A multi-dimensional demultiplexing and mixing system based on MPLC and an optimization design method thereof

Abstract

The application relates to the technical field of multi-plane light conversion, and more particularly to a multi-dimensional demultiplexing and mixing system based on MPLC and an optimization design method thereof. The system comprises: an input module for inputting multimode signal light and local oscillator light; an MPLC module for realizing unitary transformation of light in any space, comprising N cascaded phase transformation regions integrated on a reflecting mirror or a transmitting mirror; the phase transformation region is a phase sheet or a metasurface, and at least one phase transformation region is a metasurface; and an output module for receiving a single-mode Gaussian light spot after demultiplexing and mixing. Different phase regulations are realized on different wavelengths and different polarization states by the metasurface; and parallel demultiplexing of wavelengths, polarizations and modes in the multimode signal can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multi-plane light conversion, and more particularly to a multi-dimensional demultiplexing and mixing system based on MPLC and an optimization design method thereof. BACKGROUND

[0002] Multi-plane light conversion (MPLC) technology: MPLC is a technology that can perform arbitrary spatial unitary transformation. In particular, spatial multiplexing, i.e., converting N individual input Gaussian beams into N orthogonally superimposed transmission modes. In theory, MPLC can perform spatial unitary transformation through a series of phase profiles separated by optical Fourier transform. As a new high-efficiency mode multiplexer / demultiplexer, the multi-plane light converter has attracted enough attention from domestic and foreign researchers due to its excellent performance.

[0003] The core function of the multi-plane multiplexing / demultiplexing device is to multiplex (combine) and demultiplex (separate) multiple independent optical signal modes. In the multiplexing process, multiple optical signals are integrated into one optical fiber for transmission; in the demultiplexing process, the signals are separated back to the original independent modes. This technology makes full use of the multiple transmission modes in the few-mode fiber, significantly improving the transmission capacity of a single optical fiber. The working principle of the multi-plane multiplexing / demultiplexing device is based on the multi-plane light conversion technology. The core is to distribute the input optical signal to different spatial modes through special optical design, thereby realizing signal multiplexing. Although the existing commercial multi-plane demultiplexer can realize the demultiplexing of multiple modes, it cannot realize the demultiplexing of wavelength polarization because it uses polarization-independent and wavelength-insensitive phase plates. SUMMARY

[0004] The purpose of the present application is to overcome the deficiency of the prior art multi-plane multiplexing / demultiplexing device that cannot realize the demultiplexing of wavelength polarization, and to provide a multi-dimensional demultiplexing and mixing system based on MPLC and an optimization design method thereof, which can realize the parallel demultiplexing of wavelength, polarization and mode in multi-mode signals.

[0005] To solve the above technical problems, the technical solution adopted by the present application is:

[0006] A multi-dimensional demultiplexing and mixing system based on MPLC is provided, comprising:

[0007] An input module for inputting multi-mode signal light and local oscillator light;

[0008] An MPLC module for realizing unitary transformation of light in any space, comprising N cascaded phase transformation regions integrated on a reflecting mirror or a transmitting mirror; the phase transformation region is a phase plate or a metasurface, and at least one phase transformation region is a metasurface;

[0009] Output module: for receiving the single-mode Gaussian light spot after demultiplexing and mixing.

[0010] The MPLC-based multi-dimensional demultiplexing and mixing system of the application has phase transformation regions cascaded in the MPLC module, each phase transformation region corresponds to a phase sheet or a metasurface, at least one phase transformation region is a metasurface, and different phase controls are realized for different wavelengths and different polarization states through the metasurface; therefore, the system can realize parallel demultiplexing of wavelengths, polarizations and modes in the multimode signal.

[0011] Further, the phase sheet realizes wavelength-insensitive and polarization-independent mode conversion through etching depth difference, such as converting high-order modes into single-mode Gaussian light; the metasurface includes a plurality of periodic micro-nano structures, which can be nano columns, wherein the column height of the micro-nano structure is 0.2λ1~1.2λ2, λ1 represents the shortest wavelength of the working wavelength band, and λ2 represents the longest wavelength of the working wavelength band, which can support C / L wavelength demultiplexing. Corresponding wavelength-sensitive unit; the micro-nano structure includes a long axis and a short axis, which can independently control the X / Y polarization state phase, and correspond to the polarization-sensitive unit.

[0012] Further, the multimode signal light is modulated by the MPLC module to output four single-mode Gaussian light spots spatially separated, with phase differences of 0, π, π / 2 and 3π / 2, corresponding to I / Q two orthogonal components; the local oscillator light is modulated by the MPLC module to output a single-mode Gaussian light spot with the same position as the multimode signal light and a phase of 0, realizing homodyne detection; the multimode signal light and the local oscillator light are spatially matched at the output surface and directly coupled to the output module to complete coherent mixing.

[0013] Further, the arrangement mode of the metasurface and the phase sheet includes alternating arrangement, segmented arrangement, disordered arrangement or full metasurface arrangement.

[0014] Further, the MPLC module includes a first mirror, a second mirror and the phase transformation region, the first mirror and the second mirror are arranged parallel to each other, and the phase transformation region is integrated on the first mirror and / or the second mirror. Or, the MPLC module includes a first mirror, a transmission mirror, a second mirror and the phase transformation region, the first mirror, the transmission mirror and the second mirror are arranged parallel to each other, the transmission mirror is located between the first mirror and the second mirror, and the phase transformation region is integrated on the transmission mirror.

[0015] Further, the input module comprises a single-fiber collimator or a double-fiber collimator; the output module comprises 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, and the coaxial input adopts a single-fiber collimator, and the spatially separated input can pass through a double-fiber collimator.

[0016] The application further provides an optimization design method of a multi-dimensional demultiplexing and mixing system based on MPLC, comprising the following steps:

[0017] 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 the C / L waveband X / Y polarization is simulated;

[0018] S2. Iterative optimization of N phase transformation regions:

[0019] S21. Initialization of a random phase matrix;

[0020] 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;

[0021] S23. Repeating step S22 until a preset convergence condition is reached.

[0022] 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 the phase transformation regions are completely 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 are cooperatively optimized.

[0023] 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, and the distance S between the input face and the first phase transformation region. I, the distance S of the output surface from the last phase transformation region O , the maximum iteration number i MAX or the preset parameter of the output light field.

[0024] Further, the step S22 comprises:

[0025] S221. After initialization, iteration starts from the iteration number 1 and the first phase transformation region.

[0026] S222. Determine whether the current phase transformation region is a metasurface; if yes, go to step S223; if no, go to step S224.

[0027] 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 a plurality of phase matrices under different wavelengths and polarization states in 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.

[0028] 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.

[0029] Further, the step S23 comprises:

[0030] S231. Determine whether it is the last phase transformation region; if no, iterate the next phase transformation region, and repeat steps S222-S224.

[0031] S232. If yes, determine whether the iteration number reaches the maximum iteration number i MAX or 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.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] 1. The multi-dimensional demultiplexing and mixing system based on MPLC can realize wavelength, polarization and mode demultiplexing and mixing in parallel; by the integration of metasurface and MPLC, the traditional separate mode demultiplexer, wavelength division multiplexer (WDM) and polarization beam splitter (PBS), and 90° optical hybrid function are integrated into a single device, eliminating the insertion loss, alignment error and mode crosstalk problems caused by multi-device cascade. And it can reduce the number of devices, significantly reduce the packaging, calibration and maintenance costs. And through the integrated design, the interface and coupling node in the optical path are reduced, the influence of environmental disturbance (such as temperature, vibration) on the stability of the system is reduced, and the reliability is improved.

[0034] 2. The optimization design method of the multi-dimensional demultiplexing and mixing system based on MPLC can realize three-dimensional parallel demultiplexing and mixing design of wavelength, polarization and mode; the combination strategy of metasurface and phase sheet can be dynamically adjusted according to actual needs, and the collaborative optimization of metasurface and phase sheet is realized. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a structure schematic diagram of the multi-dimensional demultiplexing and mixing system based on MPLC in an embodiment;

[0036] Figure 2 It is a schematic diagram of the spatial separation input mode of multimode signal light and local oscillator light in an embodiment;

[0037] Figure 3 It is a schematic diagram of the coaxial input mode of multimode signal light and local oscillator light in an embodiment;

[0038] Figure 4 It is a schematic diagram of the input and output of multimode signal light and local oscillator light in an embodiment;

[0039] Figure 5 It is a schematic diagram of the phase transformation region distribution mode in an embodiment;

[0040] Figure 6 It is a schematic diagram of the arrangement mode of metasurface and phase sheet in an embodiment;

[0041] Figure 7 It is a flowchart of the optimization design method of the multi-dimensional demultiplexing and mixing system based on MPLC in an embodiment;

[0042] Figure 8 It is a schematic diagram of updating the phase of the phase sheet in an embodiment;

[0043] Figure 9 It is a schematic diagram of updating the metasurface in an embodiment.

[0044] In the drawing: 1, fiber array; 2, microlens; 3, phase transformation area; 4, first mirror; 5, second mirror; 6, collimator; 7, few-mode fiber; 8, single-mode fiber. DETAILED DESCRIPTION

[0045] The application will be further described below in connection with the specific embodiments. In the drawings, only for exemplary illustration, the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the application; in order to better illustrate the embodiments of the application, some components in the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures in the drawings and their descriptions can be omitted.

[0046] The same or similar reference numerals in the drawings of the embodiments of the application correspond to the same or similar components; in the description of the application, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate the orientation or positional relationship shown in the drawings, only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the positional relationship described in the drawings is only for exemplary illustration, and cannot be understood as a limitation on the application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0047] Embodiment one

[0048] This embodiment is a first embodiment of a multi-dimensional demultiplexing and mixing system based on MPLC, comprising:

[0049] Input module: for inputting multimode signal light and local oscillator light;

[0050] MPLC module: for realizing unitary transformation of light in any space, comprising N cascaded phase transformation areas 3 integrated on a mirror or a transmission mirror; the phase transformation area 3 is a phase sheet or a metasurface, and at least one phase transformation area 3 is a metasurface;

[0051] Output module: for receiving demultiplexed and mixed single-mode Gaussian light spot.

[0052] In this embodiment, the phase plate achieves wavelength-insensitive and polarization-independent mode conversion through differences in etching depth, such as converting a higher-order mode into single-mode Gaussian light. The metasurface includes several periodic micro / nanostructures, which can be nanopillars with a pillar height of 0.2λ1~1.2λ2, where λ1=1530nm and λ2=1625nm, supporting C / L band wavelength demultiplexing. These correspond to wavelength-sensitive units. The micro / nanostructures include a long axis and a short axis, enabling independent modulation of the X / Y polarization phase, corresponding to polarization-sensitive units. In this example, the operating wavelength (demultiplexing wavelength) is λ1=1530nm and λ2=1625nm. The metasurface includes several periodic micro / nanostructures, called meta-atoms. These meta-atoms can be nanopillars and include a long axis and a short axis, used to achieve different phase modulations of the X / Y polarization states. Optical simulations are used to obtain the phase modulation of the meta-atoms for different operating wavelengths and polarization states, thereby establishing a meta-atom library for metasurface design.

[0053] 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 quadrature components. After the local oscillator light is modulated by the MPLC module, it outputs a single-mode Gaussian light spot with the same position and phase of 0 as the multimode signal light, realizing zero-difference detection. The multimode signal light and the local oscillator light are spatially matched at the output plane and directly coupled to the output module to complete coherent mixing.

[0054] In this embodiment, for N cascaded phase transformation regions 3, each phase transformation region 3 can be a metasurface or a phase plate; when some phase transformation regions 3 are phase plates and other phase transformation regions 3 are metasurfaces, the arrangement of the metasurfaces and phase plates includes alternating arrangement, segmented arrangement, and disordered arrangement; such as Figure 6 As shown in (A), (B), and (C) in this embodiment, all phase transformation regions 3 can also be set as metasurfaces, i.e., a full metasurface arrangement, as shown in... Figure 6 As shown in (D) in the diagram.

[0055] In this embodiment, as Figure 1 As shown, the MPLC module includes a first reflector 4, a second reflector 5, and a phase transformation region 3. The first reflector 4 and the second reflector 5 are arranged parallel to each other, and the phase transformation 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 transformation 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. The phase transformation region 3 is integrated on the transmission mirror.

[0056] In the embodiment, the input module includes a collimator 6, which can be a single-fiber collimator or a double-fiber collimator; and 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 adopts a single-fiber collimator, as shown in FIG. 1A; and the spatially separated input can pass through a double-fiber collimator, as shown in FIG. 1B. Figure 3 Figure 2

[0057] The MPLC module includes a first mirror 4, a second mirror 5, and a plurality of phase transformation regions 3. The first mirror 4 and the second mirror 5 are arranged in parallel. The plurality of phase transformation regions 3 are arranged on the first mirror 4, and each of the plurality of phase transformation regions 3 is a metasurface. The metasurface is composed of a periodic array of rectangular silicon nanocolumns, and different phase control is achieved for different wavelengths and different polarization states.

[0058] Embodiment Two

[0059] The second embodiment of the MPLC-based multi-dimensional demultiplexing and mixing system is similar to the first embodiment. As shown in FIG. 2B, the input module includes a double-fiber collimator. One input is a multi-mode signal light (containing LP01, LP11, and other high-order modes, with a wavelength range of 1530-1625 nm, and X / Y polarization mixed), and the other input is a local oscillator light (single-mode Gaussian beam, with a wavelength matched with the signal light, and X / Y polarization mixed). The input light field diagram of the double-fiber collimator is shown in FIG. 2C. Figure 1 Figure 2

[0060] The MPLC module includes a first mirror 4, a second mirror 5, and a plurality of phase transformation regions 3. The first mirror 4 and the second mirror 5 are arranged in parallel. The plurality of phase transformation regions 3 are arranged on the first mirror 4, and each of the plurality of phase transformation regions 3 is a metasurface. The metasurface is composed of a periodic array of rectangular silicon nanocolumns, and different phase control is achieved for different wavelengths and different polarization states.

[0061] The output module includes an n*m fiber array 1, and each fiber end face is integrated with a microlens 2, which is aligned with a single-mode Gaussian spot on the output surface of the MPLC module, as shown in FIG. 3B. For a signal light with a certain wavelength, polarization, and mode, four spots with phase differences of 0, π, π / 2, and 3π / 2 are output, corresponding to I / Q two orthogonal components. The local oscillator light is output in the same position as the signal light, with a phase of 0, to achieve mixing. Figure 4

[0062] Figure 1 ​​​​​​As shown, the input light is first emitted from the collimator 6, and the emission direction of the collimator 6 has a preset angle relationship with the extension direction of the first mirror 4, which is a non-right angle relationship. After the light passes through the collimator 6, it will hit the first phase transformation area 3 of the first mirror 4, and then the light will be reflected by the first mirror 4 to the second mirror 5 and then reflected by the second mirror 5 back to the first mirror 4. At this time, the light will reach the second phase transformation area 3 of the first mirror 4, and the light will propagate back and forth between the first mirror 4 and the second mirror 5 from one phase transformation area 3 to the next phase transformation area 3. As can be seen, the angle relationship between the collimator 6 and the first mirror 4 depends on the setting distance between the adjacent two phase transformation areas 3 and the spacing between the two mirrors, and only needs to ensure that the light can propagate from one phase transformation area 3 to a new phase transformation area 3.

[0063] The working principle of the embodiment is as follows:

[0064] The input light is emitted from the collimator 6, one of which is a multi-mode signal light, and the other is a local oscillator light. The input light is irradiated to the MPLC module and converted back and forth between the first mirror 4 and the second mirror 5. Since N super surfaces are integrated on the first mirror 4, the super surfaces are composed of a periodic array of rectangular silicon nanocolumns, thereby realizing different phase control for different wavelengths and different polarization states. The light after the MPLC module is injected into the output module, and the output module is aligned with the single-mode Gaussian spot on the output surface of the MPLC. For a certain wavelength, polarization, and mode, the multi-mode signal light outputs four phase difference spots of 0, π, π / 2, and 3π / 2, corresponding to I / Q two orthogonal components. The local oscillator light is output in the same position as the multi-mode signal light and has a phase of 0, thereby realizing frequency mixing.

[0065] Through the action of the MPLC module, the signal light and the local oscillator light input by the double-fiber collimator are converted as shown in Figure 2 As shown, the signal light is coaxial with multiple modes, and the local oscillator light is a Gaussian light (fundamental mode) converted as shown in Figure 4 As shown, Figure 4 Only two modes in the multi-mode signal light and two operating wavelengths are shown, and the actual device can process more modes and wavelengths. After passing through the MPLC module, a certain mode under a certain wavelength and a certain polarization state of the signal light is converted into four Gaussian spots with phase differences of 0, π, π / 2, and 3π / 2 on the output surface. The local oscillator light of the corresponding wavelength and polarization is converted into a Gaussian spot with the same position and a phase of 0.

[0066] Embodiment Three

[0067] The embodiment is an embodiment of an optimization design method of a multi-dimensional demultiplexing and mixing system based on an MPLC. The embodiment is used for optimizing the system provided in Embodiment One or Embodiment Two. In the embodiment, as shown in FIG. 16, the method comprises the following steps. Figure 7

[0068] Step S1. Establishing a meta-atom library: a meta-atom library of a metasurface unit phase response is established by simulation software, the phase modulation amount of a nanocolumn long axis, a nanocolumn short axis, and a nanocolumn height on a target waveband X / Y polarization is scanned, and a meta-atom library is obtained. In this step, the phase and amplitude responses of different aspect ratio nanocolumns on C / L waveband X / Y polarization are simulated.

[0069] Step S2. Iterative optimization of N phase transformation regions 3:

[0070] S21. Initializing a random phase matrix; inputting the meta-atom library, setting related parameters, including: demultiplexing wavelengths λ1~λN, mode numbers mode1~modeM, phase transformation region 3N1~NK, phase sheet numbers and corresponding phase transformation regions 3, metasurface numbers and corresponding phase transformation regions 3, a distance S between phase transformation regions 3, a distance S between an input surface and the first phase transformation region 3, a distance S between an output surface and the last phase transformation region 3, a maximum iteration number i, or preset parameters of an output light field. I O MAX

[0071] S22. Calculating a target phase by forward and reverse light field propagation; matching the meta-atom library to update the micro-nano structure of the metasurface. Specifically, the method comprises:

[0072] S221. After initialization, iteration starts from the first phase transformation region 3 with an iteration number of 1.

[0073] S222. Judging whether the current phase transformation region 3 is a metasurface; if yes, step S223 is entered; if no, step S224 is entered.

[0074] S223. Calculating the phase matrix corresponding to the current phase transformation region 3 under different wavelengths and polarization states by forward propagation of the input light field and reverse propagation of the target light field to the phase transformation region 3 under different wavelengths and polarization states, obtaining multiple phase matrices of different wavelengths and polarization states under the current phase transformation region 3, matching each dimension of the obtained phase matrix with the meta-atom library to obtain the meta-atom distribution of the current phase transformation region 3, and obtaining the metasurface phase distribution corresponding to the current phase transformation region 3.

[0075] ​​​​S224. Calculate the phase matrix corresponding to the current phase transformation region 3 according to the results of forward propagation of all input light fields and backward propagation of target light fields to the current phase transformation region 3, and the phase distribution of the corresponding phase sheet.

[0076] S23. Repeat step S22 until a preset convergence condition is reached. Specifically, it includes:

[0077] S231. Determine whether it is the last phase transformation region 3, if not, proceed to the iteration of the next phase transformation region 3, and repeat steps S222-S224;

[0078] S232. If yes, determine whether the iteration number reaches the maximum iteration number i MAX or 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 3, repeat steps S222-S224 until the requirements are met, then stop iteration, and the obtained phase transformation region 3 is the final optimized phase transformation region 3.

[0079] In the specific content of the above specific embodiments, each technical feature can be combined arbitrarily without contradiction. In order to make the description simple, all possible combinations of the above technical features are not described, but as long as the combination of these technical features does not exist contradiction, it should be considered as the scope of the present disclosure.

[0080] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A multi-dimensional demultiplexing and mixing system based on MPLC, characterized in that, The application relates to a wavelength division multiplexing (WDM) coherent mixer, which comprises the following modules: an input module for inputting multimode signal light and local light; an MPLC module for realizing a unitary transformation of light in any space, which comprises N cascaded phase transformation regions integrated on a reflecting mirror or a transmitting mirror; the phase transformation regions are phase sheets or metasurfaces, and at least one phase transformation region is a metasurface; and an output module for receiving single-mode Gaussian light spots after demultiplexing and mixing. The phase sheet realizes wavelength-insensitive and polarization-independent mode conversion through etching depth difference; the metasurface comprises a plurality of periodic micro-nano structures, wherein the column height of the micro-nano structure is 0.2 lambda 1~1.2 lambda 2, lambda 1 represents the shortest wavelength of the working wavelength band, and lambda 2 represents the longest wavelength of the working wavelength band, and the metasurface can support C / L wavelength demultiplexing; the micro-nano structure comprises a long axis and a short axis, and can independently control the X / Y polarization state phase; and the arrangement mode of the metasurface and the phase sheet comprises alternative arrangement, segmented arrangement, disordered arrangement or full metasurface arrangement. After the multimode signal light is modulated by the MPLC module, four single-mode Gaussian light spots are outputted, and the phase difference is 0, pi, pi / 2 and 3pi / 2; after the local light is modulated by the MPLC module, a single-mode Gaussian light spot with a phase of 0 is outputted at the same position as the multimode signal light; the multimode signal light and the local light are spatially matched at the output surface and directly coupled to the output module to complete coherent mixing. The MPLC module comprises a first reflecting mirror, a second reflecting mirror and the phase transformation regions, the first reflecting mirror and the second reflecting mirror are arranged in parallel with each other, and the phase transformation regions are integrated on the first reflecting mirror and / or the second reflecting mirror; or the MPLC module comprises a first reflecting mirror, a transmitting mirror, a second reflecting mirror and the phase transformation regions, the first reflecting mirror, the transmitting mirror and the second reflecting mirror are arranged in parallel with each other, the transmitting mirror is located between the first reflecting mirror and the second reflecting mirror, and the phase transformation regions are integrated on the transmitting mirror. The input module comprises a single-fiber collimator or a double-fiber collimator; and the output module comprises a fiber array or a photodetector array, wherein the end face of each fiber of the fiber array is integrated with a microlens.

2. The MPLC-based multi-dimensional demultiplexing and mixing system of claim 1, wherein, The application further discloses a wavelength division multiplexing (WDM) coherent mixing method, which comprises the following steps:

3. The MPLC-based multi-dimensional demultiplexing and mixing system of claim 2, wherein, S1. establishing a metasurface unit phase response meta-atom library, scanning the phase modulation amount of the target waveband X / Y polarization by the nanometer column long axis, short axis and column height, and obtaining a meta-atom library; 4. The MPLC-based multi-dimensional demultiplexing and mixing system of claim 3, wherein, S2. iteratively optimizing N phase transformation regions:

5. A method for the optimal design of a MPLC-based multi-dimensional demultiplexing and mixing system according to any one of claims 1 to 4, characterized in that, S21. initializing a random phase matrix; S22. calculating a target phase by forward and reverse light field propagation, matching the meta-atom library, and updating the micro-nano structure of the metasurface; S23. repeating step S22 until a preset convergence condition is reached. The step S22 comprises: S221. after initialization, starting iteration from the iteration number 1 and the first phase transformation region; S222. judging whether the current phase transformation region is a metasurface; if yes, entering step S223; if no, entering step S224; 6. The method of claim 5, wherein the method is characterized by: The step S21 comprises: inputting a meta-atom library, setting related parameters, including: demultiplexing wavelengths λ1-λN, mode numbers mode1-modeM, phase transformation regions N1-NK, phase sheet numbers and corresponding phase transformation regions, super surface numbers and corresponding phase transformation regions, a distance S between phase transformation regions, a distance S between an input surface and a first phase transformation region I , a distance S between an output surface and a last phase transformation region O , a maximum iteration number i MAX , or outputting a preset parameter of a light field.

7. The method of claim 5, wherein the method is characterized by: S223. updating the phase of the current phase transformation region according to the meta-atom library; and S224. updating the phase of the current phase transformation region according to the meta-atom library. ​ S223. The results of forward propagation of input light fields of different wavelengths and different polarization states and reverse propagation of target light fields to the phase transformation region are calculated to obtain the phase matrices corresponding to the current phase transformation region under different wavelengths and polarization states, and a plurality of phase matrices of different wavelengths and different polarization states are obtained under the current phase transformation region. According to the matching of the obtained phase matrices in each dimension with the meta-atom library, the meta-atom distribution of the current phase transformation region is obtained; S224. The phase matrix corresponding to the current phase transformation region is calculated according to the results of forward propagation of all input light fields and reverse propagation of target light fields to the current phase transformation region.

8. The method of claim 7, wherein the method is characterized by: Step S23 includes: S231. It is judged whether it is the last phase transformation region, if not, the iteration of the next phase transformation region is performed, and steps S222-S224 are repeated; S232. If yes, determine whether the iteration number reaches the maximum iteration number i MAX or 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 requirement is met, then stop iteration, and the obtained phase transformation region is the final optimized phase transformation region.

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