Calibration method and device for pixel-level phase response of spatial light modulator based on diffraction measurement

Abstract

The application discloses a kind of based on diffractive measurement spatial light modulator pixel level phase response calibration method and device, the method includes: constructing diffractive measurement optical path;In the effective modulation area of spatial light modulator, load periodic gray modulation structure with variable contrast, produce multistage diffracted light;By spatial filtering, target order diffracted light is selected and focused imaging, obtain the diffracted light intensity data under each contrast;Based on the relationship between target order diffracted light intensity and the diffractive physical model of modulation phase, phase-gray response is inverted using two-step nonlinear fitting, and the joint mapping of gray value about pixel coordinates and target phase is established by three-dimensional polynomial model, off-line generation per-pixel gray-phase lookup table and be used for real-time phase modulation.The application does not need complex interference optical path, can be in situ pixel level calibration in system, with the advantages of simple structure, high stability and high calibration precision, applicable to precision imaging, wavefront control and adaptive optics etc.

Description

Technical Field

[0001] This invention relates to the fields of optical wavefront modulation, computational imaging, and precision optical measurement, specifically to a pixel-level calibration method and apparatus for spatial light modulators, and more particularly to an in-situ calibration technique for spatial light modulators based on diffraction measurements. This technique is used to obtain the response relationship between the grayscale and phase of a spatial light modulator and to achieve accurate calibration modeling of spatially non-uniform phase response. It is applicable to various optical imaging and light field modulation systems involving high-precision wavefront control and aberration correction techniques. Background Technology

[0002] A spatial light modulator (SLM) is a programmable optical device that modulates the phase of an incident light wavefront by loading a grayscale image. It is widely used in wavefront shaping, beam manipulation, and high-resolution microscopy. In practical applications, the grayscale value loaded by the SLM typically exhibits a non-linear relationship with the resulting phase delay. Furthermore, due to manufacturing errors and variations in the driving circuitry, the phase response characteristics at different spatial locations are not entirely consistent. Therefore, the grayscale-phase response relationship of the SLM needs to be calibrated before precise wavefront manipulation.

[0003] In existing technologies, the calibration methods for the phase response of spatial light modulators (SLMs) typically employ interferometric techniques, such as the Mach-Zehnder interferometry or the Thyman-Green interferometry. These methods invert the phase response characteristics of the SLM by analyzing the phase changes of the interference fringes, thus achieving global calibration of the entire modulation region of the SLM. However, these methods still have the following shortcomings in practical applications: (1) Interferometric measurement has high requirements for environmental stability and is easily affected by factors such as air disturbance and mechanical vibration, which can cause the interference fringes to jitter, thereby reducing the measurement stability and repeatability. At the same time, phase-shifting interferometry usually requires the acquisition of multiple frames of images for calculation, making the measurement process complex and inefficient. (2) Existing interferometric calibration methods usually require the SLM to be separated from the actual optical system and the calibration process to be completed in an independent optical path. This is a non-in-situ measurement method, which cannot guarantee that the incident light conditions (such as incident angle, polarization state, etc.) during calibration are consistent with the actual working state. The phase response of the SLM is sensitive to the incident conditions, which leads to deviations between the calibration results and the actual application. (3) Traditional methods are mostly based on global calibration strategies, which usually obtain the response relationship in the sense of spatial average. They are difficult to reflect the response differences between different regions or even different pixels of SLM, and cannot meet the modeling requirements of high-precision wavefront modulation for spatial non-uniformity. (4) In applications such as high-resolution microscopy, spatial light modulators are often used to finely control the light field distribution at the nanoscale, which puts forward higher requirements for phase modulation accuracy. Traditional calibration methods are difficult to balance accuracy and spatial resolution, which limits their application effect in high-end imaging systems.

[0004] Furthermore, existing methods often rely on complex optical interference structures or manual adjustment processes, lacking efficient and automated calibration mechanisms suitable for practical system environments, making it difficult to maintain stable performance under different experimental conditions. Meanwhile, diffraction-based intensity measurement methods, due to their lack of the need for a reference beam, simple system structure, and strong resistance to environmental disturbances, show great application potential in the field of phase information acquisition. However, existing diffraction-based calibration methods are mostly used for the overall average characteristic characterization of optical components, and a spatial light modulator calibration technology with high-precision spatial resolution and modeling capabilities is still lacking.

[0005] Therefore, there is an urgent need for a spatial light modulator calibration method that can achieve in-situ measurement in actual optical systems and has pixel-level resolution and high-precision modeling capabilities, in order to meet the requirements for precise control of the light field in complex optical imaging systems. Summary of the Invention

[0006] The present invention aims to overcome the problems of complex system structure, high environmental stability requirements, difficulty in reflecting the spatial non-uniformity of the device, and difficulty in in-situ application in actual optical systems in the calibration process of spatial light modulators under the existing technology, and provides a pixel-level phase response calibration method and device for spatial light modulators based on diffraction measurement.

[0007] This invention constructs a diffraction measurement phase acquisition mechanism that does not require a reference beam, enabling in-situ calibration of the gray-scale and phase response relationship of a spatial light modulator under actual optical system operating conditions. Furthermore, it generates a pixel-by-pixel gray-scale-phase lookup table through spatial continuous function modeling and offline calculation, establishing a pixel-level high-precision phase response model that can be used for real-time wavefront modulation, thereby achieving pixel-level phase response calibration of the spatial light modulator.

[0008] To achieve the above objectives, this invention proposes a pixel-level phase response calibration method for spatial light modulators based on diffraction measurements, the method comprising the following steps: 1) Construct a diffraction measurement optical path for phase response calibration of the spatial light modulator, so that the light emitted from the light source is collimated, expanded and polarized in sequence to form a collimated beam with a preset polarization state, and incident on the effective modulation region of the spatial light modulator at a preset angle; 2) A periodic grayscale modulation structure with variable contrast is sequentially loaded at multiple sampling positions in the effective modulation region to generate multi-level diffraction light by the spatial light modulator. 3) Spatial filtering is performed on the multi-order diffracted light to retain only the target order diffracted light signal, wherein the target order diffracted light is a non-zero order diffracted light; 4) Focus the diffracted light of the target order to obtain diffracted light intensity data corresponding to periodic gray-scale modulation structures with different contrasts; 5) Based on the diffraction physical model relationship between the target order diffraction intensity and the modulation phase, the diffraction intensity data is fitted and calculated to obtain the phase-grayscale response model at each sampling position. 6) Perform spatial continuous function modeling on the phase-grayscale response model obtained from multiple sampling locations, and construct a spatial continuous joint mapping model of grayscale values ​​with respect to pixel coordinates and target phase; 7) Generate a pixel-by-pixel gray-phase lookup table based on the spatial continuous joint mapping model to obtain the pixel-level phase response calibration result of the spatial light modulator, and realize the real-time phase modulation of the spatial light modulator based on the lookup table in the actual wavefront modulation process.

[0009] Preferably, in step 2), sampling positions are selected along multiple concentric circles with different radii, with the center of the effective modulation region as a reference, or sampling positions are selected in a two-dimensional grid manner, so as to cover the entire effective modulation region of the spatial light modulator and characterize the spatial non-uniformity of its phase response. Preferably, the periodic grayscale modulation structure in step 2) is a grayscale phase grating, which includes a reference grayscale region and a variable grayscale region; wherein the pixel grayscale of the reference grayscale region is fixed at a reference grayscale value, and the pixel grayscale of the variable grayscale region changes gradually within a preset grayscale value range.

[0010] Preferably, the target order diffraction light signal in step 3) is the +1st order diffraction light.

[0011] Preferably, the phase-grayscale response model described in step 5) is based on the diffraction physics model and is fitted and calculated using the following diffraction intensity formula: (1) in The target order diffraction intensity, Here is the phase-grayscale response model of the spatial light modulator at this sampling location, where A is the modulation amplitude coefficient and B is the background bias term; The calculation employs a two-step nonlinear fitting method: a polynomial function is used for approximate fitting, and a low-order fitting is used to obtain initial parameters, followed by a high-order fitting for optimization.

[0012] Preferably, the spatial continuous function modeling in step 6) employs a three-dimensional polynomial. Establish a spatially continuous joint mapping model between grayscale values, pixel coordinates, and target phase, wherex , y Representing the pixel coordinates of the spatial light modulator; the three-dimensional polynomial is then expressed according to the phase variable. Expanding this, we obtain a one-dimensional polynomial in terms of phase: (2) For response model coefficients Offline calculations are performed in advance and stored as response model coefficients of the spatial light modulator to enable the spatial light modulator to quickly calculate gray values ​​based on the one-dimensional polynomial during runtime.

[0013] Preferably, the generation process of the pixel-by-pixel grayscale-phase lookup table in step 7) includes: discrete sampling within a preset phase value range; and based on the response model coefficients... The grayscale value corresponding to each sampling phase at each pixel coordinate is calculated and stored according to the spatial continuous joint mapping model to obtain the pixel-by-pixel grayscale-phase lookup table; in the actual wavefront modulation process, the grayscale image loaded on the spatial light modulator is generated by looking up the table or by interpolation to realize real-time phase modulation.

[0014] The present invention also proposes a spatial light modulator pixel-level calibration device for implementing the above method, comprising: a light source module, a beam shaping module, a spatial light modulator control module, a diffraction light filtering module, an optical signal acquisition module, and a data processing module arranged sequentially along the same optical axis; The light beam emitted by the light source module is then shaped by the beam shaping module and incident at a preset angle onto the spatial light modulator in the spatial light modulator control module. The spatial light modulator is loaded with a periodic grayscale modulation structure to generate multi-level diffraction light; The diffraction light filtering module is located after the spatial light modulator control module. It performs spatial filtering on the multi-level diffraction light in the Fourier plane, allowing only the target order diffraction light to pass through. The optical signal acquisition module focuses and images the target order diffracted light and acquires its light intensity image. The data processing module is electrically connected to the spatial light modulator control module and the optical signal acquisition module, respectively. It controls the loading of grayscale images and processes and analyzes the acquired target order diffraction intensity data, outputting the pixel-by-pixel grayscale-phase lookup table and phase response calibration results of the spatial light modulator.

[0015] Preferably, each module is composed of the following optoelectronic devices, which are arranged sequentially in the optical path order to form a diffraction measurement optical path: The light source module includes a single-mode continuous laser, a coupler, and a single-mode polarization-maintaining fiber; the spatial light emitted from the single-mode continuous laser is coupled into the single-mode polarization-maintaining fiber via the coupler; the single-mode polarization-maintaining fiber filters out higher-order modes of the laser and optimizes the spot shape to obtain stable single-mode linearly polarized continuous laser output. The beam shaping module includes a collimator and a beam expanding system; the collimator converts the divergent beam output by the light source module into a parallel beam; the beam expanding system is located after the collimator and expands the beam aperture according to the system design requirements so that the incident light covers the effective modulation area of ​​the spatial light modulator. The spatial light modulator control module includes a half-wave plate, a spatial light modulator, and a host computer. The half-wave plate is placed in the incident light path in front of the spatial light modulator to adjust the polarization direction of the incident light to match the phase modulation requirements of the spatial light modulator. Under the control of the host computer, the spatial light modulator sequentially loads a periodic grayscale modulation structure with variable contrast at the sampling position to generate multi-level diffraction light. The diffraction light filtering module includes a 4f lens group and a spatial filter element. The 4f lens group is disposed in the outgoing light path after the spatial light modulator. The spatial filter element is located on the Fourier surface of the 4f lens group, which filters out the target order diffraction light and suppresses the zeroth order light and higher order diffraction light. The optical signal acquisition module includes a focusing lens and a camera. The focusing lens is used to converge the target order diffracted light after spatial filtering to the camera target surface. The camera acquires the target order diffracted light intensity image and transmits it to the host computer for data processing. A CCD camera or a CMOS camera can be selected. The data processing module includes a host computer and data analysis software, which is configured to process and analyze the target order diffraction intensity image acquired by the optical signal acquisition module, and output the phase-grayscale response and pixel-level phase calibration results of the spatial light modulator.

[0016] The working principle of this invention is as follows: By loading a periodic grayscale modulation structure with variable contrast within the effective modulation region, an equivalent phase grating is formed at the sampling position of the spatial light modulator. Based on the diffraction physics model, the modulation phase, which is difficult to measure directly, is converted into a stably measurable diffraction intensity. A mapping relationship between diffraction intensity and modulation phase is established by spatial filtering and focusing imaging of the target-order diffracted light. Based on this mapping relationship, a two-step nonlinear fitting method combining low-order fitting initialization and high-order polynomial optimization is used to calculate the phase-grayscale response at each sampling position. Furthermore, a pixel-by-pixel grayscale-phase lookup table is obtained through spatial continuity modeling and function expansion, achieving in-situ precise calibration of the pixel-level phase response of the spatial light modulator.

[0017] Through the above technical approach, this invention transforms the phase measurement problem in spatial light modulator calibration, which relies on interference fringes, into a light intensity measurement problem based on diffraction light, thereby avoiding the influence of complex interference optical paths and environmental disturbances on measurement stability. At the same time, by sampling and modeling in an actual optical system, the incident conditions during calibration are kept consistent with the actual working state of the device, achieving in-situ high-precision calibration. Through spatial modeling, a continuous and real-time callable pixel-level phase response model is obtained, improving the accuracy, stability, and application efficiency of spatial light modulators in wavefront modulation and aberration correction.

[0018] The innovation of this invention lies in proposing a pixel-level in-situ calibration mechanism for spatial light modulators based on diffraction intensity inversion. Through a technical approach involving local diffraction measurement, two-step nonlinear fitting, spatial continuous function modeling, and offline calculation of lookup tables, the calibration results of spatial light modulators are transformed from global averaging to pixel-by-pixel precise modeling. Under the condition of not requiring an interference reference optical path, a highly stable, high-precision phase response calibration applicable to practical optical systems is achieved, providing a directly callable pixel-level phase response model for real-time wavefront modulation.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) By constructing a phase calibration method based on diffraction measurement, this invention avoids the strict requirements of optical path stability and alignment accuracy in traditional interferometric measurement systems, simplifies the system structure, and reduces the difficulty of experimental setup and debugging by eliminating the need for a reference beam and complex interferometric optical path. (2) This invention achieves pixel-level phase calibration by sampling the effective area of ​​the spatial light modulator and establishing a mapping relationship between pixel coordinates and phase-grayscale response. Compared with the traditional global calibration method, it can effectively characterize spatial non-uniformity and significantly improve calibration accuracy. (3) The present invention can be directly calibrated in actual optical systems, keeping the incident light conditions consistent with the actual working state, realizing in-situ calibration, thereby improving the accuracy and reliability of calibration results in practical applications, and is applicable to a variety of optical imaging and light field control systems; (4) The present invention acquires phase information based on diffraction intensity measurement, which avoids the sensitivity of interference fringes to environmental disturbances, reduces the influence of air disturbances and mechanical vibrations on the measurement results, thereby improving the stability and repeatability of data acquisition; (5) The present invention generates a pixel-by-pixel gray-phase lookup table by offline expansion, which can be directly called in the subsequent wavefront modulation and aberration correction process to realize real-time high-speed phase modulation of the spatial light modulator. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system device used in this invention; Figure 2 This is a flowchart of the method of the present invention; Figure 3 This is a schematic diagram of concentric circle sampling of the effective modulation region of the spatial light modulator of the present invention; Figure 4 The image is a partial grayscale grating loaded at a single sampling position of the spatial light modulator of the present invention and the corresponding diffraction focused light spot image recorded by the camera; Figure 5(a) shows the relationship between the diffraction-focused light intensity recorded by the camera at a single sampling position and the gray level G applied by the spatial light modulator; Figure 5(b) shows the modulation phase applied to the beam by the spatial light modulator at a single sampling position. The relationship between the phase and gray level G, i.e., the phase-gray level response curve; Figure 6(a) is a schematic diagram comparing the curve range of the SLM pixel-level phase response calibration of the present invention with the linear global response; Figure 6(b) is the modulation phase applied by the SLM of the present invention. A schematic diagram of grayscale differences within the effective modulation region when = 2π. Detailed Implementation

[0021] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described below are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Furthermore, the technical features involved in each embodiment can be combined with each other without conflict.

[0022] Example 1

[0023] This embodiment provides a pixel-level phase response calibration method for spatial light modulators based on diffraction measurements, the process of which is as follows: Figure 2 As shown, it includes the following steps: 1) Constructing such Figure 1 The diffraction measurement optical path shown is used for phase response calibration of the spatial light modulator. It enables the light emitted from the light source to be collimated, expanded and polarized to form a collimated beam with a preset polarization state, and then incident on the effective modulation region of the spatial light modulator at a preset angle. In this embodiment, the light source is a linearly polarized continuous laser, the incident light power is set to not exceed the device damage threshold and meet the camera signal-to-noise ratio requirements, and the angle between the incident light and the surface normal of the spatial light modulator is set in the range of 0° to 10°, which is set to about 5° in this embodiment. 2) Select multiple sampling positions within the effective modulation region of the spatial light modulator, and sequentially load a periodic modulation structure with variable contrast at each sampling position to generate multi-level diffraction light from the spatial light modulator. In this embodiment, the sampling location is according to Figure 3 As shown, the center of the effective modulation region is used as a reference, and multiple concentric circles with different radii are selected to characterize the radial or circumferential phase response differences. In addition to the above method, other sampling methods such as rectangular grid sampling, polar coordinate grid sampling, and adaptive sparse sampling can also be used to adapt to different calibration accuracy and measurement time requirements. The number of sampling points is set according to the comprehensive trade-off between calibration accuracy and calibration efficiency: increasing the number of sampling points can improve the spatial modeling accuracy, while reducing the number of sampling points and interpolating with the subsequent modeling results can shorten the calibration time and improve the overall calibration efficiency. In this embodiment, the periodic modulation structure is as follows: Figure 4 The circular grayscale grating shown includes a reference grayscale region and a variable grayscale region in each cycle; the pixel grayscale of the reference grayscale region remains a fixed value, which is set to 0 in this embodiment; the pixel grayscale of the variable grayscale region is denoted as G, and changes step by step within a preset grayscale value range, which is set to 0 ~ 255 in this embodiment; the change step size is set according to the accuracy requirements, which is set to 5 in this embodiment. 3) Spatial filtering of multi-order diffracted light: By setting spatial filtering elements on the Fourier plane of the 4f system, unmodulated light, higher-order diffracted light and stray light are filtered out, and only the light signal of the +1 diffraction order is retained. 4) Focus the filtered target order diffracted light to obtain diffracted light intensity images corresponding to grayscale gratings of different contrasts. In this embodiment, the focused target order diffraction intensity image is acquired by a CMOS or CCD camera, and the total energy of the light spot is extracted as diffraction intensity data by an image processing algorithm. 5) Based on the phase grating diffraction physical model, establish the functional relationship between the target diffraction order intensity and the modulation phase: (1) In this embodiment, a two-step nonlinear fitting method is used for the measurement data: first, a second-order polynomial is used to fit the initial parameters, and then a sixth-order polynomial is used for higher-order fitting optimization, thereby obtaining the phase-grayscale response model at each sampling position. ; 6) Model the phase response at multiple sampling locations using spatially continuous functions, establishing a spatially continuous joint mapping model of grayscale values ​​with respect to pixel coordinates and target phase; employing a three-dimensional polynomial... Perform fitting, where x , y These represent the pixel coordinates of the spatial light modulator. For phase variables; 7) Arrange the three-dimensional polynomial according to the phase variable Expanding this, we obtain a one-dimensional polynomial in terms of phase: (2) For response model coefficients Offline calculations are performed beforehand and stored as response model coefficients for the spatial light modulator; then, discrete sampling is performed within a preset phase range, based on the response model coefficients. The grayscale value corresponding to each sampling phase at each pixel coordinate is calculated and stored according to the spatial continuous joint mapping model, and a pixel-by-pixel grayscale-phase lookup table is generated offline. In the actual wavefront modulation process, the loaded grayscale value is obtained by looking up the table or by interpolation, so as to realize the real-time phase modulation of the spatial light modulator.

[0024] The pixel-level phase response calibration of the spatial light modulator in a practical optical system can be completed through the above steps.

[0025] Example 2

[0026] This embodiment combines Figure 1 Figure 6 illustrates an apparatus for implementing the pixel-level phase response calibration method for a spatial light modulator based on diffraction measurements as described in Embodiment 1. This embodiment not only presents the apparatus structure but also explains the calibration experimental procedure, data processing method, and calibration results. Under actual optical system conditions, this embodiment performs pixel-level phase response calibration on the effective modulation region of a reflective liquid crystal spatial light modulator, illustrating the structural composition and working process of the apparatus of this invention.

[0027] In this embodiment, combined with Figure 1 A pixel-level phase response calibration device for a spatial light modulator based on diffraction measurement is provided. The device includes a light source module, a beam shaping module, a spatial light modulator control module, a diffraction light filtering module, an optical signal acquisition module, and a data processing module arranged sequentially along the same optical axis. The light source module is used to provide incident light with stable power and polarization state; The beam shaping module is used to collimate and expand the incident light to form a uniformly polarized beam that meets the modulation requirements of the spatial light modulator. The spatial light modulator control module is used to sequentially load periodic grayscale modulation structures with variable contrast at different sampling positions to generate multi-level diffraction light. The diffraction light filtering module is used to filter out unmodulated light and non-target diffraction order light signals, allowing only target order diffraction light to pass through; The optical signal acquisition module is used to focus and image the target order diffracted light and acquire a light intensity image; The data processing module is used to control the loading of grayscale images and process and analyze the collected light intensity data. Based on the target-order diffraction light intensity data, it obtains the phase-grayscale response model of each sampling position, constructs a spatial continuous joint mapping model between grayscale values, pixel coordinates and target phase, and outputs the pixel-level phase response calibration result of the spatial light modulator. The above modules work together to complete the entire calibration experiment process, including grayscale grating loading, diffraction light filtering, light intensity data acquisition, and phase response inversion.

[0028] The light source module 1 includes a single-mode continuous laser, a coupler, and a single-mode polarization-maintaining fiber; the power of the single-mode continuous laser is adjustable, and the output power is set to a range that does not exceed the damage threshold of optical components and does not cause camera saturation. In this embodiment, the single-mode continuous laser is a semiconductor-pumped all-solid-state red laser with an emission wavelength of 640 nm and a power of 100 mW.

[0029] The beam shaping module includes a collimator 2 and a beam expanding system 3; the collimator 2 converts the divergent beam output from the single-mode polarization-maintaining fiber in the light source module into a parallel beam; the beam expanding system 3 expands the parallel beam size according to the system design requirements. In this embodiment, the beam expanding system 3 uses a 4f lens group to magnify the output beam of the collimator 2 by 4 times, resulting in a light spot with uniform intensity distribution and a diameter of 4 mm.

[0030] The spatial light modulator control module includes a half-wave plate 4, a spatial light modulator 5, and a host computer. The outgoing light from the beam expander system 3 is polarized by the half-wave plate 4 and then incident on the spatial light modulator 5, and reflected by the spatial light modulator 5 into the subsequent optical path. The host computer controls the loading of grayscale images on the spatial light modulator 5, so as to sequentially load grayscale phase gratings with variable contrast at the sampling positions in the effective modulation area, thereby generating +1st order diffraction light with gradually changing intensity. In this embodiment, the grayscale phase grating includes a reference grayscale region and a variable grayscale region; wherein the pixel grayscale of the reference grayscale region is fixed at a reference grayscale value of 0, and the pixel grayscale of the variable grayscale region is G, which changes gradually within a preset grayscale value range. During the calibration process, G gradually increases from 0 to 255, and the grating patterns corresponding to some G values ​​are as follows. Figure 4 As shown; In this embodiment, the spatial light modulator 5 is a reflective liquid crystal spatial light modulator with a resolution of 1272. 1024; The light beam on the spatial light modulator 5 adopts a small-angle inclined incident mode, with an incident angle of approximately 5°.

[0031] The diffraction light filtering module includes a 4f lens group and a spatial filter element 7. The 4f lens group consists of a first lens 6 and a second lens 8, both of which are cemented doublet achromatic convex lenses, used as relays for the reflected beam of the spatial light modulator 5. The spatial filter element 7 is a variable aperture stop located on the Fourier plane of the 4f lens group, used to filter out stray light, higher-order diffraction light and zero-order reflected light that has not been phase-modulated by the spatial light modulator 5, and to filter out +1st-order diffraction light.

[0032] The optical signal acquisition module includes a focusing lens 9, a camera 10, and a host computer; the focusing lens 9 converges and images the +1st order diffracted light in the front optical path onto the camera 10; the camera 10 is a CCD camera, acquiring signals such as... Figure 4 The diffraction-focused light intensity image shown is transmitted to the host computer.

[0033] The data processing module performs data analysis and processing through a host computer. The phase-grayscale response model is constructed based on the physical diffraction model relationship between diffraction intensity and modulation phase. The contrast of the grayscale grating at the sampling position of the spatial light modulator is changed, and the +1st order diffraction intensity is calculated based on the correspondingly changing focused spot image. In this embodiment, the focused spot of the +1st order diffraction light acquired by the camera has an approximately Gaussian distribution. To improve the stability and noise resistance of the light intensity measurement, each image is processed as follows: 1) The focused spot is fitted using a two-dimensional Gaussian model; 2) The integral intensity within the fitted range is extracted as the +1st order diffraction light intensity under this grayscale condition. In this embodiment, based on the phase grating diffraction physical model, a functional relationship between the +1st order diffraction intensity and the modulation phase is established: (1) The phase response at the sampling location is obtained through a two-step nonlinear fitting process. The intensity of the focused spot of the first-order diffracted light. Here is the phase-grayscale response model of the spatial light modulator at this sampling location, where A is the modulation amplitude coefficient and B is the background bias term; Subsequently, a spatially continuous joint mapping model of grayscale values ​​with respect to SLM pixel coordinates and target phase was established through three-dimensional polynomial fitting, using a function... It means that, among them x , y This represents the pixel coordinates of the spatial light modulator; the three-dimensional polynomial is expanded into a polynomial with respect to phase. One-dimensional polynomial form: (2) For response model coefficients Offline calculations are performed in advance and stored as response model coefficients for the spatial light modulator. A pixel-by-pixel phase-grayscale lookup table that can be called in real time is generated offline based on the coefficients to obtain the final pixel-level calibration result of the spatial light modulator.

[0034] Figures 5(a) and 5(b) illustrate the phase inversion process at a single sampling location in this embodiment; Figure 5(a) shows the relationship between the intensity of the +1st order diffraction focused light and the gray level G of the grating when a gray level grating is loaded at a certain sampling point of the SLM. It can be observed that the light intensity changes significantly with the gray level in a periodic nonlinear manner, and the curve shows a typical sinusoidal square change trend, which indicates that the local area of ​​the SLM is equivalent to forming a phase grating. Figure 5(b) shows the phase-grayscale response curve of the SLM at the pixel coordinates of the sampling point obtained by diffraction focusing light intensity inversion. It can be seen that the phase increases monotonically with grayscale, and the response curve deviates from the ideal linear relationship, indicating that there is a nonlinear response between grayscale and phase of the SLM. This result shows that phase response inversion can be achieved based on diffraction measurement.

[0035] Figures 6(a) and 6(b) illustrate the statistical analysis of the calibration results at multiple sampling locations of the SLM in this embodiment; Figure 6(a) shows a comparison between the curve range and mean of the SLM pixel-level phase response calibration and the global linear response provided by the manufacturer. It can be observed that the response at different spatial locations has obvious discrete distribution and differs from the global linear response provided by the manufacturer. The deviation is more obvious in the phase interval of 3 / 4π to 3 / 2π. This result shows that traditional global calibration cannot accurately describe the spatial non-uniformity of the SLM phase response. Figure 6(b) shows the uniform modulation phase applied on the SLM. When the gray value loaded in the effective modulation area is 2π, it is observed that the gray value to be loaded in the effective modulation area shows obvious spatial distribution differences, and the gray value difference at different locations can reach several gray levels or more. This result indicates that there are spatial distribution differences in the gray values ​​corresponding to different locations on the SLM when achieving the same target phase modulation. If a globally consistent phase-gray response model is adopted, different phase errors will be generated in different regions of the SLM.

[0036] In summary, this embodiment demonstrates that the method and apparatus of the present invention can achieve in-situ calibration of the pixel-level phase response of a spatial light modulator through diffraction measurement in a practical optical system; by sampling and modeling in the effective modulation region, a spatially continuous joint mapping model between gray values, pixel positions, and target phases is established, and a pixel-by-pixel gray-phase lookup table can be obtained for phase modulation control of the spatial light modulator, which is applicable to various optical imaging and wavefront modulation systems.

[0037] The above embodiments are merely one implementation of the present invention and are not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is defined by claims 1 to 9, and any equivalent substitutions or structural adjustments based on the principles of the present invention should be included within the scope of protection of this patent. Those skilled in the art should understand that the specific embodiments described in the specification and drawings are only illustrative of technical solutions and should not be regarded as limitations on the scope of protection. Any reasonable modifications, equivalent substitutions, or improvements made to the method steps, parameter adjustments, or system modules within the spirit and principles of this patent are within the scope of protection of this patent.

Claims

1. A pixel-level phase response calibration method for spatial light modulators based on diffraction measurements, characterized in that, Includes the following steps: 1) Construct a diffraction measurement optical path for phase response calibration of the spatial light modulator, so that the light emitted from the light source is collimated, expanded and polarized to form a collimated beam with a preset polarization state, and incident on the effective modulation region of the spatial light modulator at a preset angle; 2) A periodic grayscale modulation structure with variable contrast is sequentially loaded at multiple sampling positions within the effective modulation region, so that the spatial light modulator generates multi-level diffraction light. 3) Spatial filtering is performed on the multi-order diffracted light to retain only the target order diffracted light signal, wherein the target order diffracted light is a non-zero order diffracted light; 4) Focus the target order diffracted beam to obtain diffracted light intensity data corresponding to periodic gray-scale modulation structures with different contrasts. 5) Based on the diffraction physical model relationship between the target order diffraction intensity and the modulation phase, the diffraction intensity data is fitted and calculated to obtain the phase-grayscale response model at each sampling position. 6) Perform spatial continuous function modeling on the phase-grayscale response model obtained from multiple sampling locations, and construct a spatial continuous joint mapping model of grayscale values ​​with respect to pixel coordinates and target phase; 7) Generate a pixel-by-pixel gray-phase lookup table for the spatial light modulator based on the spatial continuous joint mapping model to obtain pixel-level phase response calibration results.

2. The method according to claim 1, characterized in that, In step 2), sampling positions are selected along multiple concentric circles of different radii, with the center of the effective modulation region as a reference, or sampling positions are selected in a two-dimensional grid manner.

3. The method according to claim 1, characterized in that, Step 2) The periodic gray-scale modulation structure is a gray-scale phase grating, which includes a reference gray-scale region and a variable gray-scale region; The pixel grayscale of the reference grayscale region is fixed at the reference grayscale value, while the pixel grayscale of the variable grayscale region changes gradually within a preset grayscale value range.

4. The method according to claim 1, characterized in that, The target order diffraction light signal mentioned in step 3) is the +1st order diffraction light.

5. The method according to claim 1, characterized in that, Step 5) describes a phase-grayscale response model based on a diffraction physics model, which is then fitted and calculated.

6. The method according to claim 1, characterized in that, Step 6) describes the modeling of the spatially continuous function using a three-dimensional polynomial. Establish a spatially continuous joint mapping model between grayscale values ​​and pixel coordinates and target phase, where x , y These are the pixel coordinates of the spatial light modulator; The three-dimensional polynomial is arranged according to the phase variable Expanding this yields a one-dimensional polynomial concerning the phase.

7. The method according to claim 6, characterized in that, Step 7) describes the generation process of the pixel-by-pixel grayscale-phase lookup table, which includes: performing discrete sampling within a preset phase value range; and based on the response model coefficients. The grayscale value corresponding to each sampling phase at each pixel coordinate is calculated and stored according to the spatial continuous joint mapping model to obtain the pixel-by-pixel grayscale-phase lookup table.

8. An apparatus for implementing the pixel-level calibration method for spatial light modulators based on diffraction measurements as described in any one of claims 1 to 7, characterized in that, It includes the following modules arranged sequentially along the same optical axis: a light source module, a beam shaping module, a spatial light modulator control module, a diffraction light filtering module, an optical signal acquisition module, and a data processing module; The light beam emitted by the light source module is collimated and expanded by the beam shaping module, and then incident at a preset angle onto the spatial light modulator in the spatial light modulator control module. The spatial light modulator is loaded with a periodic grayscale modulation structure to generate multi-level diffraction light; The diffraction light filtering module is located after the spatial light modulator control module. It performs spatial filtering on the multi-level diffraction light in the Fourier plane, allowing only the target order diffraction light to pass through. The optical signal acquisition module focuses and images the target order diffracted light and acquires its light intensity image. The data processing module is electrically connected to the spatial light modulator control module and the optical signal acquisition module, respectively. It controls the loading of grayscale images and processes and analyzes the acquired target order diffraction intensity data, outputting the pixel-by-pixel grayscale-phase lookup table and phase response calibration results of the spatial light modulator.

9. The apparatus according to claim 8, characterized in that, Each module is composed of the following optoelectronic devices, which are arranged sequentially in the optical path sequence to form the diffraction measurement optical path: The light source module includes a single-mode continuous laser, a coupler, and a single-mode polarization-maintaining fiber. The output light of the single-mode continuous laser is coupled into the single-mode polarization-maintaining fiber through the coupler to obtain a stable single-mode linearly polarized continuous laser output. The beam shaping module includes a collimator and a beam expanding system. The collimator converts the divergent beam output by the light source module into a parallel beam. The beam expanding system is located after the collimator to enlarge the beam aperture so that the incident light covers the effective modulation area of ​​the spatial light modulator. The spatial light modulator control module includes a half-wave plate, a spatial light modulator, and a host computer. The half-wave plate is placed in the incident light path in front of the spatial light modulator to adjust the polarization direction of the incident light to match the phase modulation requirements of the spatial light modulator. Under the control of the host computer, the spatial light modulator sequentially loads periodic grayscale modulation structures with variable contrast at the sampling positions to generate multi-level diffraction light. The diffraction light filtering module includes a 4f lens group and a spatial filter element. The 4f lens group is disposed in the outgoing light path after the spatial light modulator. The spatial filter element is located on the Fourier surface of the 4f lens group, which filters out the target order diffraction light and suppresses the zeroth order light and higher order diffraction light. The optical signal acquisition module includes a focusing lens and a camera. The focusing lens converges the spatially filtered target order diffracted light to the camera target surface. The camera acquires the target order diffracted light intensity image and transmits it to the host computer for data processing. The data processing module includes a host computer and data analysis software, which is configured to process and analyze the target order diffraction intensity image acquired by the optical signal acquisition module, and output the phase-grayscale response and pixel-level phase response calibration results of the spatial light modulator.

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