WO2023141626A1

WO2023141626A1 - Optical modulator and method of operation

Info

Publication number: WO2023141626A1
Application number: PCT/US2023/061092
Authority: WO
Inventors: Thomas W. Baehr-Jones
Original assignee: Luminous Computing, Inc.
Priority date: 2022-01-21
Filing date: 2023-01-23
Publication date: 2023-07-27

Abstract

In variants, an optical modulator can include: an optical signal source, an input waveguide, an optical splitter, a set of modulators and/or arm waveguides connected to the optical splitter outputs, a set of reflectors arranged at the ends of the modulators and/or arm waveguides, an electrical signal source electrically connected to the set of modulators, and an output waveguide. In an example, the optical modulator can reflect a forward-propagating signal back into the incident modulator, such that the same optical modulation is also applied to the backward-propagating signal.

Description

OPTICAL MODULATOR AND METHOD OF OPERATION

TECHNICAL FIELD

This invention relates generally to the optics field, and more specifically to a new and useful optical modulator in the optics field.

BRIEF DESCRIPTION OF THE FIGURES

FIGURE i is a schematic representation of a variant of the optical modulator.

FIGURE 2 is a schematic representation of a variant of a method of optical modulator operation.

FIGURE 3 is a schematic representation of an example of optical modulator operation, where at least one optical path is a phase-modulated path, and the optical paths are optionally biased.

FIGURE 4 is a schematic representation of a second example of optical modulator operation, including an example of optical signal reflection.

FIGURE 5 is a schematic representation of an example of the optical modulator with optional biasing components.

FIGURE 6 is a schematic representation of an example of the optical modulator with different -length phase modulators.

FIGURE 7 is a schematic representation of an example of the optical modulator with a Sagnac loop reflector.

FIGURE 8 is a schematic representation of an example of the optical modulator with different voltages applied across each phase modulator.

FIGURE 9 is a schematic representation of an example of the optical modulator with the same voltage applied across each phase modulator.

FIGURE io is a schematic representation of an example of the optical modulator with a single phase modulator.

FIGURE n is a schematic representation of an example of the optical modulator with at least one reverse-biased PN phase modulator. FIGURE 12 is a schematic representation of a specific example of the optical modulator with interdigitated electrodes cooperatively defining arm waveguides.

FIGURE 13 is a schematic representation of a specific example of the optical modulator.

FIGURE 14A-14D are schematic representations of an example optical splitter propagating an optical signal forward; an example optical splitter propagating an optical signal backward (e.g., with the modulator turned off); an example optical splitter propagating an optical signal backward (e.g., with the modulator turned on); and a second example optical splitter propagating an optical signal backward (e.g., with the modulator turned on), respectively.

DETAILED DESCRIPTION

The following description of the embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable any person skilled in the art to make and use this invention.

1. Overview.

As shown in FIGURE 1, the optical modulator 100 can include: an optical signal source 220, an input waveguide 200, an optical splitter 300, a set of arm waveguides 420, a set of electrodes 440, a set of reflectors 460, an electrical signal source electrically connected to the set of arm waveguides, and an output waveguide 600. The optical modulator 100 can optionally include a set of feedback elements 800, a biasing component 500, and/or any other suitable set of components.

In an illustrative example of optical modulator operation (e.g., specific examples shown in FIGURE 3, FIGURE 5, FIGURE 6, FIGURE 7, FIGURE 8, FIGURE 9, FIGURE 10, FIGURE 11, FIGURE 12, and FIGURE 13), an input optical signal 10 is split into a set of optical sub-signals 30 (e.g., example shown in FIGURE 14A), wherein each sub-signal is propagated through a different arm waveguide 420. As the optical sub-signal 30 propagates forward through the respective arm waveguide 420, a change in a parameter of the optical sub-signal 30 (e.g., an optical phase shift) is induced by an electrical signal applied to the respective arm waveguide 420. The optical sub-signal 30 is reflected back through the respective arm waveguide 420 at the end of said arm waveguide 420, and is subjected to another parameter change induced by the applied electrical signal. The reflected optical sub-signals can have the same mode as the forwardpropagating optical sub-signals. The reflected optical sub-signals 30 are then recombined, wherein parameter differences between the reflected optical sub-signals 30 result in a change in a secondary optical signal parameter (e.g., due to interference), thereby encoding the electrical signal onto the secondary optical signal parameter . In variants, the changed parameter of the optical sub-signals 30 can additionally be changed at a slower rate (e.g., by the biasing component 500). In a specific example, an applied electrical signal can induce an optical phase change in the optical sub-signals 30 propagating forward and backward through each arm waveguide 420, wherein the resultant optical phase differences between the reflected optical sub-signals 30 modulate the amplitude (e.g., intensity) of the recombined optical signal, thereby encoding the electrical signal onto the amplitude of the optical signal (e.g., wherein the optical signal modulator is an amplitude modulator). The optical phase differences between the reflected optical sub-signals 30 can optionally steer the recombined optical signal through the input of the optical splitter (e.g., example shown in FIGURE 14B), the output of the optical splitter (e.g., example shown in FIGURE 14C), and/ or both the input and output of the optical splitter (e.g., example shown in FIGURE 14D). However, the optical signal modulator can operate in any other suitable manner.

2. Technical advantages

Variants of the optical modulator 100 can confer benefits over conventional systems.

First, variants of the optical modulator 100 can reduce the chip footprint without sacrificing performance, which can increase the bandwidth density of optical interconnects 700. In a first example, this can be accomplished by reflecting the optical sub-signal 30 back through the arm waveguide 420, which halves the physical length of the arm waveguide 420 needed to achieve the same performance. In a second example, this can be accomplished by interdigitating the electrical signal electrodes 440 and/ or using boustrophedonic arm waveguides 420. However, the footprint can be otherwise reduced relative to conventional optical modulators.

Second, variants of the optical modulator 100 can be more efficient than conventional optical modulators. In a first example, this can be accomplished by applying the same optical parameter modulation (e.g., the same phase shift) to each optical subsignal 30 twice: once when the optical sub-signal 30 propagates forward through the arm waveguide 420, and a second time when the optical sub-signal 30 propagates backward through the same arm waveguide 420 in the same mode in the reverse propagating direction. This can decrease the power consumption by a power of 2, which results in a lower power requirement for the optical modulator 100, less power loss, and less waste heat. In a second example, increased efficiency can be achieved by minimizing the cardinal distance between any point within the arm waveguide 420 and any point on the electrode 440 (e.g., that is applying the electrical signal). However, other aspects of the optical modulator 100 can result in increased efficiency over conventional systems.

However, further advantages can be provided by the system and method disclosed herein.

3. System.

The optical modulator 100 can include: an optical signal source 220, an input waveguide 200, an optical splitter 300, a set of arm waveguides 420, a set of electrodes 440, a set of reflectors 460, an electrical signal source electrically connected to the set of arm waveguides, and an output waveguide 600. The optical modulator 100 can optionally include a set of feedback elements 800, a biasing component 500, and/or any other suitable set of components. The optical modulator 100 functions to encode a data signal (e.g., electrical signal) onto an optical signal (e.g., light stream, carrier signal) by modulating a parameter of the optical signal. In an example, the optical modulator 100 reflects a forward-propagating signal 12 back into the incident phase modulator 400 (e.g., examples shown in black open-headed arrows in the FIGURES), such that the same phase modulation is also applied to the backward-propagating signal 22 (e.g., examples shown in gray open-headed arrows in the FIGURES).

The optical modulator 100 can be used in or with an optical interconnect 700. The optical interconnect 700 can be part of or assembled onto a printed circuit board, die (e.g., silicon die), or other computing component, and be used for chip-scale data movement (e.g., on length scales longer than icm, less than icm, etc.). However, the optical interconnect 700 can be otherwise used and/or configured. The optical modulator 100 preferably defines a linear system (e.g., including only or substantially only linear optical effects), but can alternatively define a nonlinear system (e.g., including nonlinear optical effects).

In variants, the optical modulator 100 can be used to implement one or more modulation schemes. Example modulation schemes that can be implemented include: telecommunications modulation schemes (e.g., NRZ, PAM4, etc.); coherent modulation formats (e.g., QPSK; wherein the optical modulator 100 can be incorporated within a nested Mach-Zehnder structure in these variants; etc.); analog modulation (e.g., an arbitrary waveform); and/or any other suitable modulation scheme. The optical modulator 100 preferably operates at a high data transmission speed (e.g., higher than 3oGbps, 4oGbps, soGbps, 6oGpbs, etc.), but can additionally or alternatively operate at any other suitable data transmission speed.

The optical modulator 100 can be manufactured in a single package, from multiple components, and/ or otherwise manufactured.

In a first variant, the components of the optical modulator 100 are monolithically integrated into an optical material (e.g., onto a single die, chip, wafer, etc.). The optical material can include a silicon-on-insulator material, Lithium Niobate, Indium Phosphide, electro-optic crystals, electro-optic polymers (e.g., organic polymers), and/or any other suitable electro-optic material. The electro-optic material is preferably nonlinear, but can alternatively be linear. The electro-optic material can be manufactured using CMOS methods and/or other fabrication methods. The optical modulator 100 components can be manufactured using CMOS infrastructure and/ or other fabrication infrastructure. In an example, the waveguides (e.g., input waveguide 200, arm waveguides 420, output waveguide 600, etc.), control circuitry (e.g., for the electrical signal source and/or the biasing components 500), and/or electrical connections (e.g., metal traces) are directly fabricated into the top silicon layer of a silicon-on-insulator material.

In a second variant, the components of the optical modulator 100 are individually manufactured as separate components and assembled together (e.g., onto a common board). The optical modulator 100 components can be manufactured as individual dies (e.g., CMOS dies), packages, and/or in other form factors, and can be electrically connected together using wafer bumping processes (e.g., solder bump bonding, ball bumping, etc.), wire bonding, and/or any other suitable electrical connection technique.

However, the optical modulator 100 can be otherwise manufactured and/or assembled.

The optical modulator 100 preferably has an overall footprint smaller than 0.1mm², but can additionally or alternatively have an overall footprint smaller than: 0.01mm², 0.05mm², 0.07mm², 0.2mm², 0.3mm², 0.4mm², 0.5mm², 1cm²; larger than 0.5mm²; a footprint smaller than or comparable to other components of the optical interconnect 700, and/or have any other suitable footprint.

The optical modulator 100 preferably lacks electrical transmission lines superimposed over the optical waveguides, but can additionally or alternatively include electrical transmission lines over the optical waveguides.

The optical signal source 220 functions to provide an input optical signal 10 (e.g., carrier signal) for modulation. The input optical signal 10 (e.g., carrier signal) is preferably a beam of light, but can additionally or alternatively be any other optical signal. The input optical signal 10 is preferably unmodulated, but can alternatively be modulated. The input optical signal 10 is preferably continuous (e.g., unbroken), but can additionally or alternatively be intermittent, periodic, and/or have any other suitable discretization. The optical signal source 220 can be a laser (e.g., a continuous wave laser, pulsed laser, ultrafast laser, etc.), another collimated light source, and/or any other optical signal source 220. The laser beam is preferably monochromatic, but can have any suitable wavelength and/or set thereof. The optical modulator 100 can include one or more optical signal sources 220, wherein different optical signal sources 220 can be operated contemporaneously (e.g., concurrently) or asynchronously (e.g., serially). Different optical signal sources 220 preferably vary in at least one parameter (e.g., frequency, phase, amplitude, polarization, etc.) that is different from the parameters being modulated by the optical modulator 100, but can alternatively emit optical signals having the same set of parameters. In variants, the optical signal source 220 can include an isolator arranged within the optical path between the optical signal source 220 and the input of the optical splitter 300; alternatively, the optical signal source 220 can lack an isolator.

The input waveguide 200 functions to optically connect the optical signal source 220 to the optical splitter 300. The input waveguide 200 is preferably manufactured from an optical material and/or electro-optical material (e.g., silicon, Lithium Niobate, Indium Phosphide, electro-optic polymers, etc.), but can be otherwise manufactured. In an example, the input waveguide 200 can be fabricated in the top silicon layer of a silicon-on-insulator material. The system can include one or more input waveguides 200. For example, the system can include an input waveguide 200 for each optical signal source 220.

The optical splitter 300 functions to split the input optical signal 10 into two or more optical sub-signals 30 (e.g., split optical signals); example shown in FIGURE 14A. The optical splitter 300 can optionally recombine the reflected optical sub-signals 30 into an output optical signal 20 (e.g., example shown in FIGURES 14B-FIGURE 14D). The optical splitter 300 preferably evenly splits the input optical signal 10 into X optical subsignals 30, but can alternatively unevenly split the input signal into X optical sub-signals 30. The optical splitter 300 preferably splits the input optical signal 10 into two optical sub-signals 30 (e.g., X=2); additionally or alternatively, X can be the number of arm waveguides 420 in the system, or be any other number. The optical sub-signal 30 preferably has a different amplitude but the same mode, phase, frequency, and/ or other parameters as the input optical signal 10, but can additionally or alternatively have the same or different parameter values. The system can include a single optical splitter 300 for each input signal, a single optical splitter 300 for each input waveguide 200, multiple optical splitters 300 for a single input signal or input waveguide 200, a single optical splitter 300 for multiple input signals or input waveguides 200, and/ or any other number of optical splitters 300 with any other suitable input signal/waveguide pairing. The optical splitter 300 is preferably a directional coupler (e.g., a 3-db directional coupler), but can additionally or alternatively be an MMI interferometer (e.g., multimodal interference coupler, a 2x2 MMI interferometer, etc.), a half-slivered mirror (e.g., with a metallic coating, dichroic coating, etc.), a dichroic mirrored prism, and/or any other suitable optical signal splitter. The optical splitter 300 preferably evenly splits the input optical signal 10 into the optical sub-signals 30, but can alternatively unevenly split the input optical signal 10. The resultant optical sub-signals 30 preferably have the same optical properties (e.g., same mode, phase, amplitude, frequency, wavelength, etc.), but can alternatively have different optical properties. The optical splitter 300 is preferably connected to the input waveguide 200 and/or the output waveguide 600 at a first end (e.g., the input), and is preferably connected to the arm waveguides 420 at the optical splitter 300's one or more second ends (e.g., outputs).

The arm waveguides 420 function to define optical paths (e.g., path, split path, etc.) and propagate optical signals (e.g., the optical sub-signals 30) forward and/ or backward. The optical signals are preferably propagated forward and backward in the same mode; alternatively, the optical signals can propagate forward and backward in different modes. The arm waveguides 420 ("arm") can optionally facilitate optical signal parameter modulation, and define parameter modulation paths (e.g., phase modulating paths). The system preferably includes a set of X arm waveguides 420, but can additionally or alternatively include less than X arm waveguides 420, more than X arm waveguides 420, and/or any other number of arm waveguides 420. X is preferably 2, but can alternatively be greater. Each arm waveguide 420 is preferably manufactured from an optical material and/or electro-optical material (e.g., silicon, Lithium Niobate, Indium Phosphide, electro-optic polymers, etc.), but can be otherwise manufactured. One or more of the arm waveguides can define a PN junction, a PIN junction, and/ or any other suitable junction (e.g., wherein the arm waveguide material is doped with ions, such as Boron, Phosphorous, or other ions, using ion implantation techniques and/ or any other suitable doping technique), but can be otherwise configured.

Each arm waveguide 420 is preferably connected (e.g., optically, physically, etc.) to an output of the optical splitter 300 (e.g., at a first end of the arm waveguide 420), but can additionally or alternatively be connected (e.g., directly or indirectly) to the input waveguide 200, output waveguide 600, and/or any other suitable component.

The arm waveguides 420 within the system preferably have substantially the same dimensions (e.g., apparent length, true length, width, cross-section, etc.), material, and/or other parameter (e.g., within a predetermined margin of error), but can alternatively have varying waveguide parameter values. The true length of the arm waveguide 420 (e.g., total path length traveled by an optical signal propagating through the arm waveguide 420) can be determined based on the operation speed of the optical signal modulator (e.g., wherein shorter arm waveguides 420 are used for faster operation speeds), the transmission speed, the switching speed, the group index bitrate, and/or otherwise determined. The absolute length or other dimension of the waveguide (e.g., the dimensions of a projection of the arm waveguides 420) can be determined based on the overall package size, or be otherwise determined. The arm waveguide 420 preferably defines a boustrophedonic optical path (e.g., with 1, 2, 3, and/or any other number of turns; examples shown in FIGURE 12 and FIGURE 13), but can additionally or alternatively define a linear path, a curved path, a serpentine path, a spiral path, and/ or a path with any other suitable shape.

In a first variant, the arm waveguides 420 have the same length. In a second variant, the arm waveguides 420 can have different lengths, wherein the length difference can be: arbitrary, selected based on a desired phase shift, selected based on the wavelength of the optical signal, and/ or otherwise determined.

However, the arm waveguides 420 can be otherwise configured.

The electrodes 440 function to apply an electrical signal (e.g., information signal) to the optical sub-signals 30 propagating through the arm waveguides 420, which modulates an optical sub-signal 30 parameter. In variants, the electrodes 440 can function to define a parameter modulation section of the arm waveguides 420 (e.g., a high-speed modulation section; a high-speed phase modulation section; etc.). The system preferably includes a set of electrodes 440 for each arm waveguide 420, but can additionally or alternatively include a set of electrodes 440 for all arm waveguides 420, multiple electrodes 440 for each arm waveguide 420, and/or any other number of electrodes 440 with any other arm waveguide 420 cardinality. Each set of electrodes 440 preferably includes a pair of electrodes 440 (e.g., two electrodes 440), but can alternatively include a single electrode 440 and/or more than two electrodes 440. Each arm waveguide 420 preferably has a set of associated electrodes 440 (e.g., wherein the arm waveguides 420 can be phase modulator waveguides); alternatively, some or all of the arm waveguides 420 can lack electrodes 440. Each arm waveguide 420 is preferably paired with (e.g., associated with) a different set of electrodes 440; alternatively, different arm waveguides 420 can share a set of electrodes 440. The arm waveguides 420 and associated electrode set preferably cooperatively form a phase modulator 400 (e.g., a Mach-Zehnder arm, phase modulating path, phase shifter, etc.), but can alternatively form any other suitable electro-optic modulator.

The electrodes 440 are preferably arranged along opposing walls of the respective arm waveguide 420, but can be otherwise arranged. The electrodes 440 (and/or the parameter modulation section defined by the electrodes) are preferably arranged proximal the reflector, more preferably adjacent the reflector (e.g., contiguous with the reflector, immediately adjacent the reflector along the optical path, etc.), but can alternatively be arranged distal the reflector (e.g., separated by one or more intervening components, optical path segments, etc.). The length of the parameter modulation section can be determined based on the modulation frequency (e.g., the electrode modulation frequency), be a predetermined length (e.g., between 100-500 microns, 200-300 microns, 300-400 microns, below 100 microns, above 500 microns, etc.), and/or be otherwise determined.

The electrodes 440 are preferably monolithically integrated into the arm waveguides 420 and/or the optical material forming the arm waveguides 420, but can alternatively be separate conductors assembled with the arm waveguides 420 after fabrication.

The electrodes 440 preferably contact a PN junction formed from doped arm waveguide material (e.g., examples shown in FIGURE 11 and FIGURE 13), wherein the material can be doped with ions (e.g., Boron, Phosphorous, etc.) using ion implantation techniques and/or any other suitable doping technique. However, the electrodes 440 can be otherwise arranged relative to the arm waveguide material. The PN junction preferably overlaps with the optical mode guided by the arm waveguide 420, but can alternatively have any other relationship with the arm waveguide 420 attributes. In a first variant, electrodes 440 can include a parallel plate capacitor (e.g., formed by metal traces, etc.), placed across the arm waveguide 420 width (e.g., extending along the arm waveguide 420 length). Additionally or alternatively, the electrodes 440 can exclude metal traces or plates.

In a second variant, the electrodes 440 can include doped material (e.g., doped semiconductor material; doped arm waveguide material; etc.). The doped material can be degenerately doped or otherwise doped.

However, the electrodes 440 can be otherwise constructed.

In some variants, the electrodes 440 can define geometries that: minimize the distance (e.g., cartesian distance, physical distance, absolute distance, etc.) between any point on the arm waveguide 420 and the electrode 440; minimize the distance between any point on the electrode 440 and the electrical contact point (e.g., while maintaining the same arm waveguide length); maximize the contact area between each electrode 440 (e.g., each electrode 440 branch) and the arm waveguide 420; and/or confer other benefits. The electrical contact point can be the driver circuitry connection point, the arm waveguide 420 contact point, and/or any other contact point. In a variant, each electrode 440 can have one or more branches. In a first embodiment, the electrode 440 can be unbranched. In a second embodiment, the electrode 440 can include two or more branches. When the opposing electrode 440 also includes multiple branches, the branches of the opposing electrodes 440 can be interdigitated (e.g., thereby cooperatively forming a boustrophedonic optical path; examples shown in FIGURE 12 and FIGURE 13), or be otherwise arranged. However, any other distance-minimizing geometry can be used.

In operation, each set of electrodes 440 preferably cooperatively apply a voltage across the respective arm waveguide 420, wherein the voltage induces a phase shift in the optical sub-signal 30 (propagating through the arm waveguide 420) while the amplitude and frequency of the optical sub-signal 30 remain constant. For example, the applied voltage can modulate the phase of the optical sub-signal 30 (e.g., carrier signal) by changing the refractive index of the arm waveguide 420 material, or modulate the optical sub-signal phase using any other mechanism. In variants, a timeseries of phase shifts can be induced within the optical sub-signal 30 (e.g., carrier signal) when a timeseries of information signal voltage levels (e.g., amplitude) is applied to said optical sub-signal 30. However, any other suitable optical sub-signal 30 parameter (e.g., amplitude, frequency, polarization, etc.) can be modulated in any other suitable manner (e.g., by applying current, a magnetic field, an optical field, etc.), and/or the electrical signal can be encoded within the optical sub-signal 30 parameters in any other suitable manner.

In a first variant, the phase shift can be induced by applying a reverse bias to the optical sub-signal 30 propagating within the arm waveguide 420 (e.g., by operating the PN junction in depletion mode, such that the N electrode is at a higher voltage than the P electrode; example shown in FIGURE 11). In an example, this can operate the electrodes 440 as a reverse biased PN diode.

In a second variant, the phase shift can be induced by applying a forward bias (e.g., using carrier injection; by applying a higher voltage to the P electrode than the N electrode). In an example, this can operate the electrodes 440 as a forward biased PN diode.

However, the electrodes 440 can be otherwise operated to induce the phase shift.

Different electrode sets (e.g., paired with different arm waveguides 420) can apply the same or different electrical signal. In a first variant, the same electrical signal (e.g., information signal) is applied to all electrode sets and/or arm waveguides 420 (e.g., example shown in FIGURE 9). In a second variant, the electrical signal is applied to a subset of the arm waveguides 420 and/or electrode sets (e.g., wherein a subset of the optical paths are phase modulating paths; example shown in FIGURE 10). For example, the electrical signal can be applied by a first electrode set to a first arm waveguide 420, while no electrical signal is applied by a second electrode set to a second arm waveguide 420. In a third variant, different electrical signals are applied to different electrode sets: concurrently, contemporaneously, or asynchronously (e.g., example shown in FIGURE 8). For example, a first and second arm waveguide 420 can be differentially driven by opposing polarity voltages (e.g., opposing polarity voltages are applied to the first and second associated electrode sets, respectively). In another example, different voltages are applied to the first and second waveguide 420. However, the electrical signals can be applied by any other suitable set of electrodes 440 to any other suitable set of arm waveguides 420.

However, the electrodes 440 can be otherwise configured.

The optical modulator 100 can optionally include or be connected to a set of electrical signal driver circuitry 442, which functions to control electrode 440 operation. The electrical signal driver circuitry 442 can generate the electrical signal (e.g., information signal), convert an upstream information signal into varying voltage levels, and/or perform other functionalities. The information signal can be received from an information signal source, such as a processing unit, memory, or other computing component. The electrical signal driver circuitry 442 can be monolithically integrated with the waveguides (e.g., wherein metal traces can be fabricated to directly connect to the electrodes 440) or be a separate component (e.g., a separate die, separate chip, etc.). The electrical signal driver circuitry 442 can include amplifiers (e.g., CMOS amplifiers) and/or any other suitable driver component. Each set of electrodes 440 preferably includes a different driver circuit; alternatively, all or a subset of electrode sets can be controlled by the same driver circuit.

The electrical signal driver circuitry 442 can optionally include or be connected to a power source that is used to power the electrodes 440. The power source can include wall power, a portable battery, and/or any other suitable power source.

However, the electrical signal driver circuitry 442 can be otherwise configured.

The reflectors 460 function to reflect the optical sub-signal 30 that was propagating forward through the arm waveguide 420. The reflector 460 preferably reflects the optical sub-signal 30 back through the originating arm waveguide 420 (e.g., the arm waveguide 420 that the optical sub-signal 30 was propagating forward through), which enables the phase shift induced within the originating arm waveguide 420 to be applied again to the optical signal during the backward pass. The reflected optical subsignal 30 preferably has the same mode as the forward-propagating optical sub-signal 30, but can alternatively have a different mode. Alternatively, the reflector 460 can reflect the optical sub-signal 30 back through a different arm waveguide 420 or to any other suitable endpoint. The reflector 460 is preferably arranged at the end of an arm waveguide 420 (e.g., the end opposing the splitter; the end opposing the input; etc.), but can be otherwise arranged. Each arm waveguide 420 is preferably optically connected to its own reflector 460; alternatively, multiple arm waveguides 420 can share a single reflector 460, or each arm waveguide 420 can include multiple reflectors 460. The reflector 460 is preferably a Sagnac loop, but can alternatively be a Bragg grating or any other suitable reflector 460. The Sagnac loop preferably includes a reflector optical splitter 470 and a reflector waveguide 480 connecting the splitter outputs, but can be otherwise constructed. The reflector optical splitter 470 can be: a directional coupler, a half-slivered mirror (e.g., with a metallic coating, dichroic coating, etc.), a dichroic mirrored prism, and/or any other beamsplitter. In an example of Sagnac loop operation, the Sagnac loop reflector consists of a the reflector optical splitter 470 with only a single input/output and two output/inputs, and the reflector waveguide 480 with two opposing outputs, configured so that the optical sub-signal 30 exiting the arm waveguide 420 is split into two sub-sub- signals by the reflector optical splitter 470, e.g. a Y-splitter, wherein the sub-sub-signals are directed and/or reflected into the two opposing reflector optical splitter 470 outputs (e.g., example shown in FIGURE 4). The sub-sub-signals are then recombined by the reflector optical splitter 470 and propagated back into the incident arm waveguide 420. The reflector 460 provides a simple and compact broadband reflector for silicon photonic waveguides. However, the Sagnac loop can operate in any other manner.

However, the reflectors 460 can be otherwise configured.

The electrical signal source functions to provide the electrical signal to be encoded onto the optical signal. The electrical signal can be a data signal, a digital bit stream, and/or be any other suitable electrical signal. The electrical signal preferably includes a timeseries of voltages, but can be otherwise constructed. The electrical signal source is preferably a data source, such as a processing unit, memory, or other data source, but can alternatively be any other signal source.

The output waveguide 600 functions to receive the output optical signal 20. The output waveguide 600 is preferably manufactured from an optical material and/or electro-optical material (e.g., silicon, Lithium Niobate, Indium Phosphide, electro-optic polymers, etc.), but can be otherwise manufactured. The system can include one or more output waveguides 600. The output waveguide 600 is preferably optically connected to the optical splitter 300 at a first end (e.g., the output waveguide's input) and optically connected to the optical interconnect 700 at a second end (e.g., the output waveguide's output), but can additionally or alternatively be connected to any other suitable component. However, the output waveguide 600 can be otherwise configured.

The optical modulator 100 can optionally include a set of feedback elements 800, which function to monitor a parameter of the optical signal propagating into and/or out of the device. The feedback elements 800 can monitor the input optical signal 10, the output optical signal 20, the optical sub-signals 30 (e.g., propagating forward and/or backward), and/ or any other suitable optical signal. In a first variant, a feedback element 800 only monitors the optical signals traveling in one direction (e.g., forward or backward). In a second variant, a feedback element 800 can monitor optical signals traveling in both directions (e.g., both forward and backward). However, the feedback elements 800 can be otherwise configured.

The feedback elements 800 can measure the optical power, the amplitude, phase, frequency, and/or any other parameter of the monitored optical signal. The measured parameter can be used to adjust bias component operation (e.g., adjust the magnitude and/ or duration of large-scale phase adjustment), used to adjust electrode 440 operation (e.g., used to adjust the voltage applied to the arm waveguides 420), and/or otherwise used.

The feedback elements 800 are preferably coupled to the waveguide propagating the monitored optical signal, but can additionally or alternatively be coupled to any other component. The feedback element 800 can be coupled in-line (e.g., in series) or in parallel with the optical path. The feedback element 800 can be located at: the input waveguide 200 (e.g., upstream of the splitter), the output waveguide 600 (e.g., downstream of the splitter), at the splitter, at the splitter, at the splitter-arm waveguide 420 junction, within the arm waveguide 420 (e.g., at the inlet, along the body, and/or at the end), at the reflector 460, and/or at any other suitable location within the optical modulator 100. In a first example, the optical modulator 100 can include a first and second feedback element 800 monitoring the input and output waveguides. Additionally or alternatively, the optical modulator 100 can include a third feedback element 800 monitoring the input waveguide 200. In a second example, the optical modulator 100 can include a single feedback element 800 monitoring both the input and output waveguides. The feedback elements 800 are preferably electrically connected to the biasing component driver circuitry 520, but can additionally or alternatively be electrically connected to any other suitable monitoring and/ or feedback system.

The feedback element 800 can be fabricated monolithically with the monitored waveguide, or be a separate component assembled to the waveguide.

In a first variant, the feedback element 800 is a photodiode (e.g., monitoring photodiode (MPD)) that taps into the optical signal propagating through a waveguide (e.g., using a directional coupler) to measure the optical power propagating through the waveguide.

In a second variant, the feedback element 800 is a temperature sensor configured to measure the temperature of the waveguide.

However, any other suitable feedback element 800 can be used.

The optical modulator 100 can optionally include a biasing component 500, which functions to correct for manufacturing errors (e.g., unintentional arm waveguide length discrepancies, other fabrication variations, etc.), bias the modulator to operate in a desirable regime (e.g., in a quadrature), and/ or otherwise used. The biasing component 500 preferably biases the optical signal parameter (e.g., the optical signal phase) at a rate slower than the electrical signal-induced optical signal parameter shift (e.g., at 30kHz or less, 40kHz or less, etc.), but can alternatively bias a different optical signal parameter from that modulated within the arm waveguides 420. The optical signal parameter bias (e.g., shift) imposed by the biasing component 500 is preferably larger than the optical signal parameter modulation imposed by the electrodes 440 within the arm waveguides 420 (e.g., an order of magnitude larger, multiple orders of magnitude larger, 2x, 3x, 4x, IOOX, etc.), but can alternatively be of the same magnitude or smaller.

The biasing component 500 preferably biases the parameters of the optical sub-signals 30 (e.g., propagating forward and/or backward), but can additionally or alternatively bias the parameters of the input optical signal 10, the output optical signal 20, and/ or any other optical signal. The biasing component 500 preferably modulates the parameters of the optical sub-signals 30 at a lower speed (e.g., lower frequency) than that induced by the electrodes, but can alternatively modulate the parameters of the optical sub-signals 30 at any other suitable speed. The biasing component 500 can change the optical signal parameters for the optical signals propagating in: a subset of the arm waveguides 420, all arm waveguides 420, and/or any other suitable set of waveguides. Each arm waveguide 420 preferably includes its own biasing component 500; alternatively, multiple arm waveguides 420 can share a biasing component 500, or each arm waveguide 420 can include multiple biasing components 500 (e.g., for different biasing resolutions, configured to bias different optical signal parameters, etc.). The biasing component 500 is preferably connected between the optical splitter 300 and the respective arm waveguide 420, but can additionally or alternatively be connected directly to the respective arm waveguide 420 (e.g., to a wall of the arm waveguide 420), define a segment of the arm waveguide 420, and/ or be otherwise connected to the arm waveguide 420. The biasing component 500 is preferably arranged before the electrodes 440 (e.g., wherein the optical sub-signal 30 propagates through the biasing component 500 segment before propagating through the electrode 440 segment; example shown in FIGURE 5), but can additionally or alternatively be colocalized with the electrodes 440 (e.g., surround the electrodes 440, be interdigitated with the electrodes 440, etc.), be arranged after the electrodes 440 (e.g., between the electrodes 440 and the reflector 460), and/or be otherwise arranged.

The biasing component 500 can be active or passive.

In a first variant, an active biasing component 500 includes a thermal phase shifter, which biases the associated waveguide (e.g., arm waveguide 420) and/or associated optical sub-signal 30 by selectively heating and/ or cooling the waveguide.

In a second variant, an active biasing component 500 includes electro-optic cladding on the associated waveguide, wherein the electro-optic cladding induces a large optical phase shift when a fixed or varying voltage is applied across the material. The electro-optic cladding can be made from an electro-optic polymer, capacitive plates, and/or any other suitable material.

In a third variant, a passive biasing component 500 includes the arm waveguides 420. In this variant, the arm waveguides 420 have slightly different lengths (e.g., true lengths), such that the optical modulator 100 can be biased by changing the optical wavelength of the optical signal (e.g., example shown in FIGURE 6). The length difference can be determined based on the optical signal wavelength, a desired phase shift, the transmission speed, the switching speed, the group index bitrate, and/or otherwise determined. In some embodiments, this variant can remove the need for an active phase shifter, which can result in a smaller device area requirement and/or lower power consumption. Alternatively, an active phase shifter can be used in conjunction with this variant.

However, the biasing component 500 can be otherwise configured.

The biasing component 500 can include or be connected to biasing component driver circuitry 520, which functions to control biasing component 500 operation. The biasing component driver circuitry 520 can monitor feedback signals (e.g., from the feedback elements 800, from the output signal error, etc.), determine the required phase shift (e.g., calculate the required phase shift) based on the feedback signals, and control the biasing components sooto achieve the required phase shift. However, the biasing component driver circuitry 520 can perform any other suitable functionality. The biasing component driver circuitry 520 can be monolithically integrated with the waveguides (e.g., wherein metal traces can be fabricated to directly connect to the biasing component 500) or be a separate component (e.g., a separate die, separate chip, etc.). The biasing component driver circuitry 520 can include amplifiers (e.g., CMOS amplifiers) and/or any other suitable driver component.

The biasing component driver circuitry 520 can optionally include or be connected to a power source that is used to power the biasing components 500. The power source can include wall power, a portable battery, and/ or any other suitable power source. The power source can be the same or different from that powering the electrodes 440 and/or electrical signal driver circuitry 442.

However, the biasing component driver circuitry 520 can be otherwise configured.

However, the optical modulator 100 can include any other suitable component.

4. Method.

As shown in FIGURE 2, the optical signal modulation method can include: splitting an input optical signal Sioo; modulating a parameter of the split optical signal based on an electrical signal S200; reflecting each split optical signal at the end of each path S300; optionally modulating the parameter of the reflected split optical signal based on the electrical signal S400; and recombining the split optical signals S500, wherein a second parameter of the optical signal encodes the electrical signal. The method can be performed by the system disclosed above, or by any other suitable system. The method can be performed: continuously, intermittently, responsive to an electrical signal encoding event, and/ or at any other time.

Splitting an input optical signal Sioo functions to generate at least two split optical signals (e.g., optical sub-signal 30), each propagating along different paths (e.g., split paths), that can be independently modulated and constructively or destructively interfered to encode the electrical signal. The input optical signal 10 is preferably split by the initial beam splitter but can be otherwise split.

Modulating the parameter of the split optical signal S200 based on the electrical signal functions to change the optical signal according to the electrical signal to be encoded. The modulated parameter is preferably the phase, but can alternatively be the amplitude, frequency, polarization, and/ or any other parameter of the optical signal. The parameter is preferably modulated by applying a voltage (e.g., determined based on the electrical signal) to the path that the optical signal is propagating within (e.g., the MZ arm; the arm waveguide 420; etc.), but can additionally or alternatively be otherwise modulated. The voltage is preferably applied by the electrodes 440 of the path, but can be otherwise applied. S200 preferably modulates at least one split optical signal.

In a first variant, S200 includes modulating all split optical signals (e.g., all paths are phase-modulating paths). In this variant, all split optical signals can be modulated with the same or different electrical signals. In an example where the beam splitter generates two split optical signals, S200 can include modulating both split optical signals.

In a second variant, S200 includes modulating a subset of the split optical signals (e.g., only a subset of the paths are phase-modulating paths). In an example where the beam splitter generates two split optical signals, S200 can include modulating a single split optical signal, and not modulating the other split optical signal. Reflecting each split optical signal at the end of each path S300 functions to return the split optical signal back through the incident path (e.g., back through the same waveguide). This can function to: decrease the overall physical waveguide dimensions required to achieve the same overall apparent path length (e.g., halve the physical waveguide length required to achieve the same overall distance traveled by a split optical signal); and/ or confer any other set of technical benefits. In an example, the reflected split optical signal is the reverse propagating mode (e.g., the reverse of the forward propagating mode) and/ or has the same optical parameters as the forward propagating split optical signal (e.g., except for the modulated parameter); alternatively or additionally, the reflected optical signal can have different optical parameters from the forward-propagating split optical signal. In a specific example, the reflected split optical signal is in the same waveguide, and is the reverse propagating mode. The split optical signal is preferably reflected back into the incident path by the reflector 460 (e.g., discussed above), but can be otherwise reflected.

Optionally modulating the parameter of the reflected split optical signal based on the electrical signal S400 functions to double the optical parameter shift incurred by a single pass of the path (e.g., apply the phase modulation twice to the split optical signal; apply two times the phase modulation to the split optical signal; modulate the phase of the split optical signal twice; etc.). This can decrease the power needed to achieve the same extent of parameter modulation and/or decrease the overall footprint required to achieve a comparable optical phase shift, but can confer any other set of technical benefits. S400 is preferably performed in a similar manner to S200, except that the split optical signal is propagating backward instead of forward; however, S400 can be otherwise performed. The electrical signal applied to each split optical signal is preferably the same as that in S200, but can alternatively be a different electrical signal. In a first example where the phases of all forward-propagating split optical signals are modulated, the phases of all backpropagating split optical signals are also modulated. In a second example where the phases of a subset (e.g., one of two) of the forward-propagating split optical signals are modulated, the phases of the same subset (e.g., the same paths) of the backpropagating split optical signals are also modulated (e.g., only the split optical signals reflected on the phase modulating path are modulated). Alternatively, the backward- propagating split signals that are modulated can be different from the forwardpropagating split signals that are modulated. In variants, the backpropagating split optical signal experiences the same phase bias induced by the same electrical signal (e.g., the prior electrical signal), thereby halving the power needed by eliminating the need to bias another set of electrodes 440.

Recombining the split optical signals S500 function to encode the electrical signal in a second parameter of the combined optical signal. The second parameter is preferably different from the parameter modulated within the split paths, but can alternatively be the same. The second parameter is preferably the optical amplitude, but can additionally or alternatively be the polarization and/or any other parameter. The split optical signals are preferably recombined by the initial beam splitter, but can alternatively be combined by any other suitable component. Recombining the split optical signals can cause the returning phase-modulated split optical signals to interfere constructively or destructively, wherein any difference (e.g., in the phase) between the two split optical signals results in an amplitude (e.g., intensity) change in the output optical signal 20, thereby encoding the electrical signal into said amplitude. In a specific example, the relative phase shift between the reflected optical signals can interfere (e.g., coherently or incoherently), which can steer the resultant output optical signal 20 to exit out of the input of the initial beam splitter, the output of the initial beam splitter, and/ or both the input and the output of the initial beam splitter.

The method can optionally include: biasing the optical signal S600, which can include measuring a parameter of the optical signals, and adjusting a parameter of the optical signals based on the measurement. This is preferably continuously performed, but can alternatively be intermittently performed. This can be performed concurrently with S100-S500, and/or performed at any other time. S600 can modulate one or more parameters of the optical signals (e.g., the phase) at a slower speed (e.g., lower frequency, lower rate, over a longer period of time, etc.; IOX slower, IOOX slower, IOOOX slower, and/or any other suitable multiple or order of magnitude slower) than parameter modulation in S200 and/or S400, and/or modulate the parameters at any other suitable relative speed.

Measuring a parameter of the optical signals functions to determine if and/or how much: the system is drifting, a path is drifting, the paths are mismatched, and/or determine any other suitable system metric or measurement. The monitored parameter is preferably the optical power of one or more optical signals, but can alternatively be any other parameter. The monitored optical signals are preferably the input and/ or output optical signals, but can alternatively be the forward-propagating split optical signal, the backward-propagating split optical signal, and/ or be any other suitable signal. The parameter is preferably measured by the feedback elements 800, but can be otherwise monitored.

Adjusting a parameter of the optical signals based on the measurement functions to correct for the drift or mismatch. The adjusted parameter is preferably the same parameter that is modulated on the paths (e.g., the phase of the optical signals), but can alternatively be a different parameter. The optical signals that are adjusted are preferably the split optical signals propagating forward and backward, but can alternatively only be the forward-propagating split optical signal, only be the backwardpropagating split optical signal, be the input and/or output optical signal, and/or be any other suitable optical signal. The parameter can be adjusted: at all times, when a difference between the measurements for the optical signals exceeds a threshold (e.g., the optical power of the output optical signal 20 differs by more than a threshold amount from the optical power of the input optical signal 10), and/or at any other time. The parameter can be adjusted based on the measurement value (e.g., valence and value), the absolute value of the measurement, the measurement difference between two or more optical signals, the measurement value change over time (e.g., for a given optical signal), and/or otherwise based on the measurement(s). The parameter can be adjusted for a single path, all paths (e.g., equally, unequally adjusted, etc.), and/or any other suitable optical path. Adjusting a parameter of the optical signals is preferably performed by the biasing component 500, but can be otherwise performed. Adjusting a parameter of the optical signals can include: heating a path (e.g., the shorter path), applying heat to an optical signal, applying a voltage to the path (e.g., wherein the voltage is larger than the voltage applied in S200 and/or S400), adjusting the optical wavelength of the optical signal, applying a magnetic field to the path, and/or otherwise adjusting the parameter. 5- Illustrative examples.

In a first illustrative example, the optical modulator 100 is a Mach-Zehnder modulator ("MZM"), and can include: an input waveguide 200; a beam splitter optically connected to two phase modulators 400; a first and second reflector 460 located at the end of each phase modulator 400; and an output waveguide 600. Each phase modulator 400 (e.g., a Mach-Zehnder arm ("MZ arm"), a path, a split path, etc.) can include an arm waveguide 420 and a pair of opposing electrodes 440. In a specific example, the phase modulator 400 can be a PN phase shifter, wherein the arm waveguide's optical material is doped to form a PN junction across its width (e.g., examples shown in FIGURE 11 and FIGURE 13). In a specific example, the electrodes (e.g., opposing electrodes) can be interdigitated. In a first embodiment, the phase modulators 400 have substantially the same length (e.g., within fabrication tolerances). In a second embodiment, the phase modulators 400 have different lengths. The reflector 460 can be a Sagnac loop, which can include a beam splitter and a waveguide connecting the beam splitter outputs (e.g., example shown in FIGURE 7). The MZM can optionally include feedback elements 800 (e.g., photodiodes; monitoring photodiodes (MPDs)) located at the input and output waveguides that measure the optical power of the input and output optical signals; active bias components configured to bias the phase of the split beams (e.g., at a larger and/or slower scale than the bias imposed by the electrodes 440); and/or driver circuitry configured to control the phase modulators 400 and/or bias components.

In operation, an input optical signal 10 (e.g., carrier signal) propagating within the input waveguide 200 is split into two paths, each propagating through a different phase modulator 400 . A voltage (e.g., from the electrical signal) is applied to each phase modulator 400 (e.g., by the respective electrode pair), which induces a phase shift in the carrier signal propagating therein. The voltage can be applied by the electrodes 440, wherein the electrodes 440 can be operated such that a PN junction defined across the phase modulator 400 is operated as a reverse-bias PN diode (e.g., reverse bias PN junction diode). The phase-modulated carrier signal 12 is reflected back into the respective phase modulator 400 (e.g., wherein the reflected phase-modulated carrier signal is the reverse propagating mode), wherein the voltage induces the same phase shift in the backward-propagating carrier signal 22. The two beams are then recombined (e.g., by the beam splitter) into an exiting signal, wherein interference between the beams controls (e.g., modulates) the amplitude or intensity of the exiting signal, thereby encoding the electrical signal into the exiting signal amplitude. The interference between the beams can optionally steer the exiting signal to exit out of the beam splitter input (e.g., when the modulator is turned off; example shown in FIGURE 14B), the beam splitter output (e.g., when the modulator is turned on; example shown in FIGURE 14C), and/ or a combination of the beam splitter input and output (e.g., example shown in FIGURE 14D).

In a second illustrative example, the optical modulator 100 includes an input waveguide 200, a beam splitter 300, an arm waveguide 420, a phase modulator 400, first and second reflector 460 optically connected to the output ends of the arm waveguide 420 and the phase modulator 400, respectively, and an output waveguide 600. The phase modulator 400 (e.g., a Mach-Zehnder arm ("MZ arm")) can include an arm waveguide 420 and a pair of opposing electrodes 440. In a specific example, the phase modulator 400 can be a PN phase shifter, wherein the arm waveguide's optical material is doped to form a PN junction across its width. The reflector 460 can be a Sagnac loop, which can include a beam splitter and a waveguide connecting the beam splitter outputs. The optical modulator 100 can optionally include feedback elements 800 (e.g., photodiodes) located at the input and output waveguides that measure the optical power of the input and output optical signals; active bias components configured to bias the phase of the split beams (e.g., at a larger and/ or slower scale than the bias imposed by the electrodes 440); and/or driver circuitry configured to control the phase modulators 400 and/or bias components.

In operation, an input optical signal 10 (e.g., carrier signal) propagating within the input waveguide 200 is split into two paths, one propagating through the phase modulator 400 and the other propagating through the arm waveguide 420. A voltage (e.g., from the electrical signal) is applied to the phase modulator 400 (e.g., by the respective electrode 440 pair), which induces a phase shift in the carrier signal propagating therein. The voltage can be applied by the electrodes 440, wherein the electrodes 440 can be operated as a reverse-bias PN diode. When the beams reach the end of their respective paths, the beams are reflected back into the respective path (e.g., the unmodulated beam back into the arm waveguide 420 and the modulated beam back into the phase modulator 400), wherein the voltage induces the same phase shift in the backward-propagating carrier signal within the phase modulating path. The reflected beam preferably has the same mode as the forward-propagating beam. The two beams are then recombined (e.g., by the beam splitter) into the output waveguide 600, wherein interference between the beams controls (e.g., modulates) the amplitude or intensity of the exiting signal, thereby encoding the electrical signal into the exiting signal amplitude.

In a third illustrative example, the optical modulator can be Mach- Zehnder modulator with a reflector (e.g., a Sagnac loop) at the ends of each phase modulating arm or path.

In a fourth illustrative example, the optical modulator is configured to reflect a forward-propagating signal back into the incident modulator, such that the same optical modulation (e.g., phase modulation) is also applied to the backward-propagating signal. The reflected signal can have the same mode as the forward-propagating signal. However, the optical modulator 100 can be otherwise configured and/or operated.

Different processes and/ or elements discussed above can be performed and controlled by the same or different entities. In the latter variants, different subsystems can communicate via: APIs (e.g., using API requests and responses, API keys, etc.), requests, and/or other communication channels. Elements shown in broken line can be optional in some variants.

Alternative embodiments implement the above methods and/or processing modules in non-transitory computer-readable media, storing computer-readable instructions that, when executed by a processing system, cause the processing system to perform the method(s) discussed herein. The instructions can be executed by computerexecutable components integrated with the computer-readable medium and/ or processing system. The computer-readable medium may include any suitable computer readable media such as RAMs, ROMs, flash memory, EEPROMs, optical devices (CD or DVD), hard drives, floppy drives, non-transitory computer readable media, or any suitable device. The computer-executable component can include a computing system and/or processing system (e.g., including one or more collocated or distributed, remote or local processors) connected to the non-transitory computer-readable medium, such as CPUs, GPUs, TPUS, microprocessors, or ASICs, but the instructions can alternatively or additionally be executed by any suitable dedicated hardware device.

Embodiments of the system and/or method can include every combination and permutation of the various elements discussed above, and/ or omit one or more of the discussed elements, wherein one or more instances of the method and/or processes described herein can be performed asynchronously (e.g., sequentially), concurrently (e.g., in parallel), or in any other suitable order by and/or using one or more instances of the systems, elements, and/ or entities described herein. As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the embodiments of the invention without departing from the scope of this invention defined in the following claims.

Claims

We Claim:

1. An electro-optic modulator, comprising: an input silicon waveguide for inputting an input optical signal; a beam splitter connected to the input silicon waveguide and comprising a first output and a second output configured for splitting the input optical signal into a first subsignal onto the first output and a second sub-signal onto the second output, and for combining the first sub-signal and the second sub-signal into an output optical signal; a first silicon waveguide connected to the first output of the beam splitter; a phase modulator along the first silicon waveguide configured to modulate a phase of the first sub-signal based on an applied information signal; a second silicon waveguide connected to the second output of the beam splitter; a first Sagnac loop connected to an end of the first silicon waveguide configured to reflect the first sub-signal back into the first silicon waveguide, the first Sagnac loop consisting of: a first reflector optical splitter having only a single first splitter input coupled to the end of the first silicon waveguide, and two first splitter outputs, and a first reflector waveguide connecting the two first splitter outputs; a second Sagnac loop connected to an end of the second waveguide, wherein the second Sagnac loop configured to reflect the second sub-signal back into the the second silicon waveguide, the second Sagnac loop consisting of a second reflector optical splitter having only a single second splitter input coupled to the end of the second silicon waveguide, and two second splitter outputs, and a second reflector waveguide connecting the two first splitter outputs; and an output silicon waveguide connected to the beam splitter for outputting the output optical signal.

2. The electro-optic modulator of claim 1, wherein a footprint of the electro-optic modulator is smaller than o.i mm².

3. The electro-optic modulator of claim 1, wherein the electro-optic modulator is monolithically fabricated onto a single die.

4. The electro-optic modulator of claim 1, wherein the phase modulator comprises: a first set of electrodes along the first silicon waveguide configured to modulate the phase of the first sub-signal;_ a first phase modulation section of the first silicon waveguide; a second set of electrodes along the second silicon waveguide configured to modulate a phase of the second sub-signal; and a second phase modulation section of the second silicon waveguide.

5. The electro-optic modulator of claim 4, wherein the first phase modulation section of the first silicon waveguide comprises a first PN junction; and wherein the second phase modulation section of the second silicon waveguide comprises a second PN junction.

6. The electro-optic modulator of claim 5, further comprising electrical signal driver circuitry configured to drive the first PN junction and the second PN junction differentially with opposing polarity voltages.

7. The electro-optic modulator of claim 4, wherein the set of electrodes comprises doped semiconductor material along the phase modulation section.

8. The electro-optic modulator of claim 4, wherein the set of electrodes comprises a first branched electrode and a second branched electrode, wherein the first branched electrode and the second branched electrode are interdigitated.

9. The electro-optic modulator of claim i, wherein the first sub-signal and the second subsignal propagating backward through the first silicon waveguide and the second silicon waveguide, respectively, have a same optical mode as the first sub-signal and the second sub-signal propagating forward through the first silicon waveguide and the second silicon waveguide, respectively.

10. The electro-optic modulator of claim 1, further comprising an optical signal source connected to the input waveguide configured for generating the input optical signal, wherein the optical signal source comprises a continuous wave laser. n. The electro-optic modulator of claim 1, further comprising: a set of feedback elements configured to measure a first optical power of the input optical signal and a second optical power of the output optical signal; and a biasing component configured to bias the phase modulator based on the first optical power and the second optical power.

12. A method for encoding a data signal onto an input optical signal, comprising: splitting the input optical signal into a first sub-signal on a first path, and a second sub-signal on a second path reflecting the first sub-signal back into the first path with a first Sangac loop connected to an end of the first path, the first Sagnac loop consisting of:. a first reflector optical splitter having only a single first splitter input coupled to the end of the first path, and two first splitter outputs, and a first reflector waveguide connecting the two first splitter outputs; reflecting the second sub-signal back into the second paths with a second Sagnac loop, the second Sagnac loop consisting of: a second reflector optical splitter having only a single second splitter input coupled to the end of the second path, and two second splitter outputs, and a second reflector waveguide connecting the two first splitter outputs; modulating a phase of the first sub-signal and/ or the second sub-signal within the first path and/or the second path, respectively, in both forward and backward propagating directions with a phase modulator, such that the phase of the first subsignal and/ or the second sub-signal is modulated twice; and recombining the first sub-signal and the second sub-signal, wherein the data signal is encoded in a combined output optical signal.

13. The method of claim 12, wherein the phase modulator comprises: a first set of electrodes along the first path configured to modulate the phase of the first sub-signal; a first phase modulating section of a first silicon waveguide in the first path; a second set of electrodes along the second path configured to modulate a phase of the second sub-signal; and a second phase modulating section of a second silicon waveguide in the second path.

14. The method of claim 13, wherein the first phase-modulating section comprises a first

PN junction spanning the first silicon waveguide; wherein the second phase-modulating section comprises a second PN junction spanning the second silicon waveguide.

15. The method of claim 14, wherein further comprising driving the first PN junction and the second PN junction differentially with opposing polarity voltages.

16. The method of claim 12, further comprising: measuring a first optical power of the input optical signal and a second optical power of the output optical signal; and biasing a phase of the first and/or the second paths based on the first and second optical power.

17. The method of claim 15, further comprising: measuring a first optical power of the first sub-signal and a second optical power of the second sub-signal; and biasing an optical signal parameter of the first sub-signal and the second sub-signal based on the first optical power and the second optical power.

18. The electro-optic modulator of claim 1, further comprising: a set of feedback elements configured to measure a first optical power of the first sub-signal and a second optical power of the second sub-signal; and a biasing component configured to bias an optical signal parameter of the phase modulator based on the first optical power and the second optical power.