Optical communication method using orbital angular momentum multiplexing coding and based on transfer learning decoding

Abstract

The invention discloses an optical communication method using orbital angular momentum multiplexing coding and based on transfer learning decoding, and relates to the technical field of optical communication, and the method comprises the steps: converting a binary bit stream corresponding to a to-be-transmitted image into a plurality of code element symbols according to a preset coding scheme; the preset coding scheme comprises a one-to-one correspondence relationship between each code element symbol and each multiplexed light beam in the light beam set; the light beam set comprises orbital angular momentum multiplexing light beams formed by superposition of orders and weights of different orbital angular momentums; obtaining a multiplexed light beam according to the spiral phase diagram; carrying out coaxial interference on the multiplexed light beam and the Gaussian plane wave to obtain an interference light beam; the interference light beam is interfered by the atmosphere to obtain an interfered interference light beam; inputting the intensity diagram of the interfered interference beam into the trained transfer learning network to obtain an orbital angular momentum spectrum; and recovering the to-be-transmitted image according to the orbital angular momentum spectrum and the preset coding scheme. According to the invention, the coding capacity and efficiency can be improved, the bit error rate is reduced, and reliable transmission is realized.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to an optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding. Background Art

[0002] In recent years, the development of physical resource dimensions such as wavelength, phase, amplitude, frequency and polarization of light beams has reached its upper limit. In order to further meet people's demand for high-speed and high-bandwidth communications, new ways need to be sought to increase channel capacity. Orbital Angular Momentum (OAM) beams, OAM eigenvalues ​​correspond to different OAM modes, and OAM beams with different topological charges are mutually orthogonal. This property provides a new dimension of information transmission for optical communications, which can greatly improve the channel capacity and communication rate of communication systems. In the laboratory, vortex beams with large topological charges are difficult to generate. Therefore, how to use limited OAM mode values ​​for encoding for large-capacity and high-speed communications and improve coding capacity and efficiency is a question worth considering.

[0003] In some special cases, the intensity patterns obtained after the conjugated orbital angular momentum is multiplexed with different weights have no difference or the difference is difficult to distinguish with the naked eye. Similar situations also occur when the weight difference of the superposition of conjugated orbital angular momentum is small. Therefore, how to increase the difference in the intensity patterns of these multiplexed beams, the coding capacity and efficiency, and reduce the bit error rate are also issues that need further consideration. Summary of the invention

[0004] The purpose of this application is to provide an optical communication method using orbital angular momentum multiplexing coding and decoding based on transfer learning, which can encode capacity and efficiency, reduce bit error rate, and achieve reliable transmission.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides an optical communication method based on orbital angular momentum using orbital angular momentum multiplexing encoding and based on transfer learning decoding, comprising:

[0007] Converting a binary bit stream corresponding to the image to be transmitted into a plurality of codeword symbols according to a preset coding scheme; the preset coding scheme includes a one-to-one correspondence between each codeword symbol and each orbital angular momentum multiplexing beam in the beam set; the beam set includes a plurality of orbital angular momentum multiplexing beams formed by superimposing the order of each preset orbital angular momentum with each preset superposition weight;

[0008] According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing light beam corresponding to the code element symbol is obtained;

[0009] Performing coaxial interference between the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave to obtain an interference beam;

[0010] The interference beam is subjected to atmospheric interference simulated by the atmospheric turbulence phase screen to obtain an interference beam after interference;

[0011] At the receiving end, a CCD camera is used as an image acquisition device to collect the intensity map of the interference light beam after interference, and the collected intensity map is input into the trained transfer learning network to obtain the orbital angular momentum spectrum of the interference light beam after interference;

[0012] The image to be transmitted is restored according to the orbital angular momentum spectrum of the interference light beam after interference and a preset coding scheme.

[0013] Optionally, converting a binary bit stream corresponding to the image to be transmitted into a plurality of code element symbols according to a preset coding scheme specifically includes:

[0014] Binary-encode the image to be transmitted to obtain a binary bit stream corresponding to the image to be transmitted;

[0015] According to a preset coding scheme, a bit stream segment in a binary bit stream corresponding to an image to be transmitted is converted into a code element symbol to obtain a plurality of code element symbols; the bit stream segment is composed of n continuous bit streams; n is a positive integer greater than 1.

[0016] Optionally, the preset encoding scheme includes 2 n The code element symbol and the beam set 2 n One-to-one correspondence between the orbital angular momentum multiplexed beams.

[0017] Optionally, obtaining an orbital angular momentum multiplexing beam corresponding to any code element symbol according to a spiral phase diagram corresponding to the code element symbol specifically includes:

[0018] A spatial light modulator is used to load the spiral phase image corresponding to the code element symbol to obtain an orbital angular momentum multiplexing light beam corresponding to the code element symbol.

[0019] Optionally, the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave are coaxially interfered to obtain an interference beam, specifically:

[0020] The orbital angular momentum multiplexing light beam corresponding to the code element symbol modulated by the spatial light modulator is coaxially interfered with a Gaussian plane wave to obtain an interference light beam.

[0021] Optionally, the atmospheric turbulence phase screen construction method is specifically as follows:

[0022] The phase power spectrum of the random phase screen is obtained by simulating the power spectrum of the atmospheric turbulence, and the atmospheric turbulence phase screen is constructed by the phase power spectrum of the random phase screen.

[0023] Optionally, the training process of the transfer learning network specifically includes:

[0024] Acquiring a sample image and an orbital angular momentum spectrum of the sample image;

[0025] Converting a binary bit stream corresponding to the sample image into a plurality of code element symbols according to a preset coding scheme;

[0026] According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing light beam corresponding to the code element symbol is obtained;

[0027] Performing coaxial interference between the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave to obtain a sample interference beam;

[0028] The sample interference beam is subjected to atmospheric interference simulated by an atmospheric turbulence phase screen to obtain a disturbed sample interference beam;

[0029] The receiving end uses a CCD camera as an image acquisition device to collect the intensity map of the sample interference beam after interference;

[0030] The orbital angular momentum spectrum of the sample image is used as a label, and the transfer learning network is trained according to the collected intensity map and the orbital angular momentum spectrum of the sample image to obtain a trained transfer learning network.

[0031] Optionally, the transfer learning network is a transfer learning architecture based on VGG16.

[0032] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0033] The present application provides an optical communication method utilizing orbital angular momentum multiplexing coding and decoding based on transfer learning. An interference beam is obtained by coaxially interfering an orbital angular momentum multiplexing beam corresponding to an image to be transmitted with a Gaussian plane wave. The method of interfering the orbital angular momentum multiplexing beam with the plane wave is used to increase the difference in light intensity performance of these orbital angular momentum multiplexing beams, thereby further improving the recognition accuracy of the transfer learning network, reducing the bit error rate, and achieving reliable transmission. Previous coding symbols did not utilize weighted coding of OAM modes, and only 7 code element symbols could be encoded using three OAM modes. However, the preset coding scheme of the present application utilizes weighted coding of OAM modes, and multiple code element symbols can be encoded using limited OAM modes, thereby improving coding capacity and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A flow chart of an optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding provided in an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of an optical communication device using orbital angular momentum multiplexing encoding and transfer learning-based decoding provided in an embodiment of the present invention;

[0037] Figure 3 The light intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference provided by an embodiment of the present invention;

[0038] Figure 4 An interference light intensity distribution diagram after the orbital angular momentum multiplexing light beam provided in an embodiment of the present invention interferes with a plane wave;

[0039] Figure 5 A one-to-one correspondence between an interference light intensity distribution diagram and a code element symbol after interference between an orbital angular momentum multiplexed light beam with different weights provided in an embodiment of the present invention and a plane wave;

[0040] Figure 6 A schematic diagram of orbital angular momentum spectrum analysis performed by a transfer learning network provided in an embodiment of the present invention;

[0041] Figure 7 A schematic diagram of layered simulation of atmospheric turbulence provided by an embodiment of the present invention;

[0042] Figure 8 A schematic diagram of a transfer learning architecture provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0044] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0045] By utilizing the completely orthogonal property of vortex beams with different mode values, vortex beams with different OAM mode values ​​(orders of orbital angular momentum) can be multiplexed as channels with different loaded digital information. Traditional orbital angular momentum multiplexing is obtained by coaxial interference of vortex beams with different OAM mode values, and the weights of different OAM mode values ​​are all 1. However, vortex beams with large topological charge are usually difficult to produce in the laboratory, and it is also difficult for the receiving end to identify them when using them for communication. Therefore, the present application introduces the weights of different vortex beams when they are superimposed, uses it as a dimension of encoding, adds positive and negative superposition, and introduces the idea of ​​interference, stipulating that the sum of the weights of vortex beams carrying different OAM mode values ​​when superimposed is 1. At this time, limited OAM mode values ​​can be used for encoding to achieve large-capacity and high-speed communication, coding capacity and efficiency. When using orbital angular momentum for communication, a very important issue is how to quickly and accurately identify the OAM mode values ​​of different vortex beams at the receiving end to achieve demodulation. Since the intensity distribution of vortex beams of different OAM mode values ​​in the composite state after multiplexing is generally different, the detection and identification of OAM mode values ​​at the receiving end can be regarded as an image classification problem. In recent years, the Convolution Neural Network (CNN) in deep learning has made great progress in image classification and target detection due to its powerful feature extraction capabilities. Compared with traditional vortex beam detection methods, deep learning methods do not require complex equipment, have high recognition accuracy, and fast recognition speed, so they have been widely used in the field of optical communications. Based on this, the present application provides an optical communication method using orbital angular momentum multiplexing encoding and decoding based on transfer learning, such as Figure 1 and Figure 6 As shown, the following steps are included:

[0046] Step 201: Convert the binary bit stream corresponding to the image to be transmitted into multiple codeword symbols according to a preset coding scheme; the preset coding scheme includes a one-to-one correspondence between each codeword symbol and each orbital angular momentum multiplexing beam in the beam set; the beam set includes multiple orbital angular momentum multiplexing beams formed by superimposing the order of each preset orbital angular momentum with each preset superposition weight. For example, for any order of the preset orbital angular momentum, the order is superimposed with each preset weight to obtain multiple orbital angular momentum multiplexing beams corresponding to the order, and the same operation is performed for other orders to finally form a beam set.

[0047] Step 202: According to the spiral phase diagram corresponding to any code element symbol, the orbital angular momentum multiplexing beam corresponding to the code element symbol is obtained. Specifically, there is a one-to-one mapping relationship between the code element symbol and the orbital angular momentum multiplexing beam corresponding to the image to be transmitted, and the spiral phase diagram of the orbital angular momentum multiplexing beam corresponding to each code element symbol is loaded on the spatial light modulator to generate the orbital angular momentum multiplexing beam.

[0048] Step 203: coaxially interfering the orbital angular momentum multiplexing beam corresponding to the code element symbol with the Gaussian plane wave to obtain an interference beam.

[0049] Step 204: The interference light beam undergoes atmospheric interference simulated by the atmospheric turbulence phase screen to obtain an interference light beam after interference.

[0050] Step 205: The receiving end uses a CCD camera as an image acquisition device to acquire the intensity map of the interference light beam after the interference, and inputs the acquired intensity map into the trained transfer learning network to obtain the orbital angular momentum spectrum of the interference light beam after the interference. The orbital angular momentum spectrum contains each order and the weight of the order.

[0051] Step 206: restore the image to be transmitted according to the orbital angular momentum spectrum of the interfered light beam and the preset encoding scheme.

[0052] In practical applications, the binary bit stream corresponding to the image to be transmitted is converted into multiple code element symbols according to a preset coding scheme, specifically including:

[0053] The image to be transmitted is binary-encoded to obtain a binary bit stream corresponding to the image to be transmitted.

[0054] According to the preset coding scheme, the bit stream segment in the binary bit stream corresponding to the image to be transmitted is converted into a code symbol to obtain a plurality of code symbol symbols; the bit stream segment is composed of n continuous bit streams; n is a positive integer greater than 1. When n is 5, the preset coding scheme is specifically shown in Table 1.

[0055] Table 1 Preset encoding scheme

[0056] Symbol Encoding Compound vortex beam Weight of beam superposition Symbol encoding Compound vortex beam Weight of beam superposition 00000 L1=-2,L2=2,L3=1 (0，0，0) 10000 L1=-2,L3=1 (0.4，0.6) 00001 L1=-2,L2=2,L3=1 (0，0，1) 10001 L1=-2,L3=1 (0.6，0.4) 00010 L1=-2,L2=2,L3=1 (0，1，0) 10010 L1=-2,L3=1 (0.1，0.9) 00011 L1=-2,L2=2,L3=1 (1，0，0) 10011 L2=2,L3=1 (0.9，0.1) 00100 L1=-2,L2=2 (0.1，0.9) 10100 L2=2,L3=1 (0.5，0.5) 00101 L1=-2,L2=2 (0.9，0.1) 10101 L2=2,L3=1 (0.3，0.7) 00110 L1=-2,L2=2 (0.5，0.5) 10110 L2=2,L3=1 (0.7，0.3) 00111 L1=-2,L2=2 (0.3，0.7) 10111 L2=2,L3=1 (0.4，0.6) 01000 L1=-2,L2=2 (0.7，0.3) 11000 L2=2,L3=1 (0.6，0.4) 01001 L1=-2,L2=2 (0.4，0.6) 11001 L1=-2, L2=2,L3=1 (0.1，0.7，0.2) 01010 L1=-2,L2=2 (0.6，0.4) 11010 L1=-2, L2=2,L3=1 (0.7，0.1，0.2) 01011 L1=-2,L3=1 (0.1，0.9) 11011 L1=-2, L2=2,L3=1 (0.1，0.2，0.7) 01100 L1=-2,L3=1 (0.9，0.1) 11100 L1=-2, L2=2,L3=1 (0.3，0.3，0.4) 01101 L1=-2,L3=1 (0.5，0.5) 11101 L1=-2, L2=2, L3=1 (0.1，0.8，0.1) 01110 L1=-2,L3=1 (0.3，0.7) 11110 L1=-2, L2=2,L3=1 (0.8，0.1，0.1) 01111 L1=-2,L3=1 (0.7，0.3) 11111 L1=-2, L2=2,L3=1 (0.1，0.1，0.8)

[0057] In practical applications, the preset coding scheme includes a one-to-one correspondence between 2n code element symbols and 2n orbital angular momentum multiplexed beams in the beam set.

[0058] In practical applications, according to the spiral phase diagram corresponding to any symbol, the orbital angular momentum multiplexing beam corresponding to the symbol is obtained; the orbital angular momentum multiplexing beam corresponding to the symbol is coaxially interfered with a Gaussian plane wave to obtain an interference beam, specifically:

[0059] The light field expression of a Laguerre-Gauss (LG) beam transmitted along the z-axis in a cylindrical coordinate system is:

[0060]

[0061] Where P is the radial index, λ is the wavelength, l is the OAM mode value, is the waist radius of the LG beam at z, w0 is the waist radius of the fundamental mode Gaussian beam at z = 0, z R =πw0 2 / λ is the Rayleigh distance, is the wave number of the beam, is the Gouy phase, is the normalized Laguerre polynomial. When p = 0, is 1, and the light field expression of the LG beam is:

[0062]

[0063] The light field expression of the vortex beam can be expanded according to the following formula:

[0064]

[0065] in,

[0066]

[0067] The light field intensity of the lth spiral harmonic is:

[0068]

[0069] Therefore, the intensity weight of each OAM mode in the orbital angular momentum multiplexed beam is expressed by the following equation:

[0070]

[0071] When p = 0, LG beams with different OAM mode values ​​are multiplexed according to a certain weight to generate a weighted orbital angular momentum multiplexed beam, and its light field expression is:

[0072]

[0073] Taking the three OAM mode values ​​of {-2, 2, 1} as an example, OAM multiplexing with different weights is performed. The Laguerre-Gaussian beams with three OAM mode values ​​are respectively weighted (0, 0, 0), (0, 0, 1), (0, 1, 0), (1, 0, 0), (0.1, 0.9, 0), (0.9, 0.1, 0), (0.5, 0.5, 0), (0.3, 0.7, 0), (0.7, 0.3, 0), (0.4, 0.6, 0), (0.6, 0.4, 0), (0.1, 0, 0.9), (0.9, 0, 0.1), (0.5, 0, 0.5), (0.3, 0, 0.7), (0. 7, 0, 0.3), (0.4, 0, 0.6), (0.6, 0, 0.4), (0, 0.1, 0.9), (0, 0.9, 0.1), (0, 0.5, 0.5), (0, 0.3, 0.7), (0, 0.7, 0.3), (0, 0.4, 0.6), (0, 0.6, 0.4), (0.1, 0.7, 0.2), (0.7, 0.1, 0.2), (0.1, 0.2, 0.7) (0.3, 0.3, 0.4), (0.1, 0.8, 0.1), (0.8, 0.1, 0.1), (0.1, 0.1, 0.8) can be superimposed to produce 32 intensity patterns.

[0074] Generally speaking, after different OAM mode values ​​are multiplexed according to different weights, their intensity distributions are generally different. However, there are special cases. For example, the intensity patterns obtained after the conjugated orbital angular momentum -2 and 2 are multiplexed with weights (0, 1) and (1, 0) respectively have no difference. Similar cases include -2 and 2 superimposed with weights (0.1, 0.9) and (0.9, 0.1) respectively, and the difference in their intensity patterns is difficult to distinguish with the naked eye. Similar situations also occur when the weights of the superposition of conjugated orbital angular momentum are relatively small, such as when the OAM mode values ​​-2 and 2 are superimposed with weights of (0.4, 0.6), (0.6, 0.4), (0.5, 0.5), (0.3, 0.7), and (0.7, 0.3) respectively. If the multiplexed vortex beam is transmitted directly, it will inevitably cause an increase in the bit error rate of the decoding module. Therefore, the plane wave and the weighted vortex beam are coaxially interfered to generate an interference beam to increase the difference in the intensity performance of these weighted reused vortex beams. Taking the OAM mode values ​​{-2, 2} as an example, the weights (0, 1) and (1, 0) are reused respectively. Before interference, Figure 3 As shown, Figure 3 (a) shows the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00000, the preset orbital angular momentum order is L1=-2, L2=2, L3=1, and the preset superposition weight is (0, 0, 0). Figure 3(b) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00001, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0, 1). Figure 3 (c) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00010, L1=-2, L2=2, L3=1, and the superposition weight is (0, 1, 0). Figure 3 (d) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00011, L1=-2, L2=2, L3=1, and the superposition weight is (1, 0, 0). Figure 3 (e) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0.9, 0). Figure 3 (f) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0.1, 0). Figure 3 (g) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0.5, 0). Figure 3 (h) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 00111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0.7, 0). Figure 3 (i) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0.3, 0). Figure 3 (j) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0.6, 0). Figure 3 (k) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01010, L1=-2, L2=-2, L3=1, and the superposition weight is (06, 0.4, 0). Figure 3 (l) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01011, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0, 0.9). Figure 3(m) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0, 0.1). Figure 3 Where (n) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0, 0.5). Figure 3 (o) in the figure indicates the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0, 0.7). Figure 3 Where (p) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 01111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0, 0.3). Figure 3 (q) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0, 0.6). Figure 3 (r) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.6, 0, 0.4). Figure 3 (s) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10010, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0, 0.9). Figure 3 (t) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10011, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.9, 0.1). Figure 3 (u) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10100, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.5, 0.5). Figure 3 (v) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10101, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.3, 0.7). Figure 3 (w) represents the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10110, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.7, 0.3). Figure 3 (x) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 10111, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.4, 0.6). Figure 3 (y) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11000, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.6, 0.4). Figure 3 (z) represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11001, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.7, 0.2). Figure 3 (A) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11010, L1=-2, L2=2, L3=1, and the superposition weight is (0.7, 0.1, 0.2). Figure 3 (B) shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11011, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.2, 0.7). Figure 3 (C) in the middle shows the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11100, L1=-2, L2=2, L3=1, and the superposition weight is (0.3, 0.3, 0.4). Figure 3 (D) in the figure shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11101, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.8, 0.1). Figure 3 (E) in the middle represents the intensity distribution diagram of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11110, L1=-2, L2=2, L3=1, and the superposition weight is (0.8, 0.1, 0.1). Figure 3 (F) in the figure shows the intensity distribution of the orbital angular momentum multiplexed Laguerre-Gaussian beam without plane wave interference when the symbol code is 11111, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.1, 0.8). The intensity distribution of the beams is a ring-shaped distribution with a dark core in the center. The size of the ring is exactly the same. The OAM mode value cannot be directly distinguished from the intensity distribution. After the two multiplexed beams are coaxially interfered with the plane wave, as shown in Figure 4 As shown, Figure 4 (a) shows the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00000, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0, 0). Figure 4 (b) shows the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00001, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0, 1). Figure 4 (c) shows the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00010, L1=-2, L2=2, L3=1, and the superposition weight is (0, 1, 0). Figure 4 (d) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00011, L1=-2, L2=2, L3=1, and the superposition weight is (1, 0, 0). Figure 4 (e) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0.9, 0). Figure 4 (f) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0.1, 0). Figure 4 (g) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0.5, 0). Figure 4 (h) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0.7, 0). Figure 4 (i) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0.3, 0). Figure 4 (j) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0.6, 0). Figure 4 (k) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01010, L1=-2, L2=-2, L3=1, and the superposition weight is (06, 0.4, 0). Figure 4 (l) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01011, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0, 0.9). Figure 4(m) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0, 0.1). Figure 4 Where (n) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0, 0.5). Figure 4 (o) in the figure indicates the interference intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0, 0.7). Figure 4 Where (p) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0, 0.3). Figure 4 (q) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0, 0.6). Figure 4 (r) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.6, 0, 0.4). Figure 4 (s) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10010, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.1, 0.9). Figure 4 (t) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10011, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.9, 0.1). Figure 4 (u) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10100, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.5, 0.5). Figure 4 (v) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10101, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.3, 0.7). Figure 4 (w) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10110, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.7, 0.3). Figure 4(x) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10111, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.4, 0.6). Figure 4 (y) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11000, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.6, 0.4). Figure 4 (z) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11001, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.7, 0.2). Figure 4 (A) shows the interference intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11010, L1=-2, L2=2, L3=1, and the superposition weight is (0.7, 0.1, 0.2). Figure 4 (B) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 11011, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.2, 0.7). Figure 4 (C) in the middle represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11100, L1=-2, L2=2, L3=1, and the superposition weight is (0.3, 0.3, 0.4). Figure 4 (D) in the figure represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11101, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.8, 0.1). Figure 4 (E) in the figure represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11110, L1=-2, L2=2, L3=1, and the superposition weight is (0.8, 0.1, 0.1). Figure 4 (F) in the middle represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11111, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.1, 0.8). The interference pattern appears as a fork-shaped distribution with a central dark spot. The difference is that the opening direction of the fork-shaped stripes in the former is upward, while the opening direction of the fork-shaped stripes in the latter is downward. The effect of interference is to improve the spectral analysis accuracy of the convolutional neural network in the decoding module and reduce the bit error rate.

[0075] The expression of the light intensity distribution after the weighted repeated Laguerre-Gaussian beam interferes with the plane wave is as follows:

[0076] I=|E1+E2| 2

[0077] =|∑ l w l E LG (r,φ,z)+e -ikx | 2

[0078] After plane wave interference, 32 types of multiplexed beams correspond to 32 interference patterns one by one, and each interference pattern corresponds to a code element symbol. Only three OAM modes can encode 32 code element symbols to achieve 5-bit transmission. The weights of three Laguerre-Gaussian beams with different OAM mode values ​​are used for encoding, and the weight information is effectively used. The capacity and efficiency are encoded with limited OAM mode values, and the difference in the intensity distribution of the multiplexed beams is increased by the method of plane wave interference to reduce the bit error rate of the decoding module and achieve reliable transmission. A 32ary optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding is realized, which can greatly improve the channel capacity of the communication system.

[0079] Specifically, the weighted multiplexed Laguerre-Gaussian beam and plane wave interference are used for data simulation, and the different light intensities of the interference pattern are used for encoding. 32 multiplexed intensity patterns correspond to 32 interference patterns. The data “00000-00001-00010-00011-00100-00101-00110-00111-01000-01001-01010-0 "1011-01100-01101-01110-01111-10000-10001-10010-10011-10100-10101-10110-10111-11000-11001-11010-11011-11100-11101-11110-11111" is encoded as 32 interference patterns, Figure 5 The one-to-one correspondence between the interference light intensity distribution diagram and the code element symbol after the orbital angular momentum multiplexing beam with different weights interferes with the plane wave is given. Figure 5 (a) shows the interference intensity distribution diagram after the vortex beam interferes with the plane wave when the symbol code is 00000, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0, 0). Figure 5 (b) shows the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00001, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0, 1). Figure 5 (c) shows the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00010, L1=-2, L2=2, L3=1, and the superposition weight is (0, 1, 0). Figure 5(d) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00011, L1=-2, L2=2, L3=1, and the superposition weight is (1, 0, 0). Figure 5 (e) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0.9, 0). Figure 5 (f) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 00101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0.1, 0). Figure 5 (g) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0.5, 0). Figure 5 (h) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 00111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0.7, 0). Figure 5 (i) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0.3, 0). Figure 5 (j) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0.6, 0). Figure 5 (k) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01010, L1=-2, L2=-2, L3=1, and the superposition weight is (06, 0.4, 0). Figure 5 (l) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01011, L1=-2, L2=-2, L3=1, and the superposition weight is (0.1, 0, 0.9). Figure 5 (m) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01100, L1=-2, L2=-2, L3=1, and the superposition weight is (0.9, 0, 0.1). Figure 5 Where (n) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01101, L1=-2, L2=-2, L3=1, and the superposition weight is (0.5, 0, 0.5). Figure 5(o) in the figure indicates the interference intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01110, L1=-2, L2=-2, L3=1, and the superposition weight is (0.3, 0, 0.7). Figure 5 Where (p) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 01111, L1=-2, L2=-2, L3=1, and the superposition weight is (0.7, 0, 0.3). Figure 5 (q) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10000, L1=-2, L2=-2, L3=1, and the superposition weight is (0.4, 0, 0.6). Figure 5 (r) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10001, L1=-2, L2=-2, L3=1, and the superposition weight is (0.6, 0, 0.4). Figure 5 (s) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10010, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.1, 0.9). Figure 5 (t) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10011, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.9, 0.1). Figure 5 (u) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10100, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.5, 0.5). Figure 5 (v) represents the interference light intensity distribution diagram after the vortex beam interferes with the plane wave when the symbol code is 10101, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.3, 0.7). Figure 5 (w) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10110, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.7, 0.3). Figure 5 (x) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 10111, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.4, 0.6). Figure 5 (y) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11000, L1=-2, L2=2, L3=1, and the superposition weight is (0, 0.6, 0.4). Figure 5(z) represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11001, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.7, 0.2). Figure 5 (A) shows the interference intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11010, L1=-2, L2=2, L3=1, and the superposition weight is (0.7, 0.1, 0.2). Figure 5 (B) shows the interference intensity distribution diagram of the orbital angular momentum multiplexing beam after the interference with the plane wave when the symbol code is 11011, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.2, 0.7). Figure 5 (C) in the middle represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11100, L1=-2, L2=2, L3=1, and the superposition weight is (0.3, 0.3, 0.4). Figure 5 (D) in the figure represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11101, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.8, 0.1). Figure 5 (E) in the figure represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11110, L1=-2, L2=2, L3=1, and the superposition weight is (0.8, 0.1, 0.1). Figure 5 (F) in the middle represents the interference light intensity distribution diagram after the orbital angular momentum multiplexing beam interferes with the plane wave when the symbol code is 11111, L1=-2, L2=2, L3=1, and the superposition weight is (0.1, 0.1, 0.8).

[0080] In practical applications, according to the spiral phase diagram corresponding to any code element symbol, the orbital angular momentum multiplexing beam corresponding to the code element symbol is obtained, which specifically includes:

[0081] A spatial light modulator is used to load the spiral phase image corresponding to the code element symbol to obtain an orbital angular momentum multiplexing light beam corresponding to the code element symbol.

[0082] In practical applications, the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave are coaxially interfered to obtain an interference beam, specifically:

[0083] The orbital angular momentum multiplexing light beam corresponding to the code element symbol modulated by the spatial light modulator is coaxially interfered with a Gaussian plane wave to obtain an interference light beam.

[0084] In practical applications, the atmospheric turbulence phase screen construction method is specifically as follows:

[0085] The phase power spectrum of the random phase screen is obtained by simulating the power spectrum of the atmospheric turbulence, and the atmospheric turbulence phase screen is constructed by the phase power spectrum of the random phase screen.

[0086] In practical applications, such as Figure 7 As shown in the figure, the phase power spectrum of the random phase screen is obtained by simulating the power spectrum of atmospheric turbulence, and the atmospheric turbulence phase screen is constructed as follows:

[0087] The random phase screen of the turbulent medium is generated using the Hill-Andrews spatial spectrum using the power spectrum inversion method:

[0088]

[0089] In the two-dimensional plane of space, for atmospheric turbulence, a1=1.802, a2=0.254, a1 and a2 are constants and have no practical meaning.

[0090]

[0091] where k l =3.3 / l0, k0=2π / L0, k x and k y are the wave numbers in the x and y directions, respectively, and l0 and L0 represent the inner and outer scales of the turbulence, respectively; is the atmospheric turbulence intensity, is the wave number of the beam.

[0092] The relationship between the phase spectrum and the atmospheric refractive index spectrum can be described as:

[0093]

[0094] The variance of the random phase screen frequency domain distribution is:

[0095]

[0096] Where N is the number of sampling points and Δx is the sampling interval.

[0097] The formula for calculating the phase screen in the spatial domain is:

[0098]

[0099] Where FFT stands for two-dimensional fast Fourier transform, C N×N is an N×N random phase matrix that obeys a Gaussian distribution with a mean of 0 and a variance of 1.

[0100] After the interference beam passes through the simulated atmospheric turbulence phase screen and transmits a certain distance, its electric field expression is:

[0101]

[0102] Among them, FFT -1 represents the two-dimensional fast inverse Fourier transform, Specifically, when simulating the transmission of an interference beam in an atmospheric turbulence environment, the light waist w0 is set to 2.5 cm, the wavelength λ is set to 632.8 nm, the radial index p is set to 0, the OAM mode number l1 is set to -2, l2 is set to 2, l3 is set to 1, and the turbulence intensity is set to Inner dimension l0=0.003nm, outer dimension L0=50m, phase screen resolution N=300, interval Δz=100m between phase screens.

[0103] In practical applications, the training process of the transfer learning network specifically includes:

[0104] Acquiring a sample image and an orbital angular momentum spectrum of the sample image;

[0105] Converting a binary bit stream corresponding to the sample image into a plurality of code element symbols according to a preset coding scheme;

[0106] According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing light beam corresponding to the code element symbol is obtained;

[0107] Performing coaxial interference between the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave to obtain a sample interference beam;

[0108] The sample interference beam is subjected to atmospheric interference simulated by an atmospheric turbulence phase screen to obtain a disturbed sample interference beam;

[0109] The receiving end uses a CCD camera as an image acquisition device to collect the intensity map of the sample interference beam after interference;

[0110] The orbital angular momentum spectrum of the sample image is used as a label, and the transfer learning network is trained according to the collected intensity map and the orbital angular momentum spectrum of the sample image to obtain a trained transfer learning network. Specifically, the transfer learning network can be a convolutional neural network. The convolutional neural network is first trained, and then the trained convolutional neural network is used to process the collected intensity map to obtain the orbital angular momentum spectrum of the interference light beam after interference, and then the orbital angular momentum spectrum is analyzed to restore the code element symbol corresponding to the collected intensity map to achieve decoding. The specific decoding process is to input the collected interference light intensity distribution map (collected intensity map) into the convolutional neural network trained with a large amount of data, and the convolutional neural network realizes orbital angular momentum spectrum analysis according to different intensity patterns, and restores the binary data according to the one-to-one correspondence between the intensity map and the code element symbol, thereby restoring the original image information and achieving demodulation.

[0111] In practical applications, when training a convolutional neural network, data simulation is performed based on the light field expression of the orbital angular momentum multiplexed beam and the plane wave interference beam after transmission in atmospheric turbulence to construct a data set. The image data set is the interference pattern, and the label is the corresponding OAM mode component and its weight. The portability of the features extracted by CNN can be utilized, and the pre-trained network can be used as a feature extractor to extract features from the data set and start training.

[0112] In practical applications, the transfer learning network uses the convolutional base of the VGG16 network trained on ImageNet as a feature extractor, and the softmax function acts as a classifier. The VGG16-based transfer learning architecture is used to perform orbital angular momentum spectrum analysis on the received interference pattern (intensity map of the interference beam after interference), and the code element symbol corresponding to the collected interference pattern is restored to achieve decoding. Specifically, Figure 8 As shown in the figure, the transfer learning architecture based on VGG16 includes a convolutional module and a classifier connected in sequence. The classifier includes: a Flatten layer, a Dense layer (fully connected layer), and a DropOut layer connected in sequence; the convolutional module includes five convolutional bases set in series, each of which is composed of two convolutional layers connected in sequence and a maximum pooling layer. The Flatten layer is used to convert multi-dimensional input into one dimension, and the DropOut layer is added to prevent overfitting. The convolutional bases in the architecture are frozen, that is, during the training process, the weights of one or more layers are kept unchanged.

[0113] In practical applications, when training the transfer learning architecture based on VGG16, a data set is constructed using images of interference light beams after being transmitted through simulated atmospheric turbulence to train the transfer learning architecture based on VGG16.

[0114] The present application proposes a coded optical communication method for orbital angular momentum weight reuse based on transfer learning. First, the image to be transmitted is converted into a binary code stream and then orbital angular momentum encoding is performed. Every five bits of binary information correspond to a code element symbol, and multiple code element symbols corresponding to the image to be transmitted are obtained. The spatial light modulator loads the spiral phase map corresponding to the code element symbol, thereby generating an orbital angular momentum multiplexing beam corresponding to the code element symbol, and then the orbital angular momentum multiplexing beam corresponding to the code element symbol is coaxially interfered with a Gaussian plane wave to increase the intensity pattern difference between orbital angular momentum multiplexing beams with different weights. The interference beam is transmitted through a simulated turbulent phase screen, and the interference pattern after transmission is collected at the receiving end. The received interference beam is subjected to orbital angular momentum spectrum analysis using a trained convolutional neural network (transfer learning network), and the classification of orbital angular momentum multiplexing beams with different weights is realized. The code element symbol corresponding to the interference pattern is restored, and the binary code stream is restored. After integrating and classifying the data information, the original image information is obtained.

[0115] Compared with the prior art, the present invention has the following beneficial effects:

[0116] The weight information of Laguerre-Gaussian beams with different OAM mode values ​​is fully utilized for encoding, so as to further improve the coding efficiency of digital signals under limited OAM mode values. The method of orbital angular momentum multiplexing beam and plane wave interference is used to increase the difference in the light intensity performance of these weighted multiplexed vortex beams, so as to further improve the recognition accuracy of the transfer learning network at the receiving end, reduce the bit error rate, and achieve reliable transmission.

[0117] Based on the same inventive concept, the embodiment of the present application also provides an optical communication device using orbital angular momentum multiplexing coding and transfer learning decoding for implementing the above-mentioned optical communication method using orbital angular momentum multiplexing coding and transfer learning decoding. The device, such as Figure 2 As shown, including:

[0118] The encoding module is used to convert a binary bit stream corresponding to an image to be transmitted into multiple codeword symbols according to a preset encoding scheme; the preset encoding scheme includes a one-to-one correspondence between each codeword symbol and each orbital angular momentum multiplexing beam in a beam set; the beam set includes multiple orbital angular momentum multiplexing beams formed by superimposing the orders of each preset orbital angular momentum with each preset superposition weight.

[0119] The orbital angular momentum multiplexing module is used to obtain an orbital angular momentum multiplexing beam corresponding to any code element symbol according to the spiral phase diagram corresponding to the code element symbol; and coaxially interfere the orbital angular momentum multiplexing beam corresponding to the code element symbol with a Gaussian plane wave to obtain an interference beam.

[0120] The beam transmission module is used for obtaining an interference beam after interference through atmospheric interference simulated by an atmospheric turbulence phase screen.

[0121] The beam receiving module is used to collect the intensity map of the interference light beam after interference by using a CCD camera as an image acquisition device at the receiving end, and input the collected intensity map into the trained transfer learning network to obtain the orbital angular momentum spectrum of the interference light beam after interference.

[0122] The beam decoding module is used to restore the image to be transmitted based on the orbital angular momentum spectrum of the interference beam after interference and a preset encoding scheme.

[0123] As an optional implementation, the optical communication device using orbital angular momentum multiplexing encoding and transfer learning-based decoding also includes: an image preprocessing module, which is used to binary encode the image to be transmitted to obtain a binary bit stream corresponding to the image to be transmitted.

[0124] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments 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.

[0125] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding, characterized in that: The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding includes: Converting a binary bit stream corresponding to the image to be transmitted into a plurality of codeword symbols according to a preset coding scheme; the preset coding scheme includes a one-to-one correspondence between each codeword symbol and each orbital angular momentum multiplexing beam in the beam set; the beam set includes a plurality of orbital angular momentum multiplexing beams formed by superimposing the order of each preset orbital angular momentum with each preset superposition weight; According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing light beam corresponding to the code element symbol is obtained; Performing coaxial interference between the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave to obtain an interference beam; The interference beam is subjected to atmospheric interference simulated by the atmospheric turbulence phase screen to obtain an interference beam after interference; At the receiving end, a CCD camera is used as an image acquisition device to collect the intensity map of the interference light beam after interference, and the collected intensity map is input into the trained transfer learning network to obtain the orbital angular momentum spectrum of the interference light beam after interference; The image to be transmitted is restored according to the orbital angular momentum spectrum of the interference light beam after interference and a preset coding scheme.

2. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 1, characterized in that: Converting the binary bit stream corresponding to the image to be transmitted into multiple code element symbols according to a preset coding scheme, specifically including: Binary-encode the image to be transmitted to obtain a binary bit stream corresponding to the image to be transmitted; According to a preset coding scheme, a bit stream segment in a binary bit stream corresponding to an image to be transmitted is converted into a code element symbol to obtain a plurality of code element symbols; the bit stream segment is composed of n continuous bit streams; n is a positive integer greater than 1.

3. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 2, characterized in that: The preset encoding schemes include 2 n The code element symbol and the beam set 2 n One-to-one correspondence between the orbital angular momentum multiplexed beams.

4. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 1, characterized in that: According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing beam corresponding to the code element symbol is obtained, specifically comprising: A spatial light modulator is used to load the spiral phase image corresponding to the code element symbol to obtain an orbital angular momentum multiplexing light beam corresponding to the code element symbol.

5. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 4, characterized in that: The orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave are coaxially interfered to obtain an interference beam, specifically: The orbital angular momentum multiplexing light beam corresponding to the code element symbol modulated by the spatial light modulator is coaxially interfered with a Gaussian plane wave to obtain an interference light beam.

6. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 1, characterized in that: The atmospheric turbulence phase screen construction method is specifically as follows: The phase power spectrum of the random phase screen is obtained by simulating the power spectrum of the atmospheric turbulence, and the atmospheric turbulence phase screen is constructed by the phase power spectrum of the random phase screen.

7. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 1, characterized in that: The training process of the transfer learning network specifically includes: Acquiring a sample image and an orbital angular momentum spectrum of the sample image; Converting a binary bit stream corresponding to the sample image into a plurality of code element symbols according to a preset coding scheme; According to the spiral phase diagram corresponding to any code element symbol, an orbital angular momentum multiplexing light beam corresponding to the code element symbol is obtained; Performing coaxial interference between the orbital angular momentum multiplexing beam corresponding to the code element symbol and the Gaussian plane wave to obtain a sample interference beam; The sample interference beam is subjected to atmospheric interference simulated by an atmospheric turbulence phase screen to obtain a disturbed sample interference beam; The receiving end uses a CCD camera as an image acquisition device to collect the intensity map of the sample interference beam after interference; The orbital angular momentum spectrum of the sample image is used as a label, and the transfer learning network is trained according to the collected intensity map and the orbital angular momentum spectrum of the sample image to obtain a trained transfer learning network.

8. The optical communication method using orbital angular momentum multiplexing encoding and transfer learning-based decoding according to claim 1, characterized in that: The transfer learning network is a transfer learning architecture based on VGG16.

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