Multi-wavelength orbital angular momentum mode regulation and control device and method based on orthogonal transformation

Abstract

The invention discloses a multi-wavelength orbital angular momentum mode regulation and control device and method based on orthogonal transformation. The device comprises a multi-wavelength OAM mode generation module, an orthogonal transformation modulation module and a detection module. The multi-wavelength OAM mode generation module is used for generating a plurality of coaxial vortex beams with different wavelengths and OAM modes and inputting the coaxial vortex beams into the orthogonal transformation modulation module; the orthogonal transformation modulation module is used for performing orthogonal transformation of mode transformation and spatial position regulation on the plurality of coaxial vortex beams generated by the multi-wavelength OAM mode generation module; the detection module is used for detecting light field light intensity distribution generated after the coaxial vortex light beams are subjected to orthogonal transformation through the orthogonal transformation modulation module. The OAM mode conversion efficiency of the vortex light beam can be effectively improved, and the transmission capacity of a communication system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of data processing technology, and in particular to a multi-wavelength orbital angular momentum mode control device and method based on orthogonal transformation. Background Art

[0002] With the explosive growth of demand for optical communication capacity, multi-dimensional multiplexing technology has become a key research direction to break through the Shannon limit. Traditional multiplexing technologies such as wavelength division multiplexing (WDM), polarization division multiplexing (PDM) and mode division multiplexing (MDM) improve the transmission capacity of communications by developing single physical dimension resources, but in recent years their expansion space has reached its theoretical limit.

[0003] To solve the above problems, the prior art generally uses a series combination of an arrayed waveguide grating and a spatial light modulator to independently control the wavelength channel and mode respectively. However, it is still affected by the dispersion and uniform light-split characteristics caused by the Bragg diffraction effect of the grating, resulting in low vortex beam conversion efficiency and the inability to improve the communication system capacity.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] The main purpose of the present invention is to provide a multi-wavelength orbital angular momentum mode control device and method based on orthogonal transformation, aiming to solve the problem that in the prior art, the wavelength channel and the mode are independently controlled by a series combination of an arrayed waveguide grating and a spatial light modulator, but it is still affected by the dispersion and uniform spectroscopic characteristics caused by the Bragg diffraction effect of the grating, resulting in low vortex light beam conversion efficiency and the communication system capacity cannot be improved.

[0006] To achieve the above-mentioned object, the present invention provides a multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, wherein the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation comprises a multi-wavelength OAM mode generation module, an orthogonal transformation modulation module and a detection module;

[0007] A multi-wavelength OAM mode generation module, used to generate a plurality of coaxial vortex beams of different wavelengths and OAM modes, and input them into the orthogonal transformation modulation module;

[0008] An orthogonal transformation modulation module, used for performing orthogonal transformation of mode transformation and spatial position regulation on the multiple coaxial vortex light beams generated by the multi-wavelength OAM mode generation module;

[0009] The detection module is used to detect the light field intensity distribution generated after the multiple coaxial vortex light beams are orthogonally transformed by the orthogonal transformation modulation module.

[0010] Optionally, the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, wherein the multi-wavelength OAM mode generating module includes a first tunable laser light source for generating a first Gaussian beam and a second tunable laser light source for generating a second Gaussian beam, a first vortex light generating device for modulating the first Gaussian beam into a first vortex beam, a second vortex light generating device for modulating the second Gaussian beam into a second vortex beam, and a combiner for coaxially outputting the first vortex beam and the second vortex beam.

[0011] Optionally, in the multi-wavelength orbital angular momentum pattern control device based on orthogonal transformation, the orthogonal transformation modulation module includes a multi-level phase modulation device for realizing orthogonal transformation.

[0012] Optionally, in the multi-wavelength orbital angular momentum pattern control device based on orthogonal transformation, the detection module includes a shooting device for recording the light intensity distribution of the light field, and the shooting device includes a wide-band CCD camera.

[0013] In addition, to achieve the above-mentioned purpose, the present invention also provides a multi-wavelength orbital angular momentum mode control method based on orthogonal transformation of a multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, wherein the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation includes:

[0014] Generate a plurality of coaxial vortex beams of different wavelengths and OAM modes through the multi-wavelength OAM mode generation module, and input them into the orthogonal transformation modulation module;

[0015] The orthogonal transformation modulation module performs mode transformation and spatial position control on the multiple coaxial vortex light beams generated by the multi-wavelength OAM mode generation module;

[0016] The detection module is used to detect the light field intensity distribution generated after the multiple coaxial vortex light beams are orthogonally transformed by the orthogonal transformation modulation module.

[0017] Optionally, the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation, wherein the coaxial vortex beams of multiple different wavelengths and OAM modes are generated by the multi-wavelength OAM mode generation module and input into the orthogonal transformation modulation module, specifically includes:

[0018] Generate a first Gaussian beam of a first wavelength by a first tunable laser light source, and generate a second Gaussian beam of a second wavelength by a second tunable laser light source;

[0019] Acquire a first wavefront phase of the first Gaussian beam through a first vortex light generating device, and superimpose a spiral phase on the first wavefront phase to obtain a first vortex beam;

[0020] Acquire a second wavefront phase of the second Gaussian beam by a second vortex light generating device, and superimpose a spiral phase on the second wavefront phase to obtain a second vortex beam;

[0021] The first vortex light beam and the second vortex light beam are coaxially adjusted by a beam combiner to obtain a plurality of coaxial vortex light beams, and the plurality of coaxial vortex light beams are input into the orthogonal transformation modulation module.

[0022] Optionally, the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation, wherein the orthogonal transformation of the mode transformation and spatial position control of the multiple coaxial vortex beams generated by the multi-wavelength OAM mode generation module by the orthogonal transformation modulation module specifically includes:

[0023] Calculating the loss function corresponding to each of the coaxial vortex beams through a multi-stage phase modulation device, and iteratively updating the initialization modulation plane phase according to the multiple loss functions to obtain the target modulation plane phase;

[0024] An orthogonal transformation matrix is ​​constructed according to the target modulation plane phase, and the orthogonal transformation matrix is ​​used to perform mode transformation and spatial position control processing on each of the coaxial vortex light beams.

[0025] Optionally, the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation, wherein the loss function corresponding to each of the coaxial vortex beams is calculated by a multi-level phase modulation device, and the initialization modulation plane phase is iteratively updated according to the multiple loss functions to obtain the target modulation plane phase, specifically includes:

[0026] Acquire the wavelength and OAM mode in each of the coaxial vortex beams through a multi-stage phase modulation device, perform forward propagation calculation on each of the wavelength and the OAM mode, and obtain a predicted output light field corresponding to each of the coaxial vortex beams;

[0027] Determine a target output light field through a multi-level phase modulation device, and calculate a loss function according to the target output light field and each of the predicted output light fields;

[0028] Determine the modulation plane phase by a multi-level phase modulation device, and perform initialization processing on the modulation plane phase to obtain an initialized modulation plane phase;

[0029] Calculating the phase component gradient corresponding to each loss function through a multi-level phase modulation device, and iteratively updating the initialization modulation plane phase according to each loss function and the corresponding phase component gradient;

[0030] When the number of iterations reaches a preset number of iterations or the loss function is lower than a preset loss threshold, the iterative update is stopped to obtain the target modulation plane phase.

[0031] Optionally, the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation, wherein the orthogonal transformation matrix is ​​constructed according to the target modulation plane phase, and each of the coaxial vortex beams is subjected to mode transformation and spatial position control processing by the orthogonal transformation matrix, specifically includes:

[0032] A phase modulation matrix is ​​obtained according to the target modulation plane phase by a multi-level phase modulation device, wherein the expression of the phase modulation matrix is: i (x, y) = angle[P i ];

[0033] Among them, φ i (x, y) is the target modulation plane phase, x is the spatial horizontal coordinate, y is the spatial vertical coordinate, P i is the phase modulation matrix, angle is the phase distribution calculation;

[0034] Determine a diffraction propagation matrix through a multi-level phase modulation device, and construct an orthogonal transformation matrix according to the phase modulation matrix and the diffraction propagation matrix;

[0035] Wherein, the expression of the diffraction propagation matrix is:

[0037] Among them, H(λ, f x , f y ) is the diffraction propagation matrix, λ is the wavelength, f x is the spatial frequency component of the spatial horizontal coordinate x in the frequency space, f y is the spatial frequency component of the spatial ordinate y in the frequency space, i is the imaginary unit, and d is the forward transmission distance;

[0038] Determining a preset spatial position according to the wavelength and the OAM mode of the coaxial vortex beam through the orthogonal transformation matrix, and allocating the coaxial vortex beam to the preset spatial position to obtain an off-axis vortex beam at the preset spatial position;

[0039] The off-axis vortex beam at the preset spatial position is subjected to mode conversion processing to obtain an off-axis vortex beam of a target OAM mode.

[0040] Optionally, the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation, wherein the light intensity distribution of the light field generated by the orthogonal transformation of the multiple coaxial vortex light beams after the orthogonal transformation by the orthogonal transformation modulation module is detected by the detection module, is specifically:

[0041] The off-axis vortex light beam of the target OAM mode is subjected to electrical signal conversion processing by a shooting device to obtain a light field intensity distribution.

[0042] Beneficial effect: The present invention generates a coaxial vortex light beam carrying different wavelengths and OAM modes through a multi-wavelength OAM mode generating module, and injects it onto the orthogonal transformation modulation module. The multi-level phase modulation device of the orthogonal transformation modulation module performs orthogonal transformation on the coaxial vortex light beam for mode transformation and spatial position regulation. According to the wavelength and OAM mode carried by the coaxial vortex light beam, the coaxial vortex light beam is allocated to a preset spatial position, and the OAM mode it carries is converted during the spatial separation process. Finally, the detection module is used to detect and record the light intensity distribution of different output light fields after the coaxial vortex light beam is modulated, thereby realizing the joint regulation of the wavelength and OAM mode dimensions, effectively improving the mode conversion efficiency of the coaxial vortex light beam, and thus effectively improving the transmission capacity of the communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a structural schematic diagram of a preferred embodiment of the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation of the present invention;

[0044] Figure 2 It is a flow chart of a preferred embodiment of the multi-wavelength orbital angular momentum mode control method based on orthogonal transformation of the present invention;

[0045] Figure 3 It is a schematic diagram of phase modulation matrix optimization of a preferred embodiment of the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] With the explosive growth of demand for optical communication capacity, multi-dimensional multiplexing technology has become a key research direction to break through the Shannon limit. Traditional multiplexing technologies such as wavelength division multiplexing (WDM), polarization division multiplexing (PDM), and mode division multiplexing (MDM) improve the transmission capacity of communications by developing resources in a single physical dimension, but in recent years, their expansion space has reached its theoretical limit. Due to its unique spiral phase distribution and infinite orthogonality, vortex beams can theoretically support an infinite number of orthogonal modes in a single channel. Thanks to the independence of OAM (orbital angular momentum) mode and wavelength, mode division multiplexing based on OAM mode can be well compatible with wavelength division multiplexing technology, thereby greatly improving the communication capacity and spectrum efficiency of the system.

[0048] It has been demonstrated that the communication capacity can be increased by several orders of magnitude by jointly multiplexing wavelengths and modes. However, due to the lack of effective means to suppress the inter-mode crosstalk caused by dispersion, the multi-dimensional multiplexing of wavelengths and modes still has many limitations. Current methods rely on the series combination of arrayed waveguide gratings and spatial light modulators to independently control the wavelength channels and modes, but the resulting complex system configuration and low energy efficiency hinder practical applications. Recent progress includes the proposal of a single-layer Dammann vortex grating with a two-dimensional diffraction design for parallel control of mode channels and wavelength channels. Although this method simplifies the optical design, it is still affected by the dispersion and uniform beam splitting characteristics caused by the Bragg diffraction effect of the grating, resulting in low mode conversion efficiency and large inter-mode crosstalk, limiting its application in multi-dimensional joint control.

[0049] To solve the above problems, the present invention proposes a multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, which can achieve high mode conversion efficiency, high light energy utilization and multi-wavelength OAM mode control with flexible control capability, thereby improving the transmission capacity of the communication system.

[0050] The multi-wavelength orbital angular momentum mode control device based on orthogonal transformation described in the preferred embodiment of the present invention is as follows: Figure 1 As shown, the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation includes a multi-wavelength OAM mode generation module, an orthogonal transformation modulation module and a detection module.

[0051] Specifically, a multi-wavelength OAM mode generating module is used to generate a plurality of coaxial vortex light beams with different wavelengths and OAM modes, and input them into the orthogonal transformation modulation module; an orthogonal transformation modulation module is used to perform orthogonal transformation of the mode transformation and spatial position control of the plurality of coaxial vortex light beams generated by the multi-wavelength OAM mode generating module; and a detection module is used to detect the light field intensity distribution generated after the plurality of coaxial vortex light beams are orthogonally transformed by the orthogonal transformation modulation module.

[0052] Among them, the multi-wavelength OAM mode generating module includes a first tunable laser light source a for generating a first Gaussian beam and a second tunable laser light source b for generating a second Gaussian beam, a first vortex light generating device c for modulating the first Gaussian beam into a first vortex beam, a second vortex light generating device d for modulating the second Gaussian beam into a second vortex beam, and a combiner e for coaxially outputting the first vortex beam and the second vortex beam.

[0053] like Figure 1 As shown, the multi-wavelength OAM mode generating module is composed of two or more wavelength tunable laser light sources a, b, vortex beam generating devices c, d and a beam combiner e. The tunable laser light sources a and b are used to generate Gaussian beams of different wavelengths, the vortex beam generating devices c and d are used to convert Gaussian beams into vortex beams carrying different OAM modes, and the beam combiner e is used to coaxially couple multiple vortex beams. In addition, the present invention is not limited to these devices, and other devices with corresponding functions can be used to replace the coaxial vortex beams carrying different wavelengths and OAM modes.

[0054] It can be understood that in the specific implementation process, the present invention can generate a first Gaussian beam of a first wavelength through a tunable laser light source a, and generate a second Gaussian beam of a second wavelength through a tunable laser light source b, and the first Gaussian light and the second Gaussian light are respectively incident on vortex light generating devices c and d, and the first Gaussian light and the second Gaussian light are modulated into vortex beams carrying different OAM modes through the vortex light generating devices c and d (wherein the tunable laser light source a is incident on the vortex beam generating device c and converted into an OAM mode, and the tunable laser light source b is incident on the vortex beam generating device d and converted into another OAM mode, that is, the OAM mode can be changed by the vortex beam generating device), and after passing through the combiner e, the vortex beams of multiple different OAM modes are coaxially output and incident on the orthogonal transformation modulation module.

[0055] It should be explained that the use of two wavelength tunable laser light sources in the present invention is only for the convenience of description. The present invention can realize the control of two or more multi-wavelength OAM mode light beams.

[0056] Furthermore, the vortex light generating devices c and d (i.e., the first vortex light generating device c and the second vortex light generating device d in the present invention, also referred to as spiral phase forming elements) are spiral phase plates loaded with a preset topological charge, and the operating wavelength of each element is the same as the wavelength of the incident light.

[0057] The beam combiner e is a beam splitter prism, which is used to adjust the multi-path vortex light beams to coaxial output. It should be explained that the coaxial incidence in the present invention refers to the incidence along the same optical axis, which is used to distinguish it from the spatial lateral displacement, and does not mean that the device in the present invention must have a specific incident orientation, so it cannot be understood as a limitation of the present invention.

[0058] Wherein, the orthogonal transformation modulation module includes a multi-level phase modulation device for realizing orthogonal transformation.

[0059] like Figure 1 As shown, the orthogonal transformation modulation module in the present invention is composed of a multi-level phase modulation device f that optically realizes orthogonal transformation, and the multi-level phase modulation device is loaded with the phase distribution required for optical orthogonal transformation.

[0060] The multi-level modulation plane f is a phase modulation screen loaded with the phase modulation array phase, wherein loading here means that the phase modulation screen has the required phase distribution, and the phase modulation screen here is a broad term for a device that can achieve phase modulation, which can be a spatial light modulator or a diffraction element. The spatial light modulator can drive the liquid crystal molecules to arrange by voltage to refresh the phase pattern in real time; the diffraction element can permanently solidify the phase pattern by photolithography or ion beam etching.

[0061] In addition, the multi-level phase modulation device f is composed of multiple phase modulation screens arranged in sequence in space (arranged in sequence in the light field propagation direction, and the modulation plane is perpendicular to the light field propagation direction), and can optically achieve light field control by alternately performing phase modulation and free space diffraction on the light field. The orthogonal transformation modulation module in the present invention is not limited to a multi-level phase modulation device and a phase modulation screen, and can also be composed of a single phase screen and a reflector.

[0062] The orthogonal transformation modulation module in the present invention is used to perform mode transformation and spatial position control on the coaxial vortex light beam generated by the multi-wavelength OAM mode generation module. After the coaxial vortex light beam passes through the orthogonal transformation modulation module, the orthogonal transformation modulation module will distribute the coaxial vortex light beam to a preset spatial position according to the wavelength and OAM mode it carries, and allow the OAM mode it carries to be converted during the spatial separation process.

[0063] Wherein, the detection module includes a shooting device g for recording the light intensity distribution of the light field, and the shooting device includes a wide-band CCD camera.

[0064] like Figure 1 As shown, the detection module in the present invention is composed of a shooting device g that can record the spatial distribution of light fields of each wavelength, and the shooting device g includes a CCD array of each band (a CCD array is a device that converts optical images into electronic signals, which can also be called a CCD camera. It is widely used in the field of image acquisition and processing. The CCD array converts light into electric charges through the photoelectric effect, and then converts the charges into processable electrical signals through analog circuits. The CCD array is mainly divided into two types: linear array and planar array, which are used in different image acquisition scenarios respectively).

[0065] After the coaxial vortex light beam is emitted from each wavelength channel corresponding to the orthogonal transformation modulation module, the emitted light beam is respectively irradiated onto the CCD array working in the corresponding wavelength band. The CCD array converts the optical signal into an electrical signal and displays it on the screen.

[0066] In summary, the modulation module based on orthogonal transformation of the present invention can perform independent mode conversion and spatial lateral shift (i.e., orthogonal transformation of mode conversion and spatial position regulation) according to the wavelength and OAM mode carried by the coaxial vortex light beam. Compared with the traditional wavelength and mode regulation method, the present invention has the characteristics of high mode conversion efficiency, high light energy utilization, and flexible design of regulation capability, and has broad application prospects in information processing fields such as multi-dimensional multiplexed optical communication and optical computing.

[0067] Furthermore, if Figure 2 As shown, based on the above-mentioned multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, the present invention also provides a multi-wavelength orbital angular momentum mode control method based on orthogonal transformation of the multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, wherein the multi-wavelength orbital angular momentum mode control system method based on orthogonal transformation:

[0068] Step S10: Generate a plurality of coaxial vortex beams with different wavelengths and OAM modes through the multi-wavelength OAM mode generating module, and input them into the orthogonal transformation modulation module.

[0069] Step S20, performing orthogonal transformation of mode transformation and spatial position control on the multiple coaxial vortex light beams generated by the multi-wavelength OAM mode generation module through the orthogonal transformation modulation module.

[0070] Step S30, detecting, by the detection module, the light field intensity distribution generated by the orthogonal transformation of the multiple coaxial vortex light beams by the orthogonal transformation modulation module.

[0071] Specifically, in step S10, a plurality of coaxial vortex beams with different wavelengths and OAM modes are generated by the multi-wavelength OAM mode generating module and input into the orthogonal transformation modulation module, which specifically includes the following steps:

[0072] A first Gaussian beam of a first wavelength is generated by a first tunable laser light source, and a second Gaussian beam of a second wavelength is generated by a second tunable laser light source; a first wavefront phase of the first Gaussian beam is obtained by a first vortex light generating device, and a spiral phase is superimposed on the first wavefront phase to obtain a first vortex beam; a second wavefront phase of the second Gaussian beam is obtained by a second vortex light generating device, and a spiral phase is superimposed on the second wavefront phase to obtain a second vortex beam; the first vortex beam and the second vortex beam are coaxially adjusted by a beam combiner to obtain a plurality of coaxial vortex beams, and the plurality of coaxial vortex beams are input into the orthogonal transformation modulation module.

[0073] The specific implementation process of modulating the first Gaussian light and the second Gaussian light into vortex beams carrying different OAM modes through the vortex light generating device is as follows: a spiral phase is superimposed on the wavefront phase of the incident Gaussian light through the vortex generating device, that is, exp(ilθ), where i is an imaginary unit, l is the topological charge, and θ is the azimuth angle. Depending on the specific device, the generation of the spiral phase is different. For example, the surface of the spiral phase plate has a spiral height distribution, and the thickness varies with the azimuth angle, resulting in different phase delays for light passing through different azimuth positions. The spatial light modulator dynamically modulates the phase of the incident light through an electrically controlled liquid crystal pixel array.

[0074] Specifically, in the step S20, the orthogonal transformation of the mode transformation and spatial position regulation of the multiple coaxial vortex beams generated by the multi-wavelength OAM mode generation module is performed by the orthogonal transformation modulation module, which specifically includes the following steps:

[0075] like Figure 3 As shown, the wavelength and OAM mode in each of the coaxial vortex light beams are obtained through a multi-level phase modulation device, and forward propagation calculations are performed on each of the wavelengths and the OAM mode to obtain a predicted output light field corresponding to each of the coaxial vortex light beams; the target output light field is determined through a multi-level phase modulation device, and a loss function is calculated based on the target output light field and each of the predicted output light fields; the modulation plane phase is determined through a multi-level phase modulation device, and the modulation plane phase is initialized to obtain an initialized modulation plane phase; the phase component gradient corresponding to each of the loss functions is calculated through a multi-level phase modulation device, and the initialized modulation plane phase is iteratively updated based on each of the loss functions and the corresponding phase component gradient; when the number of iterations reaches a preset number of iterations or the loss function is lower than a preset loss threshold, the iterative update is stopped to obtain the target modulation plane phase.

[0076] The multi-level modulation plane f is a phase modulation screen loaded with the phase modulation array phase, wherein loading here means that the phase modulation screen has the required phase distribution, and the phase modulation screen here is a broad term for a device that can achieve phase modulation, which can be a spatial light modulator or a diffraction element. The spatial light modulator can drive the liquid crystal molecules to arrange by voltage to refresh the phase pattern in real time; the diffraction element can permanently solidify the phase pattern by photolithography or ion beam etching.

[0077] In addition, the multi-level phase modulation device f is composed of multiple phase modulation screens arranged in sequence in space (arranged in sequence in the light field propagation direction, and the modulation plane is perpendicular to the light field propagation direction), and can optically achieve light field control by alternately performing phase modulation and free space diffraction on the light field. The orthogonal transformation modulation module in the present invention is not limited to a multi-level phase modulation device and a phase modulation screen, and can also be composed of a single phase screen and a reflector.

[0078] like Figure 3 As shown, when the number of iterations reaches the preset number or the loss function drops to the preset threshold, the phase distribution of the diffraction surface is the optimal solution. The phase distribution is loaded onto a multi-level phase modulation device to form an orthogonal transformation modulation module, thereby realizing the regulation of multi-wavelength OAM modes.

[0079] A phase modulation matrix is ​​obtained according to the target modulation plane phase by a multi-level phase modulation device, wherein the expression of the phase modulation matrix is: i (x, y) = angle[P i ]; where φ i (x, y) is the target modulation plane phase, x is the spatial horizontal coordinate, y is the spatial vertical coordinate, P i is a phase modulation matrix, and angle is a phase distribution calculation; a diffraction propagation matrix is ​​determined by a multi-level phase modulation device, and an orthogonal transformation matrix is ​​constructed according to the phase modulation matrix and the diffraction propagation matrix; wherein the expression of the diffraction propagation matrix is: Among them, H(λ, f x , f y ) is the diffraction propagation matrix, λ is the wavelength, f x is the spatial frequency component of the spatial horizontal coordinate x in the frequency space, f y is the spatial frequency component of the spatial ordinate y in the frequency space, i is the imaginary unit, and d is the forward transmission distance; the preset spatial position is determined according to the wavelength of the coaxial vortex beam and the OAM mode through the orthogonal transformation matrix, and the coaxial vortex beam is allocated to the preset spatial position to obtain the off-axis vortex beam at the preset spatial position; the off-axis vortex beam at the preset spatial position is subjected to mode transformation processing to obtain the off-axis vortex beam of the target OAM mode.

[0080] Among them, the phase modulation matrix P i Optically, the phase distribution φ can be loaded on the multi-level phase modulation device f i (x,y)=angle[P i ] is realized, that is, the present invention calculates the target modulation plane phase φ i (x, y) can obtain the corresponding phase modulation matrix P i .

[0081] The wavelength-dependent diffraction propagation matrix is ​​a propagation matrix of light in free space, satisfying the Huygens-Fresnel principle.

[0082] Furthermore, an orthogonal transformation matrix can be constructed based on the phase modulation matrix and the diffraction propagation matrix, and the orthogonal transformation matrix is ​​an important factor in the spatial position allocation and OAM mode conversion of the coaxial vortex light beam in the orthogonal transformation modulation module described in the present invention.

[0083] Among them, the equivalent formula of the orthogonal transformation modulation module is: Among them, E m represents the mth input light field, E′ m represents the mth output light field, λ m represents the wavelength of the mth input light field, x m ,y m Represents the spatial coordinate of the mth input light field, x′ m , y′ m Represents the spatial coordinates of the mth output light field, and U is the orthogonal transformation matrix that performs the linear transformation between the input light field and the output light field. Through the decomposable characteristics of the matrix (the decomposable characteristic means that a matrix X can be decomposed into the Hadmard product of multiple matrices (also known as the Hadamard product, which is a matrix multiplication operation, multiplying two matrices of the same size at the same position)), U can be decomposed into the Hadmard product of the phase modulation matrix and the diffraction propagation matrix, that is: U = P 1 ·H 1 (λ)·P 2 ·H 2 (λ)····P n ·H n+1 (λ), where H n+1 (λ) is the wavelength-dependent diffraction propagation matrix of the n+1th light field, P n is the phase modulation matrix corresponding to the n+1th light field.

[0084] The OAM mode conversion process is as follows: The OAM mode can be converted to l by the orthogonal transformation modulation module.1 The coaxial vortex beam is converted into an OAM mode of l 2 The conversion process is to modulate the wavefront phase of the coaxial vortex beam through a multi-level phase modulation module, from exp(il 1 θ) is converted to exp(il 2 θ).

[0085] It can be understood that the process of the orthogonal transformation modulation module performing free space diffraction processing on the coaxial vortex beam is as follows: through the combined effect of the multi-level phase modulation device in the orthogonal transformation modulation module and the spatial diffraction on the wavefront phase of the coaxial vortex beam, the coaxially incident multi-wavelength OAM mode mixed beam is spatially offset, wherein the offset positions of different OAM mode vortex beams of different wavelengths are different. The wavefront phase changes after the light field passes through the phase modulation screen, and the wavefront continues to change after the free space diffraction between the phase screens, and the ideal modulation effect is achieved after alternating.

[0086] The coaxially incident vortex light will be separated into different spatial positions according to the wavelength and mode, and the spatial position is allocated according to the actual situation based on the wavelength and the number of modes. In the present invention, two wavelengths and two modes are preferably provided. For example, the vortex light beam corresponding to the first wavelength and the first mode can be preset at a position slightly above the optical axis, and the vortex light beam corresponding to the second wavelength and the second mode can be preset at a position slightly below the optical axis. In the case of multiple wavelengths and multiple modes, the corresponding spatial positions can be designed as needed. Because the vortex light beam in the present invention is coaxially incident, it is better to regulate each light beam individually after spatial separation, and the demultiplexing in optical communication is satisfied from coaxial to spatial separation.

[0087] Furthermore, the off-axis vortex light beam of the target OAM mode is subjected to electrical signal conversion processing by a shooting device to obtain a light field intensity distribution.

[0088] The detection module provided in the present invention is used to detect the light intensity distribution of different output light fields after modulation. After the coaxial vortex light beams carrying different wavelengths and OAM modes are modulated by the multiple phase modulation screens of the orthogonal transformation modulation module and diffracted in free space, they are assigned to preset spatial positions according to the wavelengths and OAM modes they carry, and the OAM modes they carry are converted in the process of spatial separation. The present invention realizes the progressive control of the light field by alternating a reasonably designed phase modulation matrix and free space diffraction. Among them, by loading the modulation plane of the optimal solution and the free diffraction propagation between the planes, the wavefront of the vortex light beams of each wavelength OAM mode changes, and this change is the control process of the coaxial vortex light beam.

[0089] To summarize, the present invention generates a coaxial vortex light beam carrying different wavelengths and OAM modes through a multi-wavelength OAM mode generating module, and injects it onto the orthogonal transformation modulation module. The coaxial vortex light beam is subjected to orthogonal transformation of mode transformation and spatial position regulation through a multi-level phase modulation device of the orthogonal transformation modulation module. According to the wavelength and OAM mode carried by the coaxial vortex light beam, the coaxial vortex light beam is allocated to a preset spatial position, and the OAM mode carried by the coaxial vortex light beam is converted during the spatial separation process. Finally, the light intensity distribution of different output light fields after the coaxial vortex light beam is modulated is detected and recorded through a detection module, thereby realizing the joint regulation of the wavelength and OAM mode dimensions, effectively improving the mode conversion efficiency of the coaxial vortex light beam, and thereby effectively improving the transmission capacity of the communication system.

[0090] Beneficial effects of the present invention: The present invention generates a coaxial vortex light beam carrying different wavelengths and OAM modes through a multi-wavelength OAM mode generation module, and injects it into the orthogonal transformation modulation module. After being modulated by multiple phase modulation screens of the orthogonal transformation modulation module and diffracted in free space, it is assigned to a preset spatial position according to the wavelength and OAM mode it carries, and the OAM mode it carries is converted during the spatial separation process. Finally, the light intensity distribution of different output light fields after modulation is detected and recorded by the detection module, thereby realizing the joint regulation of wavelength and OAM mode dimensions. The present invention has the characteristics of high mode conversion efficiency, high light energy utilization, and system dynamic adjustability, and has broad application prospects in the field of multi-degree-of-freedom collaborative modulation such as multi-dimensional optical communication and optical computing.

[0091] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A multi-wavelength orbital angular momentum mode control device based on orthogonal transformation, characterized in that: The multi-wavelength orbital angular momentum mode control device based on orthogonal transformation includes: a multi-wavelength OAM mode generation module, an orthogonal transformation modulation module and a detection module; A multi-wavelength OAM mode generation module, used to generate a plurality of coaxial vortex beams of different wavelengths and OAM modes, and input them into the orthogonal transformation modulation module; An orthogonal transformation modulation module, used for performing orthogonal transformation of mode transformation and spatial position regulation on the multiple coaxial vortex light beams generated by the multi-wavelength OAM mode generation module; The detection module is used to detect the light field intensity distribution generated after the multiple coaxial vortex light beams are orthogonally transformed by the orthogonal transformation modulation module.

2. The multi-wavelength orbital angular momentum mode control device based on orthogonal transformation according to claim 1 is characterized in that: The multi-wavelength OAM mode generating module includes a first tunable laser light source for generating a first Gaussian beam and a second tunable laser light source for generating a second Gaussian beam, a first vortex light generating device for modulating the first Gaussian beam into a first vortex beam, a second vortex light generating device for modulating the second Gaussian beam into a second vortex beam, and a combiner for coaxially outputting the first vortex beam and the second vortex beam.

3. The multi-wavelength orbital angular momentum mode control device based on orthogonal transformation according to claim 1 is characterized in that: The orthogonal transformation modulation module includes a multi-level phase modulation device for realizing orthogonal transformation.

4. The multi-wavelength orbital angular momentum mode control device based on orthogonal transformation according to claim 1 is characterized in that: The detection module includes a shooting device for recording the light intensity distribution of the light field, and the shooting device includes a wide-band CCD camera.

5. A method for controlling a multi-wavelength orbital angular momentum mode based on an orthogonal transformation according to the multi-wavelength orbital angular momentum mode control device based on an orthogonal transformation according to any one of claims 1 to 4, characterized in that: The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation includes: Generate a plurality of coaxial vortex beams of different wavelengths and OAM modes through the multi-wavelength OAM mode generation module, and input them into the orthogonal transformation modulation module; The orthogonal transformation modulation module performs mode transformation and spatial position control on the multiple coaxial vortex light beams generated by the multi-wavelength OAM mode generation module; The detection module is used to detect the light field intensity distribution generated after the multiple coaxial vortex light beams are orthogonally transformed by the orthogonal transformation modulation module.

6. The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation according to claim 5 is characterized in that: The multi-wavelength OAM mode generating module generates a plurality of coaxial vortex beams with different wavelengths and OAM modes, and inputs the beams into the orthogonal transformation modulation module, specifically comprising: Generate a first Gaussian beam of a first wavelength by a first tunable laser light source, and generate a second Gaussian beam of a second wavelength by a second tunable laser light source; Acquire a first wavefront phase of the first Gaussian beam through a first vortex light generating device, and superimpose a spiral phase on the first wavefront phase to obtain a first vortex beam; Acquire a second wavefront phase of the second Gaussian beam by a second vortex light generating device, and superimpose a spiral phase on the second wavefront phase to obtain a second vortex beam; The first vortex light beam and the second vortex light beam are coaxially adjusted by a beam combiner to obtain a plurality of coaxial vortex light beams, and the plurality of coaxial vortex light beams are input into the orthogonal transformation modulation module.

7. The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation according to claim 5 is characterized in that: The orthogonal transformation of performing mode transformation and spatial position control on the multiple coaxial vortex beams generated by the multi-wavelength OAM mode generation module through the orthogonal transformation modulation module specifically includes: Calculating the loss function corresponding to each of the coaxial vortex beams through a multi-stage phase modulation device, and iteratively updating the initialization modulation plane phase according to the multiple loss functions to obtain the target modulation plane phase; An orthogonal transformation matrix is ​​constructed according to the target modulation plane phase, and the orthogonal transformation matrix is ​​used to perform mode transformation and spatial position control processing on each of the coaxial vortex light beams.

8. The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation according to claim 7 is characterized in that: The method of calculating the loss function corresponding to each of the coaxial vortex beams by a multi-level phase modulation device, and iteratively updating the initialization modulation plane phase according to the multiple loss functions to obtain the target modulation plane phase specifically includes: Acquire the wavelength and OAM mode in each of the coaxial vortex beams through a multi-stage phase modulation device, perform forward propagation calculation on each of the wavelength and the OAM mode, and obtain a predicted output light field corresponding to each of the coaxial vortex beams; Determine a target output light field through a multi-level phase modulation device, and calculate a loss function according to the target output light field and each of the predicted output light fields; Determine the modulation plane phase by a multi-level phase modulation device, and perform initialization processing on the modulation plane phase to obtain an initialized modulation plane phase; Calculating the phase component gradient corresponding to each loss function through a multi-level phase modulation device, and iteratively updating the initialization modulation plane phase according to each loss function and the corresponding phase component gradient; When the number of iterations reaches a preset number of iterations or the loss function is lower than a preset loss threshold, the iterative update is stopped to obtain the target modulation plane phase.

9. The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation according to claim 7 is characterized in that: The step of constructing an orthogonal transformation matrix according to the target modulation plane phase, and performing mode transformation and spatial position control processing on each of the coaxial vortex beams through the orthogonal transformation matrix specifically includes: A phase modulation matrix is ​​obtained according to the target modulation plane phase by a multi-level phase modulation device, wherein the expression of the phase modulation matrix is: i (x,y)=angle[P i ]; Among them, φ i (x, y) is the target modulation plane phase, x is the spatial horizontal coordinate, y is the spatial vertical coordinate, P i is the phase modulation matrix, angle is the phase distribution calculation; Determine a diffraction propagation matrix through a multi-level phase modulation device, and construct an orthogonal transformation matrix according to the phase modulation matrix and the diffraction propagation matrix; Wherein, the expression of the diffraction propagation matrix is: Among them, H(λ, f x , f y ) is the diffraction propagation matrix, λ is the wavelength, f x is the spatial frequency component of the spatial horizontal coordinate x in the frequency space, f y is the spatial frequency component of the spatial ordinate y in the frequency space, i is the imaginary unit, and d is the forward transmission distance; Determining a preset spatial position according to the wavelength and the OAM mode of the coaxial vortex beam through the orthogonal transformation matrix, and allocating the coaxial vortex beam to the preset spatial position to obtain an off-axis vortex beam at the preset spatial position; The off-axis vortex beam at the preset spatial position is subjected to mode conversion processing to obtain an off-axis vortex beam of a target OAM mode.

10. The multi-wavelength orbital angular momentum mode control method based on orthogonal transformation according to claim 9 is characterized in that: The light intensity distribution of the light field generated by the orthogonal transformation of the plurality of coaxial vortex light beams by the detection module is specifically as follows: The off-axis vortex light beam of the target OAM mode is subjected to electrical signal conversion processing by a shooting device to obtain a light field intensity distribution.

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