Fiber optic mode demultiplexing communication method and system

Abstract

The present invention belongs to the field of optical fiber communication technology and discloses a method and system for optical fiber mode demultiplexing communication. The present invention utilizes a metasurface to achieve demultiplexing of various mode types in an optical fiber and data transmission of various mode channels. The bit data loaded by each mode in the optical fiber can be simultaneously and independently transmitted in their respective working channels through the metasurface and received by different target areas on the same far-field receiving plane in the transmission space. The present invention reduces the design complexity of optical fiber mode demultiplexing, improves the transmission accuracy of optical fiber mode demultiplexing communication, and reduces the size and energy consumption of the device. In addition, the present invention can transmit and display complex images in the form of bit data, and can obtain higher quality images and richer information.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to an optical fiber mode demultiplexing communication method and system. Background Art

[0002] Fiber-optic mode multiplexing communication technology is an emerging research hotspot in the field of optical fiber communications. Traditional mode multiplexing communication systems mostly use time-domain or frequency-domain equalization algorithms to spatially separate multiple modes in the optical fiber, reduce crosstalk, and remove noise, thereby achieving mode multiplexing and demultiplexing. However, because these algorithms are derived from complex communication principles and are compatible with traditional communication components, they result in high design complexity, low transmission accuracy, large device size, and high energy consumption. Summary of the Invention

[0003] The present invention provides an optical fiber mode demultiplexing communication method and system to solve the problems of high design complexity, low transmission accuracy, large size and high energy consumption of optical fiber mode demultiplexing communication systems in the prior art.

[0004] The present invention provides a fiber mode demultiplexing communication method, comprising the following steps:

[0005] Step 1: Determine several modes that can be transmitted simultaneously and independently in the optical fiber, calculate the transverse complex amplitude distribution of each mode, and use it as the input complex amplitude distribution of several channels on the metasurface; select several independent target areas on the same far-field receiving plane in the metasurface transmission space, determine the target area intensities of several modes, and use them as the output intensity distribution of several channels on the metasurface;

[0006] Step 2: determining the structure and parameters of the metasurface according to the operating wavelength of the optical fiber and the input complex amplitude distribution and output intensity distribution of several channels on the metasurface;

[0007] Step 3: Select several groups of bit data, use a signal transmitter to load them respectively on several modes of the optical fiber in a coherent modulation manner, demultiplex and transmit them through the metasurface, and couple them into corresponding signal receivers in several target areas on the same far-field receiving plane in the metasurface transmission space. After demodulation by the signal receiver, the bit data loaded by each of the several modes are obtained.

[0008] Preferably, in step 1, the transverse complex amplitude distribution of each mode is calculated in the following manner: based on the type of the mode, the values ​​of the normalized cutoff frequency V, normalized radial constant U and attenuation constant W of each mode are determined, the transverse amplitude distribution grid is divided, and the transverse amplitude distribution of the mode is calculated; according to the characteristics of the mode, the transverse amplitude distribution is superimposed with the phase distribution to obtain the transverse complex amplitude distribution of the mode.

[0009] Preferably, in step 1, the area of ​​the target region corresponding to each mode is of the same order of magnitude as the core cross-sectional area of ​​the optical fiber, and the target regions corresponding to different modes are located at different positions on the far-field receiving plane.

[0010] Preferably, step 2 includes the following sub-steps:

[0011] Based on the input complex amplitude distribution and output intensity distribution of several channels on the metasurface, the phase distribution of the metasurface is optimized to obtain the angular arrangement of several nanostructures on the substrate of the metasurface;

[0012] Determining the operating wavelength of the metasurface according to the operating wavelength of the optical fiber, and determining the material characteristic parameters of the substrate and nanostructure of the metasurface;

[0013] Based on the working wavelength of the metasurface, the geometric parameters of the nanostructure are scanned to determine the size parameters of the substrate and the nanostructure of the metasurface, so that the metasurface has the function of a half-wave plate for polarization conversion and phase modulation;

[0014] The arrangement of the metasurface is constructed, including a substrate and a plurality of nanostructures of the same size and different rotation angles that are periodically arranged on the substrate. Based on the optimized rotation angle arrangement, the plurality of nanostructures on the substrate of the metasurface are periodically arranged to obtain the metasurface for realizing optical fiber mode demultiplexing communication.

[0015] Preferably, the output intensity distribution O is expressed as:

[0016]

[0017] Where I represents the input complex amplitude distribution, P represents the phase distribution of the metasurface, and F represents the Fourier transform;

[0018] Based on the above formula, the phase distribution of the metasurface is obtained by iterative optimization using an algorithm.

[0019] Preferably, the working wavelength of the optical fiber is used as the working wavelength of the metasurface, and the materials of the substrate and nanostructure of the metasurface are both made of single crystal silicon material with a transmittance of higher than 70% for light at the working wavelength.

[0020] Preferably, the base of the metasurface is divided into a number of periodic square units of uniform size, each of which has a side length of CS; a nanobrick with a cubic structure is provided on the working surface of each square unit, each of which has a length of L, a width of W, and a height of H;

[0021] At the operating wavelength, electromagnetic simulation software is used to scan the side length CS of the square unit and the length L, width W and height H of the nanobrick to select geometric parameters that make the polarization conversion efficiency and phase modulation amount of the metasurface meet the preset conditions.

[0022] Preferably, a coordinate system XOY is established on the working surface of the square unit, wherein the X axis and the Y axis are parallel to the two sets of sides of the working surface respectively, and the angle between the long axis direction of the nanobrick and the X axis direction is taken as the rotation angle θ of the nanobrick;

[0023] Based on the relationship between the phase distribution P of the metasurface and twice the rotation angle θ of the nanobrick, the rotation angle arrangement of the nanobrick is determined according to the determined metasurface phase distribution.

[0024] Preferably, in step 3, the bit data loaded onto each mode of the optical fiber by the signal transmitter in a coherent modulation manner comes from a number of selected transmission images, the pixel matrix of the transmission image is arranged in sequence, and a decimal-to-binary conversion is performed to generate corresponding bit data; the bit data coupled by the signal receiver in each target area is converted from binary to decimal, and restored to a pixel matrix in sequence to obtain a received image.

[0025] On the other hand, the present invention provides a fiber mode demultiplexing communication system, comprising: a signal transmitter, an optical fiber, a metasurface and a signal receiver; the fiber mode demultiplexing communication system is used to execute the steps in the above-mentioned fiber mode demultiplexing communication method.

[0026] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0027] (1) The present invention utilizes a metasurface to realize the demultiplexing of various mode types in an optical fiber and the data transmission of various mode channels. The bit data loaded in each mode in the optical fiber can be transmitted simultaneously and independently in their respective working channels through a metasurface mode demultiplexing communication platform (i.e., a metasurface for realizing optical fiber mode demultiplexing communication), and received by different target areas on the same far-field receiving plane in the transmission space. The present invention reduces the design complexity of optical fiber mode demultiplexing, improves the transmission accuracy of optical fiber mode demultiplexing communication, and promotes high efficiency, low crosstalk of optical fiber mode demultiplexing and miniaturization and integration of optical fiber communication devices. The present invention has potential research value and broad application prospects in the fields of optical fiber communication, pattern recognition, data transmission, image display, and information encryption.

[0028] (2) Compared with the technical solution based on metasurface to realize large-area simple character holographic display in space, the target of the present invention is a small area, which can concentrate the output energy into a small area, close to the core cross-sectional area of ​​the receiving optical fiber in the signal receiver, so that more energy is coupled into the signal receiver, which can reduce the volume and energy consumption of the device. In addition, the present invention can transmit and display complex images in the form of bit data, and can obtain higher quality images and richer information, thereby realizing the integrated application of spatial light modulation and optical fiber communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a working diagram of a fiber mode demultiplexing communication method provided by Example 1 of the present invention;

[0030] Figure 2 is the complex amplitude distribution of the transverse light field of each mode of the few-mode fiber in the optical fiber mode demultiplexing communication method provided in Example 1 of the present invention; wherein, Figure 2 (a) is the amplitude distribution of LP01 mode, Figure 2 (b) is the phase distribution of LP01 mode. Figure 2 (c) in the figure is the amplitude distribution of LP11 mode. Figure 2 (d) in the figure is the phase distribution of LP11 mode;

[0031] Figure 3 is the target area intensity distribution of each mode of a few-mode fiber in a fiber mode demultiplexing communication method provided in Example 1 of the present invention; wherein, Figure 3 (a) is the target area of ​​LP01 mode, Figure 3 (b) in the figure is the target area of ​​LP11 mode;

[0032] Figure 4 It is a metasurface phase distribution obtained by algorithm optimization in a fiber mode demultiplexing communication method provided in Example 1 of the present invention;

[0033] Figure 5 A schematic structural diagram of a nanometer unit in a fiber mode demultiplexing communication method provided in Example 1 of the present invention;

[0034] Figure 6 This is a curve of polarization conversion efficiency and phase modulation range of a nanometer unit in a fiber mode demultiplexing communication method provided in Example 1 of the present invention;

[0035] Figure 7 A schematic structural diagram of a metasurface in a fiber mode demultiplexing communication method provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0037] Example 1:

[0038] Example 1 provides a fiber mode demultiplexing communication method, see Figure 1 , including the following steps:

[0039] Step 1: Determine several modes that can be transmitted simultaneously and independently in the optical fiber, calculate the transverse complex amplitude distribution of each mode, and use it as the input complex amplitude distribution of several channels on the metasurface; select several independent target areas on the same far-field receiving plane in the metasurface transmission space, determine the target area intensities of several modes, and use them as the output intensity distribution of several channels on the metasurface;

[0040] Step 2: determining the structure and parameters of the metasurface according to the operating wavelength of the optical fiber and the input complex amplitude distribution and output intensity distribution of several channels on the metasurface;

[0041] Step 3: Select several groups of bit data, use a signal transmitter to load them respectively on several modes of the optical fiber in a coherent modulation manner, demultiplex and transmit them through the metasurface, and couple them into corresponding signal receivers in several target areas on the same far-field receiving plane in the metasurface transmission space. After demodulation by the signal receiver, the bit data loaded by each of the several modes are obtained.

[0042] In step 1, the transverse complex amplitude distribution of each mode is calculated by determining the values ​​of the normalized cutoff frequency V, normalized radial constant U, and attenuation constant W of each mode based on the mode type, dividing the transverse amplitude distribution into grids, and calculating the transverse amplitude distribution of the mode. Based on the characteristics of the mode, the transverse amplitude distribution is superimposed with the phase distribution to obtain the transverse complex amplitude distribution of the mode. At a certain receiving distance (i.e., a preset distance between the target area and the metasurface, for example, less than 4 cm), the area of ​​the target area corresponding to each mode is of the same order of magnitude as the core cross-sectional area of ​​the optical fiber, and the target areas corresponding to different modes are located at different positions on the far-field receiving plane.

[0043] The step 2 includes the following sub-steps: optimizing the phase distribution of the metasurface based on the input complex amplitude distribution and output intensity distribution of several channels on the metasurface to obtain the angular arrangement of several nanostructures on the substrate of the metasurface; determining the operating wavelength of the metasurface according to the operating wavelength of the optical fiber, and determining the material characteristic parameters of the substrate and nanostructure of the metasurface; scanning the geometric parameters of the nanostructure based on the operating wavelength of the metasurface to determine the size parameters of the substrate and nanostructure of the metasurface, so that the metasurface has the function of a half-wave plate for polarization conversion and phase modulation; constructing an arrangement of the metasurface, including a substrate and several nanostructures of the same size and different rotation angles that are periodically arranged on the substrate, and periodically arranging the several nanostructures on the substrate of the metasurface based on the optimized angular arrangement to obtain the metasurface for realizing optical fiber mode demultiplexing communication.

[0044] Specifically, the output intensity distribution O is expressed as:

[0045]

[0046] Where I represents the input complex amplitude distribution, P represents the phase distribution of the metasurface, and F represents the Fourier transform;

[0047] Based on the above formula, the phase distribution of the metasurface is obtained by iterative optimization using an algorithm.

[0048] The working wavelength of the optical fiber is used as the working wavelength of the metasurface, and the materials of the substrate and nanostructure of the metasurface are both made of single crystal silicon material with a transmittance of more than 70% for the working wavelength light.

[0049] The base of the metasurface is divided into a number of periodic square units of uniform size, each with a side length CS; a cubic nanobrick is provided on the working surface of each of the square units, each with a length L, a width W, and a height H; at the working wavelength, electromagnetic simulation software is used to scan the side length CS of the square unit and the length L, width W, and height H of the nanobrick, and geometric parameters are selected so that the polarization conversion efficiency and phase modulation amount of the metasurface meet preset conditions.

[0050] A coordinate system XOY is established on the working surface of the square unit, with the X-axis and Y-axis being parallel to two sets of sides of the working surface respectively, and the angle between the long axis direction of the nanobrick and the X-axis direction being taken as the rotation angle θ of the nanobrick; based on the relationship between the phase distribution P of the metasurface and twice the rotation angle θ of the nanobrick, the rotation angle arrangement of the nanobrick is determined according to the determined metasurface phase distribution.

[0051] In step 3, the bit data loaded onto each mode of the optical fiber by the signal transmitter in a coherent modulation manner comes from a number of selected transmission images, the pixel matrices of the transmission images are arranged in sequence, and a decimal-to-binary conversion is performed to generate corresponding bit data; the bit data coupled by the signal receiver in each target area is converted from binary to decimal, and restored to a pixel matrix in sequence to obtain a received image.

[0052] Example 2:

[0053] Example 2 provides a fiber mode demultiplexing communication system, comprising: a signal transmitter, an optical fiber, a metasurface, and a signal receiver; the fiber mode demultiplexing communication system is used to execute the steps in the fiber mode demultiplexing communication method described in Example 1.

[0054] Since the functions of the components in Example 2 correspond to the steps in Example 1, they can be understood by referring to the description of Example 1 and will not be described in detail here.

[0055] The present invention will be further described below with reference to parameters.

[0056] Step 1: Determine several modes in the optical fiber that can be transmitted simultaneously and independently, calculate the transverse complex amplitude distribution of each mode, and use it as the input complex amplitude distribution of several channels on the metasurface; select several independent target areas on the same far-field receiving plane in the metasurface transmission space, determine the target area intensities of several modes, and use them as the output intensity distribution of several channels on the metasurface.

[0057] (1.1) It is clear that there are several modes that can be transmitted simultaneously and independently in the optical fiber. Their transverse complex amplitude distribution is calculated and used as the input complex amplitude distribution of several channels on the metasurface mode demultiplexing communication platform (i.e., metasurface).

[0058] Specifically, a few-mode fiber supporting the transmission of linear polarization modes LP01 and LP11 is selected, with a core diameter d of 13.5 μm and a numerical aperture NA of 0.1. According to the geometric parameters of the few-mode fiber, the values ​​of the normalized cutoff frequency V, normalized radial constant U and attenuation constant W of each mode are determined, wherein the values ​​of the above parameters of the LP01 mode are 1.8242, 1.4640 and 1.0882, respectively, and the values ​​of the above parameters of the LP11 mode are 2.6754, 2.4048 and 1.1725, respectively. Based on the above parameters and the characteristic equation of the mode, the transverse amplitude distribution grid is divided, and the transverse amplitude distribution A of the LP01 and LP11 modes is calculated. 01 and A 11 , for the amplitude distribution A 01 and A 11 Phase distribution φ 01 and φ11 The superposition of the incident complex amplitude distribution I of LP01 and LP11 modes is obtained. 01 and I 11 , which can be expressed as:

[0059] (1)

[0060] (2)

[0061] That is the input complex amplitude distribution of the metasurface, such as Figure 2 As shown, Figure 2 (a) is the amplitude distribution of LP01 mode, Figure 2 (b) is the phase distribution of LP01 mode. Figure 2 (c) in the figure is the amplitude distribution of LP11 mode. Figure 2 (d) in the figure is the phase distribution of LP11 mode.

[0062] (1.2) Select several independent areas on the same receiving plane in the far field of the metasurface transmission space and determine the target area intensity of several modes, that is, the output intensity distribution of several channels on the metasurface.

[0063] To concentrate energy coupling into the signal receiver, the target area in the present invention is configured with a smaller number of pixels. Therefore, the target area of ​​each mode is of the same order of magnitude as the fiber core cross-sectional area, thus minimizing energy loss. For example, when two modes utilize the same receiving fiber, the target area can have the same or different number of pixels.

[0064] Specifically, the number of pixels of the far-field receiving plane in the metasurface transmission space is , where M=N=1000, and the number of pixels in the target area of ​​the pattern is , where m=n=10, and the target areas of the two modes are located in the second quadrant and the fourth quadrant on the receiving plane, respectively, as Figure 3 As shown, Figure 3 (a) is the target area of ​​LP01 mode, Figure 3 (b) in the figure is the LP11 mode target area. As a result, the mode light field energy is concentrated to the target area through the metasurface and coupled into the receiving fiber of the signal receiver, reducing energy loss and improving communication efficiency.

[0065] The optical fiber in the present invention specifically includes an input optical fiber (corresponding to Figure 1 The input fiber and the receiving fiber are located between the signal transmitter and the metasurface (the metasurface is located between the input fiber and the receiving fiber, which can also be understood as part of the signal receiver). The core cross-sectional areas of the input fiber and the receiving fiber are of the same magnitude.

[0066] Step 2: Determine the structure and parameters of the metasurface based on the operating wavelength of the optical fiber and the input complex amplitude distribution and output intensity distribution of several channels on the metasurface.

[0067] (2.1) Based on the input and output distributions of several working channels on the metasurface, an algorithm is used to optimize the phase distribution of the metasurface to obtain the angular arrangement of several nanostructures on the working surface of the metasurface substrate.

[0068] Specifically, based on the principles of geometric phase and Fourier off-axis holography, the metasurface can achieve continuous phase modulation of light waves and obtain the output intensity distribution of the metasurface, that is, the output intensity distribution of LP01 and LP11 modes. 01 and O 11 , which can be expressed as:

[0069] (3)

[0070] (4)

[0071] Among them, I 01 and I 11 They represent the incident complex amplitude distributions of LP01 and LP11 modes, respectively, that is, the input complex amplitude distributions of the metasurface, P represents the phase distribution of the metasurface, and F represents the Fourier transform.

[0072] Based on the above formula, the phase distribution P of the metasurface is optimized and iterated by the algorithm so that the output intensity distribution O 01 and O 11 As close as possible to the intensity distribution of the two target areas selected in step 2, determine Figure 4 The optimal metasurface phase distribution P shown here determines the rotation angle arrangement θ of several nanostructures on the working surface of the metasurface substrate.

[0073] (2.2) Determine the operating wavelength of the metasurface based on the operating wavelength of the optical fiber, thereby determining the material characteristic parameters of the metasurface substrate and the nanostructure.

[0074] Specifically, the optical fiber operating wavelength is 1550 nm, and thus the metasurface operating wavelength λ is also 1550 nm, which confirms that both the metasurface substrate and the nanostructured material are single crystal silicon materials with high transmittance for light of this wavelength.

[0075] (2.3) Based on the operating wavelength of the metasurface, the geometric size parameters of the nanostructure are scanned to determine the size parameters of the metasurface substrate and the nanostructure, so that the metasurface has the function of a half-wave plate for polarization conversion and phase modulation.

[0076] Specifically, the base of the metasurface is divided into a number of periodic square units of uniform size, each with a side length of CS; a nanobrick with a cubic structure is provided on the working surface of each square unit, each with a length of L, a width of W, and a height of H. A square unit and a nanobrick constitute a nanounit, such as Figure 5 As shown. Based on the working wavelength λ = 1550 nm of the metasurface, the electromagnetic simulation software COMSOL Multiphysics is used to scan the period of the substrate (i.e. CS) and the length L, width W and height H of the nanobrick to adjust the anisotropy of the nanostructure, converting most of the incident light into reverse polarized light with phase modulation, thereby improving the polarization conversion efficiency of the metasurface. A set of optimized geometric parameters CS = 860 nm, L = 680 nm, W = 260 nm, H = 1000 nm are obtained to construct an optimized nanostructure. The polarization conversion efficiency of the nanounit is shown as follows: Figure 6 As shown in Figure 3, when the operating wavelength λ=1550 nm, the polarization conversion efficiency is higher than 70%.

[0077] (2.4) Constructing an arrangement of the metasurface, including a substrate and a plurality of periodically arranged nanostructures of the same size but different rotation angles located on the substrate; based on the optimized rotation angle arrangement, periodically arranging the plurality of nanostructures on the substrate of the metasurface to obtain the metasurface for realizing fiber mode demultiplexing communication.

[0078] Specifically, a coordinate system XOY is established on the working surface of the square unit, where the X-axis and the Y-axis are parallel to the two sets of sides of the working surface respectively, and the angle between the long axis direction of the nanobrick and the X-axis direction is taken as the rotation angle θ of the nanobrick, as shown in FIG. Figure 5 The phase modulation range of the nanometer unit is shown as Figure 6 As shown in the figure, when the working wavelength λ = 1550 nm, the phase modulation range can cover 0 to 2π. Based on the relationship between the double of the metasurface phase distribution and the nanobrick angle arrangement in the geometric phase principle, the nanobrick angle arrangement θ is determined by the metasurface phase distribution P optimized in the previous step, and the nanostructures are arranged in sequence to obtain a metasurface that can realize fiber mode demultiplexing communication, as shown in the figure. Figure 7 shown.

[0079] Step 3: Select several groups of bit data and use a signal transmitter to load them onto several modes of the optical fiber in a coherent modulation manner, which are the transmission data of several channels on the metasurface. After demultiplexing and transmission by the metasurface, they are coupled into the signal receiver at several target areas on the same far-field plane in the transmission space. After demodulation, the bit data loaded by each of the several modes are obtained, which are the reception data of several working channels on the metasurface.

[0080] Specifically, two images are selected as the transmitted images for the LP01 and LP11 modules, respectively. The pixel matrices of these transmitted images are arranged into a sequence, and a decimal-to-binary conversion is performed to generate corresponding bit data. This data is then coherently modulated by a signal transmitter and loaded onto the LP01 and LP11 modules, respectively, as the transmission data for the working channels of the LP01 and LP11 modules on the metasurface. After demultiplexing and transmission via the metasurface, the data is coupled into a signal receiver at the target areas corresponding to the LP01 and LP11 modules, respectively. After demodulation, it is received as the working channel data for the LP01 and LP11 modules on the metasurface. In contrast to the transmission process, the received bit data is converted from binary to decimal, and the sequence is restored to a pixel matrix in the same order to obtain the received image.

[0081] In summary, the present invention proposes a new solution for realizing optical fiber mode demultiplexing communication based on metasurface, which realizes the characteristic identification of each mode type in the optical fiber and the data transmission of each mode channel by using metasurface. Specifically, the bit data emitted by each mode in the optical fiber can be transmitted simultaneously and independently in their respective working channels through the metasurface, and received by different target areas on the same far-field plane in the transmission space, and the transmission mode characteristics can be effectively identified by the intensity of the target area and the received image display. The present invention utilizes the principles of geometric phase, off-axis holography and digital communication to enable the metasurface to simultaneously realize independent phase modulation of multiple working channels, independent intensity detection of multiple target positions and independent signal transmission of multiple groups of bit data, which can realize demultiplexing and data communication of multiple modes in the optical fiber, reduce the design complexity of optical fiber mode demultiplexing, improve the transmission accuracy of optical fiber mode demultiplexing communication, promote the high efficiency, low crosstalk of optical fiber mode demultiplexing and the miniaturization and integration of optical fiber communication devices, and can be widely used in research fields such as optical fiber communication, pattern recognition, data transmission, image display and information encryption.

[0082] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A fiber mode demultiplexing communication method, characterized in that: The following steps are involved: Step 1: Determine several modes that can be transmitted simultaneously and independently in the optical fiber, calculate the transverse complex amplitude distribution of each mode, and use it as the input complex amplitude distribution of several channels on the metasurface; select several independent target areas on the same far-field receiving plane in the metasurface transmission space, determine the target area intensities of several modes, and use them as the output intensity distribution of several channels on the metasurface; Step 2: determining the structure and parameters of the metasurface according to the operating wavelength of the optical fiber and the input complex amplitude distribution and output intensity distribution of several channels on the metasurface; Step 3: Select several groups of bit data, use a signal transmitter to load them respectively on several modes of the optical fiber in a coherent modulation manner, demultiplex and transmit them through the metasurface, and couple them into corresponding signal receivers in several target areas on the same far-field receiving plane in the metasurface transmission space. After demodulation by the signal receiver, the bit data loaded by each of the several modes are obtained.

2. The optical fiber mode demultiplexing communication method according to claim 1, characterized in that: In step 1, the transverse complex amplitude distribution of each mode is calculated in the following manner: based on the type of mode, the values ​​of the normalized cutoff frequency V, normalized radial constant U and attenuation constant W of each mode are determined, the transverse amplitude distribution grid is divided, and the transverse amplitude distribution of the mode is calculated; according to the characteristics of the mode, the transverse amplitude distribution is superimposed with the phase distribution to obtain the transverse complex amplitude distribution of the mode.

3. The optical fiber mode demultiplexing communication method according to claim 1, wherein: In step 1, the area of ​​the target region corresponding to each mode is of the same order of magnitude as the core cross-sectional area of ​​the optical fiber, and the target regions corresponding to different modes are located at different positions on the far-field receiving plane.

4. The optical fiber mode demultiplexing communication method according to claim 1, wherein: Step 2 includes the following sub-steps: Based on the input complex amplitude distribution and output intensity distribution of several channels on the metasurface, the phase distribution of the metasurface is optimized to obtain the angular arrangement of several nanostructures on the substrate of the metasurface; Determining the operating wavelength of the metasurface according to the operating wavelength of the optical fiber, and determining the material characteristic parameters of the substrate and nanostructure of the metasurface; Based on the working wavelength of the metasurface, the geometric parameters of the nanostructure are scanned to determine the size parameters of the substrate and the nanostructure of the metasurface, so that the metasurface has the function of a half-wave plate for polarization conversion and phase modulation; The arrangement of the metasurface is constructed, including a substrate and a plurality of nanostructures of the same size and different rotation angles that are periodically arranged on the substrate. Based on the optimized rotation angle arrangement, the plurality of nanostructures on the substrate of the metasurface are periodically arranged to obtain the metasurface for realizing optical fiber mode demultiplexing communication.

5. The optical fiber mode demultiplexing communication method according to claim 4, characterized in that: The output intensity distribution O is expressed as: Where I represents the input complex amplitude distribution, P represents the phase distribution of the metasurface, and F represents the Fourier transform; Based on the above formula, the phase distribution of the metasurface is obtained by iterative optimization using an algorithm.

6. The optical fiber mode demultiplexing communication method according to claim 4, characterized in that: The working wavelength of the optical fiber is used as the working wavelength of the metasurface, and the materials of the substrate and nanostructure of the metasurface are both made of single crystal silicon material with a transmittance of more than 70% for the working wavelength light.

7. The optical fiber mode demultiplexing communication method according to claim 4, characterized in that: The base of the metasurface is divided into a number of periodic square units of uniform size, each with a side length of CS; a nanobrick with a cubic structure is provided on the working surface of each square unit, each with a length of L, a width of W, and a height of H; At the operating wavelength, electromagnetic simulation software is used to scan the side length CS of the square unit and the length L, width W and height H of the nanobrick to select geometric parameters that make the polarization conversion efficiency and phase modulation amount of the metasurface meet the preset conditions.

8. The optical fiber mode demultiplexing communication method according to claim 7, characterized in that: A coordinate system XOY is established on the working surface of the square unit, wherein the X-axis and the Y-axis are parallel to the two sets of sides of the working surface respectively, and the angle between the long axis direction of the nanobrick and the X-axis direction is taken as the rotation angle θ of the nanobrick; Based on the relationship between the phase distribution P of the metasurface and twice the rotation angle θ of the nanobrick, the rotation angle arrangement of the nanobrick is determined according to the determined metasurface phase distribution.

9. The optical fiber mode demultiplexing communication method according to claim 1, wherein: In step 3, the bit data loaded onto each mode of the optical fiber by the signal transmitter in a coherent modulation manner comes from a number of selected transmission images, the pixel matrices of the transmission images are arranged in sequence, and a decimal-to-binary conversion is performed to generate corresponding bit data; the bit data coupled by the signal receiver in each target area is converted from binary to decimal, and restored to a pixel matrix in sequence to obtain a received image.

10. A fiber mode demultiplexing communication system, characterized in that: include: A signal transmitter, an optical fiber, a metasurface, and a signal receiver; the optical fiber mode demultiplexing communication system is used to execute the steps in the optical fiber mode demultiplexing communication method as described in any one of claims 1-9.

Images