A phase modulation device, a system and method for converting coaxial OAM mode beams.

Abstract

This invention provides a phase modulation device, a system and method for converting coaxial OAM mode beams. The phase modulation device includes a phase mask and a mirror spaced apart. The phase mask includes a first phase plane, a second phase plane, and a third phase plane arranged side-by-side facing the mirror. A first modulation channel and a second modulation channel with opposite directions are formed between the phase mask and the mirror. Through the implementation of this solution, multiplexing and demultiplexing of multiple coaxial radial high-order OAM mode beams can be achieved using the first and second modulation channels; that is, by expanding the radial exponent of the OAM mode... p As an additional multiplexing dimension, multiple phase planes are introduced, which can convert the Gaussian beam input from the two-dimensional fiber array into multiple coaxial radial high-order OAM mode beams, and can make full use of the orthogonal mode channels supported in the fiber to achieve high-capacity communication.

Description

Technical Field

[0001] This invention belongs to the field of optical communication, and particularly relates to a phase modulation device, a system and method for converting coaxial OAM mode beams. Background Technology

[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, are approaching the upper limit of fiber optic channel capacity. Therefore, in the long run, developing new communication multiplexing methods is imperative. Space-division multiplexing (SDM), as a novel fiber optic multiplexing technology, is expected to break the capacity limitations of existing fiber optic channels. SDM transmits data through mutually orthogonal modes in space, including cylindrical vector beams (CVBs) and orbital angular momentum multiplexing (OAM). It can be used with different topological charge numbers. l and radial index p Orbital angular momentum (OAM) beams are expected to significantly improve communication capacity.

[0003] Although various methods for achieving fiber multiplexing have emerged, such as those using mode selection couplers, photonic lanterns, and fiber vortex gratings, these conventional methods are limited by the materials, structure, and manufacturing processes of the optical fiber. This results in poor multiplexing and demultiplexing performance and a limited number of supported OAM modes. In other words, the finite aperture of the optical system restricts the topology charge of the OAM modes. l The range of possible values ​​is insufficient to meet user needs. Although related technologies have emerged that use structures such as beam splitters to achieve multiplexing in free space, this approach introduces 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 beam conversion system and method, which aims to solve the problem that space division multiplexing systems in related technologies are difficult to achieve both high efficiency and low loss.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: Firstly, a phase modulation device is provided, applied to a coaxial OAM mode beam conversion system; the phase modulation device includes a phase mask and a reflector spaced apart, the phase mask including a first phase plane, a second phase plane, and a third phase plane arranged side-by-side facing the reflector; a first modulation channel and a second modulation channel with opposite directions are formed between the phase mask and the reflector, and the beam propagates in the first modulation channel, sequentially passing through the first phase plane, the reflector, the second phase plane, the reflector, and the third phase plane; the first modulation channel is used to convert a two-dimensional Gaussian array beam into an intermediate beam with a long arc-shaped intensity distribution through the first and second phase planes, and to convert the intermediate beam into a coaxial OAM mode beam with a circular intensity distribution through the third phase plane; wherein the coaxial OAM mode beam corresponds to multiple OAM modes, and the OAM modes have a value range of... radial index The range of values ​​is number of lotus The second modulation channel is used to convert the coaxial OAM mode beam into an intermediate beam through the third phase plane, and to convert the intermediate beam into a two-dimensional Gaussian array beam through the first phase plane and the second phase plane.

[0006] In a second aspect, a system for converting a coaxial OAM mode beam 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 intervals; the light source assembly is used to send a two-dimensional Gaussian array beam to a first phase plane at a first position, or the light source assembly is used to send a coaxial OAM mode beam to a third phase plane at a second position.

[0007] Thirdly, a method for converting a coaxial OAM mode beam is provided, applied to the coaxial OAM mode beam conversion system as described in the second aspect. The method includes: controlling a 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 by a phase modulation device; or, controlling a light source assembly 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 by a phase modulation device.

[0008] Compared with existing technologies, the phase modulation device, coaxial OAM mode beam conversion system, and method of this invention have the following advantages: They introduce multiple spatially discrete phase planes (i.e., a first phase plane, a second phase plane, and a third phase plane), thus expanding the radial exponent of the OAM mode. p This serves as an additional multiplexing dimension, enabling the Gaussian spot of the Gaussian array beam to 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 communication capacity; by selectively using two modulation channels with opposite directions, not only can the coaxial OAM mode beam be multiplexed, but also the coaxial OAM mode beam can be demultiplexed. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the multiplexing principle of the coaxial OAM mode beam conversion system in an embodiment of the present invention;

[0010] Figure 2 This is a schematic diagram of the device composition in the coaxial OAM mode beam conversion system in an embodiment of the present invention;

[0011] Figure 3 This is a phase distribution diagram of a phase mask provided in an embodiment of the present invention;

[0012] Figure 4 This is a schematic diagram of multiple radial higher-order OAM modes provided in an embodiment of the present invention;

[0013] Figure 5 This is a schematic diagram of the field evolution process of the forward propagating optical field provided in an embodiment of the present invention. Detailed Implementation

[0014] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0015] In the description of the embodiments of this application, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0016] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0017] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0018] The fundamental properties of orbital angular momentum beams and their application principles in communication systems are as follows:

[0019] A beam with a spiral phase structure and a ring-shaped intensity distribution is called an orbital angular momentum (OAM) beam. Due to the presence of a phase singularity, interference at all points along the axis is destructive, resulting in zero intensity. That is, the far-field diffraction pattern of an orbital angular momentum beam appears as a bright ring, while a dark spot forms in the central region. For the radial index... p A non-zero radial higher-order Laguerre-Gaussian (LG) beam has a single-ring intensity distribution in the former and a multi-ring intensity distribution in the latter.

[0020] As an eigenstate solution of orbital angular momentum in cylindrical coordinates, the Laguerre-Gaussian (LG) beam possesses radial quantum number... p And angular vector subnumber l Two indicators that satisfy the following relationship:

[0021]

[0022] in, It is the beam waist at a propagation distance of z. and p It is a characteristic index that characterizes the beam pattern; p It is the radial index; p +1 represents the radial number of nodes in the beam intensity; l It is the angular index, indicating that the phase change along the circumference of a circle is an integer multiple of 2π. It is the Gouy phase, phase factor. This indicates that the beam has orbital angular momentum.

[0023] Topological charge of orbital angular momentum beam l The possible value range is all integer values. l =0, ±1, ±2, …±∞), for electromagnetic waves of any frequency and with different topological charges, the orbital angular momentum beam is a set of mutually orthogonal eigenmodes of electromagnetic waves propagating in free space and cylindrical waveguides; therefore, they are independent and separable from each other.

[0024] Example 1:

[0025] like Figure 1-5 As shown, in this embodiment, the phase modulation device is applied to a coaxial OAM mode beam conversion system. The phase modulation device includes a phase mask and a reflector spaced apart. The phase mask includes a first phase plane, a second phase plane, and a third phase plane arranged side-by-side facing the reflector. A first modulation channel and a second modulation channel with opposite directions are formed between the phase mask and the reflector. When the beam propagates in the first modulation channel, it passes through the first phase plane, the reflector, the second phase plane, the reflector, and the third phase plane in sequence. The first modulation channel is used to convert the two-dimensional Gaussian array beam into an intermediate beam with a long arc-shaped intensity distribution through the first and second phase planes, and to convert the intermediate beam into a coaxial OAM mode beam with a circular intensity distribution through the third phase plane. The coaxial OAM mode beam corresponds to multiple OAM modes, and the OAM modes have a value range of... radial index The range of values ​​is topological charge number The second modulation channel is used to convert the coaxial OAM mode beam into an intermediate beam through the third phase plane, and to convert the intermediate beam into a two-dimensional Gaussian array beam through the first phase plane and the second phase plane.

[0026] Specifically, such as Figure 1 and 2 As shown, three phase planes are etched onto a reflective phase mask, with the phase mask and mirror positioned opposite each other, allowing the incident beam to be reflected five times within the phase modulation device. After being modulated by the three phase planes along the first modulation channel, the beam is located at ( x , y (Location input) m×n Gaussian light spots can be mapped and transformed into light spots with different topological charges. l and radial index pThe coaxial OAM mode beam is used as an input source. Furthermore, by using the coaxial OAM mode beam as an input source and incident it from the third phase plane, allowing the optical fiber to sequentially pass through the third phase plane, a mirror, the second phase plane, another mirror, and the first phase plane along the second modulation channel, the coaxial OAM mode beam can be demultiplexed into a two-dimensional Gaussian array beam. It is evident that by introducing multiple spatially discrete phase planes through this embodiment, both angular and radial OAM modes can be multiplexed simultaneously, potentially significantly improving communication capacity.

[0027] 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 an arc-shaped outer contour, and the third phase plane is used to form a phase distribution with a circular outer contour.

[0028] Specifically, such as Figure 4 and 5 As shown, the Gaussian array beam can refer to a two-dimensional 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 2N+1 (N is the number of OAM modes) multiplexing methods required in traditional schemes.

[0029] 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:

[0030] , 0≤ ≤2π

[0031] in, Indicates the first Phase values ​​corresponding to each phase plane , that is, This represents the phase value corresponding to a pixel in the first phase plane. This represents the phase value corresponding to a pixel in the second phase plane. This represents the phase value corresponding to a pixel in the third phase plane; Indicates the topology load number of the OAM mode; The radial index represents the OAM mode; This represents the optical field formed in the corresponding phase plane when the light beam propagates along the first modulation channel; This represents the optical field formed in the corresponding phase plane when the beam propagates along the second modulation channel.

[0032] Specifically, the phase values ​​of each pixel in the first, second, and third phase planes can be determined using computer algorithms. For example, a wavefront matching algorithm can be used to train the phase planes, calculate the mean square error between the light fields corresponding to the first and second modulation channels, and optimize the phase value of each pixel based on the calculation results (iterative execution). Phase matching calculations are continuously performed in each iteration until the algorithm converges. Alternatively, beam propagation algorithms and simulation algorithms can be combined to optimize the phase distribution of the phase planes; no limitations are imposed here.

[0033] Example 2:

[0034] like Figure 1-5 As shown, in this embodiment, the coaxial OAM mode beam conversion system includes a light source assembly and a phase modulation device, with the light source assembly and the phase modulation device arranged at intervals. The light source assembly is used to send a two-dimensional Gaussian array beam to a first phase plane at a first position, or the light source assembly is used to send a coaxial OAM mode beam to a third phase plane at a second position.

[0035] Specifically, when the coaxial OAM mode beam conversion system is used to achieve coaxial OAM mode beam multiplexing, a two-dimensional Gaussian array beam can be input through the light source component at the first position. Then, the two-dimensional Gaussian array beam can be converted into an intermediate beam with a long arc-shaped intensity distribution through the first and second phase planes. That is, during the propagation of the beam between the first and second phase planes, the initial Gaussian spot gradually expands, forming a long arc-shaped intensity distribution. The intermediate beam can then be converted into a coaxial OAM mode beam with a circular intensity distribution through the third phase plane. When the coaxial OAM mode beam conversion system is used to achieve coaxial OAM mode beam demultiplexing, a coaxial OAM mode beam (which can be a coaxial OAM beam with two cylindrical refractive indices) can be input through the light source component at the second position to the third phase plane. Then, the coaxial OAM mode beam can be converted into an intermediate beam with a long arc-shaped intensity distribution through the third phase plane, and the intermediate beam can be converted into a two-dimensional Gaussian array beam through the first and second phase planes.

[0036] In this embodiment, when the light source assembly is used to transmit a two-dimensional Gaussian array beam, the light source assembly includes multiple Gaussian light sources disposed toward the first phase plane, and the multiple Gaussian light sources are in a first position. m × nMatrix arrangement. This embodiment can convert the Gaussian beam input to a two-dimensional fiber array into multiple coaxial radial higher-order OAMs. The order of the radial higher-order OAMs corresponds one-to-one with the position of the input two-dimensional fiber array. That is, compared with the traditional scheme that can only reuse OAM modes with a radial dimension of 0, this embodiment can reuse OAM modes with different radial and angular dimensions, greatly improving the multiplexing efficiency. Furthermore, in some preferred embodiments, m It can be 11. n There can be 3.33 orbital angular momentum beam channels, each corresponding to 33 orbital angular momentum beams of different orders. Correspondingly, such as... Figure 4 As shown, the above "( x , y (Location input) m×n "Gaussian spot" refers to a spot consisting of 11 different... x Coordinate parameters and 3 different y The 33 coordinate positions corresponding to the coordinate parameters are Gaussian spots; by using three phase planes, the cylindrical index can be reused. p =0, 1, 2 l A total of 33 coaxial OAM mode light fields ranging from -5th to +5th order.

[0037] In this embodiment, a collimating lens is also provided between the light source assembly and the phase modulation device. 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 beams, the collimating lens can be a microlens array corresponding to a two-dimensional fiber array, thereby collimating the corresponding Gaussian beam output.

[0038] Example 3:

[0039] In this embodiment, the method for converting a coaxial OAM mode beam is applied to a coaxial OAM mode beam conversion system, and the method includes the following steps:

[0040] The control light source assembly sends a two-dimensional Gaussian array beam to the 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;

[0041] Alternatively, the control light source assembly can send a coaxial OAM mode beam to the third phase plane from the second position, so as to demultiplex the coaxial OAM mode beam into a two-dimensional Gaussian array beam through a phase modulation device.

[0042] Specifically, such as Figure 1 and 2As shown, in multiplexing mode, a two-dimensional Gaussian array beam can be input through the light source component at the first position. Then, through the first and second phase planes, the two-dimensional Gaussian array beam can be converted into an intermediate beam with a long arc-shaped intensity distribution. That is, during the propagation of the beam between the first and second phase planes, the initial Gaussian spot gradually expands, forming a long arc-shaped intensity distribution. The intermediate beam can then be converted into a coaxial OAM mode beam with a circular intensity distribution through the third phase plane. In demultiplexing mode, a coaxial OAM mode beam (which can be a coaxial OAM beam with two cylindrical refractive indices) can be input through the light source component at the second position to the third phase plane. Then, through the third phase plane, the coaxial OAM mode beam can be converted into an intermediate beam with a long arc-shaped intensity distribution. Finally, through the first and second phase planes, the intermediate beam can be converted into a two-dimensional Gaussian array beam.

[0043] Furthermore, in some specific embodiments, the above-mentioned method for converting coaxial OAM mode beams further includes: determining the transmission coefficient of each pixel 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; performing optical 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 based on the optical field model constructed during the optical field matching calculation, and controlling the first phase plane, the second phase plane, and the third phase plane to generate corresponding phase distributions based on each phase value.

[0044] Furthermore, after the above steps of performing optical field matching calculations on the first modulation channel and the second modulation channel based on the transmission coefficient to obtain the corresponding mean square error, the method further 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.

[0045] Specifically, during the design of the phase mask and the optimization and adjustment of the phase distribution in the phase plane, for the phase mask located at the first... k On a plane Transmission coefficient of the i-th pixel at the location t ,exist:

[0046]

[0047] in, Indicates amplitude; when only phase modulation is performed, It can be set to 1; Indicates the first Phase values ​​corresponding to each phase plane , that is, This represents the phase value corresponding to a pixel in the first phase plane. This represents the phase value corresponding to a pixel in the second phase plane. This represents the phase value corresponding to a pixel in the third phase plane; Represents the imaginary unit; when the light field passes through the phase plane, the light field is multiplied by the transmission coefficient. Furthermore, the transfer function of the beam propagation in free space between phase planes can be calculated using angular spectrum theory:

[0048]

[0049] Constructing a light field model: Constructing the first k Forward propagating light field at the phase plane (That is, the light field corresponding to the first modulation channel) and the first k Backpropagating optical field in the phase plane (That is, the optical field corresponding to the second modulation channel); specifically, it can be expressed as:

[0050]

[0051]

[0052] Using the aforementioned light field propagation theory, the diffracted light fields propagating forward and backward on each phase plane are obtained. The transmission coefficient of the phase plane plays a crucial role in phase modulation. To precisely control the modulated light field, a wavefront matching algorithm can be used to train the phase plane. To evaluate the... k The phase modulation performance of each phase plane can be calculated by first determining the corresponding mean square error, which is expressed as:

[0053]

[0054] The maximum mode conversion efficiency can be obtained when the forward propagation optical field of phase modulation is matched with the backward propagation optical field. That is, the phase distribution generated by each phase plane can efficiently realize multiple different topological charges. and radial index OAM mode multiplexing and demultiplexing.

[0055] When the forward and backward propagation optical fields of phase modulation are mismatched, the phase difference between the forward and backward propagation optical fields can be calculated based on the mean square error. This difference is then summed, and the phase distribution of the target phase plane is adjusted sequentially until the error is minimized (i.e., the mean square error is less than a preset error threshold). Wherein, the... k Phase on each phase plane This is given by the two-dimensional superposition of phase differences:

[0056]

[0057] in, m and n These are equal to the number of input channels in the row and column, respectively. The optimization of the phase value for each pixel is performed iteratively, with phase matching performed continuously in each iteration step until the algorithm converges.

[0058] The phase modulation device, coaxial OAM mode beam conversion system, and method provided by this invention, through the phase distribution design of three phase planes, can not only multiplex the OAM channel but also simultaneously demultiplex the coaxial AOM channel; it has fewer diffraction orders, significantly improving energy utilization. It can also satisfy [certain conditions] through multiplexing. l = ± | l | All modes can be used to further expand the number of OAM beams, potentially multiplying the number of channels. Furthermore, it is possible to explore increasing... p and l This is to further expand the orthogonal channels in fiber optic or free-space communications.

[0059] The above are merely 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 within the protection scope of the present invention.

Claims

1. A phase modulation device, characterized in that, A conversion system for coaxial OAM mode beams; the phase modulation device includes a phase mask and a reflector spaced apart, the phase mask including a first phase plane, a second phase plane, and a third phase plane arranged side by side facing the reflector; a first modulation channel and a second modulation channel with opposite directions are formed between the phase mask and the reflector, and when the beam propagates in the first modulation channel, it passes through the first phase plane, the reflector, the second phase plane, the reflector, and the third phase plane in sequence; The first modulation channel is used to convert a two-dimensional Gaussian array beam into an intermediate beam with a long arc-shaped intensity distribution through the first phase plane and the second phase plane, and to convert the intermediate beam into a coaxial OAM mode beam with a circular intensity distribution through the third phase plane; wherein, the coaxial OAM mode beam corresponds to multiple OAM modes, and the OAM mode has a value range of [value range missing]. radial index The range of values ​​is topological charge number ; 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 an arc-shaped 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 relationship: ，0≤ ≤2π in, Indicates the first The phase values ​​corresponding to each phase plane. ; Indicates the topological load number; Indicates the radial index; This represents the optical field formed in the corresponding phase plane when the light beam propagates along the first modulation channel; This represents the optical field formed in the corresponding phase plane when the light beam propagates along the second modulation channel.

4. A system for converting coaxial OAM mode beams, characterized in that, The device includes a light source assembly and a phase modulation device as described in any one of claims 1 to 3, wherein the light source assembly and the phase modulation device are arranged at intervals; the light source assembly is used to send the two-dimensional Gaussian array beam to the first phase plane at a first position, or the light source assembly is used to send the coaxial OAM mode beam to the third phase plane at a second position.

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

6. The coaxial OAM mode beam conversion system according to claim 5, characterized in that, m Equal to 11, and / or n It equals 3.

7. The coaxial OAM mode beam conversion system according to claim 4, characterized in that, A collimating lens is also provided 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 beam as described in any one of claims 4 to 7, the method comprising: The light source assembly is controlled to send the two-dimensional Gaussian array beam to the first phase plane at the first position, so that the two-dimensional Gaussian array beam can be multiplexed into the coaxial OAM mode beam by the phase modulation device; Alternatively, the light source assembly can be controlled to send the coaxial OAM mode beam to the third phase plane at the second position, so that the coaxial OAM mode beam can be demultiplexed into the two-dimensional Gaussian array beam by the phase modulation device.

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

10. The method for converting a coaxial OAM mode beam according to claim 9, characterized in that, After performing optical field matching calculations on the first modulation channel and the second modulation channel based on the transmission coefficients to obtain the 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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