Polarization demultiplexing method and system based on rotation angle and phase delay estimation of Stokes space

Abstract

The invention relates to the technical field of optical fiber communication, and particularly discloses a polarization demultiplexing method and system based on rotation angle and phase delay estimation of a Stokes space, and the method comprises the steps: obtaining two polarization multiplexing signals which are transmitted through an optical fiber and are transmitted on the same wavelength, dividing the two paths of polarization multiplexing signals into a first optical signal and a second optical signal according to a preset proportion; based on the first optical signal, calculating a rotation angle and phase delay by using a digital signal processing algorithm, and obtaining a corresponding control voltage according to the calculated rotation angle and phase delay; adjusting an arranged polarization control panel by using the obtained control voltage, so that two paths of polarization multiplexing signals of a second optical signal part are separated after the second optical signal passes through the polarization control panel; and demodulating the second optical signal passing through the polarization control board to obtain two independent paths of output optical signals which are respectively demodulated by two direct detection receivers.

Description

Technical Field

[0001] The present application relates to the field of optical fiber communication technology, and in particular to a polarization demultiplexing method and system based on Stokes space rotation angle and phase delay estimation. Background Art

[0002] Intensity modulation and direct detection (IM-DD) are mainly used in modern data center optical transmission systems. At the transmitting end, an electrical signal is used to change the intensity of the optical signal so that it changes according to the strength of the electrical signal. This modulation method is usually achieved by changing the injection current of a light source (such as a semiconductor laser or a light-emitting diode). At the receiving end, a photodetector (such as a PIN photodiode or an APD avalanche photodiode) is used to directly detect the intensity of the light and convert the change in the optical signal into a change in the electrical signal. Since the detected signal is usually very weak, it needs to be amplified and regenerated first to restore the original electrical signal. IM-DD technology has a relatively simple system structure and does not require complex signal processing circuits, so it is low in cost. In addition, direct detection technology avoids complex signal processing processes and reduces the possibility of system failure. Therefore, this technology is currently widely used in single-wavelength 100Gb / s and 200Gb / s networks in data centers.

[0003] However, the optical signal transmitted by IMDD technology only involves the dimension of amplitude. Compared with the amplitude, phase and polarization dimensions used by coherent optical transmission technology, the channel capacity that IMDD technology can transmit is one-fourth of that of coherent optical transmission technology. In order to further improve the channel capacity of IMDD technology, polarization multiplexing IMDD technology has recently become a research hotspot. This technology can double the channel capacity of IMDD technology while still maintaining the advantages of low complexity and high reliability of IMDD technology.

[0004] In the polarization multiplexing IMDD architecture, polarization state monitoring and compensation are key technologies to ensure signal transmission quality. Due to the time-varying birefringence distributed along the optical fiber, the polarization state (SOP) of the optical signal changes randomly during transmission. This change will cause signal distortion and increase the bit error rate, seriously affecting the performance and reliability of the communication system. Therefore, in order to obtain the original signal at the transmission receiving end, polarization demultiplexing is required at the receiving end. However, traditional polarization state estimation methods usually rely on the entire spectrum for processing. Although these methods can provide high accuracy, they have problems such as high complexity, high cost, and high power consumption in practical applications. In particular, the high sampling rate analog-to-digital conversion unit and digital signal processing process will significantly increase the complexity of the IMDD architecture; at the same time, the solution of polarization demultiplexing using pilots is mainly to add pilots to the signal at the transmitting end, and realize polarization demultiplexing by controlling the pilot power. However, this method of adding pilots will affect the performance of the transmitted signal, resulting in the degradation of transmission performance. Summary of the invention

[0005] The purpose of the present application is to provide a polarization demultiplexing method and system based on the rotation angle and phase delay estimation of the Stokes space, so as to solve the problems of high complexity, high cost, high power consumption, etc. of the traditional polarization state estimation method in the prior art, especially the high sampling rate analog-to-digital conversion unit and the digital signal processing process, which will significantly increase the complexity of the IMDD architecture; at the same time, the scheme of polarization demultiplexing using the pilot is mainly to add a pilot to the signal at the transmitting end, and realize polarization demultiplexing by controlling the pilot power. However, this method of adding the pilot will affect the performance of the transmission signal, resulting in the problem of degradation of the transmission performance.

[0006] To achieve the above object, the embodiment of the present application provides a polarization demultiplexing method based on the rotation angle and phase delay estimation in Stokes space, comprising the steps of:

[0007] Acquire two polarization multiplexed signals transmitted at the same wavelength through optical fiber transmission, and divide the two polarization multiplexed signals into two parts, a first optical signal and a second optical signal, according to a preset ratio;

[0008] Based on the first optical signal, a rotation angle and a phase delay are calculated using a digital signal processing algorithm, and a corresponding control voltage is obtained according to the calculated rotation angle and phase delay;

[0009] Using the obtained control voltage, adjusting the polarization control plate, so that after the second optical signal passes through the polarization control plate, two polarization multiplexing signals of the second optical signal part are separated;

[0010] The second optical signal after passing through the polarization control plate is demodulated to obtain two independent output optical signals, which are respectively provided for demodulation by two direct detection receivers.

[0011] Optionally, the calculating the rotation angle and the phase delay based on the first optical signal by using a digital signal processing algorithm includes:

[0012] The polarization multiplexed optical signal is used to obtain the Stokes vector in the optical domain, and the rotation angle and phase delay of the current state are calculated after analog-to-digital conversion.

[0013] Alternatively, use the formula:

[0014]

[0015] The Stokes vector is obtained, where X / Y represents the X / Y polarization of the signal, Re(·), Im(·) represent the real part and the imaginary part of the complex variable respectively, the superscript * represents the complex conjugate, and (S1, S2, S3) is the mapping of (X, Y) in the Stokes space, that is, the Stokes vector.

[0016] Optionally, the calculating of the rotation angle and phase delay of the current state after analog-to-digital conversion includes:

[0017] Confirm the LSP equation by SVD algorithm;

[0018] Based on the LSP equation, the normal vector of LSP is determined as Calculate the rotation angle θ and phase delay based on the normal vector

[0019]

[0020] To achieve the above-mentioned purpose, the embodiment of the present application further provides a polarization demultiplexing system based on the estimation of the rotation angle and phase delay in Stokes space, comprising: an optical beam splitter, a Stokes vector receiving and processing unit, a polarization control plate, and a first polarization beam splitter, wherein:

[0021] The input end of the optical beam splitter is used to connect to one end of an optical fiber of two polarization multiplexed signals transmitted at the same wavelength, the first optical signal output end of the optical beam splitter is connected to the input end of the Stokes vector receiving and processing unit, and the second optical signal output end of the optical beam splitter is connected to the input end of the polarization control plate;

[0022] The control voltage output terminal of the Stokes vector receiving and processing unit is connected to the control voltage input terminal of the polarization control plate;

[0023] The output end of the polarization control plate is connected to the input end of the first polarization beam splitter.

[0024] Optionally include:

[0025] A laser, a second polarization beam splitter, a first Mach-Zehnder modulator, a second Mach-Zehnder modulator, and a polarization beam combiner, wherein:

[0026] The light outlet of the laser is connected to the input end of the second polarization beam splitter;

[0027] Two output ends of the second polarization beam splitter are connected to input ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator respectively;

[0028] The two input ends of the polarization beam combiner are respectively connected to the output ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator, and the output end of the polarization beam combiner is used to connect to the other end of the optical fiber.

[0029] Optionally, the Stokes vector receiving and processing unit includes: a third polarization beam splitter, an optical mixer, a first balanced detector, a second balanced detector, a third balanced detector, and a digital signal processing board, wherein:

[0030] The input end of the third polarization beam splitter is connected to the first optical signal output end of the optical beam splitter, one output end of the third polarization beam splitter is respectively connected to one input end of the optical mixer and one input end of the first balanced detector, and the other output end of the third polarization beam splitter is respectively connected to the other input end of the optical mixer and the other input end of the first balanced detector;

[0031] The output end of the optical mixer is connected to the input end of the second balanced detector and the third balanced detector respectively;

[0032] The output ends of the first balanced detector, the second balanced detector and the third balanced detector are respectively connected to the input end of the digital signal processing board.

[0033] Optionally, the digital signal processing board includes three analog-to-digital conversion modules, one FPGA, and two digital-to-analog conversion modules.

[0034] The embodiments of the present application have the following advantages:

[0035] Compared with the prior art, the method provided by the above technical solution modulates two independent electrical signals to two polarization states respectively during the polarization multiplexing signal modulation process at the transmitting end. In the transmission scenario inside the data center, the polarization multiplexing optical signal is transmitted in a single optical fiber. After the signal light is transmitted through the optical fiber, it is divided into two parts by the optical beam splitter at the receiving end, one part of which is calculated by the Stokes vector receiving and processing unit to calculate the polarization state of the polarization multiplexing signal light, and the other part is adjusted by the polarization control plate to adjust the polarization state of the signal light. It should be pointed out that the calculated polarization state of the signal light is demodulated by the polarization control plate. After the polarization state demodulation, the optical signal passes through the polarization beam splitter to restore two independent electrical signals. If the transmitted electrical signal adopts the PAM4 modulation format, the subsequent clock recovery and signal judgment can be completed using the traditional PAM4 digital signal processing chip. Thereby, the reuse of the traditional client-side PAM4 digital signal processing chip is realized, and the low power consumption and low cost characteristics of the IMDD system are maintained. This solves the problems of high complexity, high cost, high power consumption, etc. in the traditional polarization state estimation method in the prior art. In particular, the high sampling rate analog-to-digital conversion unit and the digital signal processing process will significantly increase the complexity of the IMDD architecture. At the same time, the solution of using pilots for polarization demultiplexing is mainly to add pilots to the signal at the transmitting end, and realize polarization demultiplexing by controlling the pilot power. However, this method of adding pilots will affect the performance of the transmitted signal, resulting in the problem of degradation of the transmission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0037] Figure 1 A schematic diagram of the overall structure of a polarization demultiplexing system for estimating rotation angle and phase delay in Stokes space provided in at least one embodiment of the present application;

[0038] Figure 2 A schematic diagram of the structure of a Stokes vector receiving and processing unit of a polarization demultiplexing system based on the estimation of the rotation angle and phase delay in Stokes space provided by at least one embodiment of the present application;

[0039] Figure 3A time domain diagram of two electrical signals after signal demodulation of a polarization demultiplexing method based on Stokes space rotation angle and phase delay estimation provided in at least one embodiment of the present application.

[0040] Description of reference numerals:

[0041] 1 optical beam splitter, 2 Stokes vector receiving and processing unit, 3 polarization control board, 4 first polarization beam splitter, 5 laser, 6 second polarization beam splitter, 7 first Mach-Zehnder modulator, 8 second Mach-Zehnder modulator, 9 polarization beam combiner, 10 third polarization beam splitter, 11 optical mixer, 12 first balanced detector, 13 second balanced detector, 14 third balanced detector, 15 digital signal processing board. DETAILED DESCRIPTION

[0042] The following is a description of the implementation of the present application by specific specific embodiments. People familiar with the technology can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0043] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. Unless otherwise clearly specified and limited, the terms "set", "install", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0044] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0045] The solution provided in the embodiment of the present application uses a Stokes vector receiving architecture to calculate the Stokes vector of a dual-polarization IMDD signal in a polarization multiplexing IMDD optical fiber transmission system. After the received Stokes optical vector signal passes through a low sampling rate and low bandwidth analog-to-digital converter, a polarization demultiplexing algorithm is used to estimate the rotation angle and phase delay, thereby eliminating the change in polarization state rotation. Among them, the Stokes vector is a Stokes vector, which uses four parameters to describe the intensity and polarization state of the light wave.

[0046] The system provided in the embodiment of the present application mainly operates near the 1310nm wavelength of the O band, thereby ensuring that the system will not be affected by the fiber dispersion. In the polarization multiplexing signal modulation process at the transmitting end, two independent electrical signals are modulated to two polarization states respectively. In the transmission scenario inside the data center, the polarization multiplexing optical signal is transmitted in a single optical fiber. After the signal light is transmitted through the optical fiber, it is divided into two parts by an optical beam splitter at the receiving end, one of which is used to calculate the polarization state of the polarization multiplexing signal light through the Stokes vector receiving and processing unit, and the other part is used to adjust the polarization state of the signal light through the polarization control plate. It should be pointed out that the calculated polarization state of the signal light is demodulated by the polarization control plate. After the polarization state demodulation of the optical signal, it passes through the polarization beam splitter to restore two independent electrical signals. If the transmitted electrical signal adopts the modulation format of PAM4, the subsequent clock recovery and signal judgment can be completed using the traditional PAM4 digital signal processing chip. Thereby realizing the reuse of the traditional client-side PAM4 digital signal processing chip, maintaining the low power consumption and low cost characteristics of the IMDD system. This solves the problems of high complexity, high cost, high power consumption, etc. in the traditional polarization state estimation method in the prior art. In particular, the high sampling rate analog-to-digital conversion unit and the digital signal processing process will significantly increase the complexity of the IMDD architecture. At the same time, the solution of using pilots for polarization demultiplexing is mainly to add pilots to the signal at the transmitting end, and realize polarization demultiplexing by controlling the pilot power. However, this method of adding pilots will affect the performance of the transmitted signal, resulting in the problem of degradation of the transmission performance.

[0047] In order to realize polarization multiplexing IMDD transmission and maintain the low-cost characteristics of the IMDD architecture, it is necessary to use a simple digital signal processing method to realize polarization compensation. In this application, the polarization multiplexing IMDD system operates near 1310nm in the O band, so in short-distance scenarios, the system will not be affected by dispersion. This application focuses on realizing the polarization function in the polarization multiplexing system and does not affect the transceiver architecture of the current IMDD system. The specific method is to use a Stokes vector optical receiver at the receiving end to receive the polarization multiplexing signal and estimate the state of the polarization state. Based on the estimated polarization state, the polarization control plate is adjusted to achieve polarization demultiplexing.

[0048] In the self-coherent optical transmission system of the data center, a polarization control board is added to the transmission link to realize polarization demultiplexing of polarization multiplexed signals in the optical domain. The main innovation of this application is that the polarization demultiplexing operation is completed in the optical domain, that is, all changes to the system are made in the optical domain, so that the two-way signal at the receiving end can be received completely independently, and the demodulation of the transmitting end signal can be realized by using the traditional PAM4 digital signal processing chip, ensuring the low-cost characteristics of IMDD.

[0049] The control principle of the dual-polarization optical signal polarization control board is to use a low-bandwidth, low-sampling-rate ADC to collect three Stokes vectors respectively. Then, a digital signal processing algorithm is used to calculate the rotation angle θ and phase delay of the optical signal polarization state. Finally, based on the calculated rotation angle θ and phase delay To adjust the polarization control plate, it is ensured that after the optical signal passes through the polarization control, the two polarization multiplexing signals are successfully separated to realize two independent signals.

[0050] Figure 1 The overall system diagram implemented for this application is as follows, Figure 1 The left side describes the transmission of optical signals in two polarization states on the same wavelength through polarization multiplexing at the transmitting end. The right side of the system obtains two polarization multiplexed signals transmitted on the same wavelength through optical fiber transmission, and divides the two polarization multiplexed signals into two parts, the first optical signal and the second optical signal, according to a preset ratio of 10:90. 10% of the first optical signal enters the Stokes vector receiving and processing unit, and based on the first optical signal, the rotation angle θ and the phase delay are calculated using a digital signal processing algorithm. According to the calculated rotation angle and phase delay, corresponding control voltages V1 and V2 are obtained, and the control voltages are output to the polarization control plate, so that the polarization control plate is adjusted by using the obtained control voltage, so that after the second optical signal passes through the polarization control plate, the two polarization multiplexing signals of the second optical signal part are separated, thereby realizing two independent signals. The second optical signal received by the last receiving end after passing through the polarization control plate is demodulated by the first polarization beam splitter, and finally two independent output optical signals are obtained, so as to be further demodulated by two direct detection receivers respectively. Figure 1 In the figure, MZM is Mach-Zehnder modulator.

[0051] refer to Figure 1 The polarization demultiplexing system includes: an optical beam splitter, a Stokes vector receiving and processing unit, a polarization control plate, and a first polarization beam splitter, wherein:

[0052] The input end of the optical beam splitter is used to connect to one end of an optical fiber of two polarization multiplexed signals transmitted at the same wavelength, the first optical signal output end of the optical beam splitter is connected to the input end of the Stokes vector receiving and processing unit, and the second optical signal output end of the optical beam splitter is connected to the input end of the polarization control plate;

[0053] The control voltage output terminal of the Stokes vector receiving and processing unit is connected to the control voltage input terminal of the polarization control plate;

[0054] The output end of the polarization control plate is connected to the input end of the first polarization beam splitter.

[0055] In some embodiments, reference Figure 1 , the polarization demultiplexing system comprises:

[0056] A laser, a second polarization beam splitter, a first Mach-Zehnder modulator, a second Mach-Zehnder modulator, and a polarization beam combiner, wherein:

[0057] The light outlet of the laser is connected to the input end of the second polarization beam splitter;

[0058] Two output ends of the second polarization beam splitter are connected to input ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator respectively;

[0059] The two input ends of the polarization beam combiner are respectively connected to the output ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator, and the output end of the polarization beam combiner is used to connect to the other end of the optical fiber.

[0060] In some embodiments, reference Figure 2 , Figure 2Schematic diagram of a Stokes vector receiving and processing unit, wherein the rotation angle and phase delay are calculated based on the first optical signal using a digital signal processing algorithm, including: obtaining Stokes vectors S1, S2, S3 in the optical domain from the polarization multiplexed optical signal, and calculating the rotation angle θ and phase delay of the current state after analog-to-digital conversion

[0061] In some embodiments, the derivation of the calculation process for obtaining the Stokes vectors S1, S2, S3 includes:

[0062]

[0063] Where X / Y represents the X / Y polarization of the signal, Re(·) and Im(·) represent the real and imaginary parts of the complex variable, respectively, the superscript * represents the complex conjugate, and (S1, S2, S3) is the mapping of (X, Y) in the Stokes space, i.e., the Stokes vector.

[0064] In some embodiments, due to the combination of the received signal and the noise, (S1, S2, S3) cannot completely fall into a plane. To solve this problem, this embodiment adopts a method of finding the least squares surface (LSP) formed by the minimum distance from each Stokes vector (SV), wherein the value ∑ i d i 2 The smallest plane, d i represents the distance from the plane to the i-th SV. Assuming that the plane equation is Ax+By+Cz=0, then the normal vector of the plane is Its relationship with SV is shown in formula (2):

[0065]

[0066] Regarding the optimization problem of the above algorithm, this embodiment adopts the method of singular value decomposition (SVD). SVD is a powerful matrix decomposition technology. By decomposing the matrix into the product of three matrices, the rank defect problem of the matrix can be effectively handled and the calculation process can be simplified. Specifically, this embodiment decomposes the data matrix into the product of an orthogonal matrix and a diagonal matrix through SVD, thereby extracting the normal vector of the plane and determining the equation of the plane. This method can not only minimize the residual sum of squares, but also has high numerical stability and accuracy. Through SVD, high-precision rotation angle and phase delay estimation can still be achieved in the case of limited bandwidth resources. This provides an efficient and reliable solution for polarization state monitoring and compensation in optical communication systems.

[0067] Specifically, the calculation of the rotation angle and phase delay of the current state after analog-to-digital conversion includes: confirming that the LSP equation is Ax+By+Cz=D through the SVD algorithm, so that the normal vector of the LSP can be determined as The calculated rotation angle θ and phase delay It can be calculated as:

[0068]

[0069] The corresponding control voltages V1 and V2 can be obtained by means of a lookup table using the calculated rotation angle and phase delay.

[0070] In some embodiments, reference Figure 2 The Stokes vector receiving and processing unit includes: a third polarization beam splitter, an optical mixer, a first balanced detector, a second balanced detector, a third balanced detector, and a digital signal processing board, wherein:

[0071] The input end of the third polarization beam splitter is connected to the first optical signal output end of the optical beam splitter, one output end of the third polarization beam splitter is respectively connected to one input end of the optical mixer and one input end of the first balanced detector, and the other output end of the third polarization beam splitter is respectively connected to the other input end of the optical mixer and the other input end of the first balanced detector;

[0072] The output end of the optical mixer is connected to the input end of the second balanced detector and the third balanced detector respectively;

[0073] The output ends of the first balanced detector, the second balanced detector and the third balanced detector are respectively connected to the input end of the digital signal processing board.

[0074] In some embodiments, the digital signal processing board includes three analog-to-digital conversion modules, one FPGA, and two digital-to-analog conversion modules.

[0075] Figure 3 This is a performance diagram of the present application, which shows the demodulation result diagram of the dual-polarization PAM4 signal in the 53G baud rate scenario. It can be seen from the figure that when the polarization controllers are in the optimal state, the receiving end can obtain two independent signals, and the impact of polarization rotation is very small. Figure 3 The demodulation results of the data signal 1 and the data signal 2 are the results of further demodulating the two independent output optical signals by using the direct detection receiver 1 and the direct detection receiver 2 in the above embodiment.

[0076] Note that, unless otherwise directly stated, all features disclosed in this specification (including any attached claims, abstracts and drawings) may be replaced by alternative features for achieving the same, equivalent or similar purposes. Therefore, unless otherwise explicitly stated, each feature disclosed is only an example of a group of equivalent or similar features. Where used, further, preferably, further and more preferably are simple beginnings for elaborating another embodiment based on the aforementioned embodiment, and the content of the further, preferably, further or more preferably followed by the combination with the aforementioned embodiment constitutes a complete construction of another embodiment. Several further, preferably, further or more preferably settings following the same embodiment can be arbitrarily combined to form another embodiment.

[0077] In the implementation of functions and steps, the corresponding functions and steps in various embodiments may also occur in a different order than shown. For example, two consecutive functions and steps may actually be performed or implemented substantially in parallel, and they may sometimes be performed or implemented in the opposite order, depending on the functions involved.

[0078] Although the present application has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection claimed in the present application.

Claims

1. A polarization demultiplexing method based on the rotation angle and phase delay estimation in Stokes space, characterized in that: Includes steps: Acquire two polarization multiplexed signals transmitted at the same wavelength through optical fiber transmission, and divide the two polarization multiplexed signals into two parts, a first optical signal and a second optical signal, according to a preset ratio; Based on the first optical signal, a rotation angle and a phase delay are calculated using a digital signal processing algorithm, and a corresponding control voltage is obtained according to the calculated rotation angle and phase delay; Using the obtained control voltage, adjusting the polarization control plate, so that after the second optical signal passes through the polarization control plate, two polarization multiplexing signals of the second optical signal part are separated; The second optical signal after passing through the polarization control plate is demodulated to obtain two independent output optical signals, which are respectively provided for demodulation by two direct detection receivers.

2. The polarization demultiplexing method based on the rotation angle and phase delay estimation in Stokes space according to claim 1, characterized in that: The method of calculating the rotation angle and phase delay based on the first optical signal by using a digital signal processing algorithm includes: The polarization multiplexed optical signal is used to obtain the Stokes vector in the optical domain, and the rotation angle and phase delay of the current state are calculated after analog-to-digital conversion.

3. The polarization demultiplexing method based on the rotation angle and phase delay estimation in Stokes space according to claim 2, characterized in that: Using the formula: The Stokes vector is obtained, where X / Y represents the X / Y polarization of the signal, Re(·), Im(·) represent the real part and the imaginary part of the complex variable respectively, the superscript * represents the complex conjugate, and (S1, S2, S3) is the mapping of (X, Y) in the Stokes space, that is, the Stokes vector.

4. The polarization demultiplexing method based on the rotation angle and phase delay estimation in Stokes space according to claim 2, characterized in that: The calculation of the rotation angle and phase delay of the current state after analog-to-digital conversion includes: Confirm the LSP equation by SVD algorithm; Based on the LSP equation, the normal vector of LSP is determined as Calculate the rotation angle θ and phase delay based on the normal vector 5. A polarization demultiplexing system based on Stokes space rotation angle and phase delay estimation, characterized in that: include: An optical beam splitter, a Stokes vector receiving and processing unit, a polarization control plate, and a first polarization beam splitter, wherein: The input end of the optical beam splitter is used to connect to one end of an optical fiber of two polarization multiplexed signals transmitted at the same wavelength, the first optical signal output end of the optical beam splitter is connected to the input end of the Stokes vector receiving and processing unit, and the second optical signal output end of the optical beam splitter is connected to the input end of the polarization control plate; The control voltage output terminal of the Stokes vector receiving and processing unit is connected to the control voltage input terminal of the polarization control plate; The output end of the polarization control plate is connected to the input end of the first polarization beam splitter.

6. The polarization demultiplexing system based on Stokes space rotation angle and phase delay estimation according to claim 5, characterized in that: include: A laser, a second polarization beam splitter, a first Mach-Zehnder modulator, a second Mach-Zehnder modulator, and a polarization beam combiner, wherein: The light outlet of the laser is connected to the input end of the second polarization beam splitter; Two output ends of the second polarization beam splitter are connected to input ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator respectively; The two input ends of the polarization beam combiner are respectively connected to the output ends of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator, and the output end of the polarization beam combiner is used to connect to the other end of the optical fiber.

7. The polarization demultiplexing system based on Stokes space rotation angle and phase delay estimation according to claim 5, characterized in that: The Stokes vector receiving and processing unit includes: a third polarization beam splitter, an optical mixer, a first balanced detector, a second balanced detector, a third balanced detector, and a digital signal processing board, wherein: The input end of the third polarization beam splitter is connected to the first optical signal output end of the optical beam splitter, one output end of the third polarization beam splitter is respectively connected to one input end of the optical mixer and one input end of the first balanced detector, and the other output end of the third polarization beam splitter is respectively connected to the other input end of the optical mixer and the other input end of the first balanced detector; The output end of the optical mixer is connected to the input end of the second balanced detector and the third balanced detector respectively; The output ends of the first balanced detector, the second balanced detector and the third balanced detector are respectively connected to the input end of the digital signal processing board.

8. The polarization demultiplexing system based on Stokes space rotation angle and phase delay estimation according to claim 7, characterized in that: The digital signal processing board includes three analog-to-digital conversion modules, one FPGA, and two digital-to-analog conversion modules.

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