A self-coherent detection system and method supporting polarization multiplexing

Abstract

The application discloses a self-coherent detection system and a detection method supporting polarization multiplexing. The self-coherent detection system supporting polarization multiplexing comprises a dual-polarization IQ modulation module, a polarization module, a local oscillator module, an optical coupling module, an optoelectronic detection module, an analog-to-digital conversion module and a digital processing module, wherein the dual-polarization IQ modulation module, the optical coupling module, the optoelectronic detection module, the analog-to-digital conversion module and the digital processing module are sequentially connected. The self-coherent detection system supporting polarization multiplexing uses a polarization multiplexing mode, can realize detection of a polarization multiplexing signal without adding additional optoelectronic devices, effectively improves utilization of optical spectrum and light source power, and has the advantages of low equipment cost, small device bandwidth demand, low calculation complexity and the like.

Description

Technical Field

[0001] This invention relates to the field of optical communication, and more particularly to a self-coherent detection system, i.e., a detection method, that supports polarization multiplexing. Background Technology

[0002] In recent years, new internet-based applications have emerged in an endless stream, and the number of global internet users has grown rapidly. The demands for network bandwidth are also increasing due to technologies such as 5G (high-speed, low-latency, and ultra-large-scale access), cloud computing (remote data storage), and 4K / 8K high-definition video streaming. How to achieve high-speed, long-distance, and high-quality data transmission at low cost has become a key issue that needs to be addressed in access network communication and data center communication. Compared to coherent detection systems, self-coherent detection systems require less hardware and are expected to be widely used in data center communication. However, existing self-coherent detection systems generally suffer from problems such as high carrier signal power ratio, large computational load, and high device complexity. Furthermore, they often require additional optoelectronic devices to detect polarization-multiplexed signals, limiting their practicality in short-to-medium distance interconnection systems. Summary of the Invention

[0003] In view of the aforementioned shortcomings of the prior art, the technical problem to be solved by the present invention is that existing self-coherent detection systems mostly suffer from problems such as high carrier signal power ratio, large computational load, and high device complexity. Furthermore, they often require additional optoelectronic devices to detect polarization-multiplexed signals, thus limiting their practicality in short-to-medium distance interconnection systems. Therefore, the present invention proposes a self-coherent detection system and method supporting polarization multiplexing. This self-coherent detection system can detect polarization-multiplexed signals without adding additional optoelectronic devices, effectively improving the utilization rate of the spectrum and light source power, and has advantages such as low equipment cost, small device bandwidth requirements, and low computational complexity.

[0004] To achieve the above objectives, this invention provides a self-coherent detection system supporting polarization multiplexing, comprising a dual-polarization IQ modulation module, a polarization module, a local oscillator module, an optical coupling module, a photodetector module, an analog-to-digital conversion module, and a digital processing module, wherein the dual-polarization IQ modulation module, optical coupling module, photodetector module, analog-to-digital conversion module, and digital processing module are sequentially connected; wherein,

[0005] The dual polarization state IQ modulation module is used to split the light source signal into two mutually orthogonal polarized light waves, and modulate the data to be transmitted onto the two mutually orthogonal polarized light waves respectively;

[0006] The polarization module is connected to the optical coupling module and is used to adjust the polarization state of the light source signal to obtain the optical transmission signal, and transmit the optical transmission signal to the optical coupling module;

[0007] The local oscillator module is used to output the local oscillator signal;

[0008] An optical coupling module is used to receive an optical transmission signal and a local oscillator signal, wherein the frequency value of the local oscillator signal differs from the frequency value of the optical transmission signal by a preset offset frequency value, and a coupling signal is obtained based on the optical transmission signal and the local oscillator signal;

[0009] The photoelectric detection module, connected to the optical coupling module, is used to convert the coupled signal into an analog signal;

[0010] An analog-to-digital conversion module, connected to a photoelectric detection module, is used to sample analog signals according to a preset sampling frequency value and convert the analog signals into digital signals. The preset sampling frequency value is three times the symbol rate value of the optical transmission signal. A digital processing module, connected to the analog-to-digital conversion module, is used to process the digital signals.

[0011] Furthermore, the dual-polarization IQ modulation module is configured as a dual-polarization IQ modulator, used to split the light source signal into two mutually orthogonal polarized light waves. One of the polarized light waves is IQ modulated to obtain a complex signal, and the other polarized light wave is intensity modulated to obtain an intensity signal. The two polarized light waves are then coupled through a polarization multiplexer to obtain an optical transmission signal.

[0012] Furthermore, the light source signal is a combined light signal obtained by combining the optical transmission signal and the local oscillator signal. The polarization module is used to adjust the polarization state of the light source signal to obtain the optical transmission signal and the local oscillator signal, and transmits the optical transmission signal and the local oscillator signal to the optical coupling module respectively.

[0013] Furthermore, the preset sampling frequency value is set to be greater than or equal to twice the symbol rate value of the optical transmission signal.

[0014] Furthermore, the light source signal is a combined light signal obtained by combining the optical transmission signal and the local oscillator signal. The polarization module divides the light source signal into an optical transmission signal and a local oscillator signal, and transmits the optical transmission signal and the local oscillator signal to the optical coupling module respectively.

[0015] Furthermore, the preset sampling frequency value can be set to any value.

[0016] Furthermore, it also includes an adjustable optical attenuation module for adjusting the amplitude of the optical transmission signal and the local oscillator signal. The adjustable optical attenuation module is connected to the output of the polarization module.

[0017] Furthermore, the preset offset frequency value is set to one or more of 1 / 2, 3 / 4 and 1 times the symbol rate of the optical transmission signal.

[0018] Furthermore, the photoelectric detection module is configured with a single photoelectric detector, which serves as the receiver.

[0019] In a preferred embodiment of the present invention, the present invention provides a method for using a self-coherent detection system supporting polarization multiplexing as described above, comprising the following steps:

[0020] Three preset offset frequency values ​​and sampling frequency values ​​are set respectively;

[0021] The optical transmission signal and the local oscillator signal are transmitted to the optical coupling module respectively;

[0022] The optical coupling module couples the optical transmission signal and the local oscillator signal to obtain a coupled signal, and then transmits the coupled signal to the photodetector module;

[0023] The photoelectric detection module performs photoelectric conversion on the coupled signal to obtain an analog signal, and then transmits the analog signal to the analog-to-digital conversion module;

[0024] The analog-to-digital converter (ADC) samples the analog signal at a preset sampling frequency and converts it into a digital signal, calculating the analog signal E for every three samples. s The phase difference that exists between them;

[0025] Three sampled analog signals E s The complex signal and intensity signal of the optical transmission signal in two mutually orthogonal polarization states are obtained by calculation. It should be emphasized that one of the signals in the two polarization states is a complex signal and the other is a real signal.

[0026] The digital processing module processes the digital signal converted from the sampled analog signal to complete the demodulation of the optical transmission signal.

[0027] Furthermore, calculate the analog signal E for every three samples. s The phase difference between them specifically includes the following steps:

[0028] Assuming optical transmission signal O t Symbol rate R symbol By changing the frequency offset value of the frequency offset unit, the local oscillator signal O lo With optical transmission signal O t There is a certain frequency offset between them;

[0029] Preset frequency offset is R symbol / 2,3R symbol / 4 and R symbol ;

[0030] The analog signal E output by the photodetector is sampled at a preset sampling frequency value. s Sampling is performed, and the preset sampling frequency value is set to the optical transmission signal O. t The symbol rate is worth three times 3R. symbolThe sampling period T is 1 / 3R symbol ;

[0031] Three analog signals E sampled consecutively s This can be expressed by the following formula:

[0032]

[0033]

[0034]

[0035] Where R represents the responsivity of the photodetector. Let be the power of the IQ modulated complex signal in the X-polarization state. P is the power of the intensity signal transmitted in the Y-polarization state. LO Indicates the local oscillator signal O lo The power, β represents the optical transmission signal O. t The modulation phase, θ represents the phase noise, and 2πnΔfT represents the noise caused by the local oscillator signal O. lo With optical transmission signal O t The phase shift is caused by the frequency offset between them;

[0036] Three consecutive sampled analog signals E s phase difference between

[0037] Furthermore, the three sampled analog signals E s The complex signal and intensity signal in two mutually orthogonal polarization states of the optical transmission signal are obtained by calculation. Specifically, the in-phase component and quadrature component in the X polarization state for IQ modulation are first calculated from three sampled analog signals. Then, the intensity information in the X polarization state is subtracted from the obtained sampled analog signals to obtain the intensity information in the Y polarization state for intensity modulation, which includes:

[0038] The three consecutively sampled analog signals are represented as in-phase components of the same symbol on a complex signal subjected to IQ modulation in the X-polarization state. k and orthogonal components Q k and intensity information in the Y polarization state.

[0039]

[0040]

[0041]

[0042] In the above formula, γ is the normalization coefficient.

[0043] Technical effect

[0044] This invention provides a self-coherent detection system and method supporting polarization multiplexing. Utilizing the independence of orthogonally polarized light at beat frequencies, it directly supports polarization demultiplexing, enabling single-PD-based polarization multiplexed signal detection without the need for additional optoelectronic devices, effectively improving the utilization rate of the spectrum and light source power. By changing the preset frequency offset value, the bandwidth requirement of the device can be reduced, and beat frequency interference can be eliminated and the optical transmission signal restored through simple calculations. Therefore, this self-coherent detection system and method supporting polarization multiplexing has the advantages of low equipment cost, low device bandwidth requirement, and low computational complexity.

[0045] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a self-coherent detection system supporting polarization multiplexing, according to a preferred embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram illustrating the frequency offset between the optical transmission signal and the local oscillator signal received by an optical coupling module in a self-coherent detection method supporting polarization multiplexing, provided in another embodiment of the present invention.

[0048] Figure 3 This is a schematic diagram of the sampling period of an analog-to-digital conversion module in a self-coherent detection method supporting polarization multiplexing provided in another embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of a self-coherent detection method supporting polarization multiplexing provided in another embodiment of the present invention;

[0050] Figure 5 This is a schematic diagram of subsequent digital signal processing according to another embodiment of the present invention;

[0051] Figure 6 This is another embodiment of the present invention, showing a 16QAM constellation diagram modulated on the X-polarization state at 10 GHz in an experiment;

[0052] Figure 7 This is another embodiment of the present invention, a PAM4 signal modulated in the Y-polarization state at a polarization of 10 GHz in an experiment;

[0053] Figure 8 This is another embodiment of the present invention, showing a 16QAM constellation diagram modulated on the X-polarization state at a polarization of 15 GHz in an experiment;

[0054] Figure 9 This is another embodiment of the present invention, a PAM4 signal modulated in the Y-polarization state at a polarization of 15 GHz in an experiment;

[0055] Figure 10 This is another embodiment of the present invention, showing a 16QAM constellation diagram modulated on the X-polarization state at a polarization of 20 GHz in an experiment;

[0056] Figure 11 This is another embodiment of the present invention, a PAM4 signal modulated in the Y polarization state at a polarization of 20 GHz in an experiment. Detailed Implementation

[0057] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0058] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0059] like Figure 1 As shown, a preferred embodiment of the present invention provides a self-coherent detection system supporting polarization multiplexing, including a dual-polarization IQ modulation module 110, an optical coupling module 120, a photodetector module 130, an analog-to-digital conversion module 140, and a digital processing module 150 connected in sequence. The dual-polarization IQ modulation module 110 is used to convert the light source signal O... s The optical signal is split into two orthogonally polarized light waves, and the data to be transmitted is modulated onto each of these two orthogonally polarized light waves. A polarization combiner then combines the signals from the two polarization states to obtain the optical transmission signal O. t Optical fiber transmission is initiated; the optical coupling module 120 is used to receive the optical transmission signal O carrying information. t and local oscillator signal O lo The local oscillator signal O, which originates from the same source as the optical transmission signal. loThe frequency value differs from the frequency value of the optical transmission signal by a preset offset frequency value, which can be set to any value. The local oscillator signal from the same source changes only the phase difference between the three sampled signals by using different preset offset frequency values. Regardless of whether the preset offset frequency value is set to three different values, three samples can be obtained. The preset offset frequency value can be set to any value, and in this embodiment, the preset offset frequency values ​​are 1 / 2, 3 / 4, and 1 times the symbol rate of the optical transmission signal, respectively.

[0060] And based on the optical transmission signal O t and local oscillator signal O lo Obtain the coupling signal O m The photoelectric detection module 130 is used to convert the coupling signal O m Converted to analog signal E s ;

[0061] The analog-to-digital converter module 140 is used to convert the analog signal E according to a preset sampling frequency value. s Sample and convert the analog signal E s Converted to digital signal E d The preset sampling frequency value is set to conform to the sampling theorem, that is, it should be greater than or equal to twice the symbol rate value; the digital processing module 150 is used to process the digital signal E. d Due to the local oscillator signal O lo With optical transmission signal O t The frequency values ​​differ from the preset offset frequency, and the preset offset frequency value is the optical transmission signal O. t The symbol rate values ​​are 1 / 2, 3 / 4, and 1 times, when the optical transmission signal is transmitted at a preset sampling frequency value of O. t The symbol rate value is three times that of the local oscillator signal O. lo With optical transmission signal O t The analog signal E converted from the combined light signal s During sampling, the analog signal E can be sampled every three times. s There are phase differences of 60 degrees, 90 degrees, and 120 degrees between them, and the optical transmission signal O can be obtained from the three sampled analog signals through calculation. t Two complex signals and intensity signals in mutually orthogonal polarization states can be processed by digital processing module 150 to process the sampled analog signal E. s The converted digital signal E dThe optical transmission signal is demodulated after processing. This embodiment presents a self-coherent detection system supporting polarization multiplexing. Utilizing the independence of orthogonally polarized light at beat frequencies, it can directly support polarization demultiplexing, achieving single-PD-based polarization multiplexed signal detection without the need for additional optoelectronic devices, effectively improving the utilization rate of the spectrum and light source power. By changing the preset frequency offset value, the bandwidth requirement of the device can be reduced, and beat frequency interference can be eliminated and the optical transmission signal restored through simple calculations. Therefore, the self-coherent detection system for polarization multiplexing of this invention has the advantages of low equipment cost, low device bandwidth requirement, and low computational complexity.

[0062] The photoelectric detection module 130 is a single photoelectric detector. The photoelectric detector can be a PIN photodiode, but this embodiment does not limit it to a single type.

[0063] The optical coupling module 120 can be an optical coupler, but this embodiment does not limit it to a single type.

[0064] The local oscillator signal O received by the optical coupling module 120 lo It can be transmitted to the self-coherent detection device via an optical signal transmitting device. In this embodiment, the local oscillator signal O... lo The source is not specifically limited.

[0065] In current self-coherent detection solutions, the receiver often uses a single photodetector. However, beat frequency interference caused by the square law detection of the photodetector becomes a major factor affecting signal transmission performance. Several existing methods address beat frequency interference: guard interval method (which reduces spectral efficiency by half); iterative elimination algorithm (which often requires a high number of iterations); and Kramer-Kronig (KK) receiver (simple but with high requirements for carrier signal power ratio and sampling rate). Therefore, there is an urgent need for a self-coherent detection method with low equipment cost, low device bandwidth requirements, and low computational complexity. Furthermore, the above solutions often require additional optoelectronic devices to detect polarization-multiplexed signals, limiting their practicality in short-to-medium distance interconnection systems. Therefore, the self-coherent detection system supporting polarization multiplexing in this embodiment can detect polarization-multiplexed signals using only a single photodetector to minimize beat frequency interference, thus offering low equipment cost.

[0066] The working principle of a self-coherent detection system supporting polarization multiplexing according to an embodiment of the present invention is as follows:

[0067] like Figure 2 As shown, assuming the optical transmission signal O t The symbol rate is R symbol The local oscillator signal O can be adjusted by changing the frequency offset value of the frequency offset unit.lo With optical transmission signal O t There is a certain frequency shift between them, R symbol / 2,3R symbol / 4 and R symbol And it can be done through, for example... Figure 3 The preset sampling frequency value shown corresponds to the analog signal E output by the photodetector. s Sampling is performed, and the preset sampling frequency value is set to the optical transmission signal O. t Three times the symbol rate value (3R) symbol If the sampling period T is 1 / 3R, then... symbol .

[0068] Then the three continuously sampled analog signals E s This can be expressed by the following formula:

[0069]

[0070]

[0071]

[0072] Where R represents the responsivity of the photodetector. Let be the power of the IQ modulated complex signal in the X-polarization state. P is the power of the intensity signal transmitted in the Y-polarization state. LO Indicates the local oscillator signal O lo The power, β represents the optical transmission signal O. t The modulation phase, θ represents the phase noise, and 2πnΔfT represents the noise caused by the local oscillator signal O. lo With optical transmission signal O t The phase shift is caused by the frequency offset between the two signals. From the above formula, we can obtain the phase shift of three consecutive sampled analog signals E. s phase difference between (If the frequency offset value is R) symbol / 2, then α=π / 3; if the frequency offset value is 3R symbol / 4, then α=π / 2; if the frequency offset value is R symbol If α = 2π / 3), then the three continuously sampled analog signals E s It can be represented as:

[0073]

[0074]

[0075]

[0076] By simple calculation, the three consecutively sampled analog signals can be represented as the in-phase component I of the same symbol on a complex signal subjected to IQ modulation in the X-polarization state. k and orthogonal components Q k and intensity information in the Y polarization state.

[0077]

[0078]

[0079]

[0080] In the above formula, γ is the normalization coefficient.

[0081] Therefore, when the local oscillator signal O lo With optical transmission signal O t The frequency values ​​differ by a preset offset frequency, and the preset offset frequency is 1 / 2, 3 / 4, and 1 times the symbol rate of the optical transmission signal. When the analog signal converted from the combined optical signal composed of the local oscillator signal and the optical transmission signal is sampled at a preset sampling frequency three times the symbol rate of the optical transmission signal, a phase difference of 60 degrees, 90 degrees, and 120 degrees can be achieved between every three sampled analog signals, respectively. Furthermore, the in-phase component I of the same symbol in the complex signal with IQ modulation in the X-polarization state can be obtained through simple calculation. k and orthogonal components Q k and intensity information in the Y polarization state. The digital signal converted from the sampled analog signal can be processed by the digital processing module 150 to demodulate the optical transmission signal. This self-coherent detection system supporting polarization multiplexing utilizes the independence of orthogonally polarized light at beat frequencies, directly supporting polarization demultiplexing. It can achieve polarization multiplexed signal detection based on a single PD without adding additional optoelectronic devices, effectively improving the utilization rate of the spectrum and light source power. By changing the preset frequency offset value, the bandwidth requirement of the device can be reduced, and beat frequency interference can be eliminated and the optical transmission signal restored through simple calculations. Therefore, the self-coherent detection system supporting polarization multiplexing in this embodiment of the invention has the advantages of low equipment cost, low device bandwidth requirement, and low computational complexity.

[0082] It should be noted that the local oscillator signal O lo Frequency value F lo With optical transmission signal O t Frequency value F s The preset offset frequency value can be ±R symbol / 2,±3R symbol / 4,±R symbol .

[0083] like Figure 4 As shown, in another preferred embodiment, based on the above... Figure 1 In this embodiment, the self-coherent detection system further includes a polarization module 410 connected to the optical coupling module 120, the polarization module 410 being used to receive the light source signal O. s For the light source signal O s The polarization state is adjusted to obtain the optical transmission signal O. t and transmit optical signal O t Transmitted to optical coupling module 120.

[0084] In one embodiment, the self-coherent detection system may be equipped with a polarization module 410, which can convert the received light source signal O s The polarization state is adjusted to obtain the optical transmission signal O. t To enable optical transmission signal O t The polarization state of the IQ modulation and the local oscillator signal O lo The polarization state remains consistent, and it can be coupled with the local oscillator signal O through the optical coupling module 120. lo (Local oscillator signal O lo Frequency value and optical transmission signal O t The frequency values ​​differ from the preset offset frequency, and the preset offset frequency value is the optical transmission signal O. t The symbol rate values ​​are 1 / 2, 3 / 4, and 1 times, respectively, and then coupled to obtain the coupled signal O. m and couple signal O m The signal is transmitted to the photoelectric detection module 130, which then transmits the coupled signal O. m Photoelectric conversion is performed to obtain an analog signal E. s and the analog signal E s The signal is transmitted to the analog-to-digital converter 140, which uses a preset sampling frequency (the preset sampling frequency is the optical transmission signal O) to transmit the signal. t (three times the symbol rate) for analog signal E s Sample and convert the analog signal E s Converted to digital signal E d This enables the analog signal E to be sampled every three times. s There are phase differences of 60 degrees, 90 degrees, and 120 degrees between the three sampled analog signals E. s The optical transmission signal O can be obtained through simple calculations. t Two complex signals and intensity signals in mutually orthogonal polarization states can be processed by digital processing module 150 to process the sampled analog signal E. s The converted digital signal E dThe optical transmission signal is demodulated after processing. This self-coherent detection system supporting polarization multiplexing utilizes the independence of orthogonally polarized light at beat frequencies, directly supporting polarization demultiplexing. It achieves polarization multiplexed signal detection based on a single photodiode without the need for additional optoelectronic devices, effectively improving the utilization rate of the spectrum and light source power. By changing the preset frequency offset value, the bandwidth requirement of the device can be reduced, and beat frequency interference can be eliminated and the optical transmission signal restored through simple calculations. Therefore, this self-coherent detection system supporting polarization multiplexing has the advantages of low equipment cost, low device bandwidth requirement, and low computational complexity.

[0085] It should be noted that the polarization module 410 is a polarization controller.

[0086] The system was verified using optical communication simulation software. The light source used in the simulation was a continuous fiber laser (CW-laser) with a center wavelength of 1550.00nm and a linewidth of 0.1MHz. Another light source used was also a continuous fiber laser with center wavelengths of 1549.92nm, 1549.88nm, and 1549.84nm (with preset frequency deviations of 10GHz, 15GHz, and 20GHz from the signal path, respectively) and a linewidth of 0.1MHz.

[0087] At the transmitting end, an optical splitter divides the light source into a signal path and a local oscillator path. A polarization beam splitter further divides the signal path into two mutually orthogonal X-polarization and Y-polarization paths. The X-polarization signal path generates a binary sequence using a pseudo-random sequence generator. After bit mapping, this sequence is used by a quadrature amplitude modulation (QAM) sequence generator to produce a 16QAM modulated signal with a rate of 80 Gbit / s and a baud rate of 20 Gbaud / s. This 16QAM signal drives the X-polarization IQ modulator in the dual-polarization IQ modulator to generate an orthogonally modulated optical signal. Utilizing the carrier suppression characteristic of the IQ modulator, a carrier-free radio frequency signal is output. The Y-polarization signal path generates a binary sequence using a pseudo-random sequence generator. After bit mapping, this sequence is used by a pulse amplitude modulation (PAM) sequence generator to produce a PAM4 modulated signal with a rate of 40 Gbit / s and a baud rate of 20 Gbaud / s. This PAM4 signal drives the Y-polarization IQ modulator to generate an intensity-modulated optical signal. The frequency values ​​of the local oscillator signal and the optical transmission signal differ by a preset frequency value, which is 10GHz, 15GHz and 20GHz respectively.

[0088] At the receiving end, the signal first passes through a variable optical attenuator (VOA) to adjust the received optical power and a polarization controller (PC) to adjust its polarization state so that the X-polarization state of the IQ modulated signal is consistent with the polarization state of the local oscillator light. Then, it is input to an optical coupler (OC) with a coupling ratio of 50:50 to mix with the local oscillator light. Finally, a PIN photodetector with a bandwidth of 40 GHz and a sensitivity of 1 A / W is used to perform photoelectric conversion on the mixed optical signal.

[0089] A digital storage oscilloscope is used to receive the signal output from the PIN detector, i.e., analog-to-digital conversion (ADC). The oscilloscope's sampling rate is set to three times the signal symbol rate, i.e., 60 GSample / s. In short-to-medium distance fiber optic transmission, polarization mode dispersion and other polarization mode correlation crosstalk can be ignored. Therefore, only the signal components with the same polarization can be beat at the receiving end. The received photocurrent signal is the superposition of the photocurrents obtained by beating at the X and Y polarization states. Since this photocurrent signal contains three consecutive sampled signals, namely the in-phase component I and the quadrature component Q, which can be converted into a complex signal in the X polarization state, these three sampled signals need to be extracted from the serial signal data in a specific order. The signal reception order is as follows: Figure 3 As shown, when sampling at a sampling rate three times the symbol rate, the in-phase and quadrature components of each symbol in the X-polarization state, as well as the intensity information in the Y-polarization state, can be obtained by performing simple calculations on three consecutive sampled analog signals. Therefore, the complex signal in the X polarization state and the intensity signal in the Y polarization state can be obtained by three consecutive samples.

[0090] The subsequent digital signal processing in this scheme is as follows: Figure 5 As shown, the signal output from the oscilloscope is first resampled to three times the symbol rate. Then, the signal undergoes symbol timing and normalization processing, followed by equalization. Finally, simple calculations are performed using this method to obtain the complex signal in the X-polarization state and the intensity signal in the Y-polarization state, thus completing the recovery of the polarization multiplexed signal.

[0091] Figure 6-11 To simulate the experimental results, the optical signal-to-noise ratio was set to 35 dB, the carrier signal power ratio was set to 0 dB, and the received optical power was set to 2 dBm. Figure 6-7 Constellation diagram of simulation results for dual polarization states of optical signal-to-noise local oscillator light and signal light with a frequency offset of 10 GHz; Figure 8-9 The constellation diagram shows the simulation results of the dual polarization state of the local oscillator light and the signal light with a frequency offset of 15 GHz; Figure 10-11The diagram shows the simulated constellation results of the local oscillator light and the signal light with a 20 GHz frequency offset. It can be seen that for different frequency offsets, this self-coherent detection method can effectively eliminate the influence of beat frequency interference, and can demodulate different modulation signals in the X-polarization and Y-polarization states under different frequency offsets.

[0092] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A self-coherent detection system supporting polarization multiplexing, characterized in that, It includes a dual-polarization IQ modulation module, a polarization module, a local oscillator module, an optical coupling module, a photodetector module, an analog-to-digital conversion module, and a digital processing module, wherein the dual-polarization IQ modulation module, the optical coupling module, the photodetector module, the analog-to-digital conversion module, and the digital processing module are connected in sequence; wherein, The dual polarization state IQ modulation module is used to split the light source signal into two mutually orthogonal polarized light waves, and modulate the data to be transmitted onto the two mutually orthogonal polarized light waves respectively. The polarization module is connected to the optical coupling module and is used to adjust the polarization state of the light source signal to obtain an optical transmission signal, and transmit the optical transmission signal to the optical coupling module; The local oscillator module is used to output the local oscillator signal; The optical coupling module is used to receive the optical transmission signal and the local oscillator signal, wherein the frequency value of the local oscillator signal differs from the frequency value of the optical transmission signal by a preset offset frequency value, and a coupling signal is obtained based on the optical transmission signal and the local oscillator signal. The photoelectric detection module is used to convert the coupling signal into an analog signal; The analog-to-digital conversion module is used to sample the analog signal according to a preset sampling frequency value and convert the analog signal into a digital signal, and to calculate the analog signal every three samples. The phase difference exists between each of the three samples; where, the analog signal is calculated every three samples. The phase difference between them specifically includes the following steps: Assuming optical transmission signal symbol rate By changing the frequency offset value of the frequency offset unit, the local oscillator signal is made more accurate. With optical transmission signals There is a certain frequency offset between them; Preset frequency offset is , and ; The analog signal output by the photodetector is sampled at a preset sampling frequency value. Sampling is performed, and the preset sampling frequency value is set to the optical transmission signal. The symbol rate is worth three times. The sampling period T is ; Three analog signals sampled in succession This can be expressed by the following formula: ； ； ； Where R represents the responsivity of the photodetector. Let be the power of the complex signal subjected to IQ modulation in the X-polarization state. Let be the power of the intensity signal transmitted in the Y-polarization state. Indicates the local oscillator signal power, Indicates optical transmission signal The modulation phase, Indicates phase noise, This indicates that due to the local oscillator signal With optical transmission signals The phase shift is caused by the frequency offset between them; Three consecutive sampled analog signals phase difference between ; The digital processing module is connected to the analog-to-digital conversion module and is used to process the digital signal.

2. The self-coherent detection system supporting polarization multiplexing as described in claim 1, characterized in that, The dual polarization IQ modulation module is configured as a dual polarization IQ modulator, used to split the light source signal into two mutually orthogonal polarized light waves, perform IQ modulation on one of the polarized light waves to obtain a complex signal, perform intensity modulation on the other polarized light wave to obtain an intensity signal, and then couple the two polarized light waves through a polarization multiplexer to obtain an optical transmission signal.

3. The self-coherent detection system supporting polarization multiplexing as described in claim 1, characterized in that, The light source signal is a combined light signal obtained by combining the optical transmission signal and the local oscillator signal. The polarization module is used to adjust the polarization state of the light source signal to obtain the optical transmission signal and the local oscillator signal, and transmit the optical transmission signal and the local oscillator signal to the optical coupling module respectively.

4. The self-coherent detection system supporting polarization multiplexing as described in claim 2, characterized in that, The preset sampling frequency value is set to be greater than or equal to twice the symbol rate value of the optical transmission signal.

5. The self-coherent detection system supporting polarization multiplexing as described in claim 1, characterized in that, It also includes an adjustable optical attenuation module for adjusting the amplitude of the optical transmission signal and the local oscillator signal, and the adjustable optical attenuation module is connected to the output of the polarization module.

6. The self-coherent detection system supporting polarization multiplexing as described in claim 1, characterized in that, The preset offset frequency value is set to any value.

7. The self-coherent detection system supporting polarization multiplexing as described in claim 1, characterized in that, The photoelectric detection module is configured with a single photoelectric detector, which serves as the receiving end.

8. A method using a self-coherent detection system supporting polarization multiplexing as described in any one of claims 1-7, characterized in that, Includes the following steps: Three preset offset frequency values ​​and sampling frequency values ​​are set respectively; The optical transmission signal and the local oscillator signal are transmitted to the optical coupling module respectively; The optical coupling module couples the optical transmission signal and the local oscillator signal to obtain a coupled signal, and then transmits the coupled signal to the photodetector module. The photoelectric detection module performs photoelectric conversion on the coupled signal to obtain an analog signal, and then transmits the analog signal to the analog-to-digital conversion module; The analog-to-digital conversion module samples the analog signal at a preset sampling frequency and converts the analog signal into a digital signal, calculating the analog signal every three samples. The phase difference exists between each of the three samples; where, the analog signal is calculated every three samples. The phase difference between them specifically includes the following steps: Assuming optical transmission signal symbol rate By changing the frequency offset value of the frequency offset unit, the local oscillator signal is made more accurate. With optical transmission signals There is a certain frequency offset between them; Preset frequency offset is , and ; The analog signal output by the photodetector is sampled at a preset sampling frequency value. Sampling is performed, and the preset sampling frequency value is set to the optical transmission signal. The symbol rate is worth three times. The sampling period T is ; Three analog signals sampled in succession This can be expressed by the following formula: ； ； ； Where R represents the responsivity of the photodetector. Let be the power of the complex signal subjected to IQ modulation in the X-polarization state. Let be the power of the intensity signal transmitted in the Y-polarization state. Indicates the local oscillator signal power, Indicates optical transmission signal The modulation phase, Indicates phase noise, This indicates that due to the local oscillator signal With optical transmission signals The phase shift is caused by the frequency offset between them; Three consecutive sampled analog signals phase difference between ; Three sampled analog signals The complex signal and intensity signal in the two mutually orthogonal polarization states of the optical transmission signal were obtained by calculation. The digital processing module processes the digital signal converted from the sampled analog signal to complete the demodulation of the optical transmission signal.

9. The self-coherent detection method supporting polarization multiplexing as described in claim 8, characterized in that, Three sampled analog signals The complex signal and intensity signal of the optical transmission signal in two mutually orthogonal polarization states are obtained by calculation. Specifically, three sampled analog signals are used. First, the in-phase component and quadrature component in the X polarization state for IQ modulation are calculated. Then, the intensity information in the X polarization state is subtracted from the obtained sampled analog signals to obtain the intensity information in the Y polarization state for intensity modulation, which specifically includes: The three consecutively sampled analog signals are represented as in-phase components of the same symbol in a complex signal subjected to IQ modulation in the X-polarization state. and orthogonal components and intensity information in the Y polarization state. : ； ； ； In the above formula, This is the normalization coefficient.

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