Phase modulation method and optical device

Abstract

The invention provides a phase modulation method and an optical device, and relates to the field of optical devices. The phase modulation method is applied to the cascade-based double-layer diffractive optical device, and the double-layer diffractive optical device comprises a top-layer diffractive optical device and a bottom-layer diffractive optical device. The phase modulation method comprises the following steps: controlling a top diffraction optical device to continuously move from an initial state to a second side at a target displacement; continuous movement is completed, and cascade phase values of all channels of the double-layer diffractive optical device are obtained; and determining the top phase of the top diffractive optical device and the bottom phase of the bottom diffractive optical device according to the target light field phase and the cascade phase values of all the channels. According to the phase modulation method provided by the embodiment of the invention, phase distribution can be optimized, and the number of cascade channels is increased; when a diffraction device is manufactured, incident light is regulated and controlled based on phase distribution, so that the incident light forms a target light field in a far field.

Description

Technical Field

[0001] This application relates to the field of optical devices. Specifically, it relates to a phase modulation method and an optical device. Background Art

[0002] The phase of an optical device refers to the delay characteristic of the wavefront in the spatial distribution when light waves pass through an optical element, which directly determines the propagation direction and wavefront shape of the light waves. By precisely controlling the phase distribution, diffractive optical devices can achieve complex manipulation of light waves, such as beam deflection, focusing, beam splitting, and holographic imaging. Once a diffractive optical device is fabricated, its phase distribution is fixed and difficult to adapt to dynamic and changing application requirements.

[0003] The traditional solution is to achieve multi-channel multiplexing by adjusting attributes such as the polarization state, wavelength, incident angle, or orbital angular momentum of the incident light, thereby improving the functional utilization rate of a single device. However, this method that relies on the adjustment of incident light parameters has basically exhausted the multiplexing dimensions of a single device and is difficult to further increase the number of channels, still falling short of complex application requirements. Summary of the Invention

[0004] The purpose of the embodiments of this application is to provide a phase modulation method and an optical device. Based on the switching between cascaded channels with continuous pixel-level lateral displacement, the phase modulation method adopts a segmented optimization strategy and uses a genetic algorithm to solve the global optimal solution during this process. It can not only make the channel switching smoother and easier to align, but also encode a larger number of cascaded channels, greatly improving the accuracy and efficiency of the calculation.

[0005] In a first aspect, the embodiments of this application provide a phase modulation method. The phase modulation method is applied to a cascaded double-layer diffractive optical device, and the double-layer diffractive optical device includes a top diffractive optical device and a bottom diffractive optical device. The phase modulation method includes: controlling the top diffractive optical device to continuously move from an initial state to the second side with a target displacement, where the initial state is a state in which the starting pixels of the top diffractive optical device and the bottom diffractive optical device are aligned on the first side; completing the continuous movement to obtain the cascaded phase values of all channels of the double-layer diffractive optical device; and determining the top layer phase of the top diffractive optical device and the bottom layer phase of the bottom diffractive optical device according to the target light field phase and the cascaded phase values of all channels.

[0006] In the above implementation process, the phase modulation method proposed in this application realizes cascaded phase regulation with multi-channel dynamic tunability by controlling the continuous pixel-level lateral displacement of the top diffraction optical device relative to the bottom diffraction optical device; and uses the relative displacement of the double-layer diffraction devices to generate cascaded phases of different channels, and calculates the phase distributions of the top and bottom layers, significantly improving the number of channels and the flexibility of optical field regulation.

[0007] Optionally, in an embodiment of this application, the total number of pixels of the top diffraction optical device is N, the total number of pixels of the bottom diffraction optical device is N + M - 1, and M is the total number of channels; controlling the top diffraction optical device to continuously move from the initial state to the second side with a target displacement includes: segmenting the top diffraction optical device, and controlling each segment of the top diffraction optical device to include (M - 1) pixels with determined top phase values and (M - 1) pixels with undetermined top phase values; segmenting the bottom diffraction optical device, and controlling each segment of the bottom diffraction optical device to include 2(M - 1) pixels with undetermined bottom phase values; controlling the (M - 1) pixels with undetermined top phase values in each segment of the top diffraction optical device to be aligned with the first (M - 1) pixels with undetermined bottom phase values in the bottom diffraction optical device each time.

[0008] Optionally, in an embodiment of this application, for the i-th segment of the double-layer diffraction optical device: the segmentation of the top diffraction optical device is: α (i-1)(M-1)+1 …α i(m-1) 、α i(M-1)+1 …α (i+1)(m-1) ; where α (i-1)(M-1)+1 …α i(M-1) are determined top phase values, and are calculated from the (i - 1)-th segment, and α i(M-1)+1 …α (i+1)(M-1) are undetermined top phase values; the segmentation of the bottom diffraction optical device is: β i(M-1)+1 …β (i+2)(M-1) ; where β i(M-1)+1 …β (i+2)(M-1) are undetermined bottom phase values.

[0009] In the above implementation process, the phase modulation method provided in the embodiment of this application realizes recursive optimization by dividing the double-layer diffraction optical device into multiple sub-segments. Each segment only processes a limited number of pixels (the top layer includes M - 1 pixels with determined phases and M - 1 pixels with undetermined phases, and the bottom layer includes 2(M - 1) pixels with undetermined phases). By means of the segmentation strategy, the high-dimensional optimization problem is reduced in dimension. While ensuring the phase continuity between adjacent segments, the calculation complexity is significantly reduced, the calculation accuracy is improved, and the double-layer diffraction device can efficiently generate a multi-channel tunable optical field distribution.

[0010] Optionally, in the embodiments of the present application, determining the top layer phase of the top layer diffractive optical device and the bottom layer phase of the bottom layer diffractive optical device according to the target light field phase and the cascaded phase values of all channels includes: constructing a linear equation system between the target light field phase and the top layer phase and the bottom layer phase based on the target light field and the cascaded phase values of all channels; solving the linear equation system to obtain the top layer phase and the bottom layer phase.

[0011] Optionally, in the embodiments of the present application, the linear equation system includes: where Φ m is the cascaded phase at each pixel position of the m-th channel; A m is an N×N identity matrix; B m is an N×(N + M - 1) matrix, and starting from the m-th column, it is an N×N identity matrix; Θ is a phase vector regarding the partial top layer phase and the partial bottom layer phase.

[0012] In the above implementation process, the phase modulation method provided by the present application establishes a linear equation system (Φ = C·Θ) between the target light field phase and the cascaded phase. By solving this equation system, the static phase distributions (α and β) of the top layer and the bottom layer diffractive optical devices can be determined simultaneously, such that when the top layer device moves relatively, the cascaded phase Φ m can accurately reconstruct the target light field.

[0013] Optionally, in the embodiments of the present application, solving the linear equation system to obtain the top layer phase and the bottom layer phase includes: defining an objective function by minimizing the absolute mean square error between the target light field and the calculated light field; based on the objective function, using an objective optimization algorithm to obtain the phase approximations of the top layer diffractive optical device and the bottom layer diffractive optical device when M > 2, and obtaining the top layer phase and the bottom layer phase.

[0014] Optionally, in the embodiments of the present application, the objective function is: where is the target light field, e iCΘ is the calculated light field, Φ tar is the target phase under all channels, CΘ is the cascaded phase under all channels, and C is the coefficient matrix.

[0015] In the above implementation process, based on the switching between cascaded channels during continuous pixel-level lateral displacement, the phase modulation method provided by the embodiments of the present application adopts a segmented optimization strategy and uses a genetic algorithm to solve the global optimal solution during this process. Therefore, the phase modulation method provided by the embodiments of the present application can not only make the channel switching smoother and easier to align, but also encode a larger number of cascaded channels, greatly improving the accuracy and efficiency of the calculation.

[0016] Optionally, in the embodiments of the present application, the target displacement is an integer multiple of the single pixel size of the double-layer diffractive optical device.

[0017] In the above implementation process, the phase modulation method provided by the embodiments of the present application can precisely laterally displace the double-layer diffractive optical device by an integer multiple of the single pixel size p, realizing a multi-channel dynamically adjustable phase superposition effect. After each displacement, specific cascaded combinations of the phase distributions of the top and bottom devices are generated, thus generating different holographic images in the far field. This not only ensures the accuracy and repeatability of the phase superposition but also realizes the dynamic switching of complex optical fields through simple mechanical displacement.

[0018] Optionally, in the embodiments of the present application, the double-layer diffractive optical device includes a device with a channel interval of multiple pixels; the method further includes: dividing the device with a channel interval of multiple pixels into multiple sub-devices with a channel interval of a single pixel; respectively calculating the top layer phase of the top layer diffractive optical device and the bottom layer phase of the bottom layer diffractive optical device of each sub-device; taking the top layer phases of the multiple sub-devices as the top layer phase of the top layer diffractive optical device of the device with a channel interval of multiple pixels; and taking the bottom layer phases of the multiple sub-devices as the bottom layer phase of the bottom layer diffractive optical device of the device with a channel interval of multiple pixels.

[0019] In the above implementation process, for the design of a cascaded diffractive optical device with a channel interval of multiple pixels, it can be regarded as a combination of several cascaded diffractive optical devices with a channel interval of a single pixel.

[0020] In a second aspect, the embodiments of the present application further provide an optical device, which includes a stacked and cascaded top layer diffractive optical device and a bottom layer diffractive optical device; the top layer phase of the top layer diffractive optical device and the bottom layer phase of the bottom layer diffractive optical device are determined according to the phase modulation method in the first aspect of the present application.

[0021] In a third aspect, the embodiments of the present application further provide a computer-readable storage medium, in which computer program instructions are stored. When the computer program instructions are read and run by a processor, the steps in any of the above implementation manners are executed. Description of the Drawings

[0022] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments of the present application will be briefly introduced below. It should be understood that the following accompanying drawings only show some embodiments of the present application and should not be regarded as a limitation of the scope. For those of ordinary skill in the art, other related accompanying drawings can be obtained based on these accompanying drawings without creative efforts.

[0023] Figure 1 It is a flowchart of the phase modulation method provided by the embodiments of the present application;

[0024] Figure 2 It is a schematic diagram of generating cascaded co-phases in one-dimensional cases provided by the embodiments of the present application;

[0025] Figure 3 It is a flowchart of segmented movement provided by the embodiments of the present application;

[0026] Figure 4 It is a schematic diagram of the segmented calculation strategy provided by the embodiments of the present application;

[0027] Figure 5 It is a flowchart of phase calculation provided by the embodiments of the present application;

[0028] Figure 6 It is a flowchart of solving the approximate solution provided by the embodiments of the present application;

[0029] Figure 7 It is an example diagram of holographic images corresponding to different target displacement amounts provided by the embodiments of the present application;

[0030] Figure 8 It is a schematic diagram of the simulation and experimental results of the 12-channel cascaded multiplexed hologram provided by the embodiments of the present application. Detailed implementation manners

[0031] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions, and operations of systems, methods, and computer program products according to multiple embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than marked in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions. In addition, the functional modules in various embodiments of the present invention may be integrated together to form an independent part, or each module may exist alone, or two or more modules may be integrated to form an independent part.

[0032] Once a diffractive optical device is manufactured, its phase distribution is fixed and difficult to adapt to dynamic and diverse application requirements. The traditional solution is to achieve multi-channel multiplexing by modulating attributes such as the polarization state, wavelength, incident angle, or orbital angular momentum of the incident light, thereby improving the functional utilization rate of a single device. However, this method relying on the modulation of incident light parameters has basically exhausted the multiplexing dimensions of a single device, and there are fundamental limitations in further increasing the number of channels.

[0033] Currently, a solution has also been proposed to implement multiple channels by stacking and cascading two layers of diffractive optical devices, and to achieve channel switching by using an external mechanical force to cause in-plane lateral displacement or rotation of these two layers of diffractive optical devices.

[0034] The inventors have found through research that in the case of stacking and cascading, the selection of the objective function of the pixel-level phase modulation optimization algorithm and the switching method of the cascaded channels are not reasonable, resulting in limited number of stacking and cascading channels. In the case of spatial cascading, the micron-level spatial alignment error will cause a significant decrease in diffraction efficiency, affecting the quality of the reconstructed image; and a certain distance needs to be reserved between the two layers of diffractive optical devices, making the system large and not compact.

[0035] Based on this, the present application proposes a phase modulation method and an optical device. This phase modulation method uses continuous lateral single-pixel displacement between layers of a diffractive optical device to achieve a cascaded multiplexing channel for high-capacity holographic storage, making the switching between channels smoother and easier to align; for an optical device with a relatively large total number of pixels, a segmented calculation strategy can be adopted, so that a larger number of cascaded channels can be encoded.

[0036] Please refer to Figure 1 and Figure 2 , Figure 1 which is the flowchart of the phase modulation method provided by the embodiments of the present application; Figure 2 which is the schematic diagram of generating cascaded phase in one-dimensional case provided by the embodiments of the present application; The present application provides a phase modulation method and an optical device. The phase modulation method is applied to a cascaded double-layer diffractive optical device, and the double-layer diffractive optical device includes a top diffractive optical device and a bottom diffractive optical device. It should be noted that, in the embodiments of the present application, the top optical device and the bottom diffractive optical device form the double-layer diffractive optical device based on stacked cascading. Stacked cascading is a cascading scheme in which multiple diffractive optical devices are closely attached or stacked with a small spacing in the optical axis direction, and light passes through each layer in turn. Each layer performs step-by-step modulation on the light field, and finally superimposes a multi-channel effect.

[0037] The phase modulation method provided by the present application includes the following steps:

[0038] Step S100: Control the top diffractive optical device to continuously move from the initial state to the second side with a target displacement.

[0039] In the above step S100, control the top diffractive optical device to continuously move from the initial state to the second side with a target displacement. Please refer to Figure 2 In the embodiments of the present application, the initial state is the state where the starting pixels of the top diffractive optical device and the bottom diffractive optical device are aligned on the first side. In Figure 2 , the first side is the left side, and the second side is the right side, that is, starting from the alignment of α1 of the top diffractive optical device on the left side and β1 of the bottom diffractive optical device, control the top diffractive device to continuously move to the right with the target displacement each time. The continuous pixel-level lateral displacement can achieve the switching between channels.

[0040] Step S200: Complete the continuous movement to obtain the cascaded phase values of all channels of the double-layer diffractive optical device.

[0041] In the above step S200, perform multiple continuous movements until the cascaded phase of all channels of the double-layer diffractive optical device is obtained by completing the continuous movement calculation. Please continue to refer to Figure 2 , the top diffractive optical device ( Figure 2The red part) Every time it moves one pixel with side length p from left to right, it combines with the underlying diffractive optical device ( Figure 2 The blue part) to generate a cascaded channel (initially, the left sides of the upper and lower liquid crystals are aligned). When the upper diffractive optical device moves m - 1 pixels, the cascaded channel number is m. At this time, the nth pixel of the upper layer coincides with the (n + m - 1)th pixel of the lower layer horizontally (as Figure 2 shown), then the cascaded phase, that is, the total phase delay, can be expressed as: where α is the top layer phase of the upper diffractive optical device and β is the bottom layer phase of the underlying diffractive optical device, M is the total number of channels, and N is the total number of pixels of the upper liquid crystal, that is, the upper diffractive optical device.

[0042] It should be noted that for a two-dimensional cascaded diffractive optical device, it can be regarded as a combination of several independent one-dimensional structures.

[0043] Step S300: Determine the top layer phase of the upper diffractive optical device and the bottom layer phase of the underlying diffractive optical device according to the target light field phase and the cascaded phase values of all channels.

[0044] In the above step S300, according to the target light field phase and the cascaded phase values obtained in step S200, the top layer phase α of the upper diffractive optical device and the bottom layer phase β of the underlying diffractive optical device are calculated; after obtaining the top layer phase α and the bottom layer phase β, they are used to control the incident light so that a target light field (such as a hologram, energy distribution) is formed in the far field.

[0045] Through Figure 1 and Figure 2 it can be seen that the phase modulation method proposed in this application realizes multi-channel dynamically adjustable cascaded phase control by controlling the continuous pixel-level lateral displacement of the upper diffractive optical device relative to the underlying diffractive optical device; and uses the relative displacement of the double-layer diffractive devices to generate the cascaded phases of different channels, and calculates the phase distributions of the top layer and the bottom layer, significantly improving the number of channels and the flexibility of light field control.

[0046] Please refer to Figure 3 and Figure 4 , Figure 3 is the flowchart of the segmented movement provided by the embodiment of this application; Figure 4 is the schematic diagram of the segmented calculation strategy provided by the embodiment of this application; among them, the total number of pixels of the upper diffractive optical device is N, the total number of pixels of the underlying diffractive optical device is N + M - 1, and M is the total number of channels. When N is large enough, for example, N is greater than 50, the segmented calculation strategy can be used; the control of the upper diffractive optical device in the above step S100 to continuously move from the initial state to the second side with the target displacement can be achieved through the following steps:

[0047] Step S110: Segment the top diffractive optical device, and control each segment of the top diffractive optical device to include (M - 1) pixels with determined top layer phase values and (M - 1) pixels with undetermined top layer phase values.

[0048] Step S120: Segment the bottom diffractive optical device, and control each segment of the bottom diffractive optical device to include 2(M - 1) pixels with undetermined bottom layer phase values.

[0049] Step S130: Control the alignment of (M - 1) pixels with undetermined top layer phase values in each segment of the top diffractive optical device with the first (M - 1) pixels with undetermined bottom layer phase values in the bottom diffractive optical device each time.

[0050] In the above Steps S110 to S130, the top diffractive optical device and the bottom diffractive optical device are segmented respectively. Except for the first segmentation, ensure that each top diffractive optical device includes (M - 1) pixels with determined top layer phase values and (M - 1) pixels with undetermined top layer phase values, and ensure that each bottom diffractive optical device includes 2(M - 1) pixels with undetermined bottom layer phase values. And, as Figure 4 shown, the (M - 1) pixels with undetermined top layer phase values in the top diffractive optical device are aligned with the first (M - 1) pixels with undetermined bottom layer phase values in the bottom diffractive optical device.

[0051] In this process, the overall phase error obtained by the participation of the (M - 1) pixels with unknown phases in the upper layer in the calculation is relatively low. At the same time, it can also make the total number of pixels with unknown phases in each segment less. The smaller number of pixels with unknown phases can reduce the calculation time and improve the calculation accuracy.

[0052] For example, Figure 4 in the second segmentation in m-1 α1 to α m are the pixels with determined top layer phase values in the top layer, α 2(M-1) to α M are the pixels with undetermined top layer phase values in the top layer, β 3(M-1) to β M are the pixels with undetermined bottom layer phase values in the bottom layer; in this segmentation, α 2(M-1) to α M are aligned with β 2(M-1) to β

[0053] In the above implementation process, Figure 4 the pixels selected by the red dashed box in

[0054] In a possible embodiment, assuming that the double-layer diffractive optical device is divided into i segments, the segmentation of the i-th segment is as follows: The segmentation of the top-layer diffractive optical device is: α (i-1)(M-1)+1 …α i(M-1) 、α i(M-1)+1 …α (i+1)(M-1) ; where α (i-1)(M-1)+1 …α i(M-1) is the determined top-layer phase value, which is calculated from the (i - 1)-th segment, and α i(M-1)+1 …α (i+1)(M-1) is the undetermined top-layer phase value.

[0055] The segmentation of the bottom-layer diffractive optical device is: β i(M-1)+1 …β (i+2)(M-1) ; where β i(M-1)+1 …β (i+2)(M-1) is the undetermined bottom-layer phase value.

[0056] Through Figure 3 and Figure 4 it can be seen that the phase modulation method provided by the embodiments of the present application performs recursive optimization by dividing the double-layer diffractive optical device into multiple sub-segments. Each segment only processes a limited number of pixels (the top layer contains M - 1 determined phase and M - 1 undetermined phase pixels, and the bottom layer contains 2(M - 1) undetermined phase pixels). By using the segmentation strategy, the high-dimensional optimization problem is reduced in dimension. While ensuring the phase continuity between adjacent segments, the computational complexity is significantly reduced, the computational accuracy is improved, and the double-layer diffractive device can efficiently generate a multi-channel adjustable light field distribution.

[0057] Please refer to Figure 5 for Figure 5 the phase calculation flowchart provided by the embodiments of the present application; In an alternative embodiment of the embodiments of the present application, in the above step S300, determining the top-layer phase of the top-layer diffractive optical device and the bottom-layer phase of the bottom-layer diffractive optical device according to the target light field phase and the cascaded phase values of all channels can be achieved through the following steps:

[0058] Step S310: Based on the target light field and the cascaded phase values of all channels, construct a linear equation system between the target light field phase, the top-layer phase, and the bottom-layer phase.

[0059] In the above step S310, based on the target light field Φ and the cascaded phase values Φ m of all channels, construct a linear equation system between the target light field Φ, the top-layer phase α, and the bottom-layer phase β.

[0060] The cascaded phase value Φ m , and represent the cascaded phase at each pixel position when the channel number is m as:

[0061]

[0062] Among them,

[0063] In addition, Φ m is the cascaded phase at each pixel position of the m-th channel; A m is an N×N identity matrix; B m is an N×(N + M - 1) matrix, and starting from the m-th column, it is an N×N identity matrix; Θ is the phase vector regarding the top-layer phase and the bottom-layer phase.

[0064] Furthermore, by integrating the cascaded phase calculations for all channels, a linear equation system between the target optical field Φ and the top-layer phase α and the bottom-layer phase β is obtained:

[0065]

[0066] Among them, C is a coefficient matrix with a dimension of (M·N)×(2N + M - 1).

[0067] Step S320: Solve the linear equation system to obtain the top-layer phase and the bottom-layer phase.

[0068] In the above step S320, solve the linear equation system of the above formula (3) to obtain the top-layer phase α and the bottom-layer phase β.

[0069] When M ≤ 2, the ranks of both the matrix C and the augmented matrix [C|Φ] are equal to the number of rows M·N, and they are less than the number of variables 2N + M - 1. Therefore, the equation system (3) has infinitely many solutions.

[0070] When M > 2, the rank of the matrix C is 2N + M - 2, while the rank of the augmented matrix [C|Φ] is 2N + M - 1. Therefore, there is no exact solution for the equation system at this time. Thus, when M > 2, only an approximate solution of the phase can be obtained.

[0071] Through Figure 5 it can be known that the phase modulation method provided by this application establishes a linear equation system (Φ = C·Θ) between the target optical field phase and the cascaded phase. By solving this equation system, the static phase distributions (α and β) of the top-layer and bottom-layer diffractive optical devices can be determined simultaneously, such that when the top-layer device moves relatively, the cascaded phase Φ m can accurately reconstruct the target optical field.

[0072] Please refer to Figure 6 , Figure 6 which is the flowchart for solving the approximate solution provided by the embodiment of this application; in an alternative implementation of the embodiment of this application, when solving the approximate solution of the linear equation system between the target optical field phase and the top-layer phase and the bottom-layer phase, a genetic algorithm with global optimization ability can be used to design the phase distribution of the diffractive optical device.

[0073] In the above step S320, the linear equations are solved to obtain the top layer phase and the bottom layer phase, which can be implemented in the following ways:

[0074] Step S321: Define an objective function to minimize the absolute mean square error between the target optical field and the calculated optical field.

[0075] In the above step S321, when defining the objective function to minimize the absolute mean square error between the target optical field and the calculated optical field, considering the 2π periodicity of the phase, the objective function is defined as:

[0076]

[0077] Where, is the target optical field, e iCΘ is the calculated optical field, Φ tar is the target phase under all channels, CΘ is the cascaded phase under all channels, and C is the coefficient matrix.

[0078] Step S322: Based on the objective function, use an objective optimization algorithm to obtain the phase approximations of the top layer diffractive optical device and the bottom layer diffractive optical device when M>2, and obtain the top layer phase and the bottom layer phase.

[0079] In the above step S322, the objective optimization algorithm is a genetic algorithm with global optimization ability, etc. In this embodiment of the application, the genetic algorithm is taken as an example for expansion. In practical applications, other optimization algorithms can also be used, such as particle swarm optimization algorithm, ant colony algorithm, etc.

[0080] It should be noted that the genetic algorithm simulates the processes of natural selection, crossover, and mutation in biological evolution, and searches for the global optimal solution of the problem through generation-by-generation iteration. However, the calculation accuracy and convergence speed of the genetic algorithm will decrease sharply with the increase in the number of variables, which brings difficulties to the optimization of large-size cascaded diffractive optical devices. Therefore, in the case of a large N, the segmented calculation strategy in steps S110 to S130 in the foregoing text needs to be used; the overall is split into several small parts and calculated separately to improve the overall calculation accuracy.

[0081] Through Figure 6 It can be seen that the phase modulation method provided by this embodiment of the application switches between cascaded channels based on continuous pixel-level lateral displacement, adopts a segmented optimization strategy, and uses a genetic algorithm to solve the global optimal solution during this process; therefore, the phase modulation method provided by this embodiment of the application can not only make the channel switching smoother and easier to align, but also encode more cascaded channel numbers, and the calculation accuracy and efficiency are greatly improved.

[0082] Please refer to Figure 7 , Figure 7An exemplary diagram of holographic images corresponding to different target displacement amounts provided by the embodiments of the present application; in an alternative embodiment, the target displacement is an integer multiple of the size of a single pixel of the double-layer diffractive optical device.

[0083] For each lateral displacement amount, the total output phase is obtained by superimposing the phases of the two layers of diffractive optical devices. As Figure 7 shown, p is the size of a single pixel. In Figure 7 , the two layers of diffractive optical devices are aligned at different lateral displacement amounts (p, 2p... (m - 1)p...), and their superimposed phases generate different holographic images in the far field.

[0084] It can be seen from this that the phase modulation method provided by the embodiments of the present application can precisely laterally displace the double-layer diffractive optical device by an integer multiple of the size p of a single pixel, achieving a multi-channel dynamically adjustable phase superposition effect. After each displacement, the phase distributions of the top and bottom devices produce a specific cascaded combination, thereby generating different holographic images in the far field. This not only ensures the accuracy and repeatability of phase superposition but also realizes the dynamic switching of complex optical fields through simple mechanical displacement.

[0085] In an alternative embodiment, the double-layer diffractive optical device includes a device with a channel spacing of multiple pixels; the phase modulation method provided by the embodiments of the present application further includes:

[0086] Dividing the device with a channel spacing of multiple pixels into multiple sub-devices with a channel spacing of a single pixel; respectively calculating the top layer phase of the top layer diffractive optical device and the bottom layer phase of the bottom layer diffractive optical device of each sub-device; taking the top layer phases of the multiple sub-devices as the top layer phase of the top layer diffractive optical device of the device with a channel spacing of multiple pixels; and taking the bottom layer phases of the multiple sub-devices as the bottom layer phase of the bottom layer diffractive optical device of the device with a channel spacing of multiple pixels.

[0087] It can be seen from this that for the design of a cascaded diffractive optical device with a channel spacing of multiple pixels, it can be regarded as a combination of several cascaded diffractive optical devices with a channel spacing of a single pixel.

[0088] Please refer to Figure 8 , Figure 8 A schematic diagram of the simulation and experimental results of a 12-channel cascaded multiplexed hologram provided by the embodiments of the present application; the two layers of diffractive optical devices realize the switching of holographic channels through a lateral displacement of two pixels. Where p is the size of a single pixel.

[0089] Using liquid crystal as a diffractive optical device to demonstrate the phase tunable function of a cascaded diffractive optical device. The top layer of liquid crystal contains 500×500 pixels, while the bottom layer of liquid crystal has M - 1 more columns than the top layer to ensure equal number of effective pixels for cascaded holograms in each channel, and the size of a single pixel is set to 8.64μm.

[0090] Using the twelve constellations as target images, reconstruction is carried out under 532nm light irradiation with different lateral relative displacements. Figure 8 Cascaded holograms in each channel are demonstrated through simulation and experiment respectively, with a lateral displacement interval of two single pixels. The simulation results show that there is no crosstalk between channels, and the reconstructed image information is clearly visible. Compared with the simulation results, the background noise in the experimental results is slightly more obvious, which is mainly due to the limitation of liquid crystal manufacturing accuracy and the alignment error during the experiment.

[0091] This application also provides an optical device, which includes a stacked and cascaded top - layer diffractive optical device and a bottom - layer diffractive optical device, wherein the top - layer phase of the top - layer diffractive optical device and the bottom - layer phase of the bottom - layer diffractive optical device are determined according to the above - mentioned phase modulation method.

[0092] Based on the same inventive concept, an embodiment of this application also provides a computer - readable storage medium, in which computer program instructions are stored. When the computer program instructions are read and run by a processor, the steps in any implementation manner of the above - mentioned phase modulation method are executed.

[0093] The computer - readable storage medium can be various media that can store program codes, such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable Read - Only Memory (PROM), Erasable Programmable Read - Only Memory (EPROM), Electric Erasable Programmable Read - Only Memory (EEPROM), etc.

[0094] In this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0095] The above description is only for the embodiments of this application and is not intended to limit the protection scope of this application. For those skilled in the art, this application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A phase modulation method, characterized in that, The phase modulation method is applied to a cascaded double - layer diffractive optical device, and the double - layer diffractive optical device includes a top - layer diffractive optical device and a bottom - layer diffractive optical device; the phase modulation method includes: Controlling the top - layer diffractive optical device to continuously move from an initial state to the second side with a target displacement; wherein, the initial state is a state where the starting pixels of the top - layer diffractive optical device and the bottom - layer diffractive optical device are aligned on the first side; Completing the continuous movement to obtain the cascaded phase values of all channels of the double - layer diffractive optical device; Determining the top - layer phase of the top - layer diffractive optical device and the bottom - layer phase of the bottom - layer diffractive optical device according to the target light - field phase and the cascaded phase values of all channels.

2. The method according to claim 1, wherein Wherein, The total number of pixels of the top - layer diffractive optical device is N, and the total number of pixels of the bottom - layer diffractive optical device is N + M - 1, where M is the total number of channels; The controlling the top - layer diffractive optical device to continuously move from an initial state to the second side with a target displacement includes: Segmenting the top - layer diffractive optical device and controlling each segment of the top - layer diffractive optical device to include (M - 1) pixels with determined top - layer phase values and (M - 1) pixels with undetermined top - layer phase values; Segmenting the bottom - layer diffractive optical device and controlling each segment of the bottom - layer diffractive optical device to include 2(M - 1) pixels with undetermined bottom - layer phase values; Controlling each time to align the (M - 1) pixels with undetermined top - layer phase values in each segment of the top - layer diffractive optical device with the first (M - 1) pixels with undetermined bottom - layer phase values in the bottom - layer diffractive optical device.

3. The method according to claim 2, wherein Wherein, For the i - th segment of the double - layer diffractive optical device: The segmentation of the top diffractive optical device is: α (i-1)(M-1)+1 …α i(M-1) 、α i(M-1)+1 …α (i+1)(M-1) ; where α (i-1)(M-1)+1 …α i(M-1) is the determined top layer phase value and is calculated from the (i - 1)-th segment, and α i(M-1)+1 …α (i+1)(M-1) is the undetermined top layer phase value; The segmentation of the underlying diffractive optical device is: β i(M-1)+1 …β (i+2)(M-1) ; where β i(M-1)+1 …β (i+w)(M-1) is an undetermined underlying phase value.

4. The method according to claim 1, characterized in that, The determining the top - layer phase of the top - layer diffractive optical device and the bottom - layer phase of the bottom - layer diffractive optical device according to the target light - field phase and the cascaded phase values of all channels includes: Based on the target light - field and the cascaded phase values of all channels, constructing a linear equation system between the target light - field phase and the top - layer phase and the bottom - layer phase; Solving the linear equation system to obtain the top - layer phase and the bottom - layer phase.

5. The method according to claim 4, wherein The linear equation system includes: Among them, Φ m is the cascaded phase at each pixel position of the m-th channel; A m is an N×N identity matrix; B m is an N×(N + M - 1) matrix, and starting from the m-th column, it is an N×N identity matrix; Θ is the phase vector regarding the top layer phase and the bottom layer phase.

6. The method according to claim 4, characterized in that The solving the linear equation system to obtain the top - layer phase and the bottom - layer phase includes: Defining an objective function by minimizing the absolute mean - square error between the target light - field and the calculated light - field; Based on the objective function, using an objective optimization algorithm to obtain approximate phase values of the top - layer diffractive optical device and the bottom - layer diffractive optical device when M>2, and obtaining the top - layer phase and the bottom - layer phase.

7. The method according to claim 6, characterized in that, The objective function is: Among them, is the target optical field, e iCΘ is the calculated optical field, Φ tar is the target phase under all channels, CΘ is the cascaded phase under all channels, and C is the coefficient matrix.

8. The method according to claim 1, characterized in that, Wherein, The target displacement is an integer multiple of the single - pixel size of the double - layer diffractive optical device.

9. The method according to claim 1, wherein The double - layer diffractive optical device includes a device with a channel interval of multiple pixels; the method further includes: Dividing the device with a channel interval of multiple pixels into multiple sub - devices with a channel interval of a single pixel; Respectively calculating the top - layer phase of the top - layer diffractive optical device and the bottom - layer phase of the bottom - layer diffractive optical device for each sub - device; Taking the top - layer phases of multiple sub - devices as the top - layer phase of the top - layer diffractive optical device of the device with a channel interval of multiple pixels; and The bottom layer phases of the multiple sub-devices are used as the bottom layer phase of the bottom layer diffractive optical device of the device with a channel interval of multiple pixels.

10. An optical device, characterized in that, The optical device includes a top layer diffractive optical device and a bottom layer diffractive optical device that are stacked and cascaded; the top layer phase of the top layer diffractive optical device and the bottom layer phase of the bottom layer diffractive optical device are determined according to the phase modulation method in any one of claims 1-9.

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