An optical transmission system based on automatic polarization controller for short reach high capacity optical interconnect

Abstract

The application relates to an automatic polarization controller-based optical transmission system for short-distance high-capacity optical interconnection, comprising an optical transceiver module, an automatic polarization controller and a MIMO-free structure DSP module. The optical transceiver module divides the outgoing light field of a transmitting end laser into two parts, one part of which is modulated to obtain signal light, and the other part is used as pilot light. After passing through the automatic polarization controller, the pilot light is fed to the receiving end of the optical transceiver module together with the signal light for coherent detection, and the receiving signal is recovered through the MIMO-free structure DSP module. Meanwhile, a simple training sequence is adopted to solve the mismatch between the signal light link and the pilot light link. The application solves the problem that high-speed coherent optical communication technology is restricted by cost, bandwidth, power consumption and integration, and cannot be used in short-distance optical interconnection scenes.

Description

Technical Field

[0001] This invention relates to an optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects, belonging to the field of information transmission. Background Technology

[0002] Humanity's demand for intelligent and convenient production methods has spurred the emergence of large-scale data services such as artificial intelligence and virtual reality, posing a severe challenge and profound transformation to existing fiber optic communication systems. Currently, the internet has permeated every aspect of people's lives, and the people, things, and events of this era are being expressed and connected through data. A white paper released by Cisco in 2020 indicated that the total number of global internet users is projected to grow from 3.9 billion in 2018 (representing 51% of the global population) to 5.3 billion in 2023 (representing 66% of the global population), with a compound annual growth rate of approximately 6%.

[0003] For a long time, coherent and DSP (Digital Signal Processing) technologies, designed for long-distance high-speed optical transmission networks, have been considered unsuitable for short-distance optical interconnects due to limitations in transmission cost and power consumption. Most have adopted intensity modulation-direct detection (IMD-D) optical transmission methods. However, the inherent low sensitivity of IMD-D severely restricts the expansion and speed of optical communication. While coherent optical communication technology faces significant challenges due to its power consumption, its advantages of high spectral efficiency, high sensitivity, and linear detection make it a promising candidate for becoming the mainstream solution for low-cost, short-distance, high-capacity optical transmission in the future. Therefore, to meet the data transmission requirements of short-distance, high-capacity optical interconnects, multi-dimensional multiplexing, high-order modulation techniques, and corresponding coherent detection technologies must be employed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects. The optical transceiver module of this system employs high-order modulation, polarization multiplexing, and coherent reception technology with self-homogeneous detection, achieving high-speed, high-capacity, and high-sensitivity optical transmission, suitable for high-speed optical interconnects within data centers. Simultaneously, the automatic polarization controller can perform polarization demultiplexing in the optical domain, enabling data transmission using low-cost optical devices and a simplified MIMO (Multiple-Input Multiple-Output)-free DSP module. The use of a MIMO-free DSP and automatic polarization controller significantly reduces system complexity and cost. This system primarily addresses the current limitations of transmission speed, low spectral efficiency, and the prohibition of coherent transmission within data centers due to high costs.

[0005] The present invention adopts the following technical solution:

[0006] An optical transmission system based on an automatic polarization controller for short-range high-capacity optical interconnects includes a first optical module and a second optical module connected via a full-duplex optical fiber.

[0007] The first optical module includes a first optical transceiver module, a first automatic polarization controller module, and a first MIMO-free DSP module; the first optical transceiver module includes a first optical transmitter module and a first optical receiver module; the second optical module includes a second optical transceiver module, a second automatic polarization controller module, and a second MIMO-free DSP module; the second optical transceiver module includes a second optical transmitter module and a second optical receiver module.

[0008] The first optical transmitting module, the second automatic polarization controller module, the second optical receiving module, and the second MIMO-free DSP module are connected in sequence. The first optical transmitting module transmits to the second optical module through a circulator and a full-duplex optical fiber. The second optical transmitting module, the first automatic polarization controller module, the first optical receiving module, and the first MIMO-free DSP module are connected in sequence. The second optical transmitting module transmits to the first optical module through a circulator and a full-duplex optical fiber.

[0009] The laser output light field in the first optical emission module is divided into two parts by a power divider. One part is used as an optical carrier to perform high-order modulation on the transmitted signal after polarization beam splitting, and becomes a modulated optical signal. The other part is used as the local oscillator light.

[0010] The modulated optical signal generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber. At the same time, the local oscillator light generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber.

[0011] After the local oscillator light is fed from the first transmitting module to the second optical module, it undergoes polarization demultiplexing by the second automatic polarization controller module. The second optical receiving module recovers the received electrical signal after zero-difference coherent detection of the optical signal, and the signal is equalized and phase compensated by the DSP module with the second MIMO-free structure.

[0012] According to a preferred embodiment of the present invention, both the first optical emitting module and the second optical emitting module are of model CPRV4220A HB-ICR.

[0013] According to a preferred embodiment of the present invention, the first optical receiving module and the second optical receiving module are both multi-format optical signal transmitters IOM-901.

[0014] According to a preferred embodiment of the present invention, the model of the first MIMO-free DSP module and the second MIMO-free DSP module is: AMD Ryzen 5 4600H with Radeon Graphics.

[0015] According to a preferred embodiment of the present invention, the first automatic polarization controller module and the second automatic polarization controller module include a first-stage phase shifter, a first-stage 3dB coupler, a second-stage phase shifter, and a second-stage 3dB coupler, wherein the first-stage phase shifter, the first-stage 3dB coupler, the second-stage phase shifter, and the second-stage 3dB coupler are connected in sequence; wherein the first-stage 3dB coupler, the second-stage phase shifter, and the second-stage 3dB coupler are connected in sequence to form an MZI structure.

[0016] According to a preferred embodiment of the present invention, both the first automatic polarization controller module and the second automatic polarization controller module are automatic polarization controllers. The automatic polarization controller performs optical domain polarization demultiplexing to control the input polarization state. This means that the automatic polarization controller adjusts the phase shift to ensure that the power of the local oscillator light signal is equal after polarization and beam splitting at the receiving end. The input optical field of the automatic polarization controller and the output optical field of the MZI structure satisfy the following relationship, as shown in equation (…). As shown in the image:

[0017] ( )

[0018] in, and These represent the optical fields in the x-polarization and y-polarization states input to the automatic polarization controller, respectively. and These represent the optical fields of the output x and y polarization states of the MZI structure, respectively; express , is an imaginary number; , These represent the phase shift amounts of the first-stage phase shifter and the second-stage phase shifter, respectively.

[0019] The output of the automatic polarization controller is calculated as shown in equation ( ). ),Mode( As shown in the image:

[0020] ( )

[0021] ( )

[0022] The control objective of the automatic polarization controller is to achieve the zero-crossing flip algorithm. The specific implementation steps are as follows:

[0023] 1) The second phase shifter in the MZI structure Start from 0 rad and increment in small steps. Increasing, >0 rad, until ,in, Let be the Stokes space parameter, representing the power difference between the x and y polarization states at the current moment, expressed as: , This represents the power difference at the previous moment, when the polarization state of the local oscillator light stabilizes in the target region.

[0024] 2) Settings Second phase shifter Increase or decrease in the opposite direction;

[0025] 3) In the second phase shifter When the boundary is reached, it passes through the first-stage phase shifter. Add or subtract Invert the second phase shifter The direction of change;

[0026] 4) In the second phase shifter If the condition is met again during normal operation. Second phase shifter Change the direction of change again and return to step 2).

[0027] According to a preferred embodiment of the present invention, the DSP module of the MIMO-free structure includes two parallel convergence filters and a phase recovery module, wherein the convergence filters are non-recursive filters.

[0028] According to a preferred embodiment of the present invention, the DSP module of the MIMO-free structure performs signal equalization and phase compensation, and the specific implementation steps are as follows:

[0029] a. At the transmitting end, a 65536-bit pseudo-random sequence is used as the signal source. After serial-to-parallel conversion, a 32768-bit pseudo-random sequence is added to both the X-polarization and Y-polarization regions. Furthermore, a 2-bit training sequence is inserted every 16 bits of data sequence. The segment overhead of the training sequence is 6.25%.

[0030] b. In the DSP module of the MIMO-free structure, set the number of equalization filter taps k and the update step size. The electrical signal after multiplexing the convergent polarization solution according to the equalization formula and , and Let X and Y be the electrical signals input to the filter in polarization states, respectively, as shown in equation ( ). ),Mode( As shown in the image:

[0031] ( )

[0032] ( )

[0033] Mode( ),Mode( )middle, and These represent the filter update coefficients for the Y-polarization state at the current and previous times, respectively; and These represent the filter update coefficients for the Y-polarization state at the current and previous times, respectively; and These represent the errors of the X-polarization state and the Y-polarization state at the previous moment, respectively. and express and The conjugate of, where, and This represents the electrical signal input to the filter at the previous moment, indicating the X and Y polarization states.

[0034] Based on the equalization formula, the equalized output electrical signal is obtained. and , and The output electrical signals of the filters in the two polarization states are respectively represented by equation ( ),Mode( As shown in the image:

[0035] ( )

[0036] ( )

[0037] Mode( ),Mode( )middle, , This represents the electrical signal input to the filter at the current moment, representing the X and Y polarization states.

[0038] c. Calculate the phase difference between the received signal and the original signal based on the pre-designed training sequence, and then calculate the average phase value of N baud rates. , as in formula ( As shown in the image:

[0039] ( )

[0040] This indicates the number of baud rates generated by the training sequence; This represents the average phase of the actual output and the ideal output constellation diagram.

[0041] d. Phase compensation is achieved using the average phase difference, and the phase shift formula is as follows ( As shown in the image:

[0042] ( )

[0043] Indicates time; and These represent the output electrical signal and input electrical signal of the phase rotation module at the current moment, respectively.

[0044] The beneficial effects of this invention are as follows:

[0045] 1. The optical transceiver module of this invention adopts a 16QAM modulation format and polarization multiplexing multiplexing method, which greatly improves the transmission capacity and transmission rate, and is suitable for short-distance data transmission with high capacity and rate requirements.

[0046] 2. The optical transceiver module of this invention employs self-zero-difference coherent detection technology, realizing photoelectric detection based on polarization diversity and phase diversity, which greatly improves the sensitivity of the transmission system. Self-zero-difference detection does not need to consider the frequency and phase of the local oscillator light, improving tolerance to laser linewidth and frequency offset. It can eliminate the need for phase compensation and frequency offset compensation modules in the DSP, resulting in higher sensitivity and lower performance loss compared to traditional detection technologies.

[0047] 3. The automatic polarization controller module of this invention achieves polarization demultiplexing through automatic phase adjustment in the optical domain. It addresses link mismatch by adding training sequences, eliminating the need for a polarization demultiplexing module in the DSP, reducing complexity and power consumption, significantly lowering costs, and making implementation easier. By employing automatic polarization control technology, it achieves "optical domain innovation and optoelectronic synergy," fully unleashing the potential of short-range coherence.

[0048] 4. The DSP module of the MIMO-free structure of this invention only requires parallel channel equalization and related calculations of the training sequence, without the need for polarization demultiplexing compensation, dispersion compensation, nonlinear compensation and frequency offset compensation, which greatly reduces the complexity of the DSP in the electrical domain and simplifies the structure of the entire system.

[0049] 5. The automatic polarization controller module of the present invention can achieve automatic stabilization of the polarization state of the local oscillator light using two-stage phase shifters, without the need for a reset operation, thus reducing processing costs. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the optical transmission system based on an automatic polarization controller for short-distance, high-capacity optical interconnects according to the present invention.

[0051] Figure 2 This is a schematic diagram of the structure of the optical transceiver module of the present invention;

[0052] Figure 3 This is a schematic diagram of the automatic polarization controller module and the optical receiving module of the present invention;

[0053] Figure 4 This is a schematic diagram of the DSP module structure of the MIMO-free structure of the present invention;

[0054] Figure 5 This is a schematic diagram of the phase compensation method in the DSP module of the MIMO-free structure of the present invention;

[0055] Figure 6(a) is a schematic diagram of the constellation before phase compensation in the DSP module of the MIMO-free structure of the present invention;

[0056] Figure 6(b) is a schematic diagram of the constellation after phase compensation in the DSP module of the MIMO-free structure of the present invention. Detailed Implementation

[0057] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. However, this description is not limited thereto. All aspects not described in detail in the present invention are based on conventional techniques in the field.

[0058] Example 1

[0059] An optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects solves the problem that coherent transmission is not suitable for short-distance transmission, such as... Figure 1 As shown, it includes a first optical module and a second optical module connected by a full-duplex optical fiber;

[0060] The first optical module includes a first optical transceiver module, a first automatic polarization controller module, and a first MIMO-free DSP module; the first optical transceiver module includes a first optical transmitter module and a first optical receiver module; the second optical module includes a second optical transceiver module, a second automatic polarization controller module, and a second MIMO-free DSP module; the second optical transceiver module includes a second optical transmitter module and a second optical receiver module.

[0061] The first optical transmitting module, the second automatic polarization controller module, the second optical receiving module, and the second MIMO-free DSP module are connected in sequence. The first optical transmitting module transmits to the second optical module through a circulator and a full-duplex optical fiber. The second optical transmitting module, the first automatic polarization controller module, the first optical receiving module, and the first MIMO-free DSP module are connected in sequence. The second optical transmitting module transmits to the first optical module through a circulator and a full-duplex optical fiber.

[0062] The first and second optical modules employ high-order modulation formats and polarization multiplexing technology. The laser output light field in the first optical transmitting module is divided into two parts by a power divider. One part, after polarization beam splitting, serves as an optical carrier to perform high-order modulation on the transmitted signal, becoming a modulated optical signal. The other part serves as the local oscillator light.

[0063] The modulated optical signal generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber. At the same time, the local oscillator light generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber.

[0064] After the local oscillator light is fed from the first transmitting module to the second optical module, it undergoes polarization demultiplexing by the second automatic polarization controller module. The second optical receiving module recovers the received electrical signal after zero-difference coherent detection of the optical signal. The signal is then equalized and phase-compensated using the second MIMO-free DSP module (digital signal processing module).

[0065] This optical transmission system can be used for optical interconnection within data centers, enabling single-wavelength 400Gbps transmission over a 10km fiber optic cable.

[0066] Example 2

[0067] The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects as described in Embodiment 1 differs in that:

[0068] Both the first and second optical transmitting modules are model CPRV4220A HB-ICR. The first and second optical receiving modules are model IOM-901 multi-format optical signal transmitters. The first and second MIMO-free DSP modules are offline computer processing units with an AMD Ryzen 54600H processor and Radeon Graphics.

[0069] The first or second automatic polarization controller module utilizes the high birefringence and high electro-optic coefficient of lithium niobate crystals, and is implemented based on a compact lithium niobate thin-film pure waveguide structure. Both modules include a first-stage phase shifter, a first-stage 3dB coupler, a second-stage phase shifter, and a second-stage 3dB coupler, which are sequentially connected. The sequential connection of the first-stage 3dB coupler, second-stage phase shifter, and second-stage 3dB coupler forms an MZI (Mach-Zehnder interferometer) structure.

[0070] In such Figure 2 As shown, the same laser source is used for both the optical transmitter and receiver. The laser operates at a wavelength of 1550 nm, with a linewidth of 0.1 MHz and a transmit power of 10 dBm. Maintaining the local oscillator and signal carrier in phase and frequency is crucial. If the two links are perfectly matched, the frequency offset compensation and phase recovery modules in the digital signal processing module can be removed. However, in practice, maintaining perfect matching between the two links is difficult. A simple training sequence method can effectively solve this problem, thereby reducing the complexity and power consumption of the DSP.

[0071] The structure of the optical transceiver module is as follows: Figure 2 As shown, facing the ever-increasing explosive growth of data traffic, data transmission within data centers places higher demands on transmission capacity and transmission rate. Here, the optical transmitting module employs polarization multiplexing and a higher-order modulation format for signal multiplexing and modulation, while the optical receiving module uses self-homogeneous coherent detection for signal demodulation and recovery. The transmission section utilizes four circulators and a full-duplex fiber, ensuring that optical signals do not interfere with each other during transmission within the fiber, reducing cabling complexity and system cost.

[0072] The optical transceiver module employs polarization multiplexing and 16QAM (Quadrature Amplitude Modulation) modulation. It utilizes photoelectric detection technology with self-homogeneous reception, a feature found in coherent detection. The automatic polarization controller module automatically stabilizes the local oscillator's polarization state without requiring a reset.

[0073] The first optical transmitting module and the second optical transmitting module are as follows: Figure 2 As shown, it includes a laser, a power divider, and a dual-polarization IQ modulator connected in sequence; the first optical receiving module and the second optical receiving module are as follows. Figure 3 As shown in the diagram, there are two polarization beam splitters and two... The system includes an optical mixer and four balanced photodetectors, but an additional photonic integrated circuit is located after the local oscillator input port. This circuit integrates an automatic polarization controller module, including a first-stage phase shifter and an MZI structure. Based on the aforementioned control algorithm, the power difference between the two polarization states is minimized. Finally, the local oscillator light enters the optical receiving module and performs self-zero-difference detection with the signal light to recover the received electrical signal.

[0074] In practice, in most cases, adjusting the second-stage phase shifter is sufficient to bring the tracking algorithm to convergence. When the drive voltage of the second-stage phase shifter approaches its boundary, the first-stage phase shifter begins to adjust to change the adjustment direction of the second-stage phase shifter without affecting the stable state of the output polarization state, thereby avoiding a reset operation and achieving continuous polarization stabilization.

[0075] like Figure 4 As shown, the DSP module of the MIMO-free structure includes two parallel convergence filters and a phase recovery module, where the convergence filters are non-recursive filters. The DSP module is implemented on a PC and can process digital signals in real time. The x-polarized signal and the y-polarized signal are connected to the convergence filter and the phase recovery module, respectively. High-quality signal reception can be achieved by only completing the signal convergence equalization and phase noise compensation, eliminating the need for polarization demultiplexing, dispersion compensation, nonlinear compensation, and frequency offset compensation modules, greatly reducing system complexity.

[0076] Example 3

[0077] The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects described in Embodiment 2 differs in that:

[0078] Both the first and second automatic polarization controller modules are automatic polarization controllers. The use of automatic polarization controllers enables polarization demultiplexing in the optical domain. The control algorithm aims to ensure that the differential signal of the two feedback signals continuously crosses zero, completing coherent detection. The automatic polarization controller performs polarization demultiplexing to control the input polarization state. This means that the automatic polarization controller adjusts the phase shift to ensure that the power of the local oscillator light signal is equal after polarization and beam splitting at the receiving end. The input optical field of the automatic polarization controller and the output optical field of the MZI structure satisfy the following relationship, as shown in equation (…). As shown in the image:

[0079] ( )

[0080] in, and These represent the optical fields in the x-polarization and y-polarization states input to the automatic polarization controller, respectively. and These represent the optical fields of the output x and y polarization states of the MZI structure, respectively; express , is an imaginary number; , These represent the phase shift amounts of the first-stage phase shifter and the second-stage phase shifter, respectively.

[0081] The output of the automatic polarization controller is calculated as shown in equation ( ). ),Mode( As shown in the image:

[0082] ( )

[0083] ( )

[0084] The control objective of the automatic polarization controller is to achieve the zero-crossing flip algorithm. The specific implementation steps are as follows:

[0085] 1) The second phase shifter in the MZI structure Start from 0 rad and increment in small steps. Increasing, >0 rad, until ,in, Let be the Stokes space parameter, representing the power difference between the x and y polarization states at the current moment, expressed as: , This represents the power difference at the previous moment, when the polarization state of the local oscillator light stabilizes in the target region.

[0086] 2) Settings Second phase shifter Increase or decrease in the opposite direction;

[0087] 3) In the second phase shifter When the boundary is reached, it passes through the first-stage phase shifter. Add or subtract Invert the second phase shifter The direction of change;

[0088] 4) In the second phase shifter If the condition is met again during normal operation. Second phase shifter Change the direction of change again and return to step 2).

[0089] Example 4

[0090] The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects described in Embodiment 2 differs in that:

[0091] MIMO-free DSP modules (either the first or second MIMO-free DSP module) do not require polarization demultiplexing, dispersion compensation, nonlinearity compensation, or frequency offset compensation. They only need to perform convergence equalization and simple training sequence processing to achieve high-quality signal reception. MIMO-free DSP modules can be used for signal equalization and phase compensation, such as... Figure 5 As shown, the horizontal axis represents the in-phase component of the input electrical signal, and the vertical axis represents the quadrature component of the input electrical signal. Light gray marks the constellation diagram before phase compensation, and dark gray marks the ideal constellation diagram after phase compensation. After fitting a border to both constellation diagrams, a corner of the border is used... Figure 5 The top left corner of the border was selected to determine the aspects of the constellation chart that needed to be rotated. The specific implementation steps are as follows:

[0092] a. At the transmitting end, a 65536-bit pseudo-random sequence is used as the signal source. After serial-to-parallel conversion, a 32768-bit pseudo-random sequence is added to both the X-polarization and Y-polarization regions. Furthermore, a 2-bit training sequence is inserted every 16 bits of data sequence. The segment overhead of the training sequence is 6.25%.

[0093] b. In the DSP module of the MIMO-free structure, set the number of equalization filter taps k and the update step size. The electrical signal after multiplexing the convergent polarization solution according to the equalization formula and , and Let X and Y be the electrical signals input to the filter in polarization states, respectively, as shown in equation ( ). ),Mode( As shown in the image:

[0094] ( )

[0095] ( )

[0096] Mode( ),Mode( )middle, and These represent the filter update coefficients for the Y-polarization state at the current and previous times, respectively; and These represent the filter update coefficients for the Y-polarization state at the current and previous times, respectively; and These represent the errors of the X-polarization state and the Y-polarization state at the previous moment, respectively. and express and The conjugate of, where, and This represents the electrical signal input to the filter at the previous moment, indicating the X and Y polarization states.

[0097] Based on the equalization formula, the equalized output electrical signal is obtained. and , and The output electrical signals of the filters in the two polarization states are respectively represented by equation ( ),Mode( As shown in the image:

[0098] ( )

[0099] ( )

[0100] Mode( ),Mode( )middle, , This represents the electrical signal input to the filter at the current moment, representing the X and Y polarization states.

[0101] c. Calculate the phase difference between the received signal and the original signal based on the pre-designed training sequence, and then calculate the average phase value of N baud rates. , as in formula ( As shown in the image:

[0102] ( )

[0103] This indicates the number of baud rates generated by the training sequence; This represents the average phase of the actual output and the ideal output constellation diagram.

[0104] d. Phase compensation is achieved using the average phase difference, and the phase shift formula is as follows ( As shown in the image:

[0105] ( )

[0106] Indicates time; and These represent the output electrical signal and input electrical signal of the phase rotation module at the current moment, respectively.

[0107] This invention utilizes a simple training sequence to compensate for phase noise. First, at the optical transmitter, a fixed set of 4 bits is inserted every fixed number of bit symbols. Taking the constellation point (-3, 3) as an example, the fixed number of inserted sets is 00 11. This is then encoded and mapped into digital signals -3 and 3, which are then modulated by IQ and fed into the optical fiber channel. At the optical receiver, this invention calculates the relative phase shift of the training sequence at fixed positions. Implement phase rotation function.

[0108] The results of using a simplified training sequence to compensate for phase noise are shown in Figures 6(a) and 6(b), where Figure 6(a) is the constellation diagram before phase compensation and Figure 6(b) is the constellation diagram after phase compensation. It should be noted that the electrical signal needs to undergo MIMO-free equalization before calculating the phase of the training sequence. For coherent transmission systems with zero differential noise between data centers, phase rotation can be performed directly after equalization.

[0109] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects, characterized in that, This includes a first optical module and a second optical module connected via full-duplex optical fiber; The first optical module includes a first optical transceiver module, a first automatic polarization controller module, and a first MIMO-free DSP module; the first optical transceiver module includes a first optical transmitter module and a first optical receiver module; the second optical module includes a second optical transceiver module, a second automatic polarization controller module, and a second MIMO-free DSP module; the second optical transceiver module includes a second optical transmitter module and a second optical receiver module. The first optical transmitting module, the second automatic polarization controller module, the second optical receiving module, and the second MIMO-free DSP module are connected in sequence. The first optical transmitting module transmits to the second optical module through a circulator and a full-duplex optical fiber. The second optical transmitting module, the first automatic polarization controller module, the first optical receiving module, and the first MIMO-free DSP module are connected in sequence. The second optical transmitting module transmits to the first optical module through a circulator and a full-duplex optical fiber. The laser output light field in the first optical emission module is divided into two parts by a power divider. One part is used as an optical carrier to perform high-order modulation on the transmitted signal after polarization beam splitting, and becomes a modulated optical signal. The other part is used as the local oscillator light. The modulated optical signal generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber. At the same time, the local oscillator light generated by the first optical transmitting module is transmitted to the second optical transceiver module through a circulator in a full-duplex optical fiber. After the local oscillator light is fed from the first transmitting module to the second optical module, it undergoes polarization demultiplexing by the second automatic polarization controller module. The second optical receiving module recovers the received electrical signal after zero-difference coherent detection of the optical signal. The signal is then equalized and phase-compensated using the DSP module with the second MIMO-free structure. Both the first and second automatic polarization controller modules are automatic polarization controllers. These controllers perform optical domain polarization demultiplexing to control the input polarization state. By adjusting the phase shift, the automatic polarization controller ensures that the local oscillator signal has equal power after polarization and beam splitting at the receiving end. The specific implementation steps are as follows: 1) The second phase shifter in the MZI structure starts from 0 rad and increments in small steps. Increasing, >0 rad, until the product of the power difference between the X-polarization state and the Y-polarization state at the current moment and the power difference between the X-polarization state and the Y-polarization state at the previous moment is less than 0, at which point the polarization state of the local oscillator light stabilizes in the target region; 2) Set the step of the phase shifter to the opposite direction, and the second phase shifter in the MZI structure increases or decreases in the opposite direction; 3) When the second phase shifter reaches the boundary, add or subtract through the first-stage phase shifter. Reverse the direction of change of the second phase shifter; 4) When the second phase shifter is working normally, if the product of the power difference between the current time and the previous time is less than 0 again, the second phase shifter in the MZI structure changes its direction of change again and returns to step 2).

2. The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to claim 1, characterized in that, Both the first optical emitting module and the second optical emitting module are model CPRV4220AHB-ICR.

3. The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to claim 1, characterized in that, The first optical receiving module and the second optical receiving module are both multi-format optical signal transmitters IOM-901.

4. The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to claim 1, characterized in that, The model numbers of the first MIMO-free DSP module and the second MIMO-free DSP module are: AMD Ryzen 5 4600H with Radeon Graphics.

5. The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to claim 1, characterized in that, The first automatic polarization controller module and the second automatic polarization controller module include a first-stage phase shifter, a first-stage 3dB coupler, a second-stage phase shifter, and a second-stage 3dB coupler, which are connected in sequence; wherein, the first-stage 3dB coupler, the second-stage phase shifter, and the second-stage 3dB coupler are connected in sequence to form an MZI structure.

6. The optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to claim 1, characterized in that, The DSP module of the MIMO-free structure includes two parallel convergence filters and a phase recovery module, wherein the convergence filters are non-recursive filters.

7. An optical transmission system based on an automatic polarization controller for short-range, high-capacity optical interconnects according to any one of claims 1-6, characterized in that, The MIMO-free DSP module performs signal equalization and phase compensation. The specific implementation steps are as follows: a. Insert training sequences into the original information of the X and Y polarized light signals at the transmitting end, and form the transmitted signal after IQ modulation and polarization multiplexing; b. After coherent reception, the demultiplexed X and Y polarization state signals are passed through a parallel filter by the DSP module of the MIMO-free structure without the need for a butterfly filter. c. Calculate the phase difference between the received signal and the original signal based on the pre-designed training sequence, and then use the average phase difference to perform phase compensation to complete the compensation for link mismatch.

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