Multi-dimensional demultiplexing and mixing system based on MPLC and optimization design method thereof

Abstract

The invention relates to the technical field of multi-plane light conversion, in particular to a multi-dimensional demultiplexing and frequency mixing system based on an MPLC and an optimization design method of the multi-dimensional demultiplexing and frequency mixing system. The system comprises an input module used for inputting multimode signal light and local oscillation light; the MPLC module is used for realizing unitary transformation of light in any space, comprises N cascaded phase transformation areas and is integrated on the reflecting mirror or the transmitting mirror; the phase transformation regions are phase plates or metasurfaces, and at least one phase transformation region is a metasurface; and the output module is used for receiving the single-mode Gaussian light spots after demultiplexing and frequency mixing. According to the invention, different phases of different wavelengths and different polarization states are regulated and controlled through the metasurface; parallel demultiplexing of wavelengths, polarization and modes in multimode signals can be realized.

Description

Technical Field

[0001] The present application relates to the field of multi-plane optical conversion technology, and more specifically, to a multi-dimensional demultiplexing and mixing system based on MPLC and an optimization design method thereof. Background Art

[0002] Multi-plane light conversion (MPLC) technology: MPLC is a technique that can perform arbitrary spatial unitary transformations. Specifically, it enables spatial multiplexing, which involves converting N separate input Gaussian beams into N orthogonally superposed transmission modes. In theory, MPLC can perform spatial unitary transformations using a series of phase profiles separated by optical Fourier transforms. As an emerging and highly efficient mode multiplexer / demultiplexer, MPLC has attracted considerable attention from researchers both domestically and internationally due to its superior performance.

[0003] The core function of a multi-plane multiplexing and demultiplexing device is to multiplex (combine) and demultiplex (separate) multiple independent optical signal modes. During the multiplexing process, multiple optical signals are integrated into a single optical fiber for transmission; during the demultiplexing process, these signals are separated back into their original independent modes. This technology fully utilizes the multiple transmission modes in few-mode optical fibers, significantly improving the transmission capacity of a single optical fiber. The operating principle of a multi-plane multiplexing and demultiplexing device is based on multi-plane optical conversion technology. Its core lies in the distribution of input optical signals into different spatial modes through special optical design, thereby achieving signal multiplexing. Existing commercial multi-plane demultiplexers can achieve demultiplexing of multiple modes, but because they use polarization-independent and wavelength-insensitive phase plates to achieve this, they cannot demultiplex wavelength polarization. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiency of the existing multi-plane multiplexing and demultiplexing devices that cannot demultiplex wavelength and polarization, and to provide a multi-dimensional demultiplexing and mixing system based on MPLC and its optimized design method, which can realize parallel demultiplexing of wavelength, polarization and mode in multimode signals.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: Provided is a multi-dimensional demultiplexing and mixing system based on MPLC, comprising: Input module: used to input multimode signal light and local oscillator light; MPLC module: used to achieve unitary transformation of light in any space, including N cascaded phase shift regions integrated on a reflector or a transmissive mirror; the phase shift regions are phase plates or metasurfaces, and at least one phase shift region is a metasurface; Output module: used to receive the single-mode Gaussian light spot after demultiplexing and mixing.

[0006] The present invention discloses a multidimensional demultiplexing and mixing system based on MPLC. In the MPLC module, cascaded phase shift regions are designed. Each phase shift region corresponds to a phase plate or a metasurface. Since at least one phase shift region is a metasurface, different phase controls are achieved for different wavelengths and polarization states through the metasurface. Therefore, the system of the present invention can achieve parallel demultiplexing of wavelengths, polarizations, and modes in multimode signals.

[0007] Furthermore, the phase plate achieves wavelength-insensitive, polarization-independent mode conversion by etching with different depths, such as converting high-order modes into single-mode Gaussian light. The metasurface includes several periodic micro-nanostructures, which can be nanopillars. The micro-nanostructures have a column height of 0.2λ1 to 1.2λ2, where λ1 represents the shortest wavelength in the operating band and λ2 represents the longest wavelength in the operating band, and can support C / L band wavelength demultiplexing. This corresponds to a wavelength-sensitive unit. The micro-nanostructure includes a major axis and a minor axis, which can independently control the X / Y polarization phase, corresponding to a polarization-sensitive unit.

[0008] Furthermore, after the multimode signal light is modulated by the MPLC module, four spatially separated single-mode Gaussian spots are output, with phase differences of 0, π, π / 2, and 3π / 2, corresponding to the I / Q orthogonal components; after the local oscillator light is modulated by the MPLC module, a single-mode Gaussian spot with a phase of 0 and the same position as the multimode signal light is output, realizing homodyne detection; the multimode signal light and the local oscillator light are spatially matched on the output surface and directly coupled to the output module to complete coherent mixing.

[0009] Furthermore, the arrangement of the metasurface and the phase plate includes alternating arrangement, segmented arrangement, disordered arrangement or full metasurface arrangement.

[0010] Furthermore, the MPLC module includes a first reflector, a second reflector, and the phase shift region, wherein the first reflector and the second reflector are arranged parallel to each other, and the phase shift region is integrated into the first reflector and / or the second reflector. Alternatively, the MPLC module includes a first reflector, a transmission mirror, a second reflector, and the phase shift region, wherein the first reflector, the transmission mirror, and the second reflector are arranged parallel to each other, the transmission mirror is located between the first reflector and the second reflector, and the phase shift region is integrated into the transmission mirror.

[0011] Furthermore, the input module includes a single-fiber collimator or a dual-fiber collimator; the output module includes a fiber array or a photodetector array, wherein each fiber end face of the fiber array is integrated with a microlens. The input module supports coaxial input or spatially separated input. Coaxial input uses a single-fiber collimator, while spatially separated input can use a dual-fiber collimator.

[0012] The application also provides an optimization design method of a multi-dimensional demultiplexing and mixing system based on MPLC, comprising the following steps: S1. Establishing a meta-atom library: a meta-atom library of phase response of each unit of the metasurface is established by simulation software, the phase modulation amount of the long axis, the short axis and the height of the nanocolumn to the target waveband X / Y polarization is scanned, and the meta-atom library is obtained; the phase / amplitude response of different length-width ratio nanocolumns to C / L waveband X / Y polarization is simulated; S2. Iterative optimization of N phase transformation regions: S21. Initialization of a random phase matrix; S22. Calculation of a target phase by forward and reverse light field propagation; matching with the meta-atom library, and updating the micro-nano structure of the metasurface; S23. Repeating step S22 until a preset convergence condition is reached.

[0013] The optimization design method of the multi-dimensional demultiplexing and mixing system based on MPLC firstly establishes a meta-atom library of phase response of each unit of the metasurface by simulation software, scans the phase modulation amount of the long axis, the short axis and the height of the nanocolumn to the target waveband X / Y polarization, and obtains the meta-atom library; then iterative optimization of N cascaded phase transformation regions is started, for each phase transformation region, the target phase is calculated by forward and reverse light field propagation, then the most suitable micro-nano structure is found by matching with the meta-atom library, and the metasurface is optimized and updated; such iteration is continued until all phase transformation regions are updated and optimized, and a preset convergence condition is reached. Through the optimization design method, wavelength / polarization / mode three-dimensional parallel demultiplexing and mixing design can be realized, the combination strategy of the metasurface and the phase sheet can be dynamically adjusted according to actual needs, and the metasurface and the phase sheet can be optimized cooperatively.

[0014] Further, the step S21 comprises: inputting the meta-atom library, and setting related parameters, including: demultiplexing wavelengths λ1~λN, mode numbers mode1~modeM, phase transformation region numbers N1~NK, phase sheet numbers and corresponding phase transformation regions, metasurface numbers and corresponding phase transformation regions, the distance S between phase transformation regions, the distance S between the input surface and the first phase transformation region I , the distance S between the output surface and the last phase transformation region O , and the maximum iteration number i MAX or preset parameters of the output light field.

[0015] Further, the step S22 comprises: S221. After initialization, iteration is started from the first phase transformation region with the iteration number being 1; S222. Determine whether the phase transformation region is a metasurface; if yes, go to step S223; if no, go to step S224; S223. Calculate the phase matrix corresponding to the current phase transformation region under different wavelengths and polarization states by forward propagating the input light field and backward propagating the target light field to the phase transformation region, obtain multiple phase matrices of different wavelengths and polarization states under the current phase transformation region, and match each dimension of the obtained phase matrix with the meta-atom library to obtain the meta-atom distribution of the current phase transformation region. S224. Calculate the phase matrix corresponding to the current phase transformation region by forward propagating all input light fields and backward propagating the target light field to the current phase transformation region.

[0016] Further, the step S23 comprises: S231. Determine whether it is the last phase transformation region; if no, iterate the next phase transformation region, and repeat steps S222-S224. S232. If yes, determine whether the iteration number reaches the maximum iteration number i MAX or whether the parameter value of the output light field reaches the preset parameter value; if not, increase the iteration number by 1, start iteration from the first phase transformation region, repeat steps S222-S224, until the requirements are met, then stop iteration, and the obtained phase transformation region is the final optimized phase transformation region.

[0017] Compared with the prior art, the present application has the following advantages: 1. The multi-dimensional demultiplexing and mixing system based on MPLC can realize wavelength, polarization and mode demultiplexing and mixing in parallel. By integrating the functions of traditional separate mode demultiplexer, wavelength division multiplexer (WDM) and polarization beam splitter (PBS), and 90° optical hybrid into a single device, the insertion loss, alignment error and mode crosstalk problems caused by multi-device cascade are eliminated. The number of devices can be reduced, the packaging, calibration and maintenance costs can be significantly reduced. The integrated design reduces the interfaces and coupling nodes in the optical path, reduces the influence of environmental disturbances (such as temperature and vibration) on system stability, and improves reliability.

[0018] 2. The optimization design method of the multi-dimensional demultiplexing and mixing system based on MPLC realizes three-dimensional parallel demultiplexing and mixing design of wavelength / polarization / mode. The combination strategy of metasurface and phase sheet can be dynamically adjusted according to actual needs to realize collaborative optimization of metasurface and phase sheet. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG1 is a schematic structural diagram of a multi-dimensional demultiplexing and mixing system based on MPLC in one embodiment; Figure 2 A schematic diagram of a spatially separated input method for multimode signal light and local oscillator light in one embodiment; Figure 3 A schematic diagram of a coaxial input method for multimode signal light and local oscillator light in one embodiment; Figure 4 Schematic diagram of multi-mode signal light and local oscillator light input and output in one embodiment; Figure 5 A schematic diagram of the distribution of phase shift regions in one embodiment; Figure 6 A schematic diagram of the arrangement of the metasurface and the phase plate in one embodiment; Figure 7 A schematic flow chart of an optimized design method for a multi-dimensional demultiplexing and mixing system based on MPLC in one embodiment; Figure 8 is a schematic diagram of updating the phase of a phase plate in one embodiment; Figure 9 Updated schematic of a metasurface for one embodiment.

[0020] In the accompanying drawings: 1. Fiber array; 2. Microlens; 3. Phase shift region; 4. First reflector; 5. Second reflector; 6. Collimator; 7. Few-mode fiber; 8. Single-mode fiber. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced in size, and do not represent the actual dimensions of the products. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0022] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "up", "down", "left", "right", etc. indicate directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0023] Example 1 This embodiment is a first embodiment of a multi-dimensional demultiplexing and mixing system based on MPLC, including: Input module: used to input multimode signal light and local oscillator light; MPLC module: used to achieve unitary transformation of light in any space, including N cascaded phase transformation regions 3, integrated on a reflector or a transmissive mirror; the phase transformation regions 3 are phase plates or metasurfaces, and at least one phase transformation region 3 is a metasurface; Output module: used to receive the single-mode Gaussian light spot after demultiplexing and mixing.

[0024] In this embodiment, a phase plate achieves wavelength-insensitive, polarization-independent mode conversion through differential etching depth, for example, converting high-order modes into single-mode Gaussian light. The metasurface comprises several periodic micro-nanostructures, which can be nanopillars with a column height of 0.2λ1 to 1.2λ2, where λ1 = 1530 nm and λ2 = 1625 nm, enabling C / L band wavelength demultiplexing. These correspond to wavelength-sensitive units. The micro-nanostructures include a major axis and a minor axis, enabling independent control of the phase of the X / Y polarization states, corresponding to polarization-sensitive units. The operating wavelength (demultiplexing wavelength) in this embodiment is λ1 = 1530 nm and λ2 = 1625 nm. The metasurface comprises several periodic micro-nanostructures, called meta-atoms, which can be nanopillars with a major axis and a minor axis. These meta-atoms are used to achieve different phase control of the X / Y polarization states. Optical simulations reveal the phase control of the meta-atoms for different operating wavelengths and polarization states, and a meta-atom library is established for metasurface design.

[0025] In this embodiment, after the multimode signal light is modulated by the MPLC module, it outputs four spatially separated single-mode Gaussian light spots with phase differences of 0, π, π / 2, and 3π / 2, corresponding to the I / Q orthogonal components. After the local oscillator light is modulated by the MPLC module, it outputs a single-mode Gaussian light spot with a phase of 0 at the same position as the multimode signal light, realizing homodyne detection. The multimode signal light and the local oscillator light are spatially matched on the output surface and directly coupled to the output module to complete coherent mixing.

[0026] In this embodiment, for N cascaded phase shift regions 3, each phase shift region 3 can be a metasurface or a phase plate; when some phase shift regions 3 are phase plates and other phase shift regions 3 are metasurfaces, the arrangement of the metasurface and the phase plate includes alternating arrangement, segmented arrangement, and disordered arrangement; Figure 6 As shown in (A) (B) (C) in FIG, in this embodiment, all phase transformation regions 3 can also be set as metasurfaces, that is, full metasurface arrangement, such as Figure 6 As shown in (D) in the figure.

[0027] In this embodiment, if Figure 1 As shown, the MPLC module includes a first reflector 4, a second reflector 5, and a phase shift region 3. The first reflector 4 and the second reflector 5 are arranged parallel to each other, and the phase shift region 3 is integrated on the first reflector 4 and / or the second reflector 5. Alternatively, the MPLC module includes a first reflector 4, a transmission mirror, a second reflector 5, and a phase shift region 3. The first reflector 4, the transmission mirror, and the second reflector 5 are arranged parallel to each other, and the transmission mirror is located between the first reflector 4 and the second reflector 5, and the phase shift region 3 is integrated on the transmission mirror.

[0028] In this embodiment, the input module includes a collimator 6, which can be a single fiber collimator or a dual fiber collimator; the output module includes a fiber array 1 or a photodetector array, wherein each fiber end face of the fiber array 1 is integrated with a microlens 2. The input module supports coaxial input or spatially separated input. The coaxial input uses a single fiber collimator, such as Figure 3 As shown, the spatially separated inputs can be passed through a dual fiber collimator, such as Figure 2 shown.

[0029] The present invention provides a multi-dimensional demultiplexing and mixing system based on MPLC. In the MPLC module, cascaded phase shift regions 3 are designed. Each phase shift region 3 corresponds to a phase plate or a metasurface. Since at least one phase shift region 3 is a metasurface, the system of the present invention can achieve parallel demultiplexing of wavelength, polarization, and mode in multimode signals.

[0030] Example 2 This embodiment is a second embodiment of a multi-dimensional demultiplexing and mixing system based on MPLC. This embodiment is similar to the first embodiment. Figure 1 As shown, the input module includes a dual-fiber collimator, one of which inputs multimode signal light (including high-order modes such as LP01 and LP11, with a wavelength range of 1530-1625nm and X / Y polarization mixing), and the other inputs local oscillator light (single-mode Gaussian beam, with a wavelength matching the signal light and X / Y polarization mixing). The input light field diagram of the dual-fiber collimator is shown in Figure 2 shown.

[0031] The MPLC module includes a first reflector 4, a second reflector 5, and several phase shift regions 3. The first reflector 4 and the second reflector 5 are arranged in parallel. The phase shift regions 3 are arranged on the first reflector 4. The phase shift regions 3 are all metasurfaces. The metasurface is composed of a periodic array of rectangular silicon nanorods, which can achieve different phase control for different wavelengths and different polarization states.

[0032] The output module includes an n*m optical fiber array 1, each optical fiber end face is integrated with a micro lens 2, and the single-mode Gaussian spot is aligned with the output surface of the MPLC module, such as Figure 4As shown, for a certain wavelength, polarization, and mode, the signal light outputs four light spots with phase differences of 0, π, π / 2, and 3π / 2, corresponding to the I / Q two-way orthogonal components; the local oscillator light outputs a light spot with the same position and phase of 0 as the signal light to achieve frequency mixing.

[0033] like Figure 1 As shown, the input light is first emitted by the collimator 6. The emission direction of the collimator 6 is in a preset angular relationship with the extension direction of the first reflector 4. The preset angular relationship is a non-right-angle relationship. After passing through the collimator 6, the light will hit the first phase shift region 3 of the first reflector 4. The light will then be reflected by the first reflector 4 to the second reflector 5, and then reflected back to the first reflector 4 by the second reflector 5. At this time, the light will reach the second phase shift region 3 of the first reflector 4. The light will propagate back and forth between the first reflector 4 and the second reflector 5, from one phase shift region 3 to the next phase shift region 3. It can be seen that the angular relationship between the collimator 6 and the first reflector 4 depends on the setting distance between the two adjacent phase shift regions 3 and the spacing between the two reflectors. It only needs to ensure that the light can propagate from one phase shift region 3 to a new phase shift region 3.

[0034] The working principle of this embodiment is as follows: Input light is emitted by collimator 6, one path of which is multimode signal light, and the other is local oscillator light. The input light is irradiated by the MPLC module and switched back and forth between the first reflector 4 and the second reflector 5. Because the first reflector 4 is integrated with N metasurfaces, which are periodically arrayed with rectangular silicon nanopillars, phase control is achieved for different wavelengths and polarization states. The light modulated by the MPLC module is then injected into the output module, which is aligned with the single-mode Gaussian spot on the MPLC output surface. For a multimode signal light of a specific wavelength, polarization, and mode, the output module outputs four light spots with phase differences of 0, π, π / 2, and 3π / 2, corresponding to the two orthogonal I / Q components. The local oscillator light outputs a light spot with a phase of 0, co-located with the multimode signal light, thus achieving frequency mixing.

[0035] Through the MPLC module, the signal light and local oscillator light input by the dual fiber collimator are Figure 2 As shown, the signal light is a coaxial multiple mode, and the local oscillator light is Gaussian light (fundamental mode) converted into Figure 4 As shown, Figure 4 Only two modes and two operating wavelengths of the multimode signal light are shown. Actual devices can handle more modes and wavelengths. After passing through the MPLC module, a certain mode at a certain wavelength and polarization state in the signal light is converted into four Gaussian light spots on the output plane with phase differences of 0, π, π / 2, and 3π / 2. The local oscillator light of the corresponding wavelength and polarization is converted into a Gaussian light spot with a phase of 0 at the same position.

[0036] Example 3 This embodiment is an embodiment of an optimization design method for a multi-dimensional demultiplexing and mixing system based on MPLC. This embodiment is used to optimize the system provided in the first or second embodiment. In this embodiment, Figure 7 As shown, the following steps are included: Step S1. Establish a meta-atom library: Use simulation software to establish a meta-atom library of metasurface unit phase responses. Scan the phase modulation of the nanopillar's major axis, minor axis, and height to the target band X / Y polarization to obtain the meta-atom library. In this step, simulate the phase and amplitude responses of nanopillars with different aspect ratios to the C / L band X / Y polarization.

[0037] Step S2. Iteratively optimize N phase transformation regions 3: S21. Initialize the random phase matrix; input the meta-atom library and set relevant parameters, including: demultiplexing wavelengths λ1-λN, mode number mode1-modeM, phase shift regions 3N1-NK, number of phase plates and corresponding phase shift regions 3, number of metasurfaces and corresponding phase shift regions 3, spacing S between phase shift regions 3, and distance S from the input surface to the first phase shift region 3. I , the distance S between the output surface and the last phase change region 3 O , the maximum number of iterations i MAX Or output light field preset parameters.

[0038] S22. Calculate the target phase through forward and reverse light field propagation; match it with the meta-atom library and update the metasurface's micro-nanostructure. This includes: S221. After initialization is completed, the iteration starts from the number of iterations 1 and the first phase change region 3; S222 determines whether the phase shift region 3 is a metasurface; if so, proceeds to step S223; if not, proceeds to step S224; S223. Calculate the phase matrices corresponding to the current phase shift region 3 at different wavelengths and polarization states based on the forward propagation of the input light field and the reverse propagation of the target light field into phase shift region 3 at different wavelengths and polarization states. Calculate multiple phase matrices for different wavelengths and polarization states in the current phase shift region 3. Match the obtained phase matrices for each dimension with the meta-atom library to obtain the meta-atom distribution in the current phase shift region 3, corresponding to the metasurface phase distribution. S224. Calculate the phase matrix corresponding to the current phase transformation region 3 and the phase distribution of the corresponding phase plate based on the results of all input light fields forward propagating and the target light fields back propagating to the current phase transformation region 3.

[0039] S23. Repeat step S22 until the preset convergence condition is reached. Specifically including: S231 determines whether it is the last phase change region 3, if not, the next phase change region 3 iteration, repeating steps S222 ~ S224; S232. If yes, determine whether the number of iterations reaches the maximum number of iterations i MAX Or whether the parameter value of the output light field reaches the preset parameter value; if not, the number of iterations is increased by 1, and the iteration starts from the first phase transformation region 3, and steps S222 to S224 are repeated until the requirements are met, then the iteration is stopped, and the obtained phase transformation region 3 is the final optimized phase transformation region 3.

[0040] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0041] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A multi-dimensional demultiplexing and mixing system based on MPLC, characterized in that: include: Input module: used to input multimode signal light and local oscillator light; MPLC module: used to achieve unitary transformation of light in any space, including N cascaded phase shift regions integrated on a reflector or a transmissive mirror; the phase shift regions are phase plates or metasurfaces, and at least one phase shift region is a metasurface; Output module: used to receive the single-mode Gaussian light spot after demultiplexing and mixing.

2. The MPLC-based multi-dimensional demultiplexing and mixing system according to claim 1, wherein: The phase plate achieves wavelength-insensitive and polarization-independent mode conversion by etching depth differences; the metasurface includes several periodic micro-nanostructures, wherein the column height of the micro-nanostructure is 0.2λ1~1.2λ2, λ1 represents the shortest wavelength of the working band, and λ2 represents the longest wavelength of the working band, which can support C / L band wavelength demultiplexing; the micro-nanostructure includes a long axis and a short axis, which can independently control the X / Y polarization state phase.

3. The MPLC-based multi-dimensional demultiplexing and mixing system according to claim 2, wherein: After the multimode signal light is modulated by the MPLC module, four spatially separated single-mode Gaussian spots are output with phase differences of 0, π, π / 2, and 3π / 2; after the local oscillator light is modulated by the MPLC module, a single-mode Gaussian spot with a phase of 0 and the same position as the multimode signal light is output; the multimode signal light and the local oscillator light are spatially matched on the output surface and directly coupled to the output module to complete coherent mixing.

4. The MPLC-based multi-dimensional demultiplexing and mixing system according to claim 2, wherein: The arrangement of the metasurface and the phase plate includes alternating arrangement, segmented arrangement, disordered arrangement or full metasurface arrangement.

5. The MPLC-based multi-dimensional demultiplexing and mixing system according to any one of claims 1 to 4, characterized in that: The MPLC module includes a first reflector, a second reflector and the phase shift region, the first reflector and the second reflector are arranged parallel to each other, and the phase shift region is integrated on the first reflector and / or the second reflector; or, the MPLC module includes a first reflector, a transmission mirror, a second reflector and the phase shift region, the first reflector, the transmission mirror and the second reflector are arranged parallel to each other, and the transmission mirror is located between the first reflector and the second reflector, and the phase shift region is integrated on the transmission mirror.

6. The MPLC-based multi-dimensional demultiplexing and mixing system according to claim 5, characterized in that: The input module includes a single fiber collimator or a dual fiber collimator; the output module includes a fiber array or a photodetector array, wherein each fiber end face of the fiber array is integrated with a microlens.

7. An optimization design method for a multi-dimensional demultiplexing and mixing system based on MPLC according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Establish a meta-atom library of phase-responsive metasurface units, scan the phase modulation of the nanopillar's major axis, minor axis, and height with respect to the X / Y polarization of the target band, and obtain the meta-atom library; S2. Iteratively optimize N phase transformation regions: S21. Initialize the random phase matrix; S22. Calculate the target phase through forward and reverse light field propagation; match it with the meta-atom library and update the metasurface's micro-nanostructure; S23. Repeat step S22 until the preset convergence condition is reached.

8. The optimization design method of the MPLC-based multi-dimensional demultiplexing and mixing system according to claim 7, characterized in that: Step S21 includes: inputting the meta-atom library, setting relevant parameters, including: demultiplexing wavelength λ1~λN, mode number mode1~modeM, phase shift region N1~NK, number of phase plates and corresponding phase shift regions, number of metasurfaces and corresponding phase shift regions, spacing S between phase shift regions, distance S between the input surface and the first phase shift region I , the distance S between the output surface and the last phase change area O , the maximum number of iterations i MAX Or output light field preset parameters.

9. The optimization design method of the multi-dimensional demultiplexing and mixing system based on MPLC according to claim 7, characterized in that: The step S22 includes: S221. After initialization is completed, the iteration starts from the number of iterations 1 and the first phase change region; S222 determines whether the phase shift region is a metasurface; if so, proceeds to step S223; if not, proceeds to step S224; S223. Calculating the phase matrices corresponding to the current phase shift region at different wavelengths and polarization states based on the forward propagation of the input light field and the reverse propagation of the target light field into the phase shift region at different wavelengths and polarization states, and obtaining multiple phase matrices for different wavelengths and polarization states in the current phase shift region. Matching the obtained phase matrices for each dimension with the meta-atom library is performed to obtain the meta-atom distribution in the current phase shift region. S224. Calculate the phase matrix corresponding to the current phase transformation region based on the results of all input light fields forward propagated and the target light fields back propagated to the current phase transformation region.

10. The optimization design method of the MPLC-based multi-dimensional demultiplexing and mixing system according to claim 7, characterized in that: Step S23 includes: S231 determines whether it is the last phase change region, if not, the next phase change region iteration, repeating steps S222 ~ S224; S232. If yes, determine whether the number of iterations reaches the maximum number of iterations i MAX Or whether the parameter value of the output light field reaches the preset parameter value; if not, the number of iterations is increased by 1, and the iteration starts from the first phase transformation region, and steps S222 to S224 are repeated until the requirements are met, then the iteration is stopped, and the obtained phase transformation region is the final optimized phase transformation region.

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