Orthogonal local oscillator light-based polarization independent coherent detection method, receiver and system
By adopting the same-orthogonal polarization state homologous from zero-difference coherence detection method in the optical fiber communication system, lasers with different center wavelengths generate polarization multiplexed signal light and local oscillator light, and segmentation processing at the receiving end, the local oscillator light is solved The signal loss problem caused by the change in polarization state realizes a high-performance and low-cost optical fiber communication system.
Patent Information
- Application Number
- CN202411291954.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-03-25
- Filing Date
- 2024-09-14
- Publication Date
- 2025-01-07
AI Technical Summary
In the prior art, the polarization state change of local oscillator light in optical fiber communication systems leads to the loss of linear beat frequency terms between signal light and local oscillator light, resulting in polarization fading effect. In addition, existing solutions such as automatic polarization control and polarization-maintaining fiber links The and complementary branch receiving structures have problems such as high cost, increased hardware complexity or performance fluctuations.
Using a homologous zero-difference coherence detection method based on orthogonal polarization state, polarization multiplexed signal light and local oscillator are generated by lasers of different center wavelengths, and the signal light and the polarization beam splitter are transferred at the receiving end. The oscillating light is divided into two beams of different or the same polarization states, and is input to a synchronous coherent receiver for detection to achieve orthogonality of the polarization state and avoid polarization fading.
It realizes coherent detection without the need for a polarization controller and optical filter, reduces hardware complexity, doubles the channel rate, supports low-cost lasers, and ensures that the reception performance is independent of the signal and local oscillator polarization state changes.
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Figure CN119276369A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of optical fiber communication and discloses a polarization-independent coherent detection method based on orthogonal polarization state local oscillator light, a receiver structure and a corresponding optical fiber communication system. Background Art
[0002] Data center optical interconnection uses optical fiber communication systems for high-speed interconnection between boards, racks, and campuses. With the continued exponential growth of network traffic, the interface rate of data center optical interconnection needs to be upgraded accordingly, evolving to 800G or even 1.6T or above. Traditional data center optical interconnection is based on intensity modulation direct detection scheme to obtain advantages such as low cost and simple structure. However, the intensity modulation direct detection scheme only relies on one-dimensional light intensity modulation, which has limited spectrum efficiency and requires extremely high transceiver bandwidth to increase the rate. In addition, the intensity modulation direct detection scheme is limited by frequency selective fading caused by fiber dispersion, and the transmission distance will be further shortened as the rate increases. The typical transmission distance of 200G is only within 1km.
[0003] To this end, coherent detection is gradually being used from long-distance backbone networks to data center internal optical interconnection scenarios, achieving high spectral efficiency and four times the channel rate through four-dimensional modulation of polarization and phase, and effectively compensating for channel damage and extending transmission distance by constructing a linear complex optical field and receiving end digital signal processing. However, the cost and power consumption of coherent detection need to be further reduced to meet the low-cost requirements of short-distance scenarios.
[0004] In recent years, the homodyne coherent architecture based on fiber pairs has gradually emerged, in which the signal light and the local oscillator light are transmitted separately through a pair of optical fibers, and coherent detection is completed at the receiving end. Since the signal light and the local oscillator light come from the same laser, when the fiber length is matched, the carrier frequency offset and laser phase noise can be avoided, thereby saving the carrier frequency and phase recovery links in the digital signal processing at the receiving end, and supporting low-cost distributed feedback lasers with MHz linewidth. A key problem of this solution is that after the remote local oscillator light is transmitted through the optical fiber, its polarization state will change randomly, resulting in the loss of the linear beat frequency term of the signal light and the local oscillator light at a certain polarization state at the receiving end, that is, the polarization fading effect of the local oscillator light.
[0005] At present, there are three main methods to avoid polarization fading of local oscillator light: one is to use automatic polarization control, the second is to use polarization-maintaining fiber links, and the third is to use complementary branch receiving structures.
[0006] 1) Automatic polarization control. This method requires an automatic polarization controller to be set before the local oscillator light input port of the coherent receiver at the receiving end, and the polarization state of the local oscillator light is rotated back to the target state using a feedback algorithm. This ensures that the two polarization states of the local oscillator light and the signal light beat with each other, thereby avoiding the polarization fading effect. The disadvantage is that the tracking speed of the automatic polarization controller is slow, only in the order of 200 krad / s; and, since the local oscillator polarization state can change arbitrarily, and the control voltage value has a maximum limit, there is a reset problem.
[0007] 2) Polarization-maintaining fiber link. This method replaces the fiber that transmits the remote local oscillator light with a polarization-maintaining fiber to ensure that the polarization state of the local oscillator light remains unchanged during transmission. The disadvantage of this solution is that it will greatly increase the cost of fiber preparation, and the cost increases in direct proportion to the transmission distance.
[0008] 3) Complementary branch receiving structure. This method adds a complementary branch to the coherent receiver to ensure that when a certain polarization state of the local oscillator light fades, the complementary branch can still be used for the beat frequency of the signal light, thereby avoiding the polarization fading effect. The disadvantage is that the complementary branch receiving structure increases the hardware complexity of the coherent receiver by 50%, and the signal transmission matrix does not have the unitary matrix characteristics, so the receiving performance will still fluctuate with the change of the polarization state of the local oscillator light. Summary of the invention
[0009] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a polarization-independent coherent detection method, a receiver and an optical fiber communication system based on local oscillator light with orthogonal polarization states. Based on two sets of synchronized coherent receivers and a pair of local oscillator lights with mutually orthogonal polarization states, homodyne coherent detection that is insensitive to the polarization states of both the local oscillator light and the signal light is realized, without the need for a polarization controller and an optical filter, thereby doubling the channel rate while reducing hardware complexity.
[0010] To achieve the above object, the present invention adopts the following technical solution:
[0011] A polarization-independent coherent detection method based on orthogonal polarization state local oscillator light comprises the following steps:
[0012] The first step: using a first laser and a second laser with different central wavelengths, the first laser is used to generate a first local oscillator light and a first optical carrier, modulating an electrical signal on the first optical carrier to generate a first signal light, the second laser is used to generate a second local oscillator light and a second optical carrier, modulating an electrical signal on the second optical carrier to generate a second signal light, wherein the first signal light and the second signal light are modulated with polarization multiplexing signals, the first signal light and the second signal light are combined by an optical coupler and then transmitted in a first optical fiber, and the first local oscillator light and the second local oscillator light are combined by a polarization combiner and then transmitted in a second optical fiber; the polarization state of the first local oscillator light and the polarization state of the second local oscillator light are perpendicular to each other, and can be one horizontal, one vertical, or one left-handed circle, and one right-handed circle.
[0013] Furthermore, the polarization states of the first local oscillation light and the second local oscillation light after polarization beam combining are orthogonal to each other, and may be in X and Y linear polarization states, or in left-handed and right-handed circular polarization states, respectively.
[0014] Step 2: Split the signal light transmitted through the first optical fiber into two identical signal lights through an optical splitter with a splitting ratio of 50:50, which are called the third signal light and the fourth signal light, and input them into the signal input ports of the first coherent receiver and the second coherent receiver respectively; split the local oscillator light transmitted through the second optical fiber into two local oscillator lights with different polarization states through a polarization beam splitter, which are called the third local oscillator light and the fourth local oscillator light, and input them into the local oscillator input ports of the first coherent receiver and the second coherent receiver respectively; or split the signal light transmitted through the first optical fiber into two signal lights with different polarization states through a polarization beam splitter, which are called the fifth signal light and the sixth signal light, and input them into the local oscillator input ports of the first coherent receiver and the second coherent receiver respectively; split the local oscillator light transmitted through the second optical fiber into two identical local oscillator lights through an optical splitter with a splitting ratio of 50:50, which are called the fifth local oscillator light and the sixth local oscillator light, and input them into the signal input ports of the first coherent receiver and the second coherent receiver respectively.
[0015] Step 3: After polarization and phase diversity, the first coherent receiver outputs an X-polarization in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal The second coherent receiver outputs an X-polarized in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal Four electrical signals. In the digital signal processing at the receiving end, these eight electrical signals are sent to the signal demodulation module for real number 8×8 multiple-input multiple-output joint equalization to restore the polarization multiplexed signals on the first signal light and the second signal light;
[0016] Furthermore, the 8 electrical signals output by the first coherent receiver and the second coherent receiver can be firstly synthesized into 4 complex signals in pairs, and then complex 4×4 MIMO joint equalization is performed to restore the polarization multiplexed signals on the first signal light and the second signal light.
[0017] A polarization-independent receiver structure based on orthogonal polarization state local oscillator light for implementing the above method comprises:
[0018] An optical splitter module is connected to the first optical fiber channel and is used to split the received first signal light and the second signal light into two identical signal lights, called the third signal light and the fourth signal light, with a power ratio of 50:50;
[0019] a polarization beam splitter module, connected to the second optical fiber channel, and used for splitting the received first local oscillation light and second local oscillation light into two local oscillation lights with different polarization states, referred to as a third local oscillation light and a fourth local oscillation light;
[0020] The first coherent receiver is connected to the optical splitter module and the polarization beam splitter module to realize the coherent detection of the third signal light and the third local oscillation light, and the obtained 4-way output is an X-polarized in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal
[0021] The second coherent receiver is connected to the optical splitter module and the polarization beam splitter module to realize the coherent detection of the fourth signal light and the fourth local oscillation light, and the obtained 4-way output is an X-polarized in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal
[0022] The signal demodulation module is connected to the 8-channel electrical signals output by the first coherent receiver and the second coherent receiver, and is used to implement resampling, synchronization, channel equalization, downsampling and demodulation of the first signal light and the second signal light, and finally recover the bit information on the X polarization and the Y polarization of the first signal light and the second signal light.
[0023] Furthermore, an equivalent implementation scheme is also included:
[0024] a polarization beam splitter module, connected to the first optical fiber channel, and used to split the received first signal light and second signal light into two signal lights with different polarization states, referred to as a fifth signal light and a sixth signal light;
[0025] An optical splitter module is connected to the second optical fiber channel and is used to split the received first local oscillation light and the second local oscillation light into two beams of the same local oscillation light, which are called the fifth local oscillation light and the sixth local oscillation light, and the power ratio is 50:50;
[0026] The first coherent receiver is connected to the optical splitter module and the polarization beam splitter module to realize the coherent detection of the fifth local oscillation light and the fifth signal light, and the obtained 4-way output is an X-polarized in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal
[0027] The second coherent receiver is connected to the optical splitter module and the polarization beam splitter module to realize the coherent detection of the sixth local oscillation light and the sixth signal light, and the obtained 4-way output is an X-polarized in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal
[0028] The signal demodulation module is connected to the 8-channel electrical signals output by the first coherent receiver and the second coherent receiver, and is used to implement resampling, synchronization, channel equalization, downsampling and demodulation of the electrical signals carried by the first signal light and the second signal light, and finally recover the bit information on the X polarization and Y polarization of the first signal light and the second signal light.
[0029] Compared with the prior art, the present invention has the following positive effects:
[0030] The method of the present invention uses two local oscillator lights with orthogonal polarization states in a homodyne coherent detection system to ensure that the polarization fading effect of the local oscillator light can be avoided under any optical fiber polarization rotation, and the system transfer function has a unitary matrix characteristic, so that coherent detection without a polarization controller is realized, and the receiving performance is independent of the signal and the local oscillator polarization state changes. In addition, no optical filter is required, and simultaneous reception and demodulation of two wavelength signals are achieved, which can double the channel rate and support low-cost lasers without wavelength temperature control. This solution only requires two coherent receivers, a polarization beam splitter and a splitter, and is compatible with existing coherent detection systems. Therefore, it is a low-cost, high-performance coherent detection method, receiver and system. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 It is a schematic diagram of the coherent detection method based on orthogonal local oscillator light of the present invention.
[0032] Figure 2 yes Figure 1 Schematic diagram of the equivalent method.
[0033] Figure 3 It is a schematic diagram of the structure of a coherent receiver based on orthogonal local oscillator light according to an embodiment of the present invention.
[0034] Figure 4 for Figure 3 Schematic diagram of the equivalent structure.
[0035] Figure 5 It is a schematic diagram of a coherent detection transmission system based on orthogonal local oscillator light according to an embodiment of the present invention.
[0036] Figure 6 yes Figure 5 Schematic diagram of the equivalent system. DETAILED DESCRIPTION
[0037] The present invention is further described in detail below through specific embodiments and drawings.
[0038] The following is a schematic diagram of this embodiment Figure 1 Provide specific instructions for the implementation of the technical solution.
[0039] Step 1: Use two lasers with wavelengths of λ1 and λ2 to generate polarization-multiplexed first signal light and second signal light with bandwidth B respectively, and transmit them to the receiving end through the first optical fiber channel after beam combining; then generate first local oscillator light and second local oscillator light with orthogonal polarization states respectively, and transmit them to the receiving end through the second optical fiber channel after polarization beam combining.
[0040] Step 2: If Figure 1 As shown, the optical signal of the first optical fiber channel is split into two identical signal lights through an optical splitter, referred to as the third signal light and the fourth signal light, with a splitting ratio of 50:50, and are respectively input into the signal input ports of the first coherent receiver and the second coherent receiver; the optical signal of the second optical fiber channel is split into two local oscillator lights with different polarization states through a polarization beam splitter, referred to as the third local oscillator light and the fourth local oscillator light, and are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver;
[0041] The equivalent method for the second step is Figure 2 As shown, the optical signal of the first optical fiber channel is split into two signal lights of different polarization states through a polarization beam splitter, which are called the fifth signal light and the sixth signal light, and are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver; the optical signal of the second optical fiber channel is split into two beams of the same local oscillator light through an optical splitter, which are called the fifth local oscillator light and the sixth local oscillator light, and the splitting ratio is 50:50, and are respectively input into the signal input ports of the first coherent receiver and the second coherent receiver;
[0042] The third step is to demodulate the four electrical signals output by the first coherent receiver through the signal demodulation module, and the X-polarization in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal And the 4-way electrical signal output by the second coherent receiver, X-polarization in-phase real signal and orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal Real 8×8 or complex 4×4 multiple-input multiple-output joint equalization is performed to restore the polarization multiplexed signals on the first signal light and the second signal light.
[0043] Figure 3 The present invention is a schematic diagram of a polarization-independent coherent receiver structure based on orthogonal local oscillator light corresponding to the above method, which includes: a splitter module connected to a communication channel, used to split the signal light into two paths with a power ratio of 50:50; a polarization beam splitter module connected to the communication channel, used to decompose the local oscillator light into two polarization states; a first coherent receiver module, used to realize coherent detection of input signal light and local oscillator light, and convert them into four-path electrical signal output; a second coherent receiver module, used to realize coherent detection of input signal light and local oscillator light, and convert them into four-path electrical signal output;
[0044] Figure 4 The equivalent structure in the embodiment includes: a polarization beam splitter module, connected to the communication channel, used to decompose the signal light into two polarization states; a beam splitter module, connected to the communication channel, used to split the local oscillator light into two paths with a power ratio of 50:50; a first coherent receiver module, used to realize coherent detection of the input signal light and the local oscillator light, and convert them into four-path electrical signal output; a second coherent receiver module, used to realize coherent detection of the input signal light and the local oscillator light, and convert them into four-path electrical signal output;
[0045] Figure 5 The schematic diagram of the polarization-independent coherent detection transmission system based on orthogonal local oscillator light corresponding to the above method includes a transmitting end, an optical fiber channel and a receiving end.
[0046] The transmitting end includes: a first laser module, used to generate an optical carrier with a central wavelength of λ1; a second laser module, used to generate an optical carrier with a central wavelength of λ2; a first optical splitter module, connected to the first laser module, used to split the input optical carrier into two paths; a first optical transmitter module, connected to the first optical splitter module, used to generate a first signal light; a second optical splitter module, connected to the second laser module, used to split the input optical carrier into two paths; a second optical transmitter module, connected to the second optical splitter module, used to generate a second signal light; a first polarization combiner module, connected to the first optical splitter module and the second optical splitter module, used to polarization combine the first local oscillation light and the second local oscillation light; an optical coupler module, connected to the first optical transmitter module and the second optical transmitter module, used to combine the first signal light and the second signal light.
[0047] The optical fiber channel includes: a first optical fiber channel module connected to the optical coupler module for transmitting a first signal light and a second signal light; a second optical fiber channel module connected to the first polarization combiner module for transmitting a first local oscillation light and a second local oscillation light.
[0048] The receiving end includes: a third optical splitter module, connected to the first optical fiber channel module, used to split the signal light into two identical signal lights with a power ratio of 50:50, called the third signal light and the fourth signal light; a second polarization beam splitter module, connected to the second optical fiber channel module, used to decompose the local oscillator light into two paths of the third local oscillator light and the fourth local oscillator light with different polarization states; a first coherent receiver module, used to realize coherent detection of the third signal light and the third local oscillator light, and convert them into four-path electrical signal output; a second coherent receiver module, used to realize coherent detection of the fourth signal light and the fourth local oscillator light, and convert them into four-path electrical signal output; a signal demodulation module, connected to the 8-path electrical signals output by the first coherent receiver and the second coherent receiver, used to realize resampling, synchronization, channel equalization, downsampling and demodulation of the electrical signals carried by the first signal light and the second signal light.
[0049] Figure 6 The equivalent system in includes a transmitter and a receiver.
[0050] The transmitting end includes: a first laser module, used to generate an optical carrier with a central wavelength of λ1; a second laser module, used to generate an optical carrier with a central wavelength of λ2; a first optical splitter module, connected to the first laser module, used to split the input optical carrier into two paths; a first optical transmitter module, connected to the first optical splitter module, used to generate a first signal light; a second optical splitter module, connected to the second laser module, used to split the input optical carrier into two paths; a second optical transmitter module, connected to the second optical splitter module, used to generate a second signal light; a first polarization combiner module, connected to the first optical splitter module and the second optical splitter module, used to polarization combine the first local oscillation light and the second local oscillation light; an optical coupler module, connected to the first optical transmitter module and the second optical transmitter module, used to combine the first signal light and the second signal light.
[0051] The optical fiber channel includes: a first optical fiber channel module connected to the optical coupler module for transmitting a first signal light and a second signal light; a second optical fiber channel module connected to the first polarization combiner module for transmitting a first local oscillation light and a second local oscillation light.
[0052] The receiving end includes: a second polarization beam splitter module, connected to the first optical fiber channel module, used to decompose the signal light into two paths of fifth signal light and sixth signal light of different polarization states; a third optical splitter module, connected to the second optical fiber channel module, used to split the local oscillator light into two paths of the same local oscillator light with a power ratio of 50:50, called the fifth local oscillator light and the sixth local oscillator light; a first coherent receiver module, used to realize coherent detection of the fifth signal light and the fifth local oscillator light, and convert them into four-path electrical signal output; a second coherent receiver module, used to realize coherent detection of the sixth signal light and the sixth local oscillator light, and convert them into four-path electrical signal output; a signal demodulation module, connected to the 8-path electrical signals output by the first coherent receiver and the second coherent receiver, used to realize resampling, synchronization, channel equalization, downsampling and demodulation of the electrical signals carried by the first signal light and the second signal light.
[0053] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. A person skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be subject to the claims.
Claims
1. A polarization-independent coherent detection method based on orthogonal local oscillator light, the steps comprising: 1) The transmitting end uses a first laser to generate a first local oscillator light and a first optical carrier, modulates an electrical signal on the first optical carrier to generate a first signal light, uses a second laser to generate a second local oscillator light and a second optical carrier, and modulates an electrical signal on the second optical carrier to generate a second signal light; the first signal light and the second signal light are combined by an optical coupler and transmitted in a first optical fiber, and the first local oscillator light and the second local oscillator light are combined by a polarization combiner and transmitted in a second optical fiber; wherein the center wavelengths of the first laser and the second laser are different, and the first signal light and the second signal light are both modulated with polarization multiplexing signals; 2) The receiving end divides the signal light transmitted through the first optical fiber into two identical signal lights through an optical splitter, which are called the third signal light and the fourth signal light, and inputs them into the signal input ports of the first coherent receiver and the second coherent receiver respectively; divides the local oscillator light transmitted through the second optical fiber into two local oscillator lights with different polarization states through a polarization beam splitter, which are called the third local oscillator light and the fourth local oscillator light, and inputs them into the local oscillator input ports of the first coherent receiver and the second coherent receiver respectively; or the receiving end divides the signal light transmitted through the first optical fiber into two signal lights with different polarization states through a polarization beam splitter, which are called the fifth signal light and the sixth signal light, and inputs them into the local oscillator input ports of the first coherent receiver and the second coherent receiver respectively, and divides the local oscillator light transmitted through the second optical fiber into two identical local oscillator lights through an optical splitter, which are called the fifth local oscillator light and the sixth local oscillator light, and inputs them into the signal input ports of the first coherent receiver and the second coherent receiver respectively; 3) The first coherent receiver performs polarization and phase diversity on the input signal and outputs an X-polarized in-phase real signal Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal The input signal demodulation module converts the second coherent receiver into an X-polarized in-phase real signal after performing polarization and phase diversity on the input signal. Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal Input signal demodulation module; 4) The signal demodulation module performs multi-input multi-output joint equalization on the input signal to restore the polarization multiplexing signals on the first signal light and the second signal light.
2. The method according to claim 1, characterized in that The MIMO joint equalization is a real number MIMO joint equalization with 8 inputs and 8 outputs.
3. The method according to claim 1 or 2, characterized in that: The first local oscillation light and the second local oscillation light are combined by a polarization beam combiner to obtain local oscillation lights with mutually orthogonal polarization states.
4. The method according to claim 3, characterized in that After being combined by the polarization beam combiner, the local oscillator lights with mutually orthogonal polarization states are obtained as X-line polarized light and Y-line polarized light with different central wavelengths.
5. The method according to claim 3, characterized in that: After beam combining by the polarization beam combiner, the local oscillator lights with mutually orthogonal polarization states are obtained as left-handed circularly polarized light and right-handed circularly polarized light with different central wavelengths.
6. A polarization-independent coherent detection receiver based on orthogonal local oscillator light, characterized in that: It includes an optical splitter, a polarization beam splitter, a first coherent receiver, a second coherent receiver and a signal demodulation module; The optical splitter is used to split the signal light after being transmitted through the first optical fiber into two identical signal lights, called the third signal light and the fourth signal light, which are input into the signal input ports of the first coherent receiver and the second coherent receiver respectively; Alternatively, the local oscillator light transmitted through the second optical fiber is divided into two beams of identical local oscillator light, referred to as a fifth local oscillator light and a sixth local oscillator light, which are input into the signal input ports of the first coherent receiver and the second coherent receiver respectively; The polarization beam splitter is used to split the local oscillator light after being transmitted through the second optical fiber into two local oscillator lights of different polarization states, referred to as the third local oscillator light and the fourth local oscillator light, which are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver; or split the signal light after being transmitted through the first optical fiber into two signal lights of different polarization states, referred to as the fifth signal light and the sixth signal light, which are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver; The signal demodulation module is used to demodulate the X-polarization in-phase real signal output by the first coherent receiver. Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal and the X-polarization in-phase real signal output by the second coherent receiver Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal Performing multiple-input multiple-output joint equalization to restore polarization multiplexing signals on the first signal light and the second signal light; The first laser is used to generate a first local oscillator light and a first optical carrier, an electrical signal is modulated on the first optical carrier to generate a first signal light, the second laser is used to generate a second local oscillator light and a second optical carrier, an electrical signal is modulated on the second optical carrier to generate a second signal light, the signal light after the first optical fiber transmission is the signal light obtained by combining the first signal light and the second signal light through an optical coupler; the local oscillator light after the second optical fiber transmission is the local oscillator light obtained by combining the first local oscillator light and the second local oscillator light through a polarization combiner, the central wavelengths of the first laser and the second laser are different, and both the first signal light and the second signal light are modulated with polarization multiplexing signals.
7. A polarization-independent coherent detection system based on orthogonal local oscillator light, characterized in that: It includes a transmitting end and a receiving end; wherein, The transmitting end is used to generate a first local oscillator light and a first optical carrier by using a first laser, modulate an electrical signal on the first optical carrier to generate a first signal light, generate a second local oscillator light and a second optical carrier by using a second laser, and modulate an electrical signal on the second optical carrier to generate a second signal light; combine the first signal light and the second signal light through an optical coupler and transmit them in a first optical fiber, and combine the first local oscillator light and the second local oscillator light through a polarization combiner and transmit them in a second optical fiber; wherein the center wavelengths of the first laser and the second laser are different, and the first signal light and the second signal light are both modulated with polarization multiplexing signals; The receiving end includes an optical splitter, a polarization beam splitter, a first coherent receiver, a second coherent receiver and a signal demodulation module; The optical splitter is used to split the signal light after being transmitted through the first optical fiber into two identical signal lights, referred to as the third signal light and the fourth signal light, which are respectively input into the signal input ports of the first coherent receiver and the second coherent receiver; or split the local oscillator light after being transmitted through the second optical fiber into two identical local oscillator lights, referred to as the fifth local oscillator light and the sixth local oscillator light, which are respectively input into the signal input ports of the first coherent receiver and the second coherent receiver; The polarization beam splitter is used to split the local oscillator light after being transmitted through the second optical fiber into two local oscillator lights of different polarization states, referred to as the third local oscillator light and the fourth local oscillator light, which are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver; or split the signal light after being transmitted through the first optical fiber into two signal lights of different polarization states, referred to as the fifth signal light and the sixth signal light, which are respectively input into the local oscillator input ports of the first coherent receiver and the second coherent receiver; The signal demodulation module is used to demodulate the X-polarization in-phase real signal output by the first coherent receiver. Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal and the X-polarization in-phase real signal output by the second coherent receiver Orthogonal real signal Y-polarization in-phase real signal and orthogonal real signal Perform multiple-input multiple-output joint equalization to restore the polarization multiplexing signals on the first signal light and the second signal light.