Six-dimensional coherent detection method and receiver structure based on IQ modulation local oscillator light

Abstract

This invention provides a six-dimensional coherent detection method and receiver structure based on IQ-modulated local oscillator light, including a dual-polarization 90-degree optical mixer, a single-polarization 90-degree optical mixer, six pairs of balanced photodetectors, a polarization controller, a polarization beamsplitter, and two signal demodulation modules. By employing IQ-modulated local oscillator light carrying information, the local oscillator light signal can be separated by the polarization beamsplitter and coherently beats with the complex signal in a self-zero difference manner. This avoids cross-beat interference between the signal and the local oscillator, achieving coherent detection of a four-dimensional polarization multiplexed signal and local oscillator light carrying two-dimensional information, further expanding the signal reception dimension. Furthermore, the system capacity and spectral efficiency are improved, and low-complexity parallel signal demodulation is supported.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, specifically to a six-dimensional coherent detection method and receiver structure based on IQ modulated local oscillator light. Background Technology

[0002] With the acceleration of global informatization, optical fiber communication, with its advantages of ultra-high bandwidth, low latency, and long-distance transmission, has become the main transmission technology for critical infrastructure such as the modern Internet and data centers. In optical fiber communication systems, optical signal detection is one of the key technologies determining system performance. Generally, optical signal detection methods are divided into two types: direct detection and coherent detection. These two detection methods each have unique advantages and application areas in optical fiber communication. With technological advancements, they complement each other, jointly propelling optical fiber communication towards higher transmission efficiency and longer transmission distances.

[0003] Traditional direct detection methods modulate the desired information onto light intensity, then demodulate the signal at the receiver using a photodetector with a square-law law. This traditional intensity-modulated direct detection method has a simple system structure and is widely used in short-distance transmission scenarios. However, this method utilizes only a single dimension of modulation and demodulation, limiting the receiver's spectral efficiency. To improve spectral efficiency and transmission capacity, a series of multi-dimensional direct detection improvements have been proposed, achieving diversity reception of amplitude and phase. For example, a three-dimensional direct detection receiver can recover signals on two orthogonal polarization states by using double-sideband and single-sideband modulation on two orthogonal polarization states respectively, combined with the Stokes space inverse rotation algorithm in the digital domain. Here, the dimension is defined as the ratio of the maximum received signal rate to the intensity-modulated direct detection rate under the same receiving bandwidth.

[0004] Unlike direct detection methods, coherent detection achieves a leap forward in receiver dimensionality through structural innovation. The core of coherent detection lies in introducing a local oscillator laser to generate single-frequency local oscillator light as a phase reference. Through a dual-polarization 90-degree optical mixer and four photoelectric balanced detectors, the amplitude, phase, and polarization state information of the signal are simultaneously extracted, thus achieving four-dimensional signal reception. Furthermore, coherent detection can effectively address channel transmission impairments such as fiber dispersion and polarization mode dispersion, meeting the requirements of long-distance fiber optic transmission. For even higher-dimensional coherent receivers, one implementation scheme involves adding a single-ended photoelectric detector to achieve coherent detection of the four-dimensional polarization-multiplexed signal light and the local oscillator light carrying one-dimensional information, increasing the system dimensionality to five dimensions.

[0005] A Chinese patent with publication number CN119316065A discloses a five-dimensional coherent detection method and receiver. This invention, based on a dual-polarization 90-degree optical mixer, four pairs of balanced photodetectors, a single-ended photodetector, and a digital domain optical field reconstruction module, achieves complex optical field reconstruction of single-sideband or double-sideband modulated local oscillator light, eliminates beat frequency impairment between the local oscillator and the signal, and supports simultaneous coherent detection of polarization-multiplexed signal light and single-sideband or double-sideband modulated local oscillator light.

[0006] With the rapid development of emerging technologies such as artificial intelligence, cloud computing, and big data, the amount of data that data centers need to process is showing a continuous growth trend. The rapid development of these fields has significantly increased the demand for bandwidth and performance in data centers. However, the development of electrical bandwidth for high-speed photodetectors and analog-to-digital converters is reaching a bottleneck, and the signal rate that optical receivers can detect is severely limited. This situation does not match the demand.

[0007] To further expand the dimensions of the received signal, a six-dimensional coherent detection method and receiver structure based on IQ modulation local oscillator light are needed. Compared with the previous five-dimensional coherent detection scheme, it can further improve the electrical spectrum efficiency and channel rate, while avoiding interference between the local oscillator and the signal, and supporting a low-complexity parallel implementation of the receiver's digital signal processing flow. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a six-dimensional coherent detection method and receiver structure based on IQ modulated local oscillator light.

[0009] A six-dimensional coherent detection method based on IQ-modulated local oscillator light, provided by the present invention, includes the following steps:

[0010] Step S1: A first signal light is generated using a first laser, and a first polarization multiplexed signal light is generated using a dual-polarization transmitter and transmitted in a first optical fiber channel; a first local oscillator light is generated using a second laser, and a second and third local oscillator light are generated using a first beam splitter; the third local oscillator light is used to generate a first IQ modulated local oscillator light using a single-polarization transmitter, and together with the second local oscillator light, it is passed through a first polarization beam combiner to generate a second IQ modulated local oscillator light, which is then transmitted in a second optical fiber channel;

[0011] Step S2: The second IQ modulated local oscillator light is input to the polarization controller and polarization beam splitter through the second optical fiber channel to generate the fourth local oscillator light and the third IQ modulated local oscillator light. The fourth local oscillator light is input to the second beam splitter to split it into the fifth local oscillator light and the sixth local oscillator light.

[0012] Step S3: The fifth local oscillator light and the first polarization multiplexed signal light are input together into a dual-polarization 90-degree optical mixer. The dual-polarization 90-degree optical mixer outputs to the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector, respectively, to generate the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal. The third IQ modulated local oscillator light and the sixth local oscillator light are input into a single-polarization 90-degree optical mixer. The single-polarization 90-degree optical mixer outputs to the fifth balanced photodetector and the sixth balanced photodetector, respectively, to generate the fifth electrical signal and the sixth electrical signal.

[0013] Step S4: Input the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal into the first signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, multiple input multiple output channel equalization, downsampling, and symbol demapping.

[0014] Step S5: Input the fifth and sixth electrical signals into the second signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, single-input single-output channel equalization, downsampling and symbol demapping.

[0015] Preferably, in step S3, the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector convert the optical signal into an electrical signal and then directly enter the first signal demodulation module, without needing to reconstruct the optical field in the digital domain.

[0016] Preferably, in step S3, the fifth and sixth balanced photodetectors convert the optical signal into an electrical signal and then directly enter the second signal demodulation module, without needing to reconstruct the optical field in the digital domain.

[0017] Preferably, the first laser and the second laser are the same laser.

[0018] According to the present invention, a coherent receiver structure based on IQ-modulated local oscillator light is applied to the aforementioned six-dimensional coherent detection method based on IQ-modulated local oscillator light, comprising:

[0019] The polarization controller module receives the first IQ modulated local oscillator light input and is used to control the polarization direction of the signal.

[0020] A polarization beam splitter module, with its input end connected to the output end of the polarization controller module, is used to decompose the first IQ modulated local oscillator light into a first local oscillator light and a second IQ modulated local oscillator light.

[0021] The first beam splitter module has its input end connected to the output end of the polarization beam splitter module and receives the first local oscillator light input, and is used to split the first local oscillator light into a second local oscillator light and a third local oscillator light;

[0022] The dual-polarization 90-degree optical mixer module receives the first polarization multiplexed signal light input, and its input end is connected to the output end of the first beam splitter module. It also receives the second local oscillator light input to realize the coherent detection of the first polarization multiplexed signal light and the second local oscillator light. The output end is connected to four balanced photodetector modules respectively.

[0023] The single-polarization 90-degree optical mixer module has its input end connected to the output end of the polarization beam splitter module and the first beam splitter module, respectively, and receives the second IQ modulated local oscillator light and the third local oscillator light to realize coherent detection of the second IQ modulated local oscillator light and the third local oscillator light. Its output end is connected to two balanced photodetector modules.

[0024] The first signal demodulation module is used to recover the signal carried on the polarization multiplexed signal light;

[0025] The second signal demodulation module is used to recover the signal carried on the IQ modulated local oscillator.

[0026] Preferably, the dual-polarization 90-degree optical mixer module is used to mix the first polarization multiplexed signal light and the second local oscillator light to generate 8 optical signals. The output terminals are respectively connected to a first balanced photodetector module, a second balanced photodetector module, a third balanced photodetector module, and a fourth balanced photodetector module. The first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module, and the fourth balanced photodetector module are used to perform photoelectric conversion to generate a first electrical signal, a second electrical signal, a third electrical signal, and a fourth electrical signal, respectively.

[0027] Preferably, the input terminal of the first signal demodulation module is connected to the output terminals of the first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module, and the fourth balanced photodetector module, respectively.

[0028] Preferably, the single-polarization 90-degree optical mixer module is used to mix the second IQ modulated local oscillator light and the third local oscillator light to generate four optical signals. The output terminals are respectively connected to a fifth balanced photodetector module and a sixth balanced photodetector module. The fifth balanced photodetector module and the sixth balanced photodetector module are used to realize photoelectric conversion and generate a fifth electrical signal and a sixth electrical signal, respectively.

[0029] Preferably, the input terminal of the second signal demodulation module is connected to the output terminals of the fifth balanced photodetector module and the sixth balanced photodetector module, respectively.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention employs IQ-modulated local oscillator light to carry information. The local oscillator light signal can be separated by a polarization beam splitter and beats with the complex signal in a coherent manner with zero difference. This avoids cross-beat interference between the signal and the local oscillator, enabling coherent detection of a four-dimensional polarization multiplexed signal and a local oscillator light carrying two-dimensional information. This further expands the signal reception dimension, improves the system's capacity and spectral efficiency, and supports low-complexity parallel signal demodulation. Attached Figure Description

[0032] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0033] Figure 1 This is a schematic diagram illustrating the six-dimensional coherent detection method based on IQ modulation local oscillator light, which is the main feature of this invention.

[0034] Figure 2 This is a schematic diagram of the coherent receiver structure based on IQ modulation of local oscillator light, which is the main feature of this invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0036] Example 1

[0037] like Figure 1 As shown, a six-dimensional coherent detection method based on IQ-modulated local oscillator light provided by the present invention achieves simultaneous coherent detection of polarization-multiplexed signal light and amplitude-in-phase / quadrature component local oscillator light, including the following steps:

[0038] Step S1: A first signal light is generated using a first laser, and a first polarization multiplexed signal light is generated using a dual-polarization transmitter and transmitted in a first optical fiber channel; a first local oscillator light is generated using a second laser, and a second and third local oscillator light are generated using a first beam splitter; the third local oscillator light is generated using a single-polarization transmitter to generate a first IQ modulated local oscillator light, which is then combined with the second local oscillator light and passed through a first polarization beam combiner to generate a second IQ modulated local oscillator light, which is transmitted in a second optical fiber channel.

[0039] In step S2, the second IQ modulated local oscillator light is input to the polarization controller and polarization beam splitter through the second optical fiber channel to generate the fourth local oscillator light and the third IQ modulated local oscillator light. The fourth local oscillator light is then input to the second beam splitter to split it into the fifth local oscillator light and the sixth local oscillator light.

[0040] Step S3: The fifth local oscillator light and the first polarization multiplexed signal light are input together into a dual-polarization 90-degree optical mixer. The dual-polarization 90-degree optical mixer outputs to the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector, respectively, generating the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal. The third IQ modulated local oscillator light and the sixth local oscillator light are input into a single-polarization 90-degree optical mixer. The single-polarization 90-degree optical mixer outputs to the fifth balanced photodetector and the sixth balanced photodetector, respectively, generating the fifth electrical signal and the sixth electrical signal.

[0041] Step S4: Input the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal into the first signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, multiple input multiple output channel equalization, downsampling, and symbol demapping.

[0042] Step S5: Input the fifth and sixth electrical signals into the second signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, single-input single-output channel equalization, downsampling and symbol demapping.

[0043] In step S1, the first laser and the second laser can be the same laser.

[0044] In step S3, the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector after the dual polarization 90-degree optical mixer convert the optical signal into an electrical signal and then directly enter the first signal demodulation module without needing to go through digital domain optical field reconstruction.

[0045] In step S3, the fifth and sixth balanced photodetectors after the single-polarization 90-degree optical mixer convert the optical signal into an electrical signal and then directly enter the second signal demodulation module without needing to go through digital domain optical field reconstruction.

[0046] In step S1: A first laser is used to generate a first signal light, and a first polarization multiplexed signal light is generated through a dual-polarization transmitter. x S y ] T S x It is a complex signal in the X-polarization direction, S yIt is a complex signal in the Y-polarization direction, transmitted to the receiving end through the first optical fiber channel; a second laser is used to generate the first local oscillator light, which is then split by the first beam splitter to generate the second and third local oscillator lights. The third local oscillator light is then passed through a single-polarization transmitter to generate the first IQ modulated local oscillator light, which, together with the second local oscillator light, is passed through the first polarization beam combiner to generate the second IQ modulated local oscillator light [C, S]. C ] T Where C is the optical carrier component in the X direction, and S... C The optical signal, which is IQ modulated in the Y polarization direction, is transmitted to the receiving end through the second optical fiber channel.

[0047] In step S2: the first polarization multiplexed signal light transmitted through the first optical fiber channel is input into a dual polarization 90-degree optical mixer; the second IQ modulated local oscillator light transmitted through the second optical fiber channel is input into a polarization controller and a polarization beam splitter to generate a fourth local oscillator light and a third IQ modulated local oscillator light; the fourth local oscillator light is input into a second beam splitter to split into a fifth local oscillator light and a sixth local oscillator light.

[0048] Step 3: Input the first polarization multiplexed signal light and the fifth local oscillator light from the first optical fiber channel into a dual-polarization 90-degree optical mixer, and input the output into the first, second, third, and fourth balanced photodetectors to generate the first electrical signal I1, the second electrical signal I2, the third electrical signal I3, and the fourth electrical signal I4; the output of the dual-polarization 90-degree optical mixer, the first, second, third, and fourth electrical signals, satisfy the following:

[0049] I1=Re(R x ·C * )

[0050] I2=Im(R x ·C * )

[0051] I3=Re(R y ·C * )

[0052] I4=Im(R y ·C * )

[0053] Among them, R x R y It is a signal modulated by dual-polarized in-phase / quadrature components after being transmitted through optical fiber and having its polarization rotated.

[0054] Subsequently, the first, second, third, and fourth electrical signals are input into the first signal demodulation module to complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, multiple-input multiple-output channel equalization, downsampling, and symbol demapping.

[0055] Step 4: Input the third IQ modulated local oscillator light and the sixth local oscillator light into a single-polarization 90-degree optical mixer, and input the output into the fifth and sixth balanced photodetectors to generate the fifth electrical signal I5 and the sixth electrical signal I6; the fifth and sixth electrical signals output by the single-polarization 90-degree optical mixer satisfy:

[0056] I5=Re(R C ·C * )

[0057] I6=Im(R C ·C * )

[0058] Among them, R C It is a signal modulated by a single-polarization in-phase / quadrature component after being transmitted through optical fiber and having its polarization rotated.

[0059] Subsequently, the fifth and sixth electrical signals are input into the second signal demodulation module to complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, single-input single-output channel equalization, downsampling, and symbol demapping.

[0060] This application is potentially applicable to three scenarios: (1) Multi-channel multiplexing scenario for optical interconnection between data centers, where signal light and local oscillator light carry four-dimensional and two-dimensional information respectively, and the two channels are received and detected simultaneously; (2) Uplink and downlink multiplexing scenario for passive optical networks, where four-dimensional signal light and two-dimensional signal light beat each other, and simultaneous reception is achieved without the need for laser optical network structure; (3) Optical interconnection scenario within data centers, supporting distributed interconnection driven by a single light source.

[0061] This application utilizes a dual-polarization 90-degree optical mixer, a single-polarization 90-degree optical mixer, six pairs of balanced photodetectors, a polarization controller, a polarization beamsplitter, and two signal demodulation modules to achieve complex optical field reconstruction of IQ-modulated local oscillator light, avoiding carrier-signal beat frequency loss. It supports simultaneous parallel coherent detection of polarization-multiplexed signal light and IQ-modulated local oscillator light. Compared to standard coherent receivers, this application only requires an additional single-polarization 90-degree optical mixer and a polarization beamsplitter to transmit additional IQ modulation information using local oscillator light, extending the received signal dimension to six dimensions. Compared to standard coherent detection, it can improve channel rate and spectral efficiency by 50%, providing a scalable and integrable solution for ultra-high-speed data center optical interconnects.

[0062] Example 2

[0063] like Figure 2 As shown, a coherent receiver structure based on IQ-modulated local oscillator light provided by the present invention, applied to the six-dimensional coherent detection method based on IQ-modulated local oscillator light in Embodiment 1, includes:

[0064] The polarization controller module receives the first IQ modulated local oscillator light input and is used to control the polarization direction of the signal.

[0065] The polarization beam splitter module has its input end connected to the output end of the polarization controller module, and is used to decompose the first IQ modulated local oscillator light into the first local oscillator light and the second IQ modulated local oscillator light.

[0066] The first beam splitter module has its input end connected to the output end of the polarization beam splitter module and receives the first local oscillator light input, which is used to split the first local oscillator light into the second local oscillator light and the third local oscillator light.

[0067] The dual-polarization 90-degree optical mixer module receives the first polarization multiplexed signal light input, and its input end is connected to the output end of the first beam splitter module. It also receives the second local oscillator light input to realize the coherent detection of the first polarization multiplexed signal light and the second local oscillator light. The output end is connected to four balanced photodetector modules respectively.

[0068] The single-polarization 90-degree optical mixer module has its input end connected to the output end of the polarization beam splitter module and the first beam splitter module, respectively, and receives the second IQ modulated local oscillator light and the third local oscillator light to realize coherent detection of the second IQ modulated local oscillator light and the third local oscillator light. Its output end is connected to two balanced photodetector modules.

[0069] The first signal demodulation module is used to recover the signal carried on the polarization multiplexed signal light;

[0070] The second signal demodulation module is used to recover the signal carried on the IQ modulated local oscillator.

[0071] The dual-polarization 90-degree optical mixer module is used to mix the first polarization multiplexed signal light and the second local oscillator light to generate 8 optical signals. The output terminals are respectively connected to the first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module and the fourth balanced photodetector module. The first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module and the fourth balanced photodetector module are used to realize photoelectric conversion and generate the first electrical signal, the second electrical signal, the third electrical signal and the fourth electrical signal, respectively.

[0072] The input terminals of the first signal demodulation module are connected to the output terminals of the first, second, third, and fourth balanced photodetector modules, respectively. The first, second, third, and fourth balanced photodetector modules, following the dual-polarization 90-degree optical mixer module, convert the optical signal into an electrical signal, which then directly enters the first signal demodulation module without requiring digital domain optical field reconstruction.

[0073] The single-polarization 90-degree optical mixer module is used to mix the second IQ modulated local oscillator light and the third local oscillator light to generate four optical signals. The output terminals are respectively connected to the fifth balanced photodetector module and the sixth balanced photodetector module. The fifth balanced photodetector module and the sixth balanced photodetector module are used to realize photoelectric conversion and generate the fifth electrical signal and the sixth electrical signal, respectively.

[0074] The input terminals of the second signal demodulation module are connected to the output terminals of the fifth and sixth balanced photodetector modules, respectively. The fifth and sixth balanced photodetector modules, following the single-polarization 90-degree optical mixer module, convert the optical signal into an electrical signal, which then directly enters the second signal demodulation module without requiring digital domain optical field reconstruction.

[0075] This application employs IQ-modulated local oscillator light to carry information. The local oscillator light signal can be separated by a polarization beamsplitter and beats with the complex signal in a self-zero difference coherent manner. This avoids cross-beat interference between the signal and the local oscillator, achieving coherent detection of the four-dimensional polarization multiplexed signal and the local oscillator light carrying two-dimensional information, further expanding the signal reception dimension. Compared with standard coherent receivers, the coherent detection method and receiver structure proposed in this application can improve the spectral efficiency by 50% while avoiding cross-beat interference. Compared with five-dimensional coherent receivers, the six-dimensional coherent reception method proposed in this application can achieve higher-dimensional expansion with only a single-polarization 90-degree optical mixer, and the system capacity and spectral efficiency are improved to a certain extent, while supporting low-complexity parallel signal demodulation.

[0076] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0077] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A six-dimensional coherent detection method based on IQ-modulated local oscillator light, characterized in that, Includes the following steps: Step S1: A first signal light is generated using a first laser, and a first polarization multiplexed signal light is generated using a dual-polarization transmitter and transmitted in a first optical fiber channel; a first local oscillator light is generated using a second laser, and a second and third local oscillator light are generated using a first beam splitter; the third local oscillator light is used to generate a first IQ modulated local oscillator light using a single-polarization transmitter, and together with the second local oscillator light, it is passed through a first polarization beam combiner to generate a second IQ modulated local oscillator light, which is then transmitted in a second optical fiber channel; Step S2: The second IQ modulated local oscillator light is input to the polarization controller and polarization beam splitter through the second optical fiber channel to generate the fourth local oscillator light and the third IQ modulated local oscillator light. The fourth local oscillator light is input to the second beam splitter to split it into the fifth local oscillator light and the sixth local oscillator light. Step S3: The fifth local oscillator light and the first polarization multiplexed signal light are input together into a dual-polarization 90-degree optical mixer. The dual-polarization 90-degree optical mixer outputs to the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector, respectively, to generate the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal. The third IQ modulated local oscillator light and the sixth local oscillator light are input into a single-polarization 90-degree optical mixer. The single-polarization 90-degree optical mixer outputs to the fifth balanced photodetector and the sixth balanced photodetector, respectively, to generate the fifth electrical signal and the sixth electrical signal. Step S4: Input the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal into the first signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, multiple input multiple output channel equalization, downsampling, and symbol demapping. Step S5: Input the fifth and sixth electrical signals into the second signal demodulation module for demodulation, and complete resampling, frequency offset estimation, carrier phase recovery, frame synchronization, single-input single-output channel equalization, downsampling and symbol demapping.

2. The six-dimensional coherent detection method based on IQ modulated local oscillator light as described in claim 1, characterized in that, In step S3, the first balanced photodetector, the second balanced photodetector, the third balanced photodetector, and the fourth balanced photodetector convert the optical signal into an electrical signal and then directly enter the first signal demodulation module without needing to reconstruct the optical field in the digital domain.

3. The six-dimensional coherent detection method based on IQ modulated local oscillator light as described in claim 1, characterized in that, In step S3, the fifth and sixth balanced photodetectors convert the optical signal into an electrical signal and then directly enter the second signal demodulation module without needing to reconstruct the optical field in the digital domain.

4. The six-dimensional coherent detection method based on IQ modulated local oscillator light as described in claim 1, characterized in that, The first laser and the second laser are the same laser.

5. A coherent receiver structure based on IQ-modulated local oscillator light, applied to the six-dimensional coherent detection method based on IQ-modulated local oscillator light as described in any one of claims 1-4, characterized in that, include: The polarization controller module receives the first IQ modulated local oscillator light input and is used to control the polarization direction of the signal. A polarization beam splitter module, with its input end connected to the output end of the polarization controller module, is used to decompose the first IQ modulated local oscillator light into a first local oscillator light and a second IQ modulated local oscillator light. The first beam splitter module has its input end connected to the output end of the polarization beam splitter module and receives the first local oscillator light input, and is used to split the first local oscillator light into a second local oscillator light and a third local oscillator light; The dual-polarization 90-degree optical mixer module receives the first polarization multiplexed signal light input, and its input end is connected to the output end of the first beam splitter module. It also receives the second local oscillator light input to realize the coherent detection of the first polarization multiplexed signal light and the second local oscillator light. The output end is connected to four balanced photodetector modules respectively. The single-polarization 90-degree optical mixer module has its input end connected to the output end of the polarization beam splitter module and the first beam splitter module, respectively, and receives the second IQ modulated local oscillator light and the third local oscillator light to realize coherent detection of the second IQ modulated local oscillator light and the third local oscillator light. Its output end is connected to two balanced photodetector modules. The first signal demodulation module is used to recover the signal carried on the polarization multiplexed signal light; The second signal demodulation module is used to recover the signal carried on the IQ modulated local oscillator.

6. The coherent receiver structure based on IQ modulated local oscillator light as described in claim 5, characterized in that, The dual-polarization 90-degree optical mixer module is used to mix the first polarization multiplexed signal light and the second local oscillator light to generate 8 optical signals. The output terminals are respectively connected to the first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module and the fourth balanced photodetector module. The first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module and the fourth balanced photodetector module are used to realize photoelectric conversion and generate the first electrical signal, the second electrical signal, the third electrical signal and the fourth electrical signal respectively.

7. The coherent receiver structure based on IQ modulated local oscillator light as described in claim 6, characterized in that, The input terminal of the first signal demodulation module is connected to the output terminals of the first balanced photodetector module, the second balanced photodetector module, the third balanced photodetector module, and the fourth balanced photodetector module, respectively.

8. The coherent receiver structure based on IQ modulated local oscillator light as described in claim 5, characterized in that, The single-polarization 90-degree optical mixer module is used to mix the second IQ modulated local oscillator light and the third local oscillator light to generate four optical signals. The output terminals are respectively connected to the fifth balanced photodetector module and the sixth balanced photodetector module. The fifth balanced photodetector module and the sixth balanced photodetector module are used to realize photoelectric conversion and generate the fifth electrical signal and the sixth electrical signal, respectively.

9. The coherent receiver structure based on IQ modulated local oscillator light as described in claim 8, characterized in that, The input terminal of the second signal demodulation module is connected to the output terminals of the fifth balanced photodetector module and the sixth balanced photodetector module, respectively.

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