Phase modulation device, and coaxial OAM mode light beam conversion system and method

Abstract

The invention provides a phase modulation device and a coaxial OAM mode light beam conversion system and method.The phase modulation device comprises a phase mask plate and a reflector which are arranged at intervals, and the phase mask plate comprises a first phase plane, a second phase plane and a third phase plane which face the reflector and are arranged side by side; a first modulation channel and a second modulation channel which are opposite in direction are formed between the phase mask plate and the reflector. Through the implementation of the scheme of the invention, multiplexing and demultiplexing of multiple paths of coaxial radial high-order OAM mode light beams can be realized by using the first modulation channel and the second modulation channel; namely, by expanding the radial index p of the OAM mode as an additional multiplexing dimension and introducing a plurality of phase planes, the Gaussian beam input by the two-dimensional optical fiber array can be converted into multiple paths of coaxial radial high-order OAM mode beams, and the orthogonal mode channel supported in the optical fiber can be fully utilized to realize high-capacity communication.

Description

Technical Field

[0001] The present invention belongs to the field of optical communication, and in particular relates to a phase modulation device, a coaxial OAM mode light beam conversion system and a method. Background Art

[0002] With the rapid growth of data volume and the urgent need for higher transmission rates in modern society, traditional optical communication multiplexing technologies, such as time division multiplexing, frequency division multiplexing, code division multiplexing, and dense wavelength division multiplexing, have approached the upper limit of fiber channel capacity. Therefore, in the long run, it is imperative to develop new communication multiplexing methods. Space-Division Multiplexing (SDM), as a new type of fiber optic multiplexing technology, is expected to break the capacity limitations of existing fiber optic channels. Space-Division Multiplexing transmits data through mutually orthogonal modes in space, including cylindrical vector beam multiplexing (CVBs) and orbital angular momentum multiplexing (OAM). With different topological charges l and radial index p Orbital angular momentum (OAM) beams are expected to significantly increase communication capacity.

[0003] Although there are many methods for realizing fiber multiplexing in related technologies, such as mode selective couplers, photon lanterns, fiber vortex gratings and other devices, the above conventional methods are limited by the materials, structures and manufacturing processes of optical fibers, and the multiplexing and demultiplexing effects are poor. In addition, the number of OAM modes that can be supported is small. In other words, the limited aperture of the optical system limits the topological charge of the OAM mode. l The value range of is difficult to meet user needs. Although there are also methods in related technologies to achieve multiplexing in free space through structures such as beam splitters, this method will introduce an additional 3dB loss and is not scalable. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a phase modulation device, a coaxial OAM mode light beam conversion system and method, aiming to solve the problem in the related art that the space division multiplexing system is difficult to have the characteristics of high efficiency and low loss.

[0005] To solve the above technical problems, the present invention is implemented as follows: in a first aspect, a phase modulation device is provided, which is applied to a conversion system of a coaxial OAM mode light beam; the phase modulation device includes a phase mask and a reflector arranged at intervals, the phase mask includes a first phase plane, a second phase plane and a third phase plane facing the reflector and arranged side by side; a first modulation channel and a second modulation channel in opposite directions are formed between the phase mask and the reflector, and the light beam passes through the first phase plane, the reflector, the second phase plane, the reflector and the third phase plane in sequence when propagating in the first modulation channel; the first modulation channel is used to convert a two-dimensional Gaussian array light beam into an intermediate light beam with a long arc-shaped light intensity distribution through the first phase plane and the second phase plane, and is used to convert the intermediate light beam into a coaxial OAM mode light beam with a circular light intensity distribution through the third phase plane; wherein the coaxial OAM mode light beam corresponds to a plurality of OAM modes, and the OAM mode has a value range of Radial index and the value range is The number of load a second modulation channel for converting the coaxial OAM mode beam into an intermediate beam through a third phase plane, and for converting the intermediate beam into a two-dimensional Gaussian array beam through a first phase plane and a second phase plane.

[0006] In a second aspect, a coaxial OAM mode light beam conversion system is provided, comprising a light source assembly and a phase modulation device as described in the first aspect, wherein the light source assembly and the phase modulation device are arranged at an interval; the light source assembly is used to send a two-dimensional Gaussian array light beam to a first phase plane at a first position, or the light source assembly is used to send a coaxial OAM mode light beam to a third phase plane at a second position.

[0007] In a third aspect, a method for converting a coaxial OAM mode beam is provided, which is applied to the coaxial OAM mode beam conversion system as described in the second aspect, and the method includes: controlling the light source component to send a two-dimensional Gaussian array beam to a first phase plane at a first position, so as to multiplex the two-dimensional Gaussian array beam into a coaxial OAM mode beam through a phase modulation device; or controlling the light source component to send a coaxial OAM mode beam to a third phase plane at a second position, so as to demultiplex the coaxial OAM mode beam into a two-dimensional Gaussian array beam through a phase modulation device.

[0008] Compared with the prior art, the phase modulation device, the coaxial OAM mode beam conversion system and the method of the present invention have the following beneficial effects: introducing multiple spatially discrete phase planes (i.e., the first phase plane, the second phase plane and the third phase plane), expanding the radial index of the OAM mode p As an additional multiplexing dimension, the Gaussian spot of the 3D Gaussian array beam can be mapped and transformed into beams with different topological charges.l and different radial indices p The coaxial OAM mode beam is beneficial to significantly improve the communication capacity; through the selective use of two modulation channels in opposite directions, not only the multiplexing of coaxial OAM mode beams can be achieved, but also the demultiplexing of coaxial OAM mode beams can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a multiplexing principle diagram of a conversion system for a coaxial OAM mode light beam in an embodiment of the present invention; Figure 2 Schematic diagram of the components of the coaxial OAM mode light beam conversion system in an embodiment of the present invention; Figure 3 is a phase distribution diagram of a phase mask provided by an embodiment of the present invention; Figure 4 is a schematic diagram of multiple radial high-order OAM modes provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of the field evolution process of the forward propagation light field provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0010] In order to make the invention purpose, features, and advantages of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings 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 those skilled in the art without creative work are within the scope of protection of the present application.

[0011] In the description of the embodiments of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0012] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0013] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0014] The basic properties of orbital angular momentum beams and their application principles in communication systems are as follows: A beam with a spiral phase structure and annular intensity distribution is called an orbital angular momentum (OAM) beam. Due to the existence of the phase singularity, the interference of each point on the axis is destructive, resulting in zero intensity. That is, the far-field diffraction pattern of the orbital angular momentum beam appears as a bright ring, while the center forms a dark spot. For radial index p The radial high-order Laguerre-Gaussian (LG) beam is not zero. The former has a single-ring intensity distribution, while the latter has a multi-ring intensity distribution.

[0015] As the eigenstate solution of orbital angular momentum in cylindrical coordinates, the Laguerre-Gaussian (LG) beam has radial quantum number p and angular quanta l Two indicators, and satisfy the following relationship:

[0016] in, is the beam waist at propagation distance z. and p is the characteristic index that characterizes the beam mode; p is the radial index; p +1 represents the number of radial nodes of beam intensity; l is the angular index, indicating that the phase change along the circumference is an integer multiple of 2π. is the Gouy phase, the phase factor This shows that the light beam has orbital angular momentum.

[0017] Topological charge of orbital angular momentum beam l The possible range of values ​​is all integer values ​​( l =0, ±1, ±2, …±∞), for electromagnetic waves of arbitrary frequency and with different topological charges, the orbital angular momentum beams are a collection of mutually orthogonal eigenmodes of electromagnetic waves propagating in free space and cylindrical waveguides; therefore, they are independent and separable from each other.

[0018] Embodiment 1: like Figure 1-5 As shown, in this embodiment, the phase modulation device is applied to the conversion system of the coaxial OAM mode light beam; the phase modulation device includes a phase mask and a reflector arranged at intervals, the phase mask includes a first phase plane, a second phase plane and a third phase plane facing the reflector and arranged side by side; a first modulation channel and a second modulation channel in opposite directions are formed between the phase mask and the reflector, and the light beam passes through the first phase plane, the reflector, the second phase plane, the reflector and the third phase plane in sequence when propagating in the first modulation channel; the first modulation channel is used to convert the two-dimensional Gaussian array light beam into an intermediate light beam with a long arc-shaped light intensity distribution through the first phase plane and the second phase plane, and to convert the intermediate light beam into a coaxial OAM mode light beam with a circular light intensity distribution through the third phase plane; wherein the coaxial OAM mode light beam corresponds to multiple OAM modes, and the OAM mode has a value range of Radial index and the value range is The topological charge of a second modulation channel for converting the coaxial OAM mode beam into an intermediate beam through a third phase plane, and for converting the intermediate beam into a two-dimensional Gaussian array beam through a first phase plane and a second phase plane.

[0019] Specifically, Figure 1 and 2 As shown, three phase planes are etched on a reflective phase mask, and the phase mask and the reflector are arranged relative to each other so that the incident light beam can be reflected back and forth five times in the phase modulation device. After being modulated by three phase planes along the first modulation channel, the light beam located at ( x , y ) position input m×n Gaussian spots can be mapped and transformed into beams with different topological charges. l and radial index p In addition, the coaxial OAM mode beam is used as the input source and injected from the third phase plane, so that the optical fiber passes through the third phase plane, the reflector, the second phase plane, the reflector, and the first phase plane in sequence along the second modulation channel, and the coaxial OAM mode beam can be demultiplexed into a two-dimensional Gaussian array beam. It can be seen that through the implementation of this embodiment, multiple spatially discrete phase planes are introduced, and angular and radial OAM modes can be multiplexed simultaneously, which is expected to significantly improve the communication capacity.

[0020] like Figure 3 As shown, in this embodiment, the first phase plane is used to form a phase distribution with an elliptical outer contour, the second phase plane is used to form a phase distribution with a long arc outer contour, and the third phase plane is used to form a phase distribution with a circular outer contour.

[0021] Specifically, Figure 4 and 5 As shown in the figure, the 2D Gaussian array beam can refer to a 2D 11 × 3 Gaussian array source. Correspondingly, the 33 orbital angular momentum beam channels correspond to 33 orbital angular momentum beams of different orders. Through the above phase distribution design, multiplexing 33 OAM channels only requires 3 phase planes, which greatly reduces the number of phase planes required by the system compared to the multiplexing method of 2N+1 (N is the number of OAM modes) planes required in the traditional solution.

[0022] In this embodiment, the phase values ​​of the first phase plane, the second phase plane, and the third phase plane satisfy the following required relationship: ,(0≤ ≤2π) in, Indicates The phase value corresponding to the phase plane is , that is, represents the phase value corresponding to the pixel point in the first phase plane, represents the phase value corresponding to the pixel point in the second phase plane, Indicates the phase value corresponding to the pixel point in the third phase plane; represents the topological charge of the OAM mode; represents the radial index of the OAM mode; represents the light field formed on the corresponding phase plane when the light beam propagates along the first modulation channel; It represents the light field formed on the corresponding phase plane when the light beam propagates along the second modulation channel.

[0023] Specifically, the determination of the phase value of each pixel in the first phase plane, the second phase plane, and the third phase plane can be achieved through a computer algorithm. For example, a wavefront matching algorithm can be used to train the phase plane, calculate the mean square error between the light field corresponding to the first modulation channel and the light field corresponding to the second modulation channel, and optimize the phase value of each pixel based on the calculation result (iterative execution), and continuously perform phase matching calculations in each iterative step until the algorithm converges. The phase distribution of the phase plane can also be optimized and designed in combination with a beam propagation algorithm, a simulation algorithm, etc., which is not limited here.

[0024] Embodiment 2: like Figure 1-5As shown, in this embodiment, the conversion system of the coaxial OAM mode light beam includes a light source assembly and a phase modulation device, and the light source assembly and the phase modulation device are arranged at an interval; the light source assembly is used to send a two-dimensional Gaussian array light beam to a first phase plane at a first position, or the light source assembly is used to send a coaxial OAM mode light beam to a third phase plane at a second position.

[0025] Specifically, when the coaxial OAM mode light beam conversion system is used to realize the multiplexing of coaxial OAM mode light beams, a two-dimensional Gaussian array light beam can be input at the first position through the light source component, and then the two-dimensional Gaussian array light beam can be converted into an intermediate light beam with a long arc-shaped light intensity distribution through the first phase plane and the second phase plane, that is, in the process of the light beam propagating between the first phase plane and the second phase plane, the initial Gaussian light spot gradually expands to form a long arc-shaped light intensity distribution; the intermediate light beam can be converted into a coaxial OAM mode light beam with a circular light intensity distribution through the third phase plane. When the coaxial OAM mode light beam conversion system is used to realize the demultiplexing of coaxial OAM mode light beams, a coaxial OAM mode light beam can be input to the third phase plane through the light source component at the second position (the input can be a coaxial OAM light beam with two cylindrical refractive indices), and then the coaxial OAM mode light beam can be converted into an intermediate light beam with a long arc-shaped light intensity distribution through the third phase plane, and the intermediate light beam can be converted into a two-dimensional Gaussian array light beam through the first phase plane and the second phase plane.

[0026] In this embodiment, when the light source assembly is used to send a two-dimensional Gaussian array beam, the light source assembly includes a plurality of Gaussian light sources arranged toward the first phase plane, and the plurality of Gaussian light sources are arranged at the first position. m × n Matrix arrangement. This embodiment can convert the Gaussian beam input from the two-dimensional fiber array into multi-channel coaxial radial high-order OAM, and the order of the radial high-order OAM corresponds to the position of the input two-dimensional fiber array. That is, compared with the traditional solution that can only multiplex the radial OAM mode of 0, this embodiment can multiplex the OAM modes with different radial and angular dimensions, which greatly improves the multiplexing efficiency. Further, in some preferred embodiments, m It can be 11, n It can be 3. The 33 orbital angular momentum beam channels correspond to 33 orbital angular momentum beams of different orders, respectively. Figure 4 As shown, the above “( x , y ) position input m×n Gaussian spot refers to: 11 different x Coordinate parameters and 3 different y The Gaussian spot corresponding to the 33 coordinate positions formed by the combination of coordinate parameters; by using three-layer phase planes, the cylindrical index can be reused p =0, 1, 2l A total of 33 coaxial OAM mode light fields from -5th to +5th order.

[0027] In this embodiment, a collimating lens is further provided between the light source assembly and the phase modulation device, and the use of the collimating lens can prevent the light emitted by the light source from diverging. In a specific implementation, when used to realize the multiplexing of coaxial OAM mode light beams, the collimating lens can be a microlens array corresponding to the two-dimensional optical fiber array, so that the corresponding Gaussian beam output can be collimated.

[0028] Embodiment 3: In this embodiment, the coaxial OAM mode light beam conversion method is applied to the coaxial OAM mode light beam conversion system, and the method includes the following steps: Controlling the light source assembly to send a two-dimensional Gaussian array beam to a first phase plane at a first position, so as to multiplex the two-dimensional Gaussian array beam into a coaxial OAM mode beam through a phase modulation device; Alternatively, the light source assembly is controlled to send a coaxial OAM mode beam to a third phase plane at the second position, so as to demultiplex the coaxial OAM mode beam into a two-dimensional Gaussian array beam through a phase modulation device.

[0029] Specifically, Figure 1 and 2 As shown, in the multiplexing mode, a two-dimensional Gaussian array beam can be input at the first position through the light source component, and then the two-dimensional Gaussian array beam can be converted into an intermediate beam with a long arc-shaped light intensity distribution through the first phase plane and the second phase plane, that is, in the process of the beam propagating between the first phase plane and the second phase plane, the initial Gaussian light spot gradually expands to form a long arc-shaped light intensity distribution; the intermediate beam can be converted into a coaxial OAM mode beam with a circular light intensity distribution through the third phase plane. In the demultiplexing mode, a coaxial OAM mode beam can be input to the third phase plane through the light source component at the second position (the input can be a coaxial OAM mode beam with two cylindrical refractive indices), and then the coaxial OAM mode beam can be converted into an intermediate beam with a long arc-shaped light intensity distribution through the third phase plane, and the intermediate beam can be converted into a two-dimensional Gaussian array beam through the first phase plane and the second phase plane.

[0030] Furthermore, in some specific embodiments, the above-mentioned coaxial OAM mode light beam conversion method also includes: determining the transmission coefficient of each pixel point in the first phase plane, the second phase plane and the third phase plane based on the target light intensity distribution characteristics of the two-dimensional Gaussian array beam and the coaxial OAM mode light beam; performing light field matching calculation on the first modulation channel and the second modulation channel according to the transmission coefficient to obtain the corresponding mean square error; when the mean square error is less than a preset threshold, determining the target phase value corresponding to each pixel point based on the light field model constructed in the light field matching calculation process, and controlling the first phase plane, the second phase plane and the third phase plane to produce a corresponding phase distribution based on each phase value.

[0031] Furthermore, after the above-mentioned step of performing light field matching calculation on the first modulation channel and the second modulation channel according to the transmission coefficient to obtain the corresponding mean square error, it also includes: when the mean square error is greater than or equal to a preset threshold, adjusting the phase distribution of the target phase plane according to the mean square error; wherein the target phase plane is at least one of the first phase plane, the second phase plane and the third phase plane.

[0032] Specifically, in the design process of the phase mask and the optimization and adjustment process of the phase distribution of the phase plane, for the k on a plane The transmission coefficient of the i-th pixel corresponding to t ,exist:

[0033] in, Indicates the amplitude. When only phase modulation is performed, Can be set to 1; Indicates The phase value corresponding to the phase plane is , that is, represents the phase value corresponding to the pixel point in the first phase plane, represents the phase value corresponding to the pixel point in the second phase plane, Indicates the phase value corresponding to the pixel point in the third phase plane; Represents an imaginary unit; when the light field passes through the phase plane, the light field is multiplied by the transmission coefficient ; Then, the transfer function of the beam propagating in free space between the phase planes can be calculated using angular spectrum theory:

[0034] Constructing the light field model: Constructing the k Forward propagating light field at the phase plane (i.e., the light field corresponding to the first modulation channel) and the kBackward propagating light field in the phase plane (that is, the light field corresponding to the second modulation channel); specifically, it can be expressed as:

[0035]

[0036] Using the above light field propagation theory, the diffraction light field propagating forward and backward at each phase plane is obtained. The transmission coefficient of the phase plane plays a vital role in phase modulation. In order to accurately control the modulated light field, a wavefront matching algorithm can be used to train the phase plane. k The phase modulation performance of the phase plane can be calculated first to obtain the corresponding mean square error, which is expressed as:

[0037] When the phase modulated forward propagation light field matches the backward propagation light field, the maximum mode conversion efficiency can be obtained, that is, the phase distribution generated by each phase plane can efficiently realize multiple different topological charges. and radial index Multiplexing and demultiplexing of OAM modes.

[0038] When the phase modulated forward propagation light field does not match the backward propagation light field, the phase difference corresponding to the forward propagation light field and the backward propagation light field can be calculated based on the mean square error, and then summed up, and the phase distribution of the target phase plane is further adjusted in sequence until the error is minimized (that is, the mean square error is less than the preset error threshold); wherein, k Phase on the phase plane It is given by the two-dimensional superposition of phase differences:

[0039] in, m and n is equal to the number of input channels in rows and columns, respectively. The optimization of the phase value for each pixel is performed iteratively, and phase matching is performed continuously in each iteration step until the algorithm reaches convergence.

[0040] The phase modulation device, coaxial OAM mode light beam conversion system and method provided by the present invention can not only multiplex OAM channels, but also demultiplex coaxial AOM channels through the phase distribution design of three phase planes; the diffraction order is small, which greatly improves the energy utilization rate. It can also meet the needs of multiplexing l = ± | l | Further expanding the number of OAM beams by combining all modes of the OAM beam can increase the number of channels exponentially. In addition, it is also possible to explore increasing p and l, to further expand orthogonal channels in optical fiber or free space communications.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A phase modulation device, characterized in that: A conversion system for a coaxial OAM mode light beam; the phase modulation device comprises a phase mask and a reflector arranged at intervals, the phase mask comprises a first phase plane, a second phase plane and a third phase plane arranged side by side and facing the reflector; a first modulation channel and a second modulation channel in opposite directions are formed between the phase mask and the reflector, and the light beam passes through the first phase plane, the reflector, the second phase plane, the reflector and the third phase plane in sequence when propagating in the first modulation channel; The first modulation channel is used to convert the two-dimensional Gaussian array beam into an intermediate beam with a long arc-shaped light intensity distribution through the first phase plane and the second phase plane, and is used to convert the intermediate beam into a coaxial OAM mode beam with a circular light intensity distribution through the third phase plane; wherein the coaxial OAM mode beam corresponds to a plurality of OAM modes, and the OAM mode has a value range of Radial index and the value range is The topological charge of ; The second modulation channel is used to convert the coaxial OAM mode beam into the intermediate beam through the third phase plane, and to convert the intermediate beam into the two-dimensional Gaussian array beam through the first phase plane and the second phase plane.

2. The phase modulation device according to claim 1, characterized in that: The first phase plane is used to form a phase distribution with an elliptical outer contour, the second phase plane is used to form a phase distribution with a long arc outer contour, and the third phase plane is used to form a phase distribution with a circular outer contour.

3. The phase modulation device according to claim 1, characterized in that: The phase values ​​of the first phase plane, the second phase plane and the third phase plane satisfy the following required relationship: ，(0≤ ≤2π) in, Indicates The phase value corresponding to the phase plane, ; represents the topological charge; represents the radial index; represents the light field formed on the corresponding phase plane when the light beam propagates along the first modulation channel; It represents the light field formed on the corresponding phase plane when the light beam propagates along the second modulation channel.

4. A coaxial OAM mode light beam conversion system, characterized in that: It comprises a light source assembly and a phase modulation device as described in any one of claims 1 to 3, wherein the light source assembly is arranged at an interval from the phase modulation device; the light source assembly is used to send the two-dimensional Gaussian array light beam to the first phase plane at a first position, or the light source assembly is used to send the coaxial OAM mode light beam to the third phase plane at a second position.

5. The coaxial OAM mode light beam conversion system according to claim 4, characterized in that: When the light source assembly is used to send the two-dimensional Gaussian array light beam, the light source assembly includes a plurality of Gaussian light sources arranged toward the first phase plane, and the plurality of Gaussian light sources are arranged at the first position. m × n Matrix arrangement.

6. The coaxial OAM mode light beam conversion system according to claim 5, characterized in that: m is equal to 11, and / or, n Equals 3.

7. The coaxial OAM mode light beam conversion system according to claim 4, characterized in that: A collimating lens is also arranged between the light source assembly and the phase modulation device.

8. A method for converting a coaxial OAM mode beam, characterized in that: A conversion system for a coaxial OAM mode light beam as claimed in any one of claims 4 to 7, wherein the method comprises: Controlling the light source assembly to send the two-dimensional Gaussian array light beam to the first phase plane at the first position, so as to multiplex the two-dimensional Gaussian array light beam into the coaxial OAM mode light beam through the phase modulation device; Alternatively, the light source assembly is controlled to transmit the coaxial OAM mode light beam to the third phase plane at the second position, so as to demultiplex the coaxial OAM mode light beam into the two-dimensional Gaussian array light beam through the phase modulation device.

9. The method for converting a coaxial OAM mode beam according to claim 8, characterized in that: Also includes: Determine the transmission coefficient of each pixel point in the first phase plane, the second phase plane, and the third phase plane based on the target light intensity distribution characteristics of the two-dimensional Gaussian array beam and the coaxial OAM mode beam; According to the transmission coefficient, performing light field matching calculation on the first modulation channel and the second modulation channel to obtain corresponding mean square errors; When the mean square error is less than a preset threshold, the target phase value corresponding to each pixel point is determined based on the light field model constructed during the light field matching calculation process, and the first phase plane, the second phase plane and the third phase plane are controlled to produce a corresponding phase distribution based on each phase value.

10. The method for converting a coaxial OAM mode beam according to claim 9, characterized in that: After performing light field matching calculation on the first modulation channel and the second modulation channel according to the transmission coefficient to obtain a corresponding mean square error, the method further includes: When the mean square error is greater than or equal to a preset threshold, the phase distribution of the target phase plane is adjusted according to the mean square error; wherein the target phase plane is at least one of the first phase plane, the second phase plane and the third phase plane.

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