multiplexer. Combined light can be modulated by optical modulator 417 driven by electrical signal generator 433 to generate at each of wavelengths li and l? an optical pulse train at modulator output 418. The light outputted by modulator 417 can be split into two portions 456 and 457 using splitter 414.

In some embodiments, portion 456 can be passed directly to combiner 440 while portion 457 of can be optically delayed by delay element 419. Optionally relatively delayed portions 456 and 457 can be polarization-combined using combiner 440, configured to combine light on its two input ports onto orthogonal polarizations at its output port. In some embodiments, chromatic-dispersion-compensating optical element 470 can pre disperse polarization-multiplexed optical pulse trains. In some embodiments, modulator 417 can further be configured to imprint control information on light output 418. For example, modulator 417 can be configured to periodically extinguish light 418 for a brief amount of time. In some embodiments, modulator 417 can be configured to extinguish light 418 for a duration of 2 Ts once per period of duration 1000 Ts. In some embodiments, modulator 417 can be configured to modulate a time stamp onto light 418 for a duration of 10 Ts once per period of duration 10000 Ts. [225] In the embodiment of optical power supply 290 shown in FIG. 4F, CW laser source

410 can be free-running or wavelength-controlled by wavelength controller 431. The output of laser source 410 can be modulated by optical modulator 417 driven by electrical signal generator 433. Modulator 417 can be a polarization-diversity in-phase/quadrature (IQ) modulator (PDM-IQM), comprising a total of four Mach-Zehnder modulators (labeled Ix-MZM, Qx-MZM, Iy-MZM, and Qy-MZM, FIG. 4F) in a nested configuration, with the “Q” paths having built-in an optical phase shift of 90 degrees relative to the “I” paths. PDM-IQM 417 and signal generator 433 can be configured to produce the spectrum shown in FIG. 3E, e.g., as follows: Signals 433i_x, 433Q_x, 433i_y, and 433Q_y are configured to be electrical signals with a voltage swing that is not significantly larger than the half-wave voltage of each Mach-Zehnder modulator, and with a temporal dependence of, respectively, cos(n Rit) + cos(3n Rit), - sin(n Rit) - sin(3n Rit), cos(n Rit) + cos(3n Rit), and sin(uf¾7) + sin(3uf¾7). In some embodiments, electrical signals 433i_x, 433Q_x, 433i_y, and 433Q_y can be generated using digital-to-analog converters (not explicitly shown in FIG. 4F). In some embodiments, modulator 417 can further be configured to imprint control information on light 456 and 457. For example, modulator 417 can be configured to periodically extinguish light 456 and 457 for a brief amount of time. In some embodiments, modulator 417 can be configured to extinguish light 456 and 457 for a duration of 2 Ts once per period of duration 1000 Ts. In some embodiments, modulator 417 can be configured to modulate a time stamp onto light 456 and 457 for a duration of 10 Ts once per period of duration 10000 Ts.

[226] FIG. 5 shows a block diagram of a distributed optical transmitter 500 that can be used in optical communication system 100 of FIG. 1 according to an embodiment. Transmitter 500 comprises optical power supply 290 and a transmit module 504. As indicated in FIG. 5, optical power supply 290 can be a part of optical power supply module 103. In operation, optical power supply 290 can generate a light supply on output 242, e.g., as described in reference to one or more of FIGs. 3A-3E. Output 242 of optical power supply 290 is optically coupled to transmit module 504 by way of an optical fiber 543, which can be a part of, e.g., fiber link 102r, In different embodiments, transmit module 504 can be a part of different network elements of system 100. For illustration purposes and without any implied limitation, transmit module 504 is described herein in reference to an embodiment in which said transmit element is a part of node lOli. [227] In some embodiments, optical fiber 543 can include one or more sections of non- polarization-maintaining optical fiber. In such embodiments, light supplied by optical power supply module 103 to node lOli can experience random polarization rotation upon propagation through optical fiber 543. Owing to this random polarization rotation, light supplied by optical fiber 543 can arrive at node lOli such that the two polarized components of light output 242 are in two random, but relatively orthogonal states of polarization when entering transmit module 504 via an optical interface 510 thereof. The relative orthogonality can be maintained, e.g., because both of the two polarized components of light output 242 are subjected to substantially the same (albeit random) polarization rotations in the one or more sections of non-polarization-maintaining optical fiber.

[228] In some embodiments, optical interface 510 can comprise one or more optical connectors, one or more edge-coupling mechanisms to a photonic integrated circuit (PIC), one or more vertical coupling mechanisms to a PIC, etc. Optical interface 510 is connected to an optical polarization splitter 515. In some embodiments, the polarization splitting function of optical polarization splitter 515 can be integrated into optical interface 510. For example, in some embodiments, a polarization-diversity vertical grating coupler can be configured to simultaneously act as a polarization splitter 515 and as a part of optical interface 510. In some other embodiments, an optical connector comprising a polarization-diversity arrangement can simultaneously act as an optical interface 510 and as a polarization splitter 515.

[229] Owing to the polarization-multiplexed nature as well as the time/frequency orthogonality of the light generated by optical power supply 290 on output 242, any arbitrary polarization rotation within fiber link 102r, results in a substantially equal optical power split between output ports 516 and 517 of optical polarization splitter 515 (e.g., see a detailed description of FIGs. 7A-7D below). Therefore, light on ports 516 and 517 can be used as a relatively stable optical power supply for optical modulation within transmit module 504, which is independent of random polarization rotations that might be occurring within link 102e.

[230] Optical modulators 530i and 5302 receive supply light on respective polarization splitter outputs 516 and 517 and modulate data onto said light using one or more electrical drive signals 531i and 5312, thereby producing respective modulated optical signals on modulator outputs 532i and 5312, respectively. In various embodiments, modulation can be done in any one or more of intensity, phase, polarization, and frequency. In some embodiments, modulation can be done at a modulation symbol rate 1/7}. In some embodiments, a polarization rotator 506 can be employed to convert orthogonal output polarization states at polarization splitter outputs 516 and 517 to equal polarization states on ports 516 and 517' for subsequent modulation. For example, polarization splitter 515 can split light incident on its input port into transversal-magnetic (TM) and transversal- electric (TE) polarizations at its two outputs 516 and 517, respectively. If modulators 530 are both designed for modulating TE-polarized light, then polarization rotator 506 can be used to rotate TM-polarized light on port 517 to TE-polarized light on port 517'. In some embodiments, polarization rotator 506 can be a part of polarization splitter 515.

[231] Modulated light on modulator output ports 532i and 5322 can be passed to different respective fibers of link 102i for communication of information to another node of system 100, which in the example case shown in FIG. 5 is node IOI2. Some example signals that can be used and/or generated in transmitter 500 are described below in reference to FIG. 8.

[232] FIG. 6 shows a block diagram of an optical transmit module 600 that can be used in system 100 according to an embodiment. Transmit module 600 can be implemented using some of the same elements as transmit module 504, e.g., as indicated by the corresponding matching reference numerals in FIGs. 5 and 6. In different embodiments, transmit module 600 can be a part of different network elements of system 100. For illustration purposes and without any implied limitation, transmit module 600 is described below in reference to an embodiment in which said transmit module is a part of node lOli. [233] In operation, transmit module 600 can receive light from optical port 242 of optical power supply 290 contained within optical power supply module 103 via optical interface 510 and optical link 102e (also see FIGs. 1 and 5). Optical interface 510 is connected to optical polarization splitter 515. In some embodiments, the polarization splitting function of optical polarization splitter 515 can be integrated into optical interface 510. In some embodiments, optical polarization splitter 515 can further be connected to one or more

(e.g., cascaded) optical splitters 620, only two of which are shown in FIG. 6 for illustration purposes. In various embodiments, an optical splitter 620 can be constructed, e.g., as known in the pertinent art, using one or more of: optical power splitters, wavelength splitters, and spatial -distribution splitters, such as spatial-mode splitters or multi -core-fiber fanouts.

[234] Optical modulators 530 of transmit module 600 receive light on respective optical- splitter outputs 622 and modulate data onto said light using one or more electrical drive signals 531, thereby producing respective modulated optical signals on modulator outputs 532. In various embodiments, modulation can be done in any one or more of intensity, phase, polarization, and frequency. In some embodiments, modulation can be done at a modulation symbol rate Rs = Ri= 1/7}.

[235] In some embodiments, one or more modulators 530 can at times not modulate information onto light of outputs 622. Alternatively or in addition, one or more of the shown modulators 530 can be omitted from (i.e., not present in) the structure of transmit module 600. In such cases, light of the corresponding output(s) 622 can be passed through transmit module 600 on to other network elements of system 100, e.g., in accordance with the above-provided functional description of certain aspects of system 100 (FIG. 1). In some embodiments, some of such passed-on light 622 can be used by other network elements of system 100 as an optical power supply. In some embodiments, some of such passed-on light 622 can be received by other network elements of system 100 to extract control information therefrom. [236] In some embodiments, some modulators 530 of transmit module 600 can be configured to use more than one electrical drive signal 531 to modulate light received from the corresponding output 622. Examples of such modulators 530 include but are not limited to in-phase/quadrature (IQ) modulators and segmented-electrode modulators. In various embodiments, opto-electronic modulators 530 can comprise electro-absorption modulators, ring modulators, or Mach-Zehnder modulators. In various embodiments, opto-electronic modulators 530 can be made of semiconductor materials, materials used in Silicon Photonics, polymer materials, or Lithium Niobate. In some embodiments, opto electronic modulators 530 can at least partially be integrated in one or more PICs (not explicitly shown in FIG. 6). In various embodiments, electrical drive signals 531 can be binary or multilevel. In some embodiments, electrical drive signals 531 can be suitably pulse-shaped or can be pre-distorted using digital or analog filters, or can be electrically amplified using electrical driver amplifiers.

[237] In some embodiments, some of the light on optical splitter outputs 622 can be detected using one or more optical receivers 680 to extract information contained therein. Such information can include, without limitation, one or more frequency components, one or more time skew or clock phase values, and one or more pieces of control information embedded within the supply light generated by optical power supply module 103.

[238] In some embodiments, information extracted by optical receivers 680 can be provided to devices external to transmit module 600 on an output port 681 thereof for further use within system 100, such as for network traffic synchronization/arbitration/scheduling, database time-stamping, local clock synchronization, etc. In some embodiments, information extracted by optical receiver(s) 680 can be fed into an electronic signal processor 612. In some embodiments, electronic signal processor 612 can receive one or more electrical signals 614 and can pre-process those electrical signals to generate electrical drive signals 531 for modulators 530. In some embodiments, pre-processing can comprise any form of analog, digital, or mixed-signal manipulation, including but not limited to retiming, de-skewing, buffering, bit stuffing, bit removal, forward error correction coding, line coding, framing, insertion of pilots and packet headers, time-stamping, linear and nonlinear pre-compensation, pre-equalization, pre-emphasis, and pre-distortion. [239] In some embodiments, modulated light on modulator outputs 532 can be multiplexed in wavelength, polarization, or spatial distribution of the optical field using one or more multiplexers 624 to generate one or more optical multiplexed signals 652. Multiplexed signals 652 can then be transmitted via one or more output interfaces 650 to one or more optical fibers 102i. In some embodiments, output interfaces 650 can be implemented, e.g., as one or more optical fiber connectors, one or more edge couplers from PIC to fibers, or one or more vertical couplers from PIC to fibers. In some embodiments, certain multiplexing functions of multiplexer 624 can be integrated into certain output interfaces 650. For example, in some embodiments, a polarization-diversity vertical grating coupler can simultaneously act as a polarization multiplexer of multiplexer 624 and as a part of an output interface 650. In some other embodiments, an optical connector comprising a polarization-diversity arrangement can simultaneously act as an output interface 650 and as a polarization multiplexer 624.

[240] In some embodiments, each modulator output 532 can be passed directly to a corresponding optical fiber or to a corresponding optical fiber core of fiber link 102i via a corresponding output interface 650, i.e., without undergoing any multiplexing therebetween. In other words, multiplexer 624 or some parts thereof may not be present in some embodiments.

[241] FIGs. 7A-7D graphically show some example use cases, e.g., illustrating the polarization-rotation independent optical power splitting within transmit modules 504 and 600, that can be implemented based on embodiments of optical power supply 290 within optical power supply module 103.

[242] FIG. 7A shows a Poincare sphere, conventionally used to visualize polarization states of light. Mutually orthogonal polarization states are found at diametrically opposed locations on the sphere. For example, linear polarization states are found on the equator of the sphere, with one orthogonal pair including horizontal linear polarization (HLP) and vertical linear polarization (VLP), and another orthogonal pair including ±45-degree (LP±45-deg) linear polarizations being indicated in FIG. 7A. The orthogonal pair of right- circular polarization (RCP) and left-circular polarization (LCP) is found on the two poles of the Poincare sphere, as is also indicated in FIG. 7A.

[243] FIG. 7B shows intensity-versus-time plots of the light at the two output ports 516 and 517 of polarization splitter 515 (also see FIGs. 5 and 6) for an example case, wherein optical power supply 103 transmits CW wavelength li in HLP and CW wavelength l2 in VLP (also see FIGs. 3A-3B). Time intervals (A), (B), and (C), which are neither implied to occur in the shown temporal succession nor to be characterized by sharp transitions therebetween, correspond to three different example instantiations of random polarization rotations, wherein: during time interval (A), fiber link 102r, does not rotate the polarization; during time interval (B), fiber link 102r, rotates the polarizations to the LP±45-deg states; and during time interval (C), fiber link 102r, rotates the polarizations to the RCP/LCP states. As optical power supply 290 is configured to transmit two time/frequency-orthogonal optical fields in two orthogonal polarization states, the light intensities at output ports 516 and 517 of polarization splitter 515 will be approximately constant, irrespective of random polarization rotations at the polarization splitter input. [244] For the time interval (A), polarization splitter 515 operates to: (i) direct light of wavelength li substantially exclusively to output port 516; and (ii) direct light of wavelength l2 substantially exclusively to output port 517. For the time interval (B), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of light at wavelength li and at wavelength %2. Likewise, for the time interval (C), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of light at wavelength li and at wavelength %2. Not shown in FIG. 7B, for time intervals (B) and (C), are possible beat frequency oscillations at the difference frequency Af= ]/i -/₂I between the two CW tones at wavelengths li and %2. However, as long as D/is chosen sufficiently large compared to the symbol rate Rs, these oscillations can average out within each modulation symbol of transmitter 500 and, as such, may not significantly affect the performance. Choosing Af smaller than Rs can result in slow fading of the light output at each individual port 516 and 517. More specifically, light incident at polarization splitter 515 can periodically transition between appearing entirely on output port 516 (with no light appearing on output port 517) and appearing entirely on output port 517 (with no light appearing on output port 516).

This periodic transition of light between ports 516 and 517 can occur at a period Af, and if D/is significantly smaller than Rs can lead to some modulation time slots on each polarization splitter output port receiving no or insufficient light to modulate information onto. Choosing Af to be significantly larger than Rs lets the light transitions between ports 516 and 517 occur multiple times per symbol period, so that every symbol time slot always receives half the light supplied by optical power supply 103. Choosing Af equal to Rs can result in either constant power during the time interval (A) or in sin²( Rs t) shaped pulses during the time intervals (B) and (C) at ports 516 and 517. This particular configuration can be useful for some modes of operation. Similarly, choosing Af equal to an integer multiple of Rs (D/= n Rs, n = 1, 2, 3, ...) can be a beneficial mode of operation.

[245] FIG. 7C shows the optical power at the two output ports 516 and 517 of polarization splitter 515 for the example use case, wherein optical power supply 103 operates to transmit temporally partially overlapping pulse trains (i.e., AT < Tp) at wavelengths li and Xi in HLP and VLP (also see FIG. 3C). Time intervals (A), (B), and (C) correspond to the same three instantiations of random polarization fluctuations as in

FIG. 7B. For the time interval (A), polarization splitter 515 operates to: (i) direct the pulse train at wavelength li substantially exclusively to output port 516; and (ii) direct the pulse train at wavelength l? substantially exclusively to output port 517. For the time interval (B), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of the pulse train at wavelength li and the pulse train at wavelength X2. Likewise, for the time interval (C), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of the pulse train at wavelength li and the pulse train at wavelength X2. Not shown in FIG. 7C, for time intervals (B) and (C), are possible beat frequency oscillations at the difference frequency Af= J/i -fi\ during times when pulses at wavelength li temporally overlap with pulses at wavelength X2. However, as long as D/is chosen sufficiently large compared to the symbol rate Rs, these oscillations can average out within each modulation symbol of transmitter 500 and, as such, may not significantly affect the performance. More precisely, the total optical energy within a time period corresponding to twice the total optical pulse duration Tp measured at the polarization-splitting interface 515 can remain approximately constant, irrespective of the polarization state at the input to polarization splitter 515.

[246] FIG. 7D shows the optical power at the two output ports 516 and 517 of polarization splitter 515 for the example use case, wherein optical power supply 103 operates to transmit four tones separated by Ri , two in HLP and two in VLP (also see FIG. 3E). Time intervals (A), (B), and (C) correspond to the same three instantiations of random polarization fluctuations as in FIG. 7B. For the time interval (A), polarization splitter 515 operates to: (i) direct the two lower-frequency tones at frequencies fi - Ri /2 and fi + Ri 12 substantially exclusively to output port 516; and (ii) direct the two higher-frequency tones at frequencies fi Ri /2 and fi Ri /2 substantially exclusively to output port 517. In the time domain, output ports 516 and 517 can therefore exhibit time-aligned sin²-shaped optical intensity pulses. For the time interval (B), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of the four tones shown in FIG. 3E. Likewise, for the time interval (C), polarization splitter 515 operates to cause each of output ports 516 and 517 to have an approximately equal amount of the four tones shown in FIG. 3E. Owing to the close spacing of the two lower- frequency tones and the two higher-frequency tones, beat oscillations can be clearly visible in (B) and (C). However, due to the specific nature of the four-tone dual-polarization optical field, the pulse energy can always stay well confined near a common center-of- mass line, e.g., 710, irrespective of polarization rotations. This confinement of pulse energies at a specific temporal location within a symbol period irrespective of polarization rotations on fiber link 102r, can be beneficial for modulation within transmit module 504. [247] As exemplified by the results graphically shown in FIGs. 7B-7D, the use of various embodiments of optical power supply module 103 beneficially causes polarization splitter 515 to passively perform a substantially equal-power split between output ports 516 and 517 thereof regardless of polarization rotations within one or more sections of non- polarization-maintaining optical fiber disposed between optical power supply module 103 and the host device (e.g., transmit module 504, FIG. 5) of polarization splitter 515. This passive, equal-power split in polarization splitter 515 is enabled, e.g., by the above- described example configurations of optical power supply module 103, according to which the light outputted at output port 242 thereof has two components that are both time/frequency orthogonal to one another and polarization-orthogonal. The latter characteristic of the received light then causes polarization splitter 515 to perform the substantially equal-power split between output ports 516 and 517 thereof passively, i.e., without the use of any tuning or active power-control mechanisms. The light produced at output ports 516 and 517 can then advantageously be used, e.g., as an optical carrier onto which data information can be modulated by transmit module 504. [248] As a result of the above-described operation of polarization splitter 515, during some time intervals (e.g., time interval (A)) optical modulator 530i can receive supply light at a first optical center frequency but not at a second optical center frequency, and modulator 5302 can receive supply light at the second optical center frequency but not at the first optical center frequency; during some time intervals (not explicitly shown in FIG. 7) optical modulator 530i can receive supply light at the second optical center frequency but not at the first optical center frequency, and modulator 5302 can receive supply light at the first optical center frequency but not at the second optical center frequency; during some time intervals (e.g., time intervals (B) and (C)) optical modulator 530i can receive supply light at both the first optical center frequency and the second optical center frequency, and modulator 5302 can also receive supply light at both the first optical center frequency and the second optical center frequency. [249] FIG. 8 graphically illustrates some signals used/generated in optical transmitter 500

(FIG. 5) and the corresponding electrical signals recovered by a corresponding optical data receiver according to an example embodiment. More specifically, the following time- dependent signals are shown in FIG. 8:

(i) light supply waveforms at ports 516 and 517, respectively, corresponding to the embodiment of FIG. 3E. These waveforms are shown for three different polarization rotations in optical fiber 543, i.e., for time intervals (A), (B), and (C), as per FIG. 7D;

(ii) electrical drive signals 531i and 5312 driving optical modulators 530i and 5302, FIG. 5. For illustration purposes, the modulation format imprinted onto the supply light is binary on/off keying (OOK) in this example embodiment (a person of ordinary skill in the art will understand that any other optical modulation format can also be imprinted onto the supply light, including multi-level and multi-dimensional formats using any physical modulation dimension of the supply light’s optical field, such as its amplitude, phase, in phase/quadrature components, frequency, and polarization). The exemplary binary data sequence represented by electrical drive signal 531i is [01101010...01101010...01101010] The exemplary binary data sequence represented by electrical drive signal 531₂ is [01011100...01011100...01011100];

(iii) modulated optical output signals 532i and 5322 generated by transmit module 504 in response to the shown electrical drive signals 531i and 5312, respectively; and

(iv) electrical signals 801 and 802 generated by a direct-detection optical receiver in response to the shown modulated optical output signals 532i and 5322, respectively. The direct-detection optical receiver is modeled to have a first-order Gaussian low-pass characteristic of an electrical bandwidth equal to the symbol rate. The accurate and substantially jitter-free reconstruction of electrical data signals 531i and 5322 by electrical signals 801 and 802 is evident, irrespective of the polarization rotation exerted by optical fiber 543.

[250] FIG. 9 shows an optical communications system 900 that includes an optical power supply (also referred to as an external photon supply) 902, a first data processing apparatus

904, and a second data processing apparatus 906. The first data processing apparatus 904 includes a first chip 905, and the second data processing apparatus 906 includes a second chip 908. The system 900 enables high-speed communications between the first chip 905 and the second chip 908 using co-packaged optical interconnect modules 910 similar to those shown in, e.g., FIGS. 2-5 and 17 of U.S. application 63/145,368. Each of the first and second chips 906, 908 can be a high-capacity chip, e.g., a high bandwidth Ethernet switch chip.

[251] The first and second chips 906, 908 communicate with each other through an optical fiber interconnection cable 912 that includes a plurality of optical fibers. In some implementations, the optical fiber interconnection cable 912 can include optical fiber cores that transmit data and control signals between the first and second chips 906, 908. The optical fiber interconnection cable 912 also includes one or more optical fiber cores that transmit optical power supply light from the optical power supply or photon supply 902 to the photonic integrated circuits in the co-packaged optical interconnect modules 910 that provide optoelectronic interfaces for the first and second chips 906, 908.

[252] The optical fiber interconnection cable 912 can include single-core fibers or multi core fibers. Each single-core fiber includes a cladding and a core, typically made from glasses of different refractive indices such that the refractive index of the cladding is lower than the refractive index of the core to establish a dielectric optical waveguide. Each multi- core optical fiber includes a cladding and multiple cores, typically made from glasses of different refractive indices such that the refractive index of the cladding is lower than the refractive index of the core. More complex refractive index profiles, such as index trenches, multi-index profiles, or gradually changing refractive index profiles can also be used. More complex geometric structures such as non-circular cores or claddings, photonic crystal structures, photonic bandgap structures, or nested antiresonant nodeless hollow core structures can also be used. [253] The example of FIG. 9 illustrates a switch-to- switch use case. The external optical power supply or photon supply 902 provides optical power supply signals, which can be, e.g., continuous-wave light, one or more trains of periodic optical pulses, or one or more trains of non-periodic optical pulses. The power supply light is provided from the photon supply 902 to the co-packaged optical interconnect modules 910 through optical fibers 914 and 916, respectively. For example, the optical power supply 902 can provide continuous wave light, or both pulsed light for data modulation and synchronization, as described in U.S. patent application 16/847,705. This allows the first chip 905 to be synchronized with the second chip 908. [254] For example, the photon supply 902 can correspond to the optical power supply 103 of FIG. 1. The pulsed light from the photon supply 902 can be provided to the link 102₆ of the data processing system 200 of FIG. 20 of U.S. application 63/145,368. In some implementations, the photon supply 902 can provide a sequence of optical frame templates, in which each of the optical frame templates includes a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The modulators 417 of FIG. 20 of U.S. application 63/145,368 can load data into the respective frame bodies to convert the sequence of optical frame templates into a corresponding sequence of loaded optical frames that are output through optical fiber link

102i. [255] FIG. 10 shows an example of an optical communications system 1000 providing high-speed communications between a high-capacity chip 1002 (e.g., an Ethernet switch chip) and multiple lower-capacity chips 1004a, 1004b, 1004c, e.g., multiple network interface chips attached to computer servers using co-packaged optical interconnect modules 910 similar to those shown in FIG. 9. The high-capacity chip 1002 communicates with the lower-capacity chips 1004a, 1004b, 1004c through a high-capacity optical fiber interconnection cable 1008 that later branches out into several lower-capacity optical fiber interconnection cables 1010a, 1010b, 1010c that are connected to the lower-capacity chips 1004a, 1004b, 1004c, respectively. This example illustrates a switch-to-servers use case. [256] An external optical power supply or photon supply 1012 provides optical power supply signals, which can be continuous-wave light, one or more trains of periodic optical pulses, or one or more trains of non-periodic optical pulses. The power supply light is provided from the photon supply 1012 to the optical interconnect modules 1006 through optical fibers 1014, 1016a, 1016b, 1016c, respectively. For example, the optical power supply 1012 can provide both pulsed light for data modulation and synchronization, as described in U.S. patent application 16/847,705. This allows the high-capacity chip 1002 to be synchronized with the lower-capacity chips 1004a, 1004b, and 1004c. [257] FIG. 11 shows an optical communications system 1100 providing high-speed communications between a high-capacity chip 1102 (e.g., an Ethernet switch chip) and multiple lower-capacity chips 1104a, 1104b, e.g., multiple network interface chips, attached to computer servers using a mix of co-packaged optical interconnect modules 901 similar to those shown in FIG. 9 as well as conventional pluggable optical interconnect modules 1108.

[258] An external optical power supply or photon supply 1106 provides optical power supply signals, which can be continuous-wave light, one or more trains of periodic optical pulses, or one or more trains of non-periodic optical pulses. For example, the optical power supply 1106 can provide both pulsed light for data modulation and synchronization, as described in U.S. patent application 16/847,705. This allows the high-capacity chip 1102 to be synchronized with the lower-capacity chips 1104a and 1104b.

[259] FIGS. 9 to 11 show examples of optical communications systems 900, 1000, 1100 in which in each system an optical power supply or photon supply provides optical power supply light to photonic integrated circuits hosted in multiple communication devices (e.g., optical transponders), and the optical power supply is external to the communication devices. The optical power supply can have its own housing, electrical power supply, and control circuitry, independent of the housings, electrical power supplies, and control circuitry of the communication devices. This allows the optical power supply to be serviced, repaired, or replaced independent of the communication devices. Redundant optical power supplies can be provided so that a defective external optical power supply can be repaired or replaced without taking the communication devices off-line. The external optical power supply can be placed at a convenient centralized location with a dedicated temperature environment (as opposed to being crammed inside the communication devices, which can have a high temperature). The external optical power supply can be built more efficiently than individual power supply units, as certain common parts such as monitoring circuitry and thermal control units can be amortized over many more communication devices. The following describes implementations of the fiber cabling for remote optical power supplies.

[260] FIG. 12 is a system functional block diagram of an example of an optical communication system 1200 that includes a first communication transponder 1202 and a second communication transponder 1204. Each of the first and second communication transponders 1202, 1204 can include one or more co-packaged optical modules described above. Each communication transponder can include, e.g., one or more data processors, such as network switches, central processing units, graphics processor units, tensor processing units, digital signal processors, and/or other application specific integrated circuits (ASICs). In this example, the first communication transponder 1202 sends optical signals to, and receives optical signals from, the second communication transponder 1204 through a first optical communication link 1206. The one or more data processors in each communication transponder 1202, 1204 process the data received from the first optical communication link 1206 and outputs processed data to the first optical communication link 1206. The optical communication system 1200 can be expanded to include additional communication transponders. The optical communication system 1200 can also be expanded to include additional communication between two or more external photon supplies, which can coordinate aspects of the supplied light, such as the respectively emitted wavelengths or the relative timing of the respectively emitted optical pulses. [261] A first external photon supply 1208 provides optical power supply light to the first communication transponder 1202 through a first optical power supply link 1210, and a second external photon supply 1212 provides optical power supply light to the second communication transponder 1204 through a second optical power supply link 1214. In one example embodiment, the first external photon supply 1208 and the second external photon supply 1212 provide continuous wave laser light at the same optical wavelength. In another example embodiment, the first external photon supply 1208 and the second external photon supply 1212 provide continuous wave laser light at different optical wavelengths. In yet another example embodiment, the first external photon supply 1208 provides a first sequence of optical frame templates to the first communication transponder 1202, and the second external photon supply 1212 provides a second sequence of optical frame templates to the second communication transponder 1204. For example, as described in U.S. patent 16/847,705, each of the optical frame templates can include a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The first communication transponder 1202 receives the first sequence of optical frame templates from the first external photon supply 1208, loads data into the respective frame bodies to convert the first sequence of optical frame templates into a first sequence of loaded optical frames that are transmitted through the first optical communication link 1206 to the second communication transponder 1204. Similarly, the second communication transponder 1204 receives the second sequence of optical frame templates from the second external photon supply 1212, loads data into the respective frame bodies to convert the second sequence of optical frame templates into a second sequence of loaded optical frames that are transmitted through the first optical communication link 1206 to the first communication transponder 1202.

[262] FIG. 13A is a diagram of an example of an optical communication system 1300 that includes a first switch box 1302 and a second switch box 1304. Each of the switch boxes 1302, 1304 can include one or more data processors, such as network switches. The first and second switch boxes 1302, 1304 can be separated by a distance greater than, e.g., 1 foot, 3 feet, 10 feet, 100 feet, or 1000 feet. The figure shows a diagram of a front panel 1306 of the first switch box 1302 and a front panel 1308 of the second switch box 1304. In this example, the first switch box 1302 includes a vertical ASIC mount grid structure 1310, similar to the grid structure 870 of FIG. 43 of U.S. application 63/145,368. A co-packaged optical module 1312 is attached to a receptor of the grid structure 1310. The second switch box 1304 includes a vertical ASIC mount grid structure 1314, similar to the grid structure 870 of FIG. 43 of U.S. application 63/145,368. A co-packaged optical module 1316 is attached to a receptor of the grid structure 1314. The first co-packaged optical module 1312 communicates with the second co-packaged optical module 1316 through an optical fiber bundle 1318 that includes multiple optical fibers. Optional fiber connectors 1320 can be used along the optical fiber bundle 1318, in which shorter sections of optical fiber bundles are connected by the fiber connectors 1320.

[263] In some implementations, each co-packaged optical module (e.g., 1312, 1316) includes a photonic integrated circuit configured to convert input optical signals to input electrical signals that are provided to a data processor, and convert output electrical signals from the data processor to output optical signals. The co-packaged optical module can include an electronic integrated circuit configured to process the input electrical signals from the photonic integrated circuit before the input electrical signals are transmitted to the data processor, and to process the output electrical signals from the data processor before the output electrical signals are transmitted to the photonic integrated circuit. In some implementations, the electronic integrated circuit can include a plurality of serializers/deserializers configured to process the input electrical signals from the photonic integrated circuit, and to process the output electrical signals transmitted to the photonic integrated circuit. The electronic integrated circuit can include a first serializers/deserializers module having multiple serializer units and deserializer units, in which the first serializers/deserializers module is configured to generate a plurality of sets of first parallel electrical signals based on a plurality of first serial electrical signals provided by the photonic integrated circuit, and condition the electrical signals, in which each set of first parallel electrical signals is generated based on a corresponding first serial electrical signal. The electronic integrated circuit can include a second serializers/deserializers module having multiple serializer units and deserializer units, in which the second serializers/deserializers module is configured to generate a plurality of second serial electrical signals based on the plurality of sets of first parallel electrical signals, and each second serial electrical signal is generated based on a corresponding set of first parallel electrical signals. The plurality of second serial electrical signals can be transmitted toward the data processor. [264] The first switch box 1302 includes an external optical power supply 1322 (i.e., external to the co-packaged optical module) that provides optical power supply light through an optical connector array 1324. In this example, the optical power supply 1322 is located internal of the housing of the switch box 1302. Optical fibers 1326 are optically coupled to an optical connector 1328 (of the optical connector array 1324) and the co- packaged optical module 1312. The optical power supply 1322 sends optical power supply light through the optical connector 1328 and the optical fibers 1326 to the co-packaged optical module 1312. For example, the co-packaged optical module 1312 includes a photonic integrated circuit that modulates the power supply light based on data provided by a data processor to generate a modulated optical signal, and transmits the modulated optical signal to the co-packaged optical module 1316 through one of the optical fibers in the fiber bundle 1318. [265] In some examples, the optical power supply 1322 is configured to provide optical power supply light to the co-packaged optical module 1312 through multiple links that have built-in redundancy in case of malfunction in some of the optical power supply modules. For example, the co-packaged optical module 1312 can be designed to receive N channels of optical power supply light (e.g., N1 continuous wave light signals at the same or at different optical wavelengths, or N1 sequences of optical frame templates), N1 being a positive integer, from the optical power supply 1322. The optical power supply 1322 provides Nl+Ml channels of optical power supply light to the co-packaged optical module 1312, in which Ml channels of optical power supply light are used for backup in case of failure of one or more of the N1 channels of optical power supply light, Ml being a positive integer.

[266] The second switch box 1304 receives optical power supply light from a co-located optical power supply 1330, which is, e.g., external to the second switch box 1304 and located near the second switch box 1304, e.g., in the same rack as the second switch box 1304 in a data center. The optical power supply 1330 includes an array of optical connectors 1332. Optical fibers 1334 are optically coupled to an optical connector 1336 (of the optical connectors 1332) and the co-packaged optical module 1316. The optical power supply 1330 sends optical power supply light through the optical connector 1336 and the optical fibers 1334 to the co-packaged optical module 1316. For example, the co-packaged optical module 1316 includes a photonic integrated circuit that modulates the power supply light based on data provided by a data processor to generate a modulated optical signal, and transmits the modulated optical signal to the co-packaged optical module 1312 through one of the optical fibers in the fiber bundle 1318.

[267] In some examples, the optical power supply 1330 is configured to provide optical power supply light to the co-packaged optical module 1316 through multiple links that have built-in redundancy in case of malfunction in some of the optical power supply modules. For example, the co-packaged optical module 1316 can be designed to receive N2 channels of optical power supply light (e.g., N2 continuous wave light signals at the same or at different optical wavelengths, or N2 sequences of optical frame templates), N2 being a positive integer, from the optical power supply 1322. The optical power supply 1322 provides N2+M2 channels of optical power supply light to the co-packaged optical module 1312, in which M2 channels of optical power supply light are used for backup in case of failure of one or more of the N2 channels of optical power supply light, M2 being a positive integer.

[268] FIG. 13B is a diagram of an example of an optical cable assembly 1340 that can be used to enable the first co-packaged optical module 1312 to receive optical power supply light from the first optical power supply 1322, enable the second co-packaged optical module 1316 to receive optical power supply light from the second optical power supply 1330, and enable the first co-packaged optical module 1312 to communicate with the second co-packaged optical module 1316. FIG. 13C is an enlarged diagram of the optical cable assembly 1340 without some of the reference numbers to enhance clarity of illustration.

[269] The optical cable assembly 1340 includes a first optical fiber connector 1342, a second optical fiber connector 1344, a third optical fiber connector 1346, and a fourth optical fiber connector 1348. The first optical fiber connector 1342 is designed and configured to be optically coupled to the first co-packaged optical module 1312. For example, the first optical fiber connector 1342 can be configured to mate with a connector part of the first co-packaged optical module 1312, or a connector part that is optically coupled to the first co-packaged optical module 1312. The first, second, third, and fourth optical fiber connectors 1342, 1344, 1346, 1348 can comply with an industry standard that defines the specifications for optical fiber interconnection cables that transmit data and control signals, and optical power supply light.

[270] The first optical fiber connector 1342 includes optical power supply (PS) fiber ports, transmitter (TX) fiber ports, and receiver (RX) fiber ports. The optical power supply fiber ports provide optical power supply light to the co-packaged optical module 1312. The transmitter fiber ports allow the co-packaged optical module 1312 to transmit output optical signals (e.g., data and/or control signals), and the receiver fiber ports allow the co packaged optical module 1312 to receive input optical signals (e.g., data and/or control signals). An example of the arrangement of the optical power supply fiber ports, the transmitter ports, and the receiver ports in the first optical fiber connector 1342 are shown in FIG. 13D. [271] FIG. 13D shows an enlarged upper portion of the diagram of FIG. 13B, with the addition of an example of a mapping of fiber ports 1750 of the first optical fiber connector 1342 and a mapping of fiber ports 1752 of the third optical fiber connector 1346. The mapping of fiber ports 1750 shows the positions of the transmitter fiber ports (e.g., 1753), receiver fiber ports (e.g., 1755), and power supply fiber ports (e.g., 1751) of the first optical fiber connector 1342 when viewed in the direction 1754 into the first optical fiber connector 1342. The mapping of fiber ports 1752 shows the positions of the power supply fiber ports (e.g., 1757) of the third optical fiber connector 1346 when viewed in the direction 1756 into the third optical fiber connector 1346.

[272] The second optical fiber connector 1344 is designed and configured to be optically coupled to the second co-packaged optical module 1316. The second optical fiber connector 1344 includes optical power supply fiber ports, transmitter fiber ports, and receiver fiber ports. The optical power supply fiber ports provide optical power supply light to the co-packaged optical module 1316. The transmitter fiber ports allow the co packaged optical module 1316 to transmit output optical signals, and the receiver fiber ports allow the co-packaged optical module 1316 to receive input optical signals. An examples of the arrangement of the optical power supply fiber ports, the transmitter ports, and the receiver ports in the second optical fiber connector 1344 are shown in FIG. 13E.

[273] FIG. 13E shows an enlarged lower portion of the diagram of FIG. 13B, with the addition of an example of a mapping of fiber ports 1760 of the second optical fiber connector 1344 and a mapping of fiber ports 1762 of the fourth optical fiber connector 1348. The mapping of fiber ports 1760 shows the positions of the transmitter fiber ports (e.g., 1763), receiver fiber ports (e.g., 1765), and power supply fiber ports (e.g., 1761) of the second optical fiber connector 1344 when viewed in the direction 1764 into the second optical fiber connector 1344. The mapping of fiber ports 1762 shows the positions of the power supply fiber ports (e.g., 1767) of the fourth optical fiber connector 1348 when viewed in the direction 1766 into the fourth fiber connector 1348. [274] The third optical connector 1346 is designed and configured to be optically coupled to the power supply 1322. The third optical connector 1346 includes optical power supply fiber ports (e.g., 1757) through which the power supply 1322 can output the optical power supply light. The fourth optical connector 1348 is designed and configured to be optically coupled to the power supply 1330. The fourth optical connector 1348 includes optical power supply fiber ports (e.g., 1762) through which the power supply 1322 can output the optical power supply light. [275] In some implementations, the optical power supply fiber ports, the transmitter fiber ports, and the receiver fiber ports in the first and second optical fiber connectors 1342,

1344 are designed to be independent of the communication devices, i.e., the first optical fiber connector 1342 can be optically coupled to the second switch box 1304, and the second optical fiber connector 1344 can be optically coupled to the first switch box 1302 without any re-mapping of the fiber ports. Similarly, the optical power supply fiber ports in the third and fourth optical fiber connectors 1346, 1348 are designed to be independent of the optical power supplies, i.e., if the first optical fiber connector 1342 is optically coupled to the second switch box 1304, the third optical fiber connector 1346 can be optically coupled to the second optical power supply 1330. If the second optical fiber connector 1344 is optically coupled to the first switch box 1302, the fourth optical fiber connector 1348 can be optically coupled to the first optical power supply 1322.

[276] The optical cable assembly 1340 includes a first optical fiber guide module 1350 and a second optical fiber guide module 1352. The optical fiber guide module depending on context is also referred to as an optical fiber coupler or splitter because the optical fiber guide module combines multiple bundles of fibers into one bundle of fibers, or separates one bundle of fibers into multiple bundles of fibers. The first optical fiber guide module 1350 includes a first port 1354, a second port 1356, and a third port 1358. The second optical fiber guide module 1352 includes a first port 1360, a second port 1362, and a third port 1364. The fiber bundle 1318 extends from the first optical fiber connector 1342 to the second optical fiber connector 1344 through the first port 1354 and the second port 1356 of the first optical fiber guide module 1350 and the second port 1362 and the first port 1360 of the second optical fiber guide module 1352. The optical fibers 1326 extend from the third optical fiber connector 1346 to the first optical fiber connector 1342 through the third port 1358 and the first port 1354 of the first optical fiber guide module 1350. The optical fibers 1334 extend from the fourth optical fiber connector 1348 to the second optical fiber connector 1344 through the third port 1364 and the first port 1360 of the second optical fiber guide module 1352.

[277] A portion (or section) of the optical fibers 1318 and a portion of the optical fibers 1326 extend from the first port 1354 of the first optical fiber guide module 1350 to the first optical fiber connector 1342. A portion of the optical fibers 1318 extend from the second port 1356 of the first optical fiber guide module 1350 to the second port 1362 of the second optical fiber guide module 1352, with optional optical connectors (e.g., 1320) along the paths of the optical fibers 1318. A portion of the optical fibers 1326 extend from the third port 1358 of the first optical fiber connector 1350 to the third optical fiber connector 1346. A portion of the optical fibers 1334 extend from the third port 1364 of the second optical fiber connector 1352 to the fourth optical fiber connector 1348.

[278] The first optical fiber guide module 1350 is designed to restrict bending of the optical fibers such that the bending radius of any optical fiber in the first optical fiber guide module 1350 is greater than the minimum bending radius specified by the optical fiber manufacturer to avoid excess optical light loss or damage to the optical fiber. For example, the minimum bend radii can be 2 cm, 1 cm, 5 mm, or 2.5 mm. Other bend radii are also possible. For example, the fibers 1318 and the fibers 1326 extend outward from the first port 1354 along a first direction, the fibers 1318 extend outward from the second port 1356 along a second direction, and the fibers 1326 extend outward from the third port 1358 along a third direction. A first angle is between the first and second directions, a second angle is between the first and third directions, and a third angle is between the second and third directions. The first optical fiber guide module 1350 can be designed to limit the bending of optical fibers so that each of the first, second, and third angles is in a range from, e.g., 30° to 180°.

[279] For example, the portion of the optical fibers 1318 and the portion of the optical fibers 1326 between the first optical fiber connector 1342 and the first port 1354 of the first optical fiber guide module 1350 can be surrounded and protected by a first common sheath 1366. The optical fibers 1318 between the second port 1356 of the first optical fiber guide module 1350 and the second port 1362 of the second optical fiber guide module 1352 can be surrounded and protected by a second common sheath 1368. The portion of the optical fibers 1318 and the portion of the optical fibers 1334 between the second optical fiber connector 1344 and the first port 1360 of the second optical fiber guide module 1352 can be surrounded and protected by a third common sheath 1369. The optical fibers 1326 between the third optical fiber connector 1346 and the third port 1358 of the first optical fiber guide module 1350 can be surrounded and protected by a fourth common sheath 1367. The optical fibers 1334 between the fourth optical fiber connector 1348 and the third port 1364 of the second optical fiber guide module 1352 can be surrounded and protected by a fifth common sheath 1370. Each of the common sheaths can be laterally flexible and/or laterally stretchable, as described in, e.g., U.S. patent application 16/822,103.

[280] One or more optical cable assemblies 1340 (FIGS. 13B, 13C) and other optical cable assemblies (e.g., 1400 of FIG. 15B, 15C, 1490 of FIG. 17B, 17C) described in this document can be used to optically connect switch boxes that are configured differently compared to the switch boxes 1302, 1304 shown in FIG. 13A, in which the switch boxes receive optical power supply light from one or more external optical power supplies. For example, in some implementations, the optical cable assembly 1340 can be attached to a fiber-optic array connector mounted on the outside of the front panel of an optical switch, and another fiber-optic cable then connects the inside of the fiber connector to a co packaged optical module that is mounted on a circuit board positioned inside the housing of the switch box. The co-packaged optical module (which includes, e.g., a photonic integrated circuit, optical-to-electrical converters, such as photodetectors, and electrical-to- optical converters, such as laser diodes) can be co-packaged with a switch ASIC and mounted on a circuit board that can be vertically or horizontally oriented. For example, in some implementations, the front panel is mounted on hinges and a vertical ASIC mount is recessed behind it. See the examples in FIGS. 77A, 77B, and 78 of U.S. application 63/145,368. The optical cable assembly 1340 provides optical paths for communication between the switch boxes, and optical paths for transmitting power supply light from one or more external optical power supplies to the switch boxes. The switch boxes can have any of a variety of configurations regarding how the power supply light and the data and/or control signals from the optical fiber connectors are transmitted to or received from the photonic integrated circuits, and how the signals are transmitted between the photonic integrated circuits and the data processors. [281] One or more optical cable assemblies 1340 and other optical cable assemblies (e.g.,

1400 of FIG. 15B, 15C, 1490 of FIG. 17B, 17C) described in this document can be used to optically connect computing devices other than switch boxes. For example, the computing devices can be server computers that provide a variety of services, such as cloud computing, database processing, audio/video hosting and streaming, electronic mail, data storage, web hosting, social network, supercomputing, scientific research computing, healthcare data processing, financial transaction processing, logistics management, weather forecast, or simulation, to list a few examples. The optical power light required by the optoelectronic modules of the computing devices can be provided using one or more external optical power supplies. For example, in some implementations, one or more external optical power supplies that are centrally managed can be configured to provide the optical power supply light for hundreds or thousands of server computers in a data center, and the one or more optical power supplies and the server computers can be optically connected using the optical cable assemblies (e.g., 1340, 1400, 1490) described in this document and variations of the optical cable assemblies using the principles described in this document.

[282] FIG. 14 is a system functional block diagram of an example of an optical communication system 1380 that includes a first communication transponder 1282 and a second communication transponder 1284. The first communication transponder 1282 sends optical signals to, and receives optical signals from, the second communication transponder 1284 through a first optical communication link 1290. The optical communication system 1380 can be expanded to include additional communication transponders.

[283] An external photon supply 1382 provides optical power supply light to the first communication transponder 1282 through a first optical power supply link 1384, and provides optical power supply light to the second communication transponder 1284 through a second optical power supply link 1386. In one example, the external photon supply 1282 provides continuous wave light to the first communication transponder 1282 and to the second communication transponder 1284. In one example, the continuous wave light can be at the same optical wavelength. In another example, the continuous wave light can be at different optical wavelengths. In yet another example, the external photon supply 1282 provides a first sequence of optical frame templates to the first communication transponder 1282, and provides a second sequence of optical frame templates to the second communication transponder 1284. Each of the optical frame templates can include a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The first communication transponder 1282 receives the first sequence of optical frame templates from the external photon supply 1382, loads data into the respective frame bodies to convert the first sequence of optical frame templates into a first sequence of loaded optical frames that are transmitted through the first optical communication link 1290 to the second communication transponder 1284. Similarly, the second communication transponder 1284 receives the second sequence of optical frame templates from the external photon supply 1382, loads data into the respective frame bodies to convert the second sequence of optical frame templates into a second sequence of loaded optical frames that are transmitted through the first optical communication link 1290 to the first communication transponder 1282.

[284] FIG. 15A is a diagram of an example of an optical communication system 1390 that includes a first switch box 1302 and a second switch box 1304, similar to those in FIG.

13 A. The first switch box 1302 includes a vertical ASIC mount grid structure 1310, and a co-packaged optical module 1312 is attached to a receptor of the grid structure 1310. The second switch box 1304 includes a vertical ASIC mount grid structure 1314, and a co packaged optical module 1316 is attached to a receptor of the grid structure 1314. The first co-packaged optical module 1312 communicates with the second co-packaged optical module 1316 through an optical fiber bundle 1318 that includes multiple optical fibers.

[285] As discussed above in connection with FIGS. 13A to 13E, the first and second switch boxes 1302, 1304 can have other configurations. For example, horizontally mounted ASICs can be used. A fiber-optic array connector attached to a front panel can be used to optically connect the optical cable assembly 1340 to another fiber-optic cable that connects to a co-packaged optical module mounted on a circuit board inside the switch box. The front panel can be mounted on hinges and a vertical ASIC mount can be recessed behind it. The switch boxes can be replaced by other types of server computers.

[286] In an example embodiment, the first switch box 1302 includes an external optical power supply 1322 that provides optical power supply light to both the co-packaged optical module 1312 in the first switch box 1302 and the co-packaged optical module 1316 in the second switch box 1304. In another example embodiment, the optical power supply can be located outside the switch box 1302 (cf. 1330, FIG. 13A). The optical power supply 1322 provides the optical power supply light through an optical connector array 1324. Optical fibers 1392 are optically coupled to an optical connector 1396 and the co-packaged optical module 1312. The optical power supply 1322 sends optical power supply light through the optical connector 1396 and the optical fibers 1392 to the co-packaged optical module 1312 in the first switch box 1302. Optical fibers 1394 are optically coupled to the optical connector 1396 and the co-packaged optical module 1316. The optical power supply 1322 sends optical power supply light through the optical connector 1396 and the optical fibers 1394 to the co-packaged optical module 1316 in the second switch box 1304. [287] FIG. 15B shows an example of an optical cable assembly 1400 that can be used to enable the first co-packaged optical module 1312 to receive optical power supply light from the optical power supply 1322, enable the second co-packaged optical module 1316 to receive optical power supply light from the optical power supply 1322, and enable the first co-packaged optical module 1312 to communicate with the second co-packaged optical module 1316. FIG. 15C is an enlarged diagram of the optical cable assembly 1400 without some of the reference numbers to enhance clarity of illustration. [288] The optical cable assembly 1400 includes a first optical fiber connector 1402, a second optical fiber connector 1404, and a third optical fiber connector 1406. The first optical fiber connector 1402 is similar to the first optical fiber connector 1342 of FIGS. 13B, 13C, 13D, and is designed and configured to be optically coupled to the first co packaged optical module 1312. The second optical fiber connector 1404 is similar to the second optical fiber connector 1344 of FIGS. 13B, 13C, 13E, and is designed and configured to be optically coupled to the second co-packaged optical module 1316. The third optical connector 1406 is designed and configured to be optically coupled to the power supply 1322. The third optical connector 1406 includes first optical power supply fiber ports (e.g., 1770, FIG. 15D) and second optical power supply fiber ports (e.g., 1772). The power supply 1322 outputs optical power supply light through the first optical power supply fiber ports to the optical fibers 1392, and outputs optical power supply light through the second optical power supply fiber ports to the optical fibers 1394. The first, second, and third optical fiber connectors 1402, 1404, 1406 can comply with an industry standard that defines the specifications for optical fiber interconnection cables that transmit data and control signals, and optical power supply light.

[289] FIG. 15D shows an enlarged upper portion of the diagram of FIG. 15B, with the addition of an example of a mapping of fiber ports 1774 of the first optical fiber connector 1402 and a mapping of fiber ports 1776 of the third optical fiber connector 1406. The mapping of fiber ports 1774 shows the positions of the transmitter fiber ports (e.g., 1778), receiver fiber ports (e.g., 1780), and power supply fiber ports (e.g., 1782) of the first optical fiber connector 1402 when viewed in the direction 1784 into the first optical fiber connector 1402. The mapping of fiber ports 1776 shows the positions of the power supply fiber ports (e.g., 1770, 1772) of the third optical fiber connector 1406 when viewed in the direction 1786 into the third optical fiber connector 1406. In this example, the third optical fiber connector 1406 includes 8 optical power supply fiber ports.

[290] In some examples, optical connector array 1324 of the optical power supply 1322 can include a first type of optical connectors that accept optical fiber connectors having 4 optical power supply fiber ports, as in the example of FIG. 13D, and a second type of optical connectors that accept optical fiber connectors having 8 optical power supply fiber ports, as in the example of FIG. 15D. In some examples, if the optical connector array 1324 of the optical power supply 1322 only accepts optical fiber connectors having 4 optical power supply fiber ports, then a converter cable can be used to convert the third optical fiber connector 1406 of FIG. 15D to two optical fiber connectors, each having 4 optical power supply fiber ports, that is compatible with the optical connector array 1324.

[291] FIG. 15E shows an enlarged lower portion of the diagram of FIG. 15B, with the addition of an example of a mapping of fiber ports 1790 of the second optical fiber connector 1404. The mapping of fiber ports 1790 shows the positions of the transmitter fiber ports (e.g., 1792), receiver fiber ports (e.g., 1794), and power supply fiber ports (e.g., 1796) of the second optical fiber connector 1404 when viewed in the direction 1798 into the second optical fiber connector 1404.

[292] The port mappings of the optical fiber connectors shown in FIGS. 13D, 13E, 15D, and 15E are merely examples. Each optical fiber connector can include a greater number or a smaller number of transmitter fiber ports, a greater number or a smaller number of receiver fiber ports, and a greater number or a smaller number of optical power supply fiber ports, as compared to those shown in FIGS. 13D, 13E, 15D, and 15E. The arrangement of the relative positions of the transmitter, receiver, and optical power supply fiber ports can also be different from those shown in FIGS. 13D, 13E, 15D, and 15E.

[293] The optical cable assembly 1400 includes an optical fiber guide module 1408, which includes a first port 1410, a second port 1412, and a third port 1414. The optical fiber guide module 1408 depending on context is also referred as an optical fiber coupler (for combining multiple bundles of optical fibers into one bundle of optical fiber) or an optical fiber splitter (for separating a bundle of optical fibers into multiple bundles of optical fibers). The fiber bundle 1318 extends from the first optical fiber connector 1402 to the second optical fiber connector 1404 through the first port 1410 and the second port 1412 of the optical fiber guide module 1408. The optical fibers 1392 extend from the third optical fiber connector 1406 to the first optical fiber connector 1402 through the third port 1414 and the first port 1410 of the optical fiber guide module 1408. The optical fibers 1394 extend from the third optical fiber connector 1406 to the second optical fiber connector 1404 through the third port 1414 and the second port 1412 of the optical fiber guide module 1408.

[294] A portion of the optical fibers 1318 and a portion of the optical fibers 1392 extend from the first port 1410 of the optical fiber guide module 1408 to the first optical fiber connector 1402. A portion of the optical fibers 1318 and a portion of the optical fibers 1394 extend from the second port 1412 of the optical fiber guide module 1408 to the second optical fiber connector 1404. A portion of the optical fibers 1394 extend from the third port 1414 of the optical fiber connector 1408 to the third optical fiber connector 1406.

[295] The optical fiber guide module 1408 is designed to restrict bending of the optical fibers such that the radius of curvature of any optical fiber in the optical fiber guide module 1408 is greater than the minimum radius of curvature specified by the optical fiber manufacturer to avoid excess optical light loss or damage to the optical fiber. For example, the optical fibers 1318 and the optical fibers 1392 extend outward from the first port 1410 along a first direction, the optical fibers 1318 and the optical fibers 1394 extend outward from the second port 1412 along a second direction, and the optical fibers 1392 and the optical fibers 1394 extend outward from the third port 1414 along a third direction. A first angle is between the first and second directions, a second angle is between the first and third directions, and a third angle is between the second and third directions. The optical fiber guide module 1408 is designed to limit the bending of optical fibers so that each of the first, second, and third angles is in a range from, e.g., 30° to 180°. [296] For example, the portion of the optical fibers 1318 and the portion of the optical fibers 1392 between the first optical fiber connector 1402 and the first port 1410 of the optical fiber guide module 1408 can be surrounded and protected by a first common sheath 1416. The optical fibers 1318 and the optical fibers 1394 between the second optical fiber connector 1404 and the second port 1412 of the optical fiber guide module 1408 can be surrounded and protected by a second common sheath 1418. The optical fibers 1392 and the optical fibers 1394 between the third optical fiber connector 1406 and the third port 1414 of the optical fiber guide module 1408 can be surrounded and protected by a third common sheath 1420. Each of the common sheaths can be laterally flexible and/or laterally stretchable.

[297] FIG. 16 is a system functional block diagram of an example of an optical communication system 1430 that includes a first communication transponder 1432, a second communication transponder 1434, a third communication transponder 1436, and a fourth communication transponder 1438. Each of the communication transponders 1432, 1434, 1436, 1438 can be similar to the communication transponders 1202, 1204 of FIG.

12. The first communication transponder 1432 communicates with the second communication transponder 1434 through a first optical link 1440. The first communication transponder 1432 communicates with the third communication transponder 1436 through a second optical link 1442. The first communication transponder 1432 communicates with the fourth communication transponder 1438 through a third optical link 1444.

[298] An external photon supply 1446 provides optical power supply light to the first communication transponder 1432 through a first optical power supply link 1448, provides optical power supply light to the second communication transponder 1434 through a second optical power supply link 1450, provides optical power supply light to the third communication transponder 1436 through a third optical power supply link 1452, and provides optical power supply light to the fourth communication transponder 1438 through a fourth optical power supply link 1454.

[299] FIG. 17A is a diagram of an example of an optical communication system 1460 that includes a first switch box 1462 and a remote server array 1470 that includes a second switch box 1464, a third switch box 1466, and a fourth switch box 1468. The first switch box 1462 includes a vertical ASIC mount grid structure 1310, and a co-packaged optical module 1312 is attached to a receptor of the grid structure 1310. The second switch box

1464 includes a co-packaged optical module 1472, the third switch box 1466 includes a co packaged optical module 1474, and the third switch box 1468 includes a co-packaged optical module 1476. The first co-packaged optical module 1312 communicates with the co-packaged optical modules 1472, 1474, 1476 through an optical fiber bundle 1478 that later branches out to the co-packaged optical modules 1472, 1474, 1476.

[300] In one example embodiment, the first switch box 1462 includes an external optical power supply 1322 that provides optical power supply light through an optical connector array 1324. In another example embodiment, the optical power supply can be located external to switch box 1462 (cf. 1330, FIG. 13A). Optical fibers 1480 are optically coupled to an optical connector 1482, and the optical power supply 1322 sends optical power supply light through the optical connector 1482 and the optical fibers 1480 to the co- packaged optical modules 1312, 1472, 1474, 1476.

[301] FIG. 17B shows an example of an optical cable assembly 1490 that can be used to enable the optical power supply 1322 to provide optical power supply light to the co packaged optical modules 1312, 1472, 1474, 1476, and enable the co-packaged optical module 1312 to communicate with the co-packaged optical modules 1472, 1474, 1476. The optical cable assembly 1490 includes a first optical fiber connector 1492, a second optical fiber connector 1494, a third optical fiber connector 1496, a fourth optical fiber connector 1498, and a fifth optical fiber connector 1500. The first optical fiber connector 1492 is configured to be optically coupled to the co-packaged optical module 1312. The second optical fiber connector 1494 is configured to be optically coupled to the co- packaged optical module 1472. The third optical fiber connector 1496 is configured to be optically coupled to the co-packaged optical module 1474. The fourth optical fiber connector 1498 is configured to be optically coupled to the co-packaged optical module 1476. The fifth optical fiber connector 1500 is configured to be optically coupled to the optical power supply 1322. FIG. 17C is an enlarged diagram of the optical cable assembly 1490.

[302] Optical fibers that are optically coupled to the optical fiber connectors 1500 and 1492 enable the optical power supply 1322 to provide the optical power supply light to the co-packaged optical module 1312. Optical fibers that are optically coupled to the optical fiber connectors 1500 and 1494 enable the optical power supply 1322 to provide the optical power supply light to the co-packaged optical module 1472. Optical fibers that are optically coupled to the optical fiber connectors 1500 and 1496 enable the optical power supply 1322 to provide the optical power supply light to the co-packaged optical module 1474. Optical fibers that are optically coupled to the optical fiber connectors 1500 and 1498 enable the optical power supply 1322 to provide the optical power supply light to the co-packaged optical module 1476.

[303] Optical fiber guide modules 1502, 1504, 1506, and common sheaths are provided to organize the optical fibers so that they can be easily deployed and managed. The optical fiber guide module 1502 is similar to the optical fiber guide module 1408 of FIG. 15B. The optical fiber guide modules 1504, 1506 are similar to the optical fiber guide module 1350 of FIG. 13B. The common sheaths gather the optical fibers in a bundle so that they can be more easily handled, and the optical fiber guide modules guide the optical fibers so that they extend in various directions toward the devices that need to be optically coupled by the optical cable assembly 1490. The optical fiber guide modules restrict bending of the optical fibers such that the bending radiuses are greater than minimum values specified by the optical fiber manufacturers to prevent excess optical light loss or damage to the optical fibers. [304] The optical fibers 1480 that extend from the include optical fibers that extend from the optical 1482 are surrounded and protected by a common sheath 1508. At the optical fiber guide module 1502, the optical fibers 1480 separate into a first group of optical fibers 1510 and a second group of optical fibers 1512. The first group of optical fibers 1510 extend to the first optical fiber connector 1492. The second group of optical fibers 1512 extend toward the optical fiber guide modules 1504, 1506, which together function as a 1 :3 splitter that separates the optical fibers 1512 into a third group of optical fibers 1514, a fourth group of optical fibers 1516, and a fifth group of optical fibers 1518. The group of optical fibers 1514 extend to the optical fiber connector 1494, the group of optical fibers 1516 extend to the optical fiber connector 1496, and the group of optical fibers 1518 extend to the optical fiber connector 1498. In some examples, instead of using two 1 :2 split optical fiber guide modules 1504, 1506, it is also possible to use a 1:3 split optical fiber guide module that has four ports, e.g., one input port and three output ports. In general, separating the optical fibers in a 1 :N split (N being an integer greater than 2) can occur in one step or multiple steps. [305] FIG. 18 is a diagram of an example of a data processing system (e.g., data center)

1520 that includes N servers 1522 spread across K racks 1524. In this example, there are 6 racks 1524, and each rack 1524 includes 15 servers 1522. Each server 1522 directly communicates with a tier 1 switch 1526. The left portion of the figure shows an enlarged view of a portion 1528 of the system 1520. A server 1522a directly communicates with a tier 1 switch 1526a through a communication link 1530a. Similarly, servers 1522b, 1522c directly communicate with the tier 1 switch 1526a through communication links 1530b, 1530c, respectively. The server 1522a directly communicates with a tier 1 switch 1526b through a communication link 1532a. Similarly, servers 1522b, 1522c directly communicate with the tier 1 switch 1526b through communication links 1532b, 1532c, respectively. Each communication link can include a pair of optical fibers to allow bi directional communication. The system 1520 bypasses the conventional top-of-rack switch and can have the advantage of higher data throughput. The system 1520 includes a point- to-point connection between every server 1522 and every tier 1 switch 1526. In this example, there are 4 tier 1 switches 1526, and 4 fiber pairs are used per server 1522 for communicating with the tier 1 switches 1526. Each tier-1 switch 1526 is connected to N servers, so there are N fiber pairs connected to each tier-1 switch 1526. [306] Referring to FIG. 19, in some implementations, a data processing system (e.g., data center) 1540 includes tier-1 switches 1526 that are co-located in a rack 1540 separate from the N servers 1522 that are spread across K racks 1524. Each server 1522 has a direct link to each of the tier-1 switches 1526. In some implementations, there is one fiber cable 1542 (or a small number «N/K of fiber cables) from the tier-1 switch rack 1540 to each of the K server racks 1524.

[307] FIG. 20A is a diagram of an example of a data processing system 1550 that includes N=1024 servers 1552 spread across K=32 racks 1554, in which each rack 1554 includes N/K= 1024/32=32 servers 1552. There are 4 tier-1 switches 1556 and an optical power supply 1558 that is co-located in a rack 1560. [308] Optical fibers connect the servers 1552 to the tier-1 switches 1556 and the optical power supply 1558. In this example, a bundle of 9 optical fibers is optically coupled to a co-packaged optical module 1564 of a server 1552, in which 1 optical fiber provides the optical power supply light, and 4 pairs of (a total of 8) optical fibers provide 4 bi directional communication channels, each channel having a 100 Gbps bandwidth, for a total of 4 x 100 Gbps bandwidth in each direction. Because there are 32 servers 1552 in each rack 1554, there are a total of 256 + 32 = 288 optical fibers that extend from each rack 1554 of servers 1552, in which 32 optical fibers provide the optical power supply light, and 256 optical fibers provide 128 bi-directional communication channels, each channel having a 100 Gbps bandwidth. [309] For example, at the server rack side, optical fibers 1566 (that are connected to the servers 1552 of a rack 1554) terminate at a server rack connector 1568. At the switch rack side, optical fibers 1578 (that are connected to the switch boxes 1556 and the optical power supply 1558) terminate at a switch rack connector 1576. An optical fiber extension cable 1572 is optically coupled to the server rack side and the switch rack side. The optical fiber extension cable 1572 includes 256 + 32 = 288 optical fibers. The optical fiber extension cable 1572 includes a first optical fiber connector 1570 and a second optical fiber connector 1574. The first optical fiber connector 1570 is connected to the server rack connector 1568, and the second optical fiber connector 1574 is connected to the switch rack connector 1576. At the switch rack side, the optical fibers 1578 include 288 optical fibers, of which 32 optical fibers 1580 are optically coupled to the optical power supply 1558. The 256 optical fibers that carry 128 bi-directional communication channels (each channel having a 100 Gbps bandwidth in each direction) are separated into four groups of 64 optical fibers, in which each group of 64 optical fibers is optically coupled to a co packaged optical module 1582 in one of the switch boxes 1556. The co-packaged optical module 1582 is configured to have a bandwidth of 32 ^c 100 Gbps = 3.2 Tbps in each direction (input and output). Each switch box 1556 is connected to each server 1552 of the rack 1554 through a pair of optical fibers that carry a bandwidth of 100 Gbps in each direction.

[310] The optical power supply 1558 provides optical power supply light to co-packaged optical modules 1582 at the switch boxes 1556. In this example, the optical power supply 1558 provides optical power supply light through 4 optical fibers to each co-packaged optical module 1582, so that a total of 16 optical fibers are used to provide the optical power supply light to the 4 switch boxes 1556. A bundle of optical fibers 1584 is optically coupled to the co-packaged optical module 1582 of the switch box 1556. The bundle of optical fibers 1584 includes 64 + 16 = 80 fibers. In some examples, the optical power supply 1558 can provide additional optical power supply light to the co-packaged optical module 1582 using additional optical fibers. For example, the optical power supply 1558 can provide optical power supply light to the co-packaged optical module 1582 using 32 optical fibers with built-in redundancy.

[311] Referring to FIG. 20B, the data processing system 1550 includes an optical fiber guide module 1590 that helps organize the optical fibers so that they are directed to the appropriate directions. The optical fiber guide module 1590 also restricts bending of the optical fibers to be within the specified limits to prevent excess optical light loss or damage to the optical fibers. The optical fiber guide module 1590 includes a first port 1592, a second port 1594, and a third port 1596. The optical fibers that extend outward from the first port 1592 are optically coupled to the switch rack connector 1576. The optical fibers that extend outward from the second port 1594 are optically coupled to the switch boxes. The optical fibers that extend outward from the third port 1596 are optically coupled to the optical power supply 1558.

[312] In some implementations, each of the optical power supply or external photon supply 902 of FIG. 9, 1012 of FIG. 10, 1106 of FIG. 11, 1208, 1212 of FIG. 12, 1322,

1330 of FIG. 13 A, 1382 of FIG. 14, 1322 of FIG. 15A, 1446 of FIG. 16, 1322 of FIG.

17A, and 1558 of FIGS. 20A and 20B can have a configuration similar to any one of the optical power supplies shown in FIGS. 2 and 4 A to 4F. In some implementations, each of the optical fibers 914 and 916 of FIG. 9, 1014, 1016a, 1016b, 1016c of FIG. 10, 1210 and 1214 of FIG. 12, 1384 and 1386 of FIG. 14, 1394 of FIG. 15A, 1448, 1450, 1452, 1454 of FIG. 16, and 1580 of FIG. 20A that is optically coupled to the optical power supply can include one or more sections of non-polarization-maintaining optical fiber. Light supplied by optical power supply module can experience random polarization rotation upon propagation through the optical fiber.

[313] In some implementations, each of the co-packaged optical interconnect modules 910 of FIGS. 9 to 11, the communication transponders 1202 and 1204 of FIG. 12, the co packaged optical modules 1312 and 1316 of FIG. 13 A, the communication transponders 1282 and 1284 of FIG. 14, the co-packaged optical modules 1312 and 1316 of FIG. 15A, the communication transponders 1432, 1434, 1436, and 1438 of FIG. 16, the co-packaged optical modules 1312, 1472, 1474, and 1476 of FIG. 17A, the co-packaged optical module 1564 and 1582 of FIG. 20A, can have one or more optical transmit modules similar to the optical transmit module 504 of FIG. 5 or 600 of FIG. 6. [314] Additional details of the fiber cables that can be used to transmit light from the optical power supplies to photonic integrated circuits that include modulators that can modulate the light, and fiber-to-photonic integrated circuit connects that can be used to couple the light from the fibers to the photonic integrated circuits, can be found in, e.g., U.S. patent application 16/816,171, filed on March 11, 2020, and PCT application PCT/US2021/021953, filed on March 11, 2021, U.S. patent application 16/822,103, filed on March 18, 2020, PCT application PCT/US2021/022730, filed on March 17, 2021, and PCT application PCT/US2021/027306, filed on April 14, 2021. The entire contents of application 16/816,171, application PCT/US2021/021953, application 16/822,103, application PCT/US2021/022730, and application PCT/US2021/027306 are herein incorporated by reference. Additional details related to the photonic integrated circuits that include modulators that can modulate the light provided by the optical power supplies can be found in, e.g., U.S. provisional patent application 63/080,528, filed on September 18, 2020, the entire content of which is herein incorporated by reference. Additional details for fiber connectors that can assist in the connection of optical fiber cables to the optical power supplies and the photonic integrated circuits can be found in, e.g., U.S. provisional patent application 63/088,914, filed on October 7, 2020, the entire content of which is herein incorporated by reference.

[315] According to an example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of FIGs. 1-8, provided is an apparatus (e.g., 100, FIG. 1) for communicating optical signals modulated at a symbol rate (e.g., Rs ), the apparatus comprising an optical power supply (e.g., 290, FIG. 2) that comprises: a light source (e.g., 200, FIG. 2) and an electronic controller (e.g., 230,

FIG. 2) connected to the light source to cause the light source to generate a first light output having a first optical frequency (e.g., 212, FIGs. 2 and 3) and a second light output having a second optical frequency (e.g., 222, FIGs. 2 and 3) different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer (e.g., by a factor of 100) than one over the symbol rate; and a polarization combiner (e.g., 240, FIG. 2) connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively.

[316] In some embodiments of the above apparatus, the electronic controller is configured to cause the first light output and the second light output to be mutually time/frequency orthogonal (e.g., as per Eqs. (3) and (4)).

[317] In some embodiments of any of the above apparatus, a degree to which the first light output and the second light output are time/frequency orthogonal is greater than 0.8.

[318] In some embodiments of any of the above apparatus, the degree is greater than 0.9. [319] In some embodiments of any of the above apparatus, the degree is greater than 0.99.

[320] In some embodiments of any of the above apparatus, the first light output comprises a first continuous-wave optical field at the first optical frequency, and the second light output comprises a second continuous-wave optical field at the second optical frequency.

[321] In some embodiments of any of the above apparatus, a difference between the first optical frequency and the second optical frequency is greater than five times the symbol rate (e.g., Af = j/i-/₂| > 5 R , 212, 222, FIG. 3D).

[322] In some embodiments of any of the above apparatus, a difference between the first optical frequency and the second optical frequency is approximately an integer multiple of the symbol rate (i.e., Af~ n R , with n = 2,3,4,...).

[323] In some embodiments of any of the above apparatus, the first light output comprises a first optical pulse train of a first period, and the second light output comprises a second optical pulse train of the first period. [324] In some embodiments of any of the above apparatus, pulses of the first and second optical pulse trains have a same intensity waveform (e.g., 212, 222, FIG. 3C).

[325] In some embodiments of any of the above apparatus, pulses of the first and second optical pulse trains have different respective intensity waveforms.

[326] In some embodiments of any of the above apparatus, the first and second optical pulse trains are phase-locked with respect to one another.

[327] In some embodiments of any of the above apparatus, centers of pulses of the first optical pulse train are temporally aligned with centers of corresponding pulses of the second optical pulse train (e.g., AT ~ 0, 212, 222, FIG. 3C).

[328] In some embodiments of any of the above apparatus, centers of pulses of the first optical pulse train are temporally offset from centers of corresponding pulses of the second optical pulse train by a nonzero time shift (e.g., AT, 212, 222, FIG. 3C).

[329] In some embodiments of any of the above apparatus, the nonzero time shift is smaller than one half the first period (e.g., AT < T ll, 212, 222, FIG. 3C).

[330] In some embodiments of any of the above apparatus, the nonzero time shift is smaller than one quarter of the first period (e.g., AT < Ti /4, 212, 222, FIG. 3C). [331] In some embodiments of any of the above apparatus, the difference between the first optical frequency and the second optical frequency is twice the pulse repetition rate (i.e., Af ~ 2 Ri , 212, 222, FIG. 3E).

[332] In some embodiments of any of the above apparatus, the difference between the first optical frequency and the second optical frequency is three times the pulse repetition rate (i.e., Af ~ 3 Rf.

[333] In some embodiments of any of the above apparatus (e.g., 212, 222, FIG. 3E; 516, 517, FIG. 6D) a spectrum of the first pulse train has two first optical frequency tones; and a spectrum of the second pulse train has two second optical frequency tones different from the two first optical frequency tones.

[334] In some embodiments of any of the above apparatus, the first and second optical frequency tones are equi distantly spaced by an integer multiple of the symbol rate.

[335] In some embodiments of any of the above apparatus, the integer multiple is two.

[336] In some embodiments of any of the above apparatus, the electronic controller is further configured to imprint first control information on the first light output of the light source and second control information on the second light output of the light source.

[337] In some embodiments of any of the above apparatus, the first control information is identical to the second control information.

[338] In some embodiments of any of the above apparatus, the electronic controller imprints the first and second control information using one or more of: an intensity, a phase, a frequency, and a polarization of the first light output and the second light output.

[339] In some embodiments of any of the above apparatus, the light source comprises a first CW laser oscillating at the first optical frequency (e.g., 410, FIG. 4A), and a second CW laser oscillating at the second optical frequency (e.g., 420, FIG. 4A). [340] In some embodiments of any of the above apparatus, the electronic controller is configured to control the first CW laser and the second CW laser (e.g., 430, FIG. 4A) to controllably set a frequency difference between the first and second optical frequencies.

[341] In some embodiments of any of the above apparatus, the polarization combiner comprises one or more of: a polarization beam combiner, a polarization-maintaining optical power combiner, and a polarization-maintaining wavelength multiplexer.

[342] In some embodiments of any of the above apparatus, the light source comprises a CW laser and an optical modulator optically connected to the CW laser, the optical modulator configured to generate a first modulation tone at the first optical frequency (e.g., 424, FIG. 4B; 417, FIG. 4C).

[343] In some embodiments of any of the above apparatus, the electronic controller (e.g., 432, FIG. 4B; 433, FIG. 4C) is configured to control an optical frequency of the first modulation tone.

[344] In some embodiments of any of the above apparatus, the optical modulator is further configured to generate a second modulation tone at the second optical frequency (e.g, 417, FIG. 4B).

[345] In some embodiments of any of the above apparatus, the light source comprises an optical amplitude modulator configured to generate an optical pulse train (e.g., 417, 427,

FIG. 4D; 417, FIG. 4E).

[346] In some embodiments of any of the above apparatus, the light source comprises a pulsed laser configured to generate an optical pulse train (e.g., 410 and 417, 420 and 427, FIG. 4C). [347] In some embodiments of any of the above apparatus, the light source comprises an optical delay element configured to delay the first light output with respect to the second light output (e.g., 419, FIGs. 4D and 4E).

[348] In some embodiments of any of the above apparatus, the optical power supply comprises an optical dispersion-compensating element (e.g, 470, FIGs. 4D and 4E). [349] In some embodiments of any of the above apparatus, the light source comprises a polarization-diversity in-phase/quadrature modulator (e.g, 417, FIG. 4F).

[350] In some embodiments of any of the above apparatus (e.g, 212, 222, FIG. 3E): the polarization-diversity in-phase/quadrature modulator is configured to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization; wherein frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization are equal to one another; and wherein frequency spacing between a tone in the first polarization and a tone in the second polarization is an integer multiple of said equal frequency spacing.

[351] In some embodiments of any of the above apparatus, the phase difference between the two tones in the first polarization is equal to the phase difference between the two tones in the second polarization. [352] In some embodiments of any of the above apparatus, the apparatus further comprises an optical transmit module (e.g., 504, FIG. 5; 600, FIG. 6) optically end- connected to the output port of the polarization combiner (e.g., 242, FIG. 2) via one or more sections of optical fiber (e.g., 102e, 543, FIG. 5), the transmit module comprising: a polarization splitter (e.g., 515, FIG. 5) having an input port thereof optically connected to an end of one of the sections of the optical fiber to receive light of the optical output; a first optical data modulator (e.g., 530i, FIG. 5) connected to a first output of the polarization splitter; and a second optical data modulator (e.g., 5302, FIG. 5) connected to a second output of the polarization splitter. [353] In some embodiments of any of the above apparatus, at least one of the first and second optical data modulators is configured to modulate received light at the symbol rate.

[354] In some embodiments of any of the above apparatus, at least one of the one or more sections of the optical fiber is non-polarization-maintaining.

[355] In some embodiments of any of the above apparatus, the optical fiber is at least one meter long.

[356] In some embodiments of any of the above apparatus, the optical fiber is at least ten meters long.

[357] According to another example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of FIGs. 1-8, provided is an apparatus comprising an optical transmitter (e.g., 500, FIG. 5) that comprises: a passive polarization splitter (e.g., 515, FIG. 5) having an optical input port and first (e.g., 516, FIG. 5) and second (e.g., 517, FIG. 5) optical output ports, the optical input port being optically connected to receive an optical input signal having first and second polarization components (e.g., FIGs. 3A-3E), the first polarization component carrying light of a first optical frequency, the second polarization component carrying light of a second optical frequency different from the first optical frequency, the first and second polarization components being mutually orthogonal and jointly undergoing a state-of- polarization change during a time interval (e.g., intervals (A), (B), (C), FIGs. 7B-7D), the passive polarization splitter causing light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causing light of a second fixed polarization to be directed from the optical input port to the second optical output port, the first and second fixed polarizations being orthogonal to one another, the state-of- polarization change causing respective spectral compositions of the lights directed to the first and second optical ports to change during said time interval (e.g., FIGs. 7B-7D); and a first optical modulator (e.g., 530i, FIG. 5) connected to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom (e.g., 516, FIG. 5) in response to a first data signal (e.g., Data 1, FIG. 5).

[358] In some embodiments of the above apparatus, the optical transmitter further comprises a second optical modulator (e.g., 5302, FIG. 5) connected to the second optical output port and configured to modulate the light of the second fixed polarization received therefrom (e.g., 517, FIG. 5) in response to a second data signal (e.g., Data 2, FIG. 5). [359] In some embodiments of any of the above apparatus, the first and second optical modulators are connected to transmit the respective modulated lights (e.g., on ports 532i and 5322, FIG. 5) through different respective optical fibers.

[360] In some embodiments of any of the above apparatus, at some times of said time interval (e.g., interval (A), FIGs. 7B-7D), the first optical modulator receives from the first output port the first optical frequency but not the second optical frequency; and at some other times of said time interval, the first optical modulator receives from the first output port the second optical frequency but not the first optical frequency.

[361] In some embodiments of any of the above apparatus, at yet some other times of said time interval, the first optical modulator receives from the first output port a mix of the first and second optical frequencies (e.g., intervals (B), (C), FIGs. 7B-7D).

[362] In some embodiments of any of the above apparatus, the optical input port is optically connected to receive the optical input signal from a proximate end of a section of optical fiber (e.g., 543, FIG. 5), the optical fiber including at least one section that is non- polarization-maintaining. [363] In some embodiments of any of the above apparatus, the state-of-polarization change is due to time-varying polarization rotation in said at least one section.

[364] In some embodiments of any of the above apparatus, the time-varying polarization rotation is random.

[365] In some embodiments of any of the above apparatus, the optical transmitter further comprises an optical power supply (e.g., 290, FIG. 5) optically connected to apply the optical input signal through the optical fiber to the passive polarization splitter. [366] In some embodiments of any of the above apparatus, the optical power supply comprises: a light source (e.g., 200, FIG. 2) and an electronic controller (e.g., 230, FIG. 2) connected to the light source to cause the light source to generate a first light output having the first optical frequency (e.g., 212, FIGs. 2 and 3) and a second light output having the second optical frequency (e.g., 222, FIGs. 2 and 3), each of the first and second light outputs being steady during said time interval; and a polarization combiner (e.g., 240, FIG. 2) connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output that is coupled into the optical fiber to cause the optical input port of the polarization splitter to receive the optical input signal.

[367] In some embodiments of any of the above apparatus, the first optical modulator is a polarization-sensitive device designed to modulate optical signals having the first fixed polarization.

[368] In some embodiments of any of the above apparatus, the first optical modulator is unsuitable for modulating optical signals having the second fixed polarization.

[369] In some embodiments of any of the above apparatus, the second optical modulator is a polarization-sensitive device designed to modulate optical signals having the second fixed polarization.

[370] In some embodiments of any of the above apparatus, the second optical modulator is unsuitable for modulating optical signals having the first fixed polarization.

[371] While this disclosure includes references to illustrative embodiments, this specification is not intended to be construed in a limiting sense. Various modifications of the described embodiments, as well as other embodiments within the scope of the disclosure, which are apparent to persons skilled in the art to which the disclosure pertains are deemed to lie within the principle and scope of the disclosure, e.g., as expressed in the following claims.

[372] Some embodiments can be implemented as circuit-based processes, including possible implementation on a single integrated circuit.

[373] Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value or range. [374] It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this disclosure can be made by those skilled in the art without departing from the scope of the disclosure, e.g., as expressed in the following claims. [375] The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures.

[376] Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

[377] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” [378] Unless otherwise specified herein, the use of the ordinal adjectives “first,”

“second,” “third,” etc., to refer to an object of a plurality of like objects merely indicates that different instances of such like objects are being referred to, and is not intended to imply that the like objects so referred-to have to be in a corresponding order or sequence, either temporally, spatially, in ranking, or in any other manner. [379] Also for purposes of this description, the terms “couple,” “coupling,” “coupled,”

“connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements.

[380] As used herein in reference to an element and a standard, the term compatible means that the element communicates with other elements in a manner wholly or partially specified by the standard, and would be recognized by other elements as sufficiently capable of communicating with the other elements in the manner specified by the standard. The compatible element does not need to operate internally in a manner specified by the standard. [381] The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the disclosure is indicated by the appended claims rather than by the description and figures herein. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[382] The description and drawings merely illustrate the principles of the disclosure. It will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.

[383] The functions of the various elements shown in the figures, including any functional blocks labeled or referred to as “processors” and/or “controllers,” can be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which can be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and can implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and/or custom, can also be included. Similarly, any switches shown in the figures are conceptual only. Their function can be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementer as more specifically understood from the context.

[384] As used in this application, the term “circuitry” can refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry); (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions); and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.” This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[385] It should be appreciated by those of ordinary skill in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the disclosure.

Claims

CLAIMS What is claimed is:

1. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising an optical power supply that comprises: a light source and an electronic controller connected to the light source to cause the light source to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; and a polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively.

2. The apparatus of claim 1, wherein the electronic controller is configured to cause the first light output and the second light output to be mutually time/frequency orthogonal.

3. The apparatus of claim 1, wherein the first light output comprises a first continuous- wave optical field at the first optical frequency, and the second light output comprises a second continuous-wave optical field at the second optical frequency.

4. The apparatus of claim 1, wherein a difference between the first optical frequency and the second optical frequency is approximately an integer multiple of the symbol rate.

5. The apparatus of claim 1, wherein the first light output comprises a first optical pulse train of a first period, and the second light output comprises a second optical pulse train of the first period.

6. The apparatus of claim 5, wherein centers of pulses of the first optical pulse train are temporally aligned with centers of corresponding pulses of the second optical pulse train.

7. The apparatus of claim 5, wherein centers of pulses of the first optical pulse train are temporally offset from centers of corresponding pulses of the second optical pulse train by a nonzero time shift.

8. The apparatus of claim 5, wherein: a spectrum of the first pulse train has two first optical frequency tones; and a spectrum of the second pulse train has two second optical frequency tones different from the two first optical frequency tones.

9. The apparatus of claim 1, wherein the electronic controller is further configured to imprint first control information on the first light output of the light source and second control information on the second light output of the light source.

10. The apparatus of claim 1, wherein the light source comprises a polarization- diversity in-phase/quadrature modulator.

11. The apparatus of claim 10, wherein the polarization-diversity in-phase/quadrature modulator is configured to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization; wherein frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization are equal to one another; and wherein frequency spacing between a tone in the first polarization and a tone in the second polarization is an integer multiple of said equal frequency spacing.

12. The apparatus of claim 1, further comprising an optical transmit module optically end-connected to the output port of the polarization combiner via one or more sections of optical fiber, the transmit module comprising: a polarization splitter having an input port thereof optically connected to an end of one of the sections of the optical fiber to receive light of the optical output; a first optical data modulator connected to a first output of the polarization splitter; and a second optical data modulator connected to a second output of the polarization splitter.

13. An apparatus comprising an optical transmitter that comprises: a passive polarization splitter having an optical input port and first and second optical output ports, the optical input port being optically connected to receive an optical input signal having first and second polarization components, the first polarization component carrying light of a first optical frequency, the second polarization component carrying light of a second optical frequency different from the first optical frequency, the first and second polarization components being mutually orthogonal and jointly undergoing a state-of- polarization change during a time interval, the passive polarization splitter causing light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causing light of a second fixed polarization to be directed from the optical input port to the second optical output port, the first and second fixed polarizations being orthogonal to one another, the state-of-polarization change causing respective spectral compositions of the lights directed to the first and second optical ports to change during said time interval; and a first optical modulator connected to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal.

14. The apparatus of claim 13, wherein the optical transmitter further comprises a second optical modulator connected to the second optical output port and configured to modulate the light of the second fixed polarization received therefrom in response to a second data signal.

15. The apparatus of claim 14, wherein the first and second optical modulators are connected to transmit the respective modulated lights through different respective optical fibers.

16. The apparatus of claim 13, wherein: at some times of said time interval, the first optical modulator receives from the first output port the first optical frequency but not the second optical frequency; and at some other times of said time interval, the first optical modulator receives from the first output port the second optical frequency but not the first optical frequency.

17. The apparatus of claim 16, wherein, at yet some other times of said time interval, the first optical modulator receives from the first output port a mix of the first and second optical frequencies.

18. The apparatus of claim 13, wherein the optical input port is optically connected to receive the optical input signal from a proximate end of a section of optical fiber, the optical fiber including at least one section that is non-polarization-maintaining.

19. The apparatus of claim 18, wherein the optical transmitter further comprises an optical power supply optically connected to apply the optical input signal through the optical fiber to the passive polarization splitter.

20. The apparatus of claim 19, wherein the optical power supply comprises: a light source and an electronic controller connected to the light source to cause the light source to generate a first light output having the first optical frequency and a second light output having the second optical frequency, each of the first and second light outputs being steady during said time interval; and a polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output that is coupled into the optical fiber to cause the optical input port of the polarization splitter to receive the optical input signal.

21. The apparatus of claim 4 wherein the difference between the first optical frequency and the second optical frequency is Af, the symbol rate is Rs, and D/is within ±10% of Rs.

22. The apparatus of claim 1, comprising: a transmit module that includes at least one optical modulator configured to modulate the optical output signal from the output port of the polarization combiner; and an optical fiber that includes one or more sections of non-polarization-maintaining fiber, in which the optical fiber is optically coupled between the output port of the polarization combiner and the transmit module, and the optical fiber is configured to transmit the optical output signal from the output port of the polarization combiner to the transmit module.

23. The apparatus of claim 22 wherein the optical fiber between the transmit module and the polarization combiner is at least one meter long.

24. The apparatus of claim 22 wherein the optical fiber between the transmit module and the polarization combiner is at least ten meters long.

25. The apparatus of claim 22 wherein the transmit module comprises: a passive polarization splitter having an optical input port and first and second optical output ports, the optical input port being optically connected to receive the optical input signal from the optical power supply having first and second polarization components, the first polarization component carrying light of the first optical frequency, the second polarization component carrying light of the second optical frequency; wherein the first and second polarization components are mutually orthogonal and jointly undergoing a state-of-polarization change during a time interval, the passive polarization splitter causing light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causing light of a second fixed polarization to be directed from the optical input port to the second optical output port, the first and second fixed polarizations being orthogonal to one another, the state-of- polarization change causing respective spectral compositions of the lights directed to the first and second optical ports to change during the time interval; and a first optical modulator optically coupled to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal.

26. The apparatus of claim 25 wherein the optical transmitter comprises a second optical modulator optically coupled to the second optical output port and configured to modulate the light of the second fixed polarization received therefrom in response to a second data signal.

27. The apparatus of claim 26 wherein the first and second optical modulators are optically connected to transmit the respective modulated lights through different respective optical fibers.

28. The apparatus of claim 25 wherein at some times of the time interval, the first optical modulator receives from the first output port the first optical frequency but not the second optical frequency; and wherein at some other times of the time interval, the first optical modulator receives from the first output port the second optical frequency but not the first optical frequency.

29. The apparatus of claim 28 wherein at yet some other times of the time interval the first optical modulator receives from the first output port a mix of the first and second optical frequencies.

30. The apparatus of claim 1 wherein the polarization combiner comprises at least one of a polarization beam combiner, a polarization-maintaining optical power combiner, or a polarization-maintaining wavelength multiplexer.

31. The apparatus of claim 1, comprising a chromatic-dispersion-compensating optical element that is configured to pre-disperse the optical output signal from the polarization combiner.

32. The apparatus of claim 1 wherein the light source comprises: a first laser that is configured to generate first polarized light that has the first optical frequency, wherein the first polarized light forms the first light output of the light source; and a second laser that is configured to generate second polarized light that has the second optical frequency, wherein the second polarized light forms the second light output of the light source.

33. The apparatus of claim 1 wherein the light source comprises: a laser that is configured to generate first polarized light that has the first optical frequency; and an optical splitter that is configured to receive the first polarized light and output a first portion of the first polarized light and a second portion of the first polarized light; wherein the first portion forms the first light output of the light source; wherein the second portion is transmitted to a frequency shifter that is configured to frequency-shift the second portion to generate a frequency-shifted second portion that has the second optical frequency, and the frequency-shifted second portion forms the second light output of the light source.

34. The apparatus of claim 1 wherein the light source comprises: a laser that is configured to generate first light; a modulator that is configured to split the first light into a first spectral tone and a second spectral tone, and generate second light that includes the first and second spectral tones; a frequency splitter that is configured to frequency-split the second light into a first portion and a second portion, wherein the first portion includes the first spectral tone, and the second portion includes the second spectral tone; and wherein the first portion forms the first light output of the light source, and the second portion forms the second light output of the light source.

35. The apparatus of claim 1 wherein the light source comprises: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a first optical modulator configured to modulate the first polarized light to generate first modulated polarized light; a second optical modulator configured to modulate the second polarized light to generate second modulated polarized light; wherein the first modulated polarized light forms the first light output of the light source, and the second modulated polarized light forms the second light output of the light source.

36. The apparatus of claim 35 wherein the light source comprises an optical delay element configured to delay the second modulated polarized light before the second modulated polarized light is polarization-combined with the first modulated polarized light.

37. The apparatus of claim 35 wherein the light source comprises a signal generator configured to generate electrical signals for driving the first and second optical modulators, wherein the first laser, the first modulator, and the signal generator are configured to generate the first modulated polarized light as a first optical pulse train, and wherein the second laser, the second modulator, and the signal generator are configured to generate the second modulated polarized light as a second optical pulse train.

38. The apparatus of claim 35 wherein the light source comprises a signal generator configured to generate electrical signals for driving the first and second optical modulators, wherein the first laser, the first modulator, the second modulator, and the signal generator are configured to generate the first and second modulated polarized light as dispersion pre-distorted optical signals.

39. The apparatus of claim 35 wherein the first and second modulators are configured to modulate time stamps onto the first and second modulated polarized light.

40. The apparatus of claim 1 wherein the light source comprises: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a second polarization combiner configured to polarization-combine the first polarized light and the second polarized light to generate first combined light; an optical modulator configured to modulate the first combined light to generate a modulated combined light; and a splitter to split the modulated combined light into a first portion and a second portion, wherein the first portion forms the first light output of the light source, and the second portion forms the second light output of the light source.

41. The apparatus of claim 40 wherein the light source comprises an optical delay element configured to delay the second portion before the second portion is polarization-combined with the first portion by the polarization combiner.

42. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising: an optical power supply that comprises: a light source and an electronic controller connected to the light source to cause the light source to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; a polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, an optical output signal in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively; and a polarization-diversity in-phase/quadrature modulator that is configured to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization.

43. The apparatus of claim 42 wherein frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization are equal to each other.

44. The apparatus of claim 43 wherein frequency spacing between a tone in the first polarization and a tone in the second polarization is an integer multiple of the frequency spacing between the two tones in the first polarization.

45. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising: an optical power supply that comprises: a laser; an electronic controller electrically coupled to the laser and configured to cause the laser to generate a first polarized light output having a first optical frequency; an optical splitter that is configured to receive the first polarized light and output a first portion of the first polarized light and a second portion of the first polarized light; a frequency shifter that is configured to frequency-shift the second portion to generate a frequency-shifted second portion that has a second optical frequency different from the first optical frequency, wherein each of the first portion and the frequency-shifted second portion is steady during a time interval that is significantly longer than one over the symbol rate; a polarization combiner configured to receive the first portion and the frequency-shifted second portion, in which the polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the frequency-shifted second portion, respectively.

46. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising: an optical power supply that comprises: a laser that is configured to generate first light; a modulator that is configured to split the first light into a first spectral tone and a second spectral tone, and generate second light that includes the first and second spectral tones; a frequency splitter that is configured to frequency-split the second light into a first portion and a second portion, wherein the first portion includes the first spectral tone, and the second portion includes the second spectral tone, and each of the first portion and the second portion is steady during a time interval that is significantly longer than one over the symbol rate; a polarization combiner configured to receive the first portion and the second portion, in which the polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the second portion, respectively.

47. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising: an optical power supply that comprises: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a first optical modulator configured to modulate the first polarized light to generate first modulated polarized light; a second optical modulator configured to modulate the second polarized light to generate second modulated polarized light, and each of the first modulated polarized light and the second modulated polarized light is steady during a time interval that is significantly longer than one over the symbol rate; and a polarization combiner configured to receive the first modulated polarized light and the second modulated polarized light, in which the polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first modulated polarized light and the second modulated polarized light, respectively.

48. The apparatus of claim 47 wherein the optical power supply comprises an optical delay element configured to delay the second modulated polarized light before the second modulated polarized light is polarization-combined with the first modulated polarized light.

49. An apparatus for communicating optical signals modulated at a symbol rate, the apparatus comprising: an optical power supply that comprises: a first laser that is configured to emit first polarized light at a first wavelength; a second laser that is configured to emit second polarized light at a second wavelength; a first polarization combiner configured to polarization-combine the first polarized light and the second polarized light to generate first combined light; an optical modulator configured to modulate the first combined light to generate a modulated combined light; a splitter to split the modulated combined light into a first portion and a second portion, and each of the first modulated polarized light and the second modulated polarized light is steady during a time interval that is significantly longer than one over the symbol rate; and a polarization combiner configured to receive the first portion and the second portion, in which the polarization combiner is configured to generate, at an output port of the polarization combiner, an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first portion and the second portion, respectively.

50. The apparatus of claim 49 wherein the optical power supply comprises an optical delay element configured to delay the second portion before the second portion is polarization-combined with the first portion by the polarization combiner.

51. A method of communicating optical signals modulated at a symbol rate, the method comprising: generating a first light output having a first optical frequency; generating a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; polarization-combining the first and second light outputs and generating an optical output signal that includes first and second mutually orthogonal polarization components that carry light of the first and second light outputs, respectively; and propagating the optical output signal through an optical fiber that includes one or more sections of non-polarization-maintaining fiber to a transmit module that includes at least one optical modulator configured to modulate the optical output signal.

52. The method of claim 51, comprising configuring the first light output and the second light output to be mutually time/frequency orthogonal.

53. The method of claim 51 wherein generating the first light output comprises generating a first continuous-wave optical field at the first optical frequency, and generating the second light output comprises generating a second continuous-wave optical field at the second optical frequency.

54. The method of claim 51 wherein a difference between the first optical frequency and the second optical frequency is approximately an integer multiple of the symbol rate.

55. The method of claim 51 wherein generating the first light output comprises generating a first optical pulse train having a first period, and wherein generating the second light output comprises generating a second optical pulse train having a second period.

56. The method of claim 55, comprising temporally aligning centers of pulses of the first optical pulse train with centers of corresponding pulses of the second optical pulse train.

57. The method of claim 55, comprising temporally offsetting centers of pulses of the first optical pulse train from centers of corresponding pulses of the second optical pulse train by a nonzero time shift.

58. The method of claim 55 wherein generating a first optical pulse train comprises generating a first optical pulse train having a spectrum that includes two first optical frequency tones; and wherein generating a second optical pulse train comprises generating a second optical pulse train having a spectrum that includes two second optical frequency tones different from the two first optical frequency tones.

59. The method of claim 51, comprising imprinting first control information on the first light output and second control information on the second light output.

60. The method of claim 51, comprising using a polarization-diversity in phase/quadrature modulator to generate two tones in a first polarization and two tones in a second polarization orthogonal to the first polarization.

61. The method of claim 60 wherein frequency spacing between the two tones in the first polarization and frequency spacing between the two tones in the second polarization are equal to one another.

62. The method of claim 61 wherein frequency spacing between a tone in the first polarization and a tone in the second polarization is an integer multiple of the frequency spacing between the two tones in the first polarization.

63. The method of claim 61 comprising splitting the optical output signal into a first portion and a second portion; modulating the first portion with first data to generate a first modulated optical signal; and modulating the second portion with second data to generate a second modulated optical signal.

64. A system comprising: an optical power supply that comprises: a first light source and an electronic controller connected to the light source to cause the light source to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over a symbol rate; and a first polarization combiner connected to receive the first and second light outputs of the light source at different respective input ports thereof, the polarization combiner being configured to generate, at an output port thereof, a first optical output signal in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively.

65. The system of claim 64, comprising a first data processing apparatus that comprises: a first housing, a first data processor disposed in the first housing, and a first co-packaged optical module that is configured to convert output electrical signals from the first data processor to output optical signals that are provided to a first optical fiber cable optically coupled to the first data processing apparatus; wherein the optical power supply is configured to provide the first optical output signal to the first co-packaged optical module through a first optical link.

66. The system of claim 65 wherein the optical power supply comprises: a second light source configured to generate a first light output having a first optical frequency and a second light output having a second optical frequency different from the first optical frequency, each of the first and second light outputs being steady during a time interval that is significantly longer than one over the symbol rate; and a second polarization combiner connected to receive the first and second light outputs of the second light source at different respective input ports thereof, the second polarization combiner being configured to generate, at an output port thereof, a second optical output signal in which first and second mutually orthogonal polarization components carry light of the first and second light outputs, respectively; wherein the system comprises a second data processing apparatus that comprises: a second housing, a second data processor disposed in the second housing, and a second co-packaged optical module that is configured to convert output electrical signals from the second data processor to output optical signals that are provided to a second optical fiber cable optically coupled to the second data processing apparatus, the first and second optical fiber cables are either the same cable or different cables; wherein the optical power supply is configured to provide the second optical output signal to the second co-packaged optical module through a second optical link.

67. The system of claim 65 or 66 wherein the first co-packaged optical module comprises a transmit module that includes at least one optical modulator configured to modulate the first optical output signal from the output port of the polarization combiner; and wherein the first optical link includes one or more sections of non-polarization- maintaining fiber, in which the first optical link is optically coupled between the output port of the polarization combiner and the transmit module, and the first optical link is configured to transmit the first optical output signal from the output port of the polarization combiner to the transmit module.

68. The system of any of claims 65 to 67 wherein the system comprises a distributed data processing system, the first data processing apparatus comprises a data server, the data server comprises a circuit board on which the first data processor is mounted, the circuit board is positioned relative to the housing such that a first main surface of the circuit board is at an angle relative to a bottom panel of the housing, and the angle is in a range from 45° to 90°.

69. The system of claim 68 in which the circuit board is positioned parallel to the front panel.

70. The system of claim 68 or 69 in which the first data processor comprises at least one of a network switch, a central processor unit, a graphics processor unit, a tensor processing unit, a neural network processor, an artificial intelligence accelerator, a digital signal processor, a microcontroller, or an application specific integrated circuit (ASIC).

71. The system of any of claims 65 to 70 in which the first co-packaged optical module comprises a first photonic integrated circuit, a first optical connector part that is configured to be removably coupled to a second optical connector part that is attached to the first optical fiber cable, and an optical power supply connector that is connected to the first optical link to receive supply light from the optical power supply.

72. The system of claim 71 wherein the first optical output signal is modulated with synchronization information, the first co-packaged optical module comprises an optical splitter that splits the supply light and provides a first portion of the supply light to a receiver that is configured to extract the synchronization information.

73. The system of claim 71 in which the first co-packaged optical module comprises an optical splitter that splits the supply light and provides a first portion of the supply light to an optoelectronic modulator that is configured to modulate onto the first portion of the supply light the output electrical signals from the first data processor to generate modulated light, in which the modulated light is output through the first optical fiber cable.

74. The system of any of claims 68 to 73 in which the first co-packaged optical module is electrically coupled to the first circuit board using electrical contacts that comprise at least one of spring-loaded elements, compression interposers, or land-grid arrays.

75. The system of any of claims 64 to 75, comprising: a transmit module that includes at least one optical modulator configured to modulate the optical output signal from the output port of the polarization combiner; and an optical fiber that includes one or more sections of non-polarization-maintaining fiber, in which the optical fiber is optically coupled between the output port of the polarization combiner and the transmit module, and the optical fiber is configured to transmit the optical output signal from the output port of the polarization combiner to the transmit module.

76. The system of any of claims 65 to 75, comprising an optical cable assembly that comprises the first optical link, wherein the optical cable assembly comprises: a first optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a second optical fiber connector comprising an optical power supply fiber port; wherein the optical power supply fiber port of the first optical fiber connector is optically coupled to the optical power supply fiber port of the second optical fiber connector; wherein the first optical fiber connector is configured to be optically coupled to the first co-packaged optical module; wherein the second optical fiber connector is configured to be optically coupled to the optical power supply to receive the first optical output signal from the output port.

77. The system of claim 76 wherein the optical cable assembly comprises a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the second optical fiber connector.

78. The system of any of claims 66 to 75, comprising an optical cable assembly that comprises the first optical link and the second optical link, wherein the optical cable assembly comprises: a first optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a second optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a third optical fiber connector comprising a first optical power supply fiber port and a second optical power supply fiber port; wherein the optical power supply fiber port of the first optical fiber connector is optically coupled to the first optical power supply fiber port of the third optical fiber connector, the optical power supply fiber port of the second optical fiber connector is optically coupled to the second optical power supply fiber port of the third optical fiber connector; wherein the first optical fiber connector is configured to be optically coupled to the first co-packaged optical module, the second optical fiber connector is configured to be optically coupled to the second co-packaged optical module, and the third optical fiber connector is configured to be optically coupled to the optical power supply.

79. The system of claim 78 wherein the optical cable assembly comprises a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the third optical fiber connector.

80. The system of claim 79 wherein the optical cable assembly comprises a second optical fiber optically coupled to the optical power supply fiber port of the second optical fiber connector and the second optical power supply fiber port of the third optical fiber connector.

81. The system of claim 80 wherein the optical cable assembly comprises a third optical fiber optically coupled to the transmitter fiber port of the first optical fiber connector and the receiver fiber port of the second optical fiber connector.

82. The system of claim 81 wherein the optical cable assembly comprises a fourth optical fiber optically coupled to the receiver fiber port of the first optical fiber connector and the transmitter fiber port of the second optical fiber connector.

83. The system of claim 82 wherein the optical cable assembly comprises an optical fiber guide module comprising a first port, a second port, and a third port, wherein the first optical fiber extends through the first and third ports, the second optical fiber extends through the second and third ports, the third optical fiber extends through the first and second ports, and the fourth optical fiber extends through the first and second ports.

84. The system of claim 83 wherein the first, third, and fourth optical fibers extend from the first port of the optical fiber guide module to the first optical fiber connector.

85. The system of claim 84 wherein the second, third, and fourth optical fibers extend from the second port of the optical fiber guide module to the second optical fiber connector.

86. The system of claim 85 wherein the first and second optical fibers extend from the third port of the optical fiber guide module to the third optical fiber connector.

87. The system of any of claims 83 to 86 wherein the optical fiber guide module is configured to restrict bending of the optical fibers that pass through the optical fiber guide module such that each optical fiber within the optical fiber guide module has a bending radius greater than a predetermined value to prevent excess optical light loss or damage to the optical fiber due to bending.

88. The system of claim 78 wherein the first co-packaged optical module comprises a first photonic integrated circuit optically coupled to the first optical fiber connector and configured to receive the power supply light from the first light source through the optical power supply fiber port of the first optical fiber connector.

89. The system of claim 88 wherein the first photonic integrated circuit is configured to modulate the power supply light to generate a first modulated optical signal, and transmit the first modulated optical signal to the transmitter fiber port of the first optical fiber connector.

90. The system of claim 89 wherein the second co-packaged optical module comprises a second photonic integrated circuit optically coupled to the second optical fiber connector and configured to receive the power supply light from the second light source through the optical power supply fiber port of the second optical fiber connector.

91. The system of claim 90 wherein the second photonic integrated circuit is configured to modulate the power supply light to generate a second modulated optical signal, and transmit the second modulated optical signal to the transmitter fiber port of the second optical fiber connector.

92. The system of claim 91 wherein the first photonic integrated circuit is configured to, through the receiver fiber port of the first optical fiber connector, receive the second modulated optical signal transmitted from the second photonic integrated circuit.

93. The system of claim 92 wherein the second photonic integrated circuit is configured to, through the receiver fiber port of the second optical fiber connector, receive the first modulated optical signal transmitted from the first photonic integrated circuit.

94. The system of any of claims 78 to 93 wherein the optical power supply is optically coupled to the third optical fiber connector and configured to provide a first sequence of optical frame templates to the first optical power supply fiber port and a second sequence of optical frame templates to the second optical power supply fiber port.

95. The system of claim 94 wherein the first co-packaged optical module comprises a first photonic integrated circuit optically coupled to the first optical fiber connector and configured to receive the first sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the first optical fiber connector.

96. The system of claim 95 wherein the first photonic integrated circuit is configured to modulate the first sequence of optical frame templates to generate a first sequence of loaded optical frames, and transmit the first sequence of loaded optical frames to the transmitter fiber port of the first optical fiber connector.

97. The system of claim 96 wherein the second co-packaged optical module comprises a second photonic integrated circuit optically coupled to the second optical fiber connector and configured to receive the second sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the second optical fiber connector.

98. The system of claim 97 wherein the second photonic integrated circuit is configured to modulate the second sequence of optical frame templates to generate a second sequence of loaded optical frames, and transmit the second sequence of loaded optical frames to the transmitter fiber port of the second optical fiber connector.

99. The system of claim 98 wherein the first photonic integrated circuit is configured to, through the receiver fiber port of the first optical fiber connector, receive the second sequence of loaded optical frames transmitted from the second photonic integrated circuit.

100. The system of claim 99 wherein the second photonic integrated circuit is configured to, through the receiver fiber port of the second optical fiber connector, receive the first sequence of loaded optical frames transmitted from the first photonic integrated circuit.

101. A system compri sing : a first data processing apparatus comprising a first optical transmitter that comprises: a passive polarization splitter having an optical input port and first and second optical output ports, the optical input port being optically connected to receive an optical input signal having first and second polarization components, the first polarization component carrying light of a first optical frequency, the second polarization component carrying light of a second optical frequency different from the first optical frequency, the first and second polarization components being mutually orthogonal and jointly undergoing a state-of-polarization change during a time interval, the passive polarization splitter causing light of a first fixed polarization to be directed from the optical input port to the first optical output port and also causing light of a second fixed polarization to be directed from the optical input port to the second optical output port, the first and second fixed polarizations being orthogonal to one another, the state-of-polarization change causing respective spectral compositions of the lights directed to the first and second optical ports to change during said time interval; and a first optical modulator connected to the first optical output port and configured to modulate the light of the first fixed polarization received therefrom in response to a first data signal; and a first optical link optically connected between the optical input port and an optical power supply that provides the optical input signal.

102. The system of claim 101 wherein the first data processing apparatus comprises a first housing, and the first optical transmitter is disposed in the first housing; wherein the system comprises: a second data processing apparatus that comprises a second housing, a second optical transmitter disposed in the second housing; and a second optical link optically connected between the second optical transmitter and the optical power supply.

103. The system of claim 101 or 102 wherein the first optical link includes one or more sections of non-polarization-maintaining fiber, in which the first optical link is optically coupled between the output port of the polarization combiner and the transmit module, and the first optical link is configured to transmit the first optical output signal from the output port of the polarization combiner to the transmit module.

104. The system of claim 102 or 103 wherein the first data processing apparatus comprises a circuit board on which a first photonic integrated circuit is mounted, the first optical transmitter is part of the first photonic integrated circuit, the circuit board is positioned relative to the housing such that a first main surface of the circuit board is at an angle relative to a bottom panel of the housing, and the angle is in a range from 45° to 90°.

105. The system of claim 104 in which the circuit board is positioned parallel to a front panel of the housing.

106. The system of any of claims 101 to 105 in which the first data processing apparatus comprises a first data processor that is configured to provide the first data signal, and the first data processor comprises at least one of a network switch, a central processor unit, a graphics processor unit, a tensor processing unit, a neural network processor, an artificial intelligence accelerator, a digital signal processor, a microcontroller, or an application specific integrated circuit (ASIC).

107. The system of any of claims 101 to 106, comprising an optical cable assembly that comprises the first optical link, wherein the optical cable assembly comprises: a first optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; and a second optical fiber connector comprising an optical power supply fiber port; wherein the optical power supply fiber port of the first optical fiber connector is optically coupled to the optical power supply fiber port of the second optical fiber connector; wherein the first optical fiber connector is configured to be optically coupled to the first data processing apparatus; wherein the second optical fiber connector is configured to be optically coupled to the optical power supply.

108. The system of claim 107 wherein the optical cable assembly comprises a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the optical power supply fiber port of the second optical fiber connector.

109. The system of any of claims 102 to 106, comprising an optical cable assembly that comprises the first optical link and the second optical link, wherein the optical cable assembly comprises: a first optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a second optical fiber connector comprising an optical power supply fiber port, a transmitter fiber port, and a receiver fiber port; a third optical fiber connector comprising a first optical power supply fiber port and a second optical power supply fiber port; wherein the optical power supply fiber port of the first optical fiber connector is optically coupled to the first optical power supply fiber port of the third optical fiber connector, the optical power supply fiber port of the second optical fiber connector is optically coupled to the second optical power supply fiber port of the third optical fiber connector; wherein the first optical fiber connector is configured to be optically coupled to the first data processing apparatus, the second optical fiber connector is configured to be optically coupled to the second data processing apparatus, and the third optical fiber connector is configured to be optically coupled to the optical power supply.

110. The system of claim 109 wherein the optical cable assembly comprises a first optical fiber optically coupled to the optical power supply fiber port of the first optical fiber connector and the first optical power supply fiber port of the third optical fiber connector.

111. The system of claim 110 wherein the optical cable assembly comprises a second optical fiber optically coupled to the optical power supply fiber port of the second optical fiber connector and the second optical power supply fiber port of the third optical fiber connector.

112. The system of claim 111 wherein the optical cable assembly comprises a third optical fiber optically coupled to the transmitter fiber port of the first optical fiber connector and the receiver fiber port of the second optical fiber connector.

113. The system of claim 112 wherein the optical cable assembly comprises a fourth optical fiber optically coupled to the receiver fiber port of the first optical fiber connector and the transmitter fiber port of the second optical fiber connector.

114. The system of claim 113 wherein the optical cable assembly comprises an optical fiber guide module comprising a first port, a second port, and a third port, wherein the first optical fiber extends through the first and third ports, the second optical fiber extends through the second and third ports, the third optical fiber extends through the first and second ports, and the fourth optical fiber extends through the first and second ports.

115. The system of claim 114 wherein the first, third, and fourth optical fibers extend from the first port of the optical fiber guide module to the first optical fiber connector.

116. The system of claim 115 wherein the second, third, and fourth optical fibers extend from the second port of the optical fiber guide module to the second optical fiber connector.

117. The system of claim 116 wherein the first and second optical fibers extend from the third port of the optical fiber guide module to the third optical fiber connector.

118. The system of any of claims 114 to 117 wherein the optical fiber guide module is configured to restrict bending of the optical fibers that pass through the optical fiber guide module such that each optical fiber within the optical fiber guide module has a bending radius greater than a predetermined value to prevent excess optical light loss or damage to the optical fiber due to bending.

119. The system of claim 109 wherein the first optical transmitter is configured to receive power supply light from the optical power supply through the optical power supply fiber port of the first optical fiber connector, modulate the light of the first fixed polarization in response to the first data signal to generate a first modulated optical signal, and transmit the first modulated optical signal to the transmitter fiber port of the first optical fiber connector.

120. The system of claim 119 wherein the second optical transmitter is configured to receive power supply light from the optical power supply through the optical power supply fiber port of the second optical fiber connector, modulate the power supply light to generate a second modulated optical signal, and transmit the second modulated optical signal to the transmitter fiber port of the second optical fiber connector.

121. The system of any of claims 109 to 120, comprising the optical power supply, wherein the optical power supply is optically coupled to the third optical fiber connector and configured to provide a first sequence of optical frame templates to the first optical power supply fiber port and a second sequence of optical frame templates to the second optical power supply fiber port.

122. The system of claim 121 wherein the first optical transmitter is configured to receive the first sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the first optical fiber connector.

123. The system of claim 122 wherein the first optical transmitter is configured to modulate the first sequence of optical frame templates in response to the first data signal to generate a first sequence of loaded optical frames, and transmit the first sequence of loaded optical frames to the transmitter fiber port of the first optical fiber connector.

124. The system of claim 123 wherein the second optical transmitter is configured to receive the second sequence of optical frame templates from the optical power supply through the optical power supply fiber port of the second optical fiber connector.

125. The system of claim 124 wherein the second optical transmitter is configured to modulate the second sequence of optical frame templates to generate a second sequence of loaded optical frames, and transmit the second sequence of loaded optical frames to the transmitter fiber port of the second optical fiber connector.

126. The system of claim 125 wherein the first data processing apparatus is configured to, through the receiver fiber port of the first optical fiber connector, receive the second sequence of loaded optical frames transmitted from the second photonic integrated circuit.

127. The system of claim 126 wherein the second data processing apparatus is configured to, through the receiver fiber port of the second optical fiber connector, receive the first sequence of loaded optical frames transmitted from the first photonic integrated circuit.