KR102557191B1 - Optical transmitter based on optical time division multiplexing - Google Patents

Abstract

An optical time division multiplexing based optical transmitter is disclosed. The optical transmitter includes a variable optical signal time delay line for adjusting the phase of an optical signal having a constant pulse period; an input coupler for distributing and outputting the phase-adjusted optical signal into a plurality of optical signals; an optical modulator for optically modulating each of the optical signals of the plurality of channels into a multi-level optical signal using an electric signal; a fixed optical signal time delay line for performing a preset time delay on each of the optical signals of a plurality of channels optically modulated into the multi-level optical signals; an output coupler for optical multiplexing the time-delayed optical signals of the plurality of channels into optical time division multiplexing (OTDM) signals; and an integrated circuit for matching phases between an optical signal and an electrical signal input to the optical modulator by using a bit error rate (BER) for a portion of the optical multiplexed OTDM signal.

Description

Optical transmitter based on optical time division multiplexing {OPTICAL TRANSMITTER BASED ON OPTICAL TIME DIVISION MULTIPLEXING}

The present invention relates to an optical time-division multiplexing-based optical transmitter, and more particularly, to a structure and method capable of solving problems in the complex structure and operation of a multi-level-OTDM-based optical transmitter while using a multi-level signal modulation format and OTDM (Optical Time Division Multiplexing) technology capable of increasing the transmission speed of an optical transmitter having a limited bandwidth.

As the bandwidth required for data center interconnect (DCI) explosively increases, the data transmission rate to be provided by the optical interconnection module has increased from 100Gb/s in the past to 400Gb/s. The IEEE 400GBASE standard suggests a 8-channel × 26 Gbaud or 4-channel × 53 Gbaud transmission method based on a 4-channel multi-level modulation and demodulation signal (Pulse Amplitude Modulation, PAM) to achieve 400 Gb/s DCI.

However, in order to accommodate the continuously increasing bandwidth, the next-generation DCI must provide a transmission rate of 800 Gb/s or 1.6 Tb/s. Wavelength division multiplexing (WDM) technology, which is mainly used in optical transceivers, has limitations in increasing transmission capacity by increasing the number of channels due to problems of wavelength management, maintenance, and manufacturing costs. Normally, it is limited to a maximum of 8 channels, and at this time, a transmission rate of 200 Gb/s per wavelength must be guaranteed for 1.6 Tb/s DCI.

In addition, in the case of Parallel Single-mode fiber multiplexing (PSM) technology, as the number of channels increases, the economic cost burden increases, so about 8 channels are considered as the maximum, and a transmission rate of 200 Gb/s per channel is required like the WDM technology.

For this purpose, the 200Gb/s PAM-4 modulation type optical device must be able to operate at 100Gbaud. As the PAM level increases from level 4 to level 8, the baud rate decreases, but there is a problem in that a required signal-to-noise ratio (SNR) increases. In addition, the high spectral efficiency coherent optical transmission method used for long-distance transmission over the metro can improve the SNR problem while reducing the baud rate, but it is difficult to introduce in DCI due to problems of high power, form factor and cost.

On the other hand, as an optical receiving device capable of operating with a 200 Gb/s PAM-4 signal, there is a photodetector based on a Germanium material. Such a photodetector based on a germanium material can theoretically have a 3 dB bandwidth of 80 GHz or more, and a recently experimentally reported bandwidth of 80 GHz achieved using inductive peaking technology. In addition, since a photodetector based on a germanium material can be implemented on a silicon photonics platform, commercialization is highly likely.

However, it is difficult to find an appropriate solution for an optical modulator, which is an optical transmission device, to provide a bandwidth of 70 GHz or more for 100 Gbaud operation. A high bandwidth can be achieved by using an III-V based optical modulator, but it is expensive and incompatible with a CMOS process, making commercialization difficult. In addition, a silicon photonics-based light modulator compatible with a CMOS process also has a problem in that a bandwidth of 70 GHz or more cannot be achieved due to low photoelectric conversion efficiency compared to a III-V medium.

The present invention provides a structure and method of an optical transmitter capable of solving the problems of complex structure and operation of a multilevel-OTDM based optical transmitter while using a multilevel signal modulation format and optical time division multiplexing (OTDM) technology capable of increasing the transmission speed of an optical transmitter having limited bandwidth.

More specifically, the present invention provides a structure and method of an optical transmitter that solves the problem of time synchronization between an optical signal and an electrical signal generated in a multilevel-OTDM based optical transmitter using a Bit Error Ratio (BER) for a portion of an OTDM signal.

In addition, the present invention provides a structure and method of an optical transmitter that solves the non-uniform optical power problem between channels of an OTDM signal generated in a multilevel-OTDM based optical transmitter by using a bit error ratio (BER) for a part of the OTDM signal.

An optical transmitter according to an embodiment of the present invention includes a variable optical signal time delay line for adjusting the phase of an optical signal having a constant pulse period; an input coupler for distributing and outputting the phase-adjusted optical signal into a plurality of optical signals; an optical modulator for optically modulating each of the optical signals of the plurality of channels into a multi-level optical signal using an electric signal; a fixed optical signal time delay line for performing a preset time delay on each of the optical signals of a plurality of channels optically modulated into the multi-level optical signal; an output coupler for optical multiplexing the time-delayed optical signals of the plurality of channels into optical time division multiplexing (OTDM) signals; and an integrated circuit for matching phases between an optical signal and an electrical signal input to the optical modulator by using a bit error rate (BER) for a portion of the optical multiplexed OTDM signal.

The integrated circuit may match phases between the optical signal and the electrical signal input to the optical modulator by controlling the time delay of the optical signal by controlling the variable optical signal time delay line to minimize the bit error rate.

In the fixed optical signal time delay line, a time delay value of the optically modulated optical signal may be determined according to a modulation speed of the optical modulator and the number of channels of the OTDM signal.

An electrical signal time delay line for performing a time delay on the electrical signal input to the light modulator may be further included.

A time delay value for the electrical signal provided by the electrical signal time delay line may be the same as a time delay value provided to the light modulated optical signal provided by the fixed optical signal time delay line.

An optical transmitter according to an embodiment of the present invention includes an input coupler for distributing and outputting optical signals having a constant pulse period into optical signals of a plurality of channels; an optical power controller controlling an optical power intensity for each of the optical signals of the plurality of channels; an optical modulator for optically modulating each of the optical signals of a plurality of channels output through the optical power controller into multi-level optical signals using electric signals; a fixed optical signal time delay line for performing a preset time delay on each of the optical signals of a plurality of channels optically modulated into the multi-level optical signals; an output coupler for optical multiplexing the time-delayed optical signals of the plurality of channels into optical time division multiplexing (OTDM) signals; and an integrated circuit for equalizing optical power strength between channels of the OTDM signal by using a bit error rate (BER) for a portion of the optical multiplexed OTDM signal.

The optical power controller may be an optical power attenuator or an optical power amplifier.

The integrated circuit may equalize optical power between channels of the OTDM signal by controlling the optical power controller to minimize the bit error rate and adjust the optical power intensity of the optical signal.

In the fixed optical signal time delay line, a time delay value of the optically modulated optical signal may be determined according to a modulation speed of the optical modulator and the number of channels of the OTDM signal.

An electrical signal time delay line for performing a time delay on the electrical signal input to the light modulator may be further included.

A time delay value for the electrical signal provided by the electrical signal time delay line may be the same as a time delay value provided to the light modulated optical signal provided by the fixed optical signal time delay line.

An optical transmitter according to an embodiment of the present invention includes a variable optical signal time delay line for adjusting the phase of an optical signal having a constant pulse period; (i) an input coupler for distributing the phase-adjusted optical signal into optical signals of a plurality of channels and outputting the optical signal, (ii) an optical power controller for controlling the optical power intensity of each of the optical signals of the plurality of channels, (iii) an optical modulator for optically modulating each of the optical signals of the plurality of channels whose optical power intensity is controlled into a multi-level optical signal by using an electric signal, (iv) a fixture for performing a preset time delay on each of the optical signals of the plurality of channels optically modulated with the multi-level optical signal An optical signal time delay line and (v) a PIC (Photonic Integrated Circuit) chip integrated with an output coupler for optical multiplexing optical signals of a plurality of channels on which the time delay is performed into an OTDM (Optical Time Division Multiplexing) signal; and an integrated circuit for solving a time synchronization problem between an optical signal and an electrical signal input to the optical modulator and a non-uniform optical power problem between channels of the OTDM signal by using a bit error rate (BER) for a part of the optical multiplexed OTDM signal.

The fixed optical signal time delay line integrated in the PIC chip may be formed of a spiral silicon optical waveguide whose length is adjusted.

The PIC chip further includes an electrical signal time delay line for performing a time delay on the electrical signal input to the optical modulator, and the electrical signal time delay line may be formed of a metal electrode whose length is adjusted.

The variable optical signal time delay line may be formed of a plurality of micro ring resonators (MRRs) connected in series.

The micro ring resonator may be integrated into the PIC chip.

The integrated circuit may match phases between the optical signal and the electrical signal input to the optical modulator by controlling the time delay of the optical signal by controlling the variable optical signal time delay line to minimize the bit error rate.

The integrated circuit may equalize optical power between channels of the OTDM signal by controlling the optical power controller to minimize the bit error rate and adjust the optical power intensity of the optical signal.

The present invention uses a multilevel signal modulation format and optical time division multiplexing (OTDM) technology capable of increasing the transmission speed of an optical transmitter with limited bandwidth, and solves the problems of complex structure and operation of a multilevel-OTDM based optical transmitter. It can provide a structure and method of an optical transmitter.

More specifically, the present invention uses a bit error ratio (BER) for a part of an OTDM signal to solve the problem of time synchronization between an optical signal and an electrical signal generated in a multilevel-OTDM based optical transmitter. It can provide a structure and method.

In addition, the present invention uses the Bit Error Ratio (BER) for a part of the OTDM signal to solve the problem of non-uniform optical power between channels of an OTDM signal generated in a multilevel-OTDM based optical transmitter. It can provide a structure and method.

1 is a diagram showing the structure of an optical transmitter according to a first embodiment of the present invention.
2a and 2b are diagrams showing examples of time allocation of OTDM signals according to the first embodiment of the present invention.
3A and 3B are diagrams illustrating threshold level settings of a PAM-4 OTDM signal according to a first embodiment of the present invention.
4 is a diagram illustrating an example of maximizing light modulation performance through an electrical signal time delay line according to a first embodiment of the present invention.
5 is a diagram showing the structure of an optical transmitter according to a second embodiment of the present invention.
6 is a diagram showing the structure of an output coupler according to a second embodiment of the present invention.
7 is a diagram showing the structure of an optical transmitter according to a third embodiment of the present invention.
8 is a diagram showing the structure of an optical transmitter according to a fourth embodiment of the present invention.
9 is a diagram showing the structure of an optical transmitter according to a fifth embodiment of the present invention.
10 is a diagram showing the structure of a variable optical signal time delay line according to a fifth embodiment of the present invention.
11 is a diagram showing the structure of an optical transmitter according to a sixth embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram showing the structure of an optical transmitter according to a first embodiment of the present invention.

Referring to FIG. 1 , the optical transmitter 100 according to the first embodiment of the present invention may have four OTDM channels, but this is only an example and may have various OTDM channels.

Specifically, in the optical transmitter 100, a pulsed light source (PLS) 110, a tunable optical delay line (TODL) 120, an OTDM-based optical transmitter core (OTDM-TX Core) 130, an integrated circuit 140, and the like may be disposed on a main board. In this case, the integrated circuit 140 may be an Application Specific Integrated Circuit (ASIC) chip, but this is only one example and is not limited thereto, and may be composed of various types of chips.

First, the pulse light source 110 may output an optical signal in the form of an optical pulse train having a constant pulse period Tp, and the output optical signal may be input to the OTDM-based optical transmitter core 130 through the variable optical signal time delay line 120.

At this time, the transmission capacity of the OTDM signal output through the OTDM-based optical transmitter core 130 may be determined as follows. First, assume that the baud-rate of each channel of the N-channel OTDM signal is B. In this case, when each channel of the OTDM signal is modulated into a multi-level PAM-N signal with a relational expression of Tp=1/B, the data rate for each channel may be B×log2N. Therefore, the transmission capacity of an N-channel OTDM signal can be determined as N×B×log2N.

Meanwhile, a specific operation of the OTDM-based optical transmitter core 130 may be as follows. An optical signal input through the variable optical signal time delay line 120 may be divided by the input coupler 131 . For example, in the OTDM-based optical transmitter core 130 providing N-channel OTDM signals, a 1×N optical coupler is disposed to distribute an optical signal input through a variable optical signal time delay line 120 into N-channel optical signals.

The N-channel optical signals thus distributed may be input to the optical modulator 133 via the optical power controller 132, respectively. The N-channel optical signal optically modulated through the optical modulator 133 may be subjected to a time delay (0 × Ts, 1 × Ts, 2 × Ts, ..., (N-2) × Ts, (N-1) × Ts) by a time allocated to each through a fixed optical delay line (FODL) 134. In this case, the time delay value Ts may be determined as Ts=Tp/N in consideration of the number of channels (N) of the OTDM signal.

Thereafter, the N-channel optical signal subjected to the time delay may be optically multiplexed into an OTDM signal through the output coupler 135 in the form of an Nx1 optocoupler and output to the optical interface through the optical coupler 136. At this time, in order to generate an effective OTDM signal, the input pulse width Tpw of the pulsed light source 110 should have a value of about Tpw to Ts (approximate value). If the pulse width is too large, Inter Symbol Interference (ISI) between bits may occur, and if the pulse width is too small, the timing margin of one bit may decrease, resulting in deterioration in bit error rate (BER) performance.

For example, as shown in FIG. 2A, in the case of a 4-channel (when N = 4) OTDM-based optical transmitter 100 in which 25 Gbaud PAM-4 signals are each modulated to provide a transmission rate of 200 Gb/s, the pulse period (Tp) of the optical signal output through the pulsed light source 110 is 40 ps, and the time delay value (Ts) by the fixed optical signal time delay line 134 is 10 ps.

Accordingly, each of the N-channel optical signals input to the fixed optical signal time delay line 134 may have a time delay of 10 ps for FODL2, 20 ps for FODL3, and 30 ps for FODL4 based on FODL1. This time delay value Ts may be determined and fixed according to the modulation speed of the optical modulator 133 and the number of channels of the OTDM signal. Therefore, FODL1, FODL2, FODL3, and FODL4 constituting the fixed optical signal time delay line 134 do not require power and can be implemented using passive elements having a fixed time delay.

For effective OTDM signal generation of the 4-channel OTDM-based optical transmitter 100, the pulse width (Tpw) of the input pulse light source 110 must have an approximate value of Ts = 10 ps or less, and the OTDM-based optical transmitter core 130 assumes that there is no time delay between channels of the OTDM signal for the rest except for the fixed optical signal time delay line 134.

On the other hand, even if the time delay between N-channel optical signals is allocated using the fixed optical signal time delay line 134, the phases of the optical signal input to the optical modulator 133 and the high-speed RF electrical signal must be matched. It is very important to implement this uncomplicated and cost-effective.

As an example, FIG. 2A shows a case where the phase of a pulsed optical signal input to the optical modulator 133 and a high-speed RF electrical signal are out of phase (Td 0) is indicated. At this time, it is assumed that transmission lines of all high-speed RF electrical signals are well designed and there is no skew between channels. As shown in FIG. 2A, when the phases of the optical signal and the high-speed RF electrical signal are out of phase by the time Td, optical modulation is properly performed on OTDM channels 1 to 3, but the OTDM channel 4 is out of phase, so it is modulated in the opposite phase and causes a bit error.

On the other hand, FIG. 2B shows a case in which the phases of the pulsed optical signal input to the optical modulator 133 and the high-speed RF electrical signal coincide (Td=0). In this way, in order to match the phases of the pulsed optical signal input to the optical modulator 133 and the high-speed RF electrical signal, the optical transmitter 100 of the present invention may have a variable optical signal time delay line 120 for adjusting the time delay with an electric signal at the input terminal of the OTDM-based optical transmitter core 130.

For this operation, an optical coupler 136 and a photodetector 137 may be additionally disposed in the OTDM-based optical transmitter core 130 . More specifically, the OTDM signal output through the output coupler 135 is partially tapped by the optocoupler 136 (e.g., 1 × 2 optocoupler) and input to the photodetector 137, and then converted into an electrical signal. It can be output and transmitted to the integrated circuit 140 (e.g., an ASIC chip).

Then, the integrated circuit 140 may sweep the time delay of the variable optical time delay line 120 while counting the bit error rate (BER) of the electrical signal received from the photodetector 137 . At this time, the Td value changes according to the time delay of the variable optical time delay line 120 being swept, and the integrated circuit 140 controls the variable optical time delay line 120 to minimize the bit error rate. By adjusting the time delay of the optical signal in the form of an optical pulse train output from the pulsed light source 110, the phase between the optical signal in the form of a pulse input to the optical modulator 133 and the high-speed RF electrical signal can be matched.

As such, the optical transmitter 100 proposed in the present invention can solve the time synchronization problem for OTDM by simply adding one variable optical time delay line 120, an optical coupler 136, and a photodetector 137 and utilizing the bit error rate count function of the ASIC chip.

However, the OTDM-based optical transmitter 100 proposed in the present invention is not limited to a method of optimally setting the time delay of the variable optical time delay line 120 only with the bit error rate count function of the ASIC chip, and the time delay can be optimally set with optical power, which is a performance index other than the bit error rate, and eye diagram waveform of the optical signal. For example, the OTDM-based optical transmitter 100 sets an expected eye diagram (eye mask) waveform and optical power in the eye diagram in advance in the ASIC chip, and compares the measured eye diagram waveform with the eye diagram waveform previously set in the ASIC chip to determine whether the optical signal is normally modulated. At this time, the OTDM-based optical transmitter 100 may optimally set the time delay of the variable optical time delay line 120 through a sweep if the measured eye diagram waveform does not exist in the ASIC chip.

Meanwhile, the input coupler 131, the optical modulator 133, the fixed optical signal time delay line 134, and the output coupler 135 constituting the OTDM-based optical transmitter core 130 may have different insertion losses depending on the OTDM channel. In an optical communication system and module using a multilevel modulation format, a difference in insertion loss between OTDM channels may cause a problem of increasing a bit error rate.

3A shows an example in which OTDM channel 2 to which the multilevel modulation format of PAM-4 is applied has a larger insertion loss than other channels. The threshold level between the <00> level (level 0) and the <01> level (level 1) of the PAM-4 signal is represented by Threshold_01, the threshold level between the <01> level (level 1) and the <10> level (level 2) is represented by Threshold_12, and the threshold level between the <10> level (level 2) and the <11> level (level 3) is represented by Threshold_23.

At this time, bit errors do not occur in OTDM channels 1, OTDM channels 3, and OTDM channels 4, but significant bit errors occur in OTDM channels 2 because the set threshold level is out of sync with the signal level. Therefore, the bit error rate should be improved by equalizing the power of all OTDM channels.

For this operation, an optical power controller 132 for controlling the optical power intensity of each optical signal of a plurality of OTDM channels may be additionally disposed in the OTDM-based optical transmitter core 130. More specifically, the OTDM signal output through the output coupler 135 is partially tapped to the optocoupler 136 and input to the photodetector 137, and then converted into an electrical signal and output to the integrated circuit 140.

Then, the integrated circuit 140 may sweep the attenuation rate or amplification rate of the optical power controller 132 while counting the bit error rate of the electrical signal received from the photodetector 137 . More specifically, the integrated circuit 140 may include a sweep algorithm of attenuation or amplification. For example, when bit error rate performance is improved by amplifying optical power of about 10% for a specific channel, the integrated circuit 140 continuously amplifies the optical power, and when the bit error rate performance deteriorates again, the optical power can be attenuated to set an optimized amplification/attenuation rate.

At this time, the integrated circuit 140 controls the optical power controller 132 to minimize the bit error rate to find an optimal attenuation rate or amplification rate, thereby equalizing the optical power intensities of all OTDM channels as shown in FIG. 3B. Accordingly, the optical power controller 132 may be configured as an optical power attenuator or an optical power amplifier.

Meanwhile, in the OTDM-based optical transmitter 100 proposed in the present invention, an electrical signal time delay line 138 may be additionally disposed as shown in FIG. 4 to further improve modulation performance. In general, optical modulation performance can be maximized when a pulse-type optical signal is positioned at the center of a bit of a high-speed RF electrical signal input to the optical modulator 133 .

Therefore, the OTDM-based optical transmitter 100 can have a time delay between the electrical signals RF Signal1, RF Signal2, RF Signal3, and RF Signal4 by adding the electric signal time delay line 138 to the OTDM-based optical transmitter core 130. At this time, EDL1 to EDL4 constituting the electrical signal time delay line 138 may be designed to have a fixed or variable time delay.

If the electrical signal time delay line 138 is implemented on a PIC chip, EDL1 to EDL4 may be designed to have a fixed time delay value. At this time, the time delay values of EDL1 to EDL4 may be designed to work with the time delay values of FODL1 to FODL4, respectively. Here, since the propagation time of the pulsed optical signal is affected by the group velocity of the optical waveguide and the high-speed RF electrical signal is affected by the phase velocity of the metal transmission line, the refractive index must be carefully considered when setting the time delay values of EDL1 to EDL4 to match the time delay values of FODL1 to FODL4.

In contrast, when the electrical signal time delay line 138 is not implemented on the PIC chip, EDL1 to EDL4 may be designed to have a variable time delay value.

5 is a diagram showing the structure of an optical transmitter according to a second embodiment of the present invention.

In the optical transmitter 100 according to the first embodiment, an N-channel optical signal may be optically coupled to an OTDM signal through an output coupler 135 in the form of an N×1 optical coupler in the OTDM-based optical transmitter core 130. At this time, the optical power of the N-channel optical signal optically coupled to the OTDM signal is reduced to about 1/N while passing through the N×1 optical coupler.

For example, in the case of 4-channel OTDM with N = 4 as in the first embodiment, the optical power of each N-channel optical signal is reduced by 6dB when passing through the output coupler 135, which is a 4×1 optical coupler. In addition, since a part of the OTDM signal must be tapped through the 1×2 optical coupler 136 and inputted to the photodetector 137 for time synchronization and optical power intensity uniformity, the output optical power of the optical output port of the OTDM-based optical transmitter core 130 is reduced again.

If the output of the 4x1 coupler is 1mW, and tapping with the 1x2 optocoupler, which is a 50:50 optocoupler, the output of the 1x2 optocoupler can each output 0.5mW.

In order to prevent this problem, the optical transmitter 200 according to the second embodiment of the present invention uses the MX2 optocoupler instead of the MX1 optocoupler as the output coupler 235 as shown in FIG. That is, each of the two outputs of the 4x2 optocoupler is 1mW, like the output of the 4x1 coupler, and is input to the photodetector 236 without additional tapping, thereby solving the optical power reduction problem.

At this time, in the case of 4-channel OTDM, the optical transmitter 200 may be configured by connecting two 4x2 optical couplers, two 1x2 optical couplers and one 2x2 optical coupler in two stages as shown in FIG. Alternatively, the optical transmitter 200 may use an integrated 4x2 optical coupler.

In addition, the pulse light source 210, the variable optical signal time delay line 220, the OTDM-based optical transmitter core 230, and the integrated circuit 140 constituting the optical transmitter 200 perform the same functions as the pulse light source 110, the variable optical signal time delay line 120, the OTDM-based optical transmitter core 130, and the integrated circuit 140 constituting the optical transmitter 100. can

7 is a diagram showing the structure of an optical transmitter according to a third embodiment of the present invention.

The optical transmitter 300 according to the third embodiment of the present invention utilizes photonic integrated circuit (PIC) technology to integrate several bulky optical elements into a single chip. In the case of integrating the OTDM-based optical transmitter 300 using PIC technology, many problems (size, time synchronization, optical power uniformity between OTDM channels) that have been obstacles to commercialization can be improved. In addition, if the PIC technology based on Silicon Photonics (SiPh), which has recently been in the limelight, is used, it can be more advantageous for commercialization because it can utilize the existing CMOS process.

In the optical integrated OTDM-based optical transmitter core 330 provided in FIG. 7, an input coupler 331, an optical power controller 332, an optical modulator 333, a fixed optical signal time delay line 334, an output coupler 335, a photodetector 336, and an electrical signal time delay line 337 may be integrated on a PIC or SiPh-based PIC chip.

For example, when the OTDM-based optical transmitter core 330 is implemented with a silicon photonics-based PIC chip, the input coupler 331 and the output coupler 335 may be implemented as a directional coupler or a multimode interference coupler.

Further, when the optical power controller 332 is an optical power attenuator, it may be implemented as a P-N doped optical waveguide, a PN junction optical waveguide, or a Mach-Zehnder interferometer. At this time, the Mach-Zehnder interferometer may include a phase shifter whose optical characteristics change according to an electrical signal or heat. In contrast, when the optical power controller 332 is an optical power amplifier, it may be implemented as a semiconductor optical amplifier (SOA) based on a III-V gain medium.

In addition, the light modulator 333 may be implemented as an electro-absorption modulator (EAM), a Mach-Zehnder modulator (MZM), a micro ring modulator (MRM), and the like.

The fixed optical signal time delay line 334 can be implemented as a spiral silicon optical waveguide by adjusting the length of the silicon optical waveguide, and the electrical signal time delay line 337 can be implemented by adjusting the length of the metal electrode. Finally, the photodetector 336 may be implemented as a photodetector based on Germanium.

As described above, the optical transmitter 300 can greatly improve complexity, power consumption, and cost because the optical devices constituting the OTDM-based optical transmitter core 330 can be integrated into a single chip. In addition, a commercially available OTDM-based optical transmitter 300 can be implemented by integrating additional optical elements together to solve the problems of the existing OTDM technology (time synchronization, optical power uniformity between OTDM channels) to be solved in the present invention. The optical output of the integrated OTDM-based optical transmitter core 330 may be externally coupled through an optical interface as shown in FIG. 7 .

8 is a diagram showing the structure of an optical transmitter according to a fourth embodiment of the present invention.

The optical transmitter 400 according to the fourth embodiment of the present invention provides a case in which the pulsed light source 410 is integrated inside the OTDM-based optical transmitter core 430 in which optical devices are integrated on a PIC or SiPh-based PIC chip. In this case, the pulsed light source 410 integrated on a silicon photonics-based PIC chip may be a III-V-on-Si Mode Locked Laser in which a III-V gain medium is bonded on a silicon chip. The type of the pulse light source 410 is just one example and is not limited thereto, and various types of pulse light sources that can be installed in a silicon photonics-based PIC chip can be integrated.

9 is a diagram showing the structure of an optical transmitter according to a fifth embodiment of the present invention.

In the optical transmitter 5000 according to the fifth embodiment of the present invention, the variable optical signal time delay line 520 may be integrated inside the PIC chip together with the pulse light source 510. At this time, the variable optical signal time delay line 520 integrated on the silicon photonics-based PIC chip may be implemented in a structure of a plurality of silicon micro ring resonators (MRRs) connected in series.

At this time, the variable optical signal time delay line 520 can adjust the time delay while turning on or off each micro ring resonator. For example, when the variable optical signal time delay line 520 is implemented through 6 micro ring resonators as shown in FIG. 10, assuming that a time delay by Tr is possible per micro ring resonator, the time delay can be varied up to 6×Tr.

More specifically, when the input wavelength (λin) of the optical signal input to the variable optical signal time delay line 520 and the resonant wavelength (λres) of the micro-ring resonator match, the optical signal is optically coupled to the micro-ring resonator. After resonance, it can be output through the optical output port. At this time, the variable optical signal time delay line 520 may match or mismatch the resonance wavelength with the input wavelength by controlling the micro ring resonator with an electrical signal.

The variable optical signal time delay line 520 provided in FIG. 10 represents a case in which three micro ring resonators have a time delay of 3×Tr when λres=λin. In this way, the OTDM-based optical transmitter 500 of the present invention can mount the variable optical signal time delay line 520 on a silicon photonics PIC chip. At this time, the variable optical signal time delay line 520 may include a plurality of micro ring resonator structures connected in series as well as various types of TODLs that can be installed in a silicon photonics-based PIC chip.

11 is a diagram showing the structure of an optical transmitter according to a sixth embodiment of the present invention.

Referring to FIG. 11, in the optical transmitter 600 according to the sixth embodiment of the present invention, a pulsed light source (PLS) 610, an OTDM-based optical transmitter core (OTDM-TX Core) 620, and an integrated circuit 630 may be disposed on a main board. In this case, the integrated circuit 630 may be an Application Specific Integrated Circuit (ASIC) chip, but this is only one example and is not limited thereto, and may be configured with various types of chips.

Here, unlike the previous embodiments, the optical transmitter 600 according to the sixth embodiment may not include a Tunable Optical Delay Line (TODL).

More specifically, the pulse light source 610 may generate a light pulse signal by a signal transmitted from the integrated circuit 630, that is, an ASIC chip. In this case, the pulse light source 610 may be a Q-switching laser capable of converting an electric signal of a wide time line width coming from the outside into a very narrow optical pulse.

At this time, the integrated circuit 630 of the optical transmitter 600 can adjust the time delay of the electrical signal transmitted to the pulsed light source 610 while counting the bit error rate (BER) of the electrical signal received from the photodetector 627. That is, the optical transmitter 600 can replace the role of the variable optical signal time delay line provided in other embodiments by adjusting the time delay of the electrical signal output from the integrated circuit 630.

Meanwhile, the pulse light source 610 may be included in the PIC chip when the OTDM-TX Core 620 is a PIC chip, but may be disposed outside the PIC chip due to power consumption or heat generation.

While this specification contains many specific implementation details, they should not be construed as limiting as to the scope of any invention or claimables, but rather as a description of features that may be unique to a particular embodiment of a particular invention. Certain features that are described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments individually or in any suitable subcombination. Further, while features may operate in particular combinations and be initially depicted as such claimed, one or more features from a claimed combination may in some cases be excluded from that combination, and the claimed combination may be modified as a subcombination or variation of a subcombination.

Similarly, while actions are depicted in the drawings in a particular order, it should not be construed as requiring that those actions be performed in the specific order shown or in the sequential order, or that all depicted actions must be performed to obtain desired results. In certain cases, multitasking and parallel processing can be advantageous. Further, the separation of various device components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and devices described may generally be integrated together into a single software product or packaged into multiple software products.

On the other hand, the embodiments of the present invention disclosed in this specification and drawings are only presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. In addition to the embodiments disclosed herein, it is obvious to those skilled in the art that other modified examples based on the technical idea of the present invention can be implemented.

100: optical transmitter
110: pulse light source
120: variable optical signal time delay line
130: OTDM-based optical transmitter core
131: input coupler
132: optical power controller
133: light modulator
134: fixed optical signal time delay line
135: output coupler
136: optocoupler
137: photodetector
138: electrical signal time delay line
140: integrated circuit

Claims (18)

In the optical transmitter,
a variable optical signal time delay line for adjusting the phase of an optical signal having a constant pulse cycle;
an input coupler for distributing and outputting the phase-adjusted optical signal into a plurality of optical signals;
an optical modulator for optically modulating each of the optical signals of the plurality of channels into a multi-level optical signal using an electric signal;
a fixed optical signal time delay line for performing a preset time delay on each of the optical signals of a plurality of channels optically modulated into the multi-level optical signal;
an output coupler for optical multiplexing the time-delayed optical signals of the plurality of channels into optical time division multiplexing (OTDM) signals; and
An integrated circuit for matching a phase between an optical signal and an electrical signal input to the optical modulator by using a bit error rate (BER) for a portion of the optical multiplexed OTDM signal.
An optical transmitter comprising a. According to claim 1,
In the integrated circuit,
An optical transmitter that matches phases between an optical signal and an electrical signal input to the optical modulator by controlling the time delay of the optical signal by controlling the variable optical signal time delay line so that the bit error rate is minimized. According to claim 1,
The fixed optical signal time delay line,
wherein a time delay value of the optically modulated optical signal is determined according to a modulation rate of the optical modulator and the number of channels of the OTDM signal. According to claim 1,
An electrical signal time delay line for performing a time delay on the electrical signal input to the optical modulator.
An optical transmitter further comprising a. According to claim 4,
The time delay value for the electrical signal provided by the electrical signal time delay line,
An optical transmitter having the same time delay value provided to the optical modulated optical signal provided by the fixed optical signal time delay line. In the optical transmitter,
an input coupler for distributing and outputting an optical signal having a constant pulse period into optical signals of a plurality of channels;
an optical power controller controlling an optical power intensity for each of the optical signals of the plurality of channels;
an optical modulator for optically modulating each of the optical signals of a plurality of channels output through the optical power controller into multi-level optical signals using electric signals;
a fixed optical signal time delay line for performing a preset time delay on each of the optical signals of a plurality of channels optically modulated into the multi-level optical signal;
an output coupler for optical multiplexing the time-delayed optical signals of the plurality of channels into optical time division multiplexing (OTDM) signals; and
An integrated circuit for equalizing optical power strength between channels of the OTDM signal using a bit error rate (BER) for a portion of the optical multiplexed OTDM signal.
An optical transmitter comprising a. According to claim 6,
The optical power controller,
An optical transmitter that is an optical power attenuator or an optical power amplifier. According to claim 6,
In the integrated circuit,
An optical transmitter for equalizing the optical power intensity between channels of the OTDM signal by adjusting the optical power intensity of the optical signal by controlling the optical power controller to minimize the bit error rate. According to claim 6,
The fixed optical signal time delay line,
wherein a time delay value of the optically modulated optical signal is determined according to a modulation rate of the optical modulator and the number of channels of the OTDM signal. According to claim 6,
An electrical signal time delay line for performing a time delay on the electrical signal input to the optical modulator.
An optical transmitter further comprising a. According to claim 10,
The time delay value for the electrical signal provided by the electrical signal time delay line,
An optical transmitter having the same time delay value provided to the optical modulated optical signal provided by the fixed optical signal time delay line. In the optical transmitter,
a variable optical signal time delay line for adjusting the phase of an optical signal having a constant pulse cycle;
(i) an input coupler for distributing the phase-adjusted optical signal into optical signals of a plurality of channels and outputting the optical signal, (ii) an optical power controller for controlling the optical power intensity of each of the optical signals of the plurality of channels, (iii) an optical modulator for optically modulating each of the optical signals of the plurality of channels whose optical power intensity is controlled into a multi-level optical signal by using an electric signal, (iv) a fixture for performing a preset time delay on each of the optical signals of the plurality of channels optically modulated with the multi-level optical signal An optical signal time delay line and (v) a photonic integrated circuit (PIC) chip integrated with an output coupler for optical multiplexing optical signals of a plurality of channels on which the time delay is performed into an optical time division multiplexing (OTDM) signal; and
An integrated circuit for solving a time synchronization problem between an optical signal and an electrical signal input to the optical modulator and a non-uniform optical power problem between channels of the OTDM signal by using a bit error rate (BER) for a part of the optical multiplexed OTDM signal.
An optical transmitter comprising a. According to claim 12,
The fixed optical signal time delay line integrated in the PIC chip,
An optical transmitter formed of a spiral silicon optical waveguide whose length is adjusted. According to claim 12,
The PIC chip,
An electrical signal time delay line for performing a time delay on the electrical signal input to the optical modulator.
is further included,
The electrical signal time delay line,
An optical transmitter formed of metal electrodes whose length is adjusted. According to claim 12,
The variable optical signal time delay line,
An optical transmitter formed of a plurality of micro ring resonators (MRR) connected in series. According to claim 15,
The micro ring resonator,
An optical transmitter integrated in the PIC chip. According to claim 12,
In the integrated circuit,
An optical transmitter that matches phases between an optical signal and an electrical signal input to the optical modulator by controlling the time delay of the optical signal by controlling the variable optical signal time delay line so that the bit error rate is minimized. According to claim 12,
In the integrated circuit,
An optical transmitter for equalizing the optical power intensity between channels of the OTDM signal by adjusting the optical power intensity of the optical signal by controlling the optical power controller to minimize the bit error rate.

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