Far-field imaging system, metasurface grating and imaging terminal

Abstract

The invention discloses a far-field imaging system, a metasurface grating and an imaging terminal, and relates to the technical field of image generation. Dynamic environment compensation and imaging quality optimization are realized through cooperation of multiple modules of the system: the environment temperature is read in real time, the refractive index of the metasurface grating is corrected according to a pre-stored mapping relation, and a target wavefront function is constructed and dispersed to obtain an initial phase distribution matrix; dividing a focusing area in combination with a user sight line, and compensating and regulating a phase distribution matrix by voltage gradient; based on the divided buffer and background regions, a multi-region sampling rate is configured to generate a mask, and the collection efficiency of the key region is improved; monitoring far-field information change in real time, and selecting an interpolation or total variation strategy to update the image; by means of image definition feedback, a secondary phase correction term is superposed to optimize a phase distribution matrix; the problems of traditional far-field imaging in the aspects of environment adaptation, dynamic focusing, data acquisition and imaging quality are solved, and the method is suitable for augmented reality glasses and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of image generation, and more particularly to a far-field imaging system, a metasurface grating, and an imaging terminal. Background Art

[0002] As a cutting-edge carrier for human-computer interaction, the innovation of the optical display technology of augmented reality glasses has always been the core challenge in the industry development. The traditional surface relief grating technology forms a periodic structure on the material surface through nanoimprinting process. Although it realizes the optical waveguide transmission, the high-order diffraction energy is scattered, resulting in low light utilization rate, high backlight leakage rate, and high production cost due to the complex process. The geometric optical waveguide technology expands the field of view angle through a mirror array, but it is difficult to popularize due to the problems of bright and dark stripes and low mass production yield. Although the polarization volume holographic optical waveguide technology improves the light utilization rate and reduces the forward light leakage rate through holographic interference, its phase distribution is fixed and cannot adapt to dynamic changes such as ambient light intensity and wearing posture. The phase drift error is large in high-temperature environments, affecting the imaging stability.

[0003] On the other hand, the rapid development of augmented reality glasses poses higher requirements on the optical system. Existing products rely on optical modules with fixed parameters, resulting in significant imaging noise in low-light environments, long multi-target tracking delay time, and high system power consumption due to complex optical path design, affecting the user experience. Particularly prominent is that the optical system in the existing technology lacks the ability of dynamic regulation and cannot compensate in real time for phase drifts caused by factors such as environmental temperature changes and changes in the user's gaze area; the image sensor and the optical module are independently designed, resulting in the coexistence of problems of redundant information in key areas and missing information in background areas; at the same time, there is a lack of an effective image quality feedback mechanism, making it difficult to dynamically optimize optical parameters during the imaging process, resulting in blurred images and lost details in complex scenarios. The existing technology is difficult to achieve dynamic compensation for environmental disturbances, adapt to the user's visual focus, optimize the data acquisition efficiency, and improve the imaging quality in real time. Therefore, in order to overcome these limitations, the present invention proposes a far-field imaging system, a metasurface grating, and an imaging terminal. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a far-field imaging system, a metasurface grating, and an imaging terminal, which solve the technical problems of unstable imaging quality, insufficient dynamic focusing ability, and low data acquisition efficiency of traditional far-field imaging systems in complex environments through temperature compensation, eye movement tracking, and dynamic phase optimization technologies.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A far-field imaging system includes:

[0007] Initialize by receiving user instructions, read environmental temperature data, call the mapping relationship between temperature and refractive index to correct the refractive index of the metasurface grating and construct the target wavefront function, and discretize the target wavefront function into an initial phase distribution matrix corresponding to the metasurface grating;

[0008] Combine the user's line-of-sight direction data to divide the focusing target area of the metasurface grating, set the focusing size, and perform local high-density phase modulation on the focusing target area to obtain an adjusted phase distribution matrix;

[0009] After adjusting the metasurface grating based on the phase distribution matrix, with the focusing target area as the center, divide the buffer area and the background area of the sampling area; configure and optimize the sampling frequency, generate a sampling mask for each sampling area to obtain the number of samples in each sampling area and divide the sub-areas, and perform synchronous sampling on each sub-area to obtain the far-field information of the target scene;

[0010] Set the monitoring time window and calculate the change rate of the far-field information of the target scene, judge whether the far-field information is stable, if stable, reconstruct the initial reconstructed image, and update the change amount based on the far-field information to determine the image update strategy to update the target scene image;

[0011] Based on the image clarity index of the target scene image, determine whether the imaging quality is qualified. If not, based on the image clarity index, obtain the quadratic phase correction term, and add the value of the quadratic phase correction term to the element at the corresponding position in the phase distribution matrix to dynamically adjust the phase distribution matrix; until the imaging quality is qualified.

[0012] Specifically, the specific steps for adjusting the phase distribution matrix include:

[0013] Collect the user's line-of-sight direction data, configure the focusing time window, and within the focusing time window, calculate the change amount of each line-of-sight direction data, and judge whether the user's line of sight is focused according to the change amount;

[0014] If the user's line of sight is focused, map the line-of-sight focusing area to the metasurface grating to determine the sub-wavelength units of the metasurface grating covered by the line-of-sight focusing area, so as to divide the focusing target area of the metasurface grating;

[0015] Set the focusing size, and based on the focusing size, perform voltage gradient compensation on the sub-wavelength units within the focusing target area, and calculate the driving voltage of the sub-wavelength units within the focusing target area;

[0016] Convert the driving voltage value into an analog signal, output it to the electrodes of the sub-wavelength units in the focusing target area, and synchronously update the phase distribution matrix;

[0017] Perform boundary effect compensation on the updated phase distribution matrix and output the adjusted phase distribution matrix.

[0018] Specifically, the specific steps for dynamically adjusting the phase distribution matrix include:

[0019] Obtain the clarity index of the image acquired by the current phase distribution matrix imaging, set a clarity threshold, and determine whether the clarity index is less than the clarity threshold to determine whether the imaging quality of the current phase distribution matrix is qualified;

[0020] If it is determined that the imaging quality of the current phase distribution matrix is unqualified, start the dynamic adjustment of the phase distribution matrix, that is:

[0021] Obtain the point spread function of the image acquired by the current phase distribution matrix imaging, perform Gaussian fitting on the point spread function, and obtain its full width at half maximum to calculate the target defocus amount;

[0022] Set a defocus amount search interval centered on the target defocus amount. Within the search interval, take maximizing the clarity index as the objective function, calculate the image clarity index according to the current defocus amount, and narrow the search interval by comparing the clarity indices at different defocus amounts to obtain the optimal defocus amount.

[0023] Specifically, the specific steps for dynamically adjusting the phase distribution matrix further include:

[0024] Convert the row and column indices of the phase distribution matrix into two-dimensional coordinates on the metasurface grating;

[0025] Combine the optimal defocus amount with the metasurface grating coordinates to calculate the quadratic phase correction term corresponding to the elements of the phase distribution matrix;

[0026] Traverse each element in the phase distribution matrix, add the calculated quadratic phase correction term value to the element at the corresponding position in the original phase distribution matrix, obtain the value of each updated element of the phase distribution matrix, and automatically adjust the adjustment amplitude of the phase distribution matrix through a controller to obtain the updated phase distribution matrix;

[0027] After dynamically adjusting the phase distribution matrix, perform imaging acquisition, obtain the image clarity index, and compare the adjusted clarity index with the index before adjustment to determine whether the adjustment effect is significant;

[0028] If the adjustment effect is significant, continue to adjust the phase distribution matrix; if the adjustment effect is not significant, recalculate the quadratic phase correction term and perform superposition adjustment on the phase distribution matrix;

[0029] Configure an iteration threshold, count the number of superposition adjustments, and if the number of superposition adjustments is greater than the iteration threshold, issue an early warning for abnormal superposition adjustment.

[0030] Specifically, the specific steps for obtaining the far-field information of the target scene include:

[0031] Configure the initial sampling rate, and generate a binary matrix with the same shape as the sampling area based on the initial sampling rate as the first sampling mask;

[0032] Determine the user's focused target area, configure the buffer ratio, expand outward according to the configured buffer ratio with the focused target area as the center to form a buffer area, and use the remaining part of the sampling area as the background area;

[0033] Set the sampling rate increase threshold, and respectively set the sampling rates of the focused target area and the buffer area based on the initial sampling rate and the sampling rate increase threshold, and generate the second sampling mask and the third sampling mask;

[0034] Perform a logical OR operation on the first sampling mask, the second sampling mask, and the third sampling mask to obtain the number of samples corresponding to each sampling area;

[0035] According to the number of samples in each sampling area, divide each sampling area into multiple sub-areas, and perform synchronous sampling on each sub-area to obtain the far-field information of the target scene.

[0036] Specifically, the specific steps for updating the target scene image include:

[0037] Perform real-time monitoring on the received far-field information, configure the monitoring time window, and calculate the real-time change rate of the collected far-field information within the monitoring time window;

[0038] Set the change rate threshold. If the real-time change rate of the far-field information is less than the change rate threshold, it is determined that the far-field information is stable, and image reconstruction is started, that is:

[0039] Obtain the real-time far-field information after the far-field information is stable, perform normalization processing, input it into the built-in reconstruction algorithm for the reconstruction of the initial reconstructed image, and output the initial reconstructed image.

[0040] Specifically, the specific steps for updating the target scene image also include:

[0041] After obtaining the initial reconstructed image, continuously receive the far-field information and compare it with the far-field information of the current reconstructed image to calculate the update change amount;

[0042] Determine the image update strategy according to the magnitude of the update change amount, that is:

[0043] Configure the update change threshold, including the update change upper threshold and the update change lower threshold;

[0044] If the update change threshold is less than the update change lower threshold, adopt an interpolation-based update strategy to update the pixel values at the corresponding positions in the initial reconstructed image, thereby generating the updated target scene image;

[0045] If the update change threshold is greater than the upper update change threshold, image reconstruction is performed again based on the new far-field information to generate an updated target scene image;

[0046] Otherwise, a reconstruction algorithm based on total variation is used, with the initial reconstructed image and the new far-field information as inputs, to generate an updated target scene image;

[0047] After completing the update of the target scene image, continue to monitor the far-field information to update the target scene image.

[0048] Specifically, the specific calculation steps of the image sharpness index include:

[0049] Convert the target scene image into a grayscale image and use a filtering algorithm for denoising;

[0050] Construct gradient operators in the horizontal and vertical directions, calculate the gradient values of each pixel of the grayscale image in the horizontal and vertical directions, and calculate the gradient amplitude of each pixel;

[0051] For the division of the acquisition area, accumulate the gradient amplitudes of the pixels in each sampling area, and perform normalization based on the number of pixels in each sampling area to obtain the image sharpness index of each sampling area;

[0052] Taking the image sharpness index of the focused target area as the basic sharpness index, calculate the relative deviation of the image sharpness index between the focused target area and other areas respectively, and perform weighted adjustment on the basic sharpness index based on the relative deviation of the image sharpness index to obtain the image sharpness index of the target scene image.

[0053] A metasurface grating is composed of sub-wavelength units. The sub-wavelength units include liquid crystal molecules and transparent electrodes. By driving the rotation of the liquid crystal molecules with voltage, the optical path difference is changed to perform continuous phase modulation on light;

[0054] The metasurface grating, based on the environmental temperature sensor data, calls the temperature and refractive index mapping relationship to correct the refractive index of the metasurface grating, so as to construct a target wavefront function and generate an initial phase distribution matrix;

[0055] Combine the user's line-of-sight direction data to divide the focused target area of the metasurface grating to adjust the phase distribution matrix of the focused target area;

[0056] Based on the phase distribution matrix, control the driving voltage of the sub-wavelength units of the metasurface grating to perform imaging and obtain the target scene image;

[0057] And based on the feedback of the image sharpness index of the target scene image, dynamically adjust the phase distribution matrix by superimposing a quadratic phase correction term.

[0058] An imaging terminal includes a far-field imaging system, and also includes a display device, a central processing unit, an optical regulation system, a data acquisition component, an eye movement interaction device, a power management system, and a communication device;

[0059] The display device is used to display the reconstructed target scene image and its image clarity index in real time;

[0060] The central processing unit dynamically adjusts the phase distribution matrix according to the image clarity index, and realizes real-time image refresh based on the change amount of far-field information;

[0061] The optical regulation system includes a sub-wavelength liquid crystal unit array, a transparent electrode driving circuit and a temperature sensor to generate a dynamic phase distribution matrix and perform temperature compensation;

[0062] The data acquisition component is configured with an optical signal sensor, an analog-to-digital conversion circuit and a random number generator to perform compressive sensing sampling and far-field information acquisition;

[0063] The eye movement interaction device includes an infrared camera, an eyeball feature recognition chip and a three-dimensional attitude sensor to realize line-of-sight tracking and gesture recognition;

[0064] The power management system is used to provide power consumption control and charging functions;

[0065] The communication device is used to realize data transmission and remote control.

[0066] Advantages of the present invention:

[0067] The present invention realizes the precise optimization of the phase distribution matrix in a complex environment by integrating an environmental temperature sensor to correct the refractive index of the metasurface grating in real time, combining the eye movement tracking technology to dynamically divide the focusing area and implement local high-density phase regulation; adopts a compressive sensing differential sampling strategy to improve the information acquisition efficiency of key areas and reduce redundant data; through a closed-loop optimization mechanism of image clarity index feedback and secondary phase correction term superposition, continuously improves the imaging quality; the multi-modal image update strategy ensures the consistency between the image and the actual environment when the scene dynamically changes; the regional weighted clarity evaluation method comprehensively reflects the overall quality of the image, effectively solving the technical problems of traditional far-field imaging systems in terms of environmental adaptability, dynamic focusing ability, data acquisition efficiency and imaging stability, and providing a high-performance imaging solution for intelligent terminals such as augmented reality glasses. Description of the Drawings

[0068] Figure 1 It is a schematic structural diagram of a far-field imaging system of the present invention;

[0069] Figure 2 It is a flowchart of the specific steps for generating and adjusting the phase distribution matrix of the present invention;

[0070] Figure 3 This is a flowchart of the specific steps for dynamically adjusting the phase distribution matrix of the present invention;

[0071] Figure 4 This is a flowchart for sampling the far-field information of the target scene of the present invention;

[0072] Figure 5 This is a flowchart of the specific steps for generating an updated target scene image of the present invention. Detailed implementation manners

[0073] Embodiment 1

[0074] Please refer to Figure 1 , this embodiment introduces a far-field imaging system, including a main control module, a metasurface regulation module, a compressive sensing acquisition module, an image reconstruction module, a quality evaluation module, and a feedback display module;

[0075] The main control module is used to, when the imaging terminal is started, according to an instruction, perform initialization settings on each module of the far-field imaging system. In this embodiment, the imaging terminal is smart glasses integrated with the far-field imaging system, and the main control module is arranged in the temple main control compartment of the smart glasses. It is used to, when the user issues an instruction, by parsing the instruction, identify the user's identity and detect the scene, and allocate the work tasks of each module according to the user's instruction or a preset task plan. For example, when the user issues an imaging task, the main control module will sequentially trigger the compressive sensing acquisition module to perform data acquisition, the image reconstruction module to perform image reconstruction, etc., to ensure the orderly progress of the entire imaging process. And manage the generated data, including data storage, transmission, and invocation. Store the collected raw data, the reconstructed image, and the quality evaluation results and other data in a specified storage device.

[0076] Please refer to Figure 2 , the metasurface regulation module is used to respond to the regulation instruction of the main control module, generate a target wavefront function based on the geometric phase theory, and combine the environmental temperature sensor data to compensate for the refractive index change of the liquid crystal material to generate an initial phase distribution matrix of the metasurface grating. Specifically, establish a mapping relationship between temperature and refractive index through a look-up table method, and correct the wavefront function parameters in real time according to the current environmental temperature to ensure the accuracy of the phase distribution matrix.

[0077] When the eye movement tracking sensor detects the user's gaze area, divide the corresponding area of the metasurface and start the local high-density phase regulation mode, and adjust the phase distribution matrix by dynamically adjusting the sub-wavelength unit size and the gradient distribution of the phase distribution matrix in this area;

[0078] During the imaging process, after the quality assessment module feeds back the image sharpness index, a defocus phase plate design strategy is adopted. The phase distribution matrix is dynamically adjusted by superimposing a quadratic phase correction term. The specific implementation is as follows: a phase modulation term is added to the original phase distribution to improve the imaging quality.

[0079] In this embodiment, the metasurface grating is composed of multiple sub-wavelength units. Each unit contains vertically arranged liquid crystal molecules and transparent electrodes. Under the action of voltage, the liquid crystal molecules rotate, changing the optical path difference to achieve continuous phase modulation. This continuous phase modulation ability enables the metasurface grating to flexibly control the wavefront of light to meet different imaging requirements.

[0080] After receiving the regulation instruction from the main control module, the metasurface regulation module reads the data of the environmental temperature sensor to obtain the current environmental temperature. The change in environmental temperature will have a significant impact on the refractive index of the liquid crystal material in the metasurface grating, thereby affecting the phase modulation effect of light. To eliminate this impact, the metasurface regulation module calls the pre-stored mapping relationship between temperature and refractive index, which is obtained by fitting a large amount of experimental data and can accurately reflect the corresponding relationship between temperature and refractive index. According to this mapping relationship, the metasurface regulation module corrects the change in the refractive index of the metasurface grating to ensure that the metasurface grating can maintain stable optical performance at different environmental temperatures. Then, a target wavefront function is constructed according to the scene requirements. The scene requirements include different application scenarios such as focused imaging, beam splitting imaging, and aberration correction. For the focused imaging scenario, the metasurface regulation module constructs a focused wavefront function, which can make the metasurface grating focus the incident light to a specific position to form a clear image. For the beam splitting imaging scenario, the metasurface regulation module constructs a beam splitting wavefront function, which can split the incident light into multiple light beams to achieve multi-channel imaging. When constructing the wavefront function, the metasurface regulation module will combine the corrected refractive index and specific scene parameters such as focal length and beam splitting angle to ensure that the wavefront function can accurately describe the required light field distribution. By constructing a suitable wavefront function, it lays a foundation for generating an accurate phase distribution matrix subsequently.

[0081] Based on the constructed target wavefront function, it is discretized to adapt to the sub-wavelength unit structure of the metasurface grating. After discretization, an initial phase distribution matrix is generated according to the phase value corresponding to each sub-wavelength unit obtained by discretization. Each element in this matrix corresponds to the phase value of a sub-wavelength unit in the metasurface grating, and the dimension of the matrix matches the arrangement structure of the sub-wavelength units of the metasurface grating.

[0082] After obtaining the initial phase distribution matrix, the eye movement tracking sensor is used to monitor the user's line of sight direction in real time. When the user focuses their line of sight on a specific area, according to the layout of the metasurface grating and the specific area provided by the eye movement tracking, the corresponding focused target area on the metasurface is divided, and the local high-density phase modulation mode is activated for the focused target area to adjust the initial phase distribution matrix;

[0083] Preferably, the specific steps for adjusting the phase distribution matrix include:

[0084] When the smart glasses are started, the eye movement tracking sensor is initialized. The eye movement tracking sensor collects the user's line of sight direction data at a fixed frequency, including the horizontal and vertical angles of the eyeball and the pupil position;

[0085] Configure the focusing time window. Within the focusing time window, calculate the change amount of each line of sight direction data respectively, and judge whether the user's line of sight is focused according to the change amount. For example, set an angle change threshold. If the angle change range of the line of sight direction within the focusing time window is less than the angle change threshold, it is determined that the user's line of sight is in a focused state; otherwise, it is considered that the user's line of sight is not focused.

[0086] If the user's line of sight is focused, obtain the metasurface grating layout information, including the arrangement of sub-wavelength units, such as rectangular arrangement, hexagonal arrangement, the size and spacing of the units; and map the line of sight focusing area to the metasurface grating to determine the sub-wavelength units of the metasurface grating covered by the line of sight focusing area, so as to divide the focused target area of the metasurface grating; during the determination process, combined with boundary expansion, the sub-wavelength units around the target area are also included to ensure the focusing effect.

[0087] According to the actual focusing requirements and the performance of the metasurface grating, set the focusing size. The focusing size can be adjusted according to different application scenarios. Based on the electrical characteristics of the sub-wavelength units, use the voltage-phase model, which is obtained by fitting a large amount of experimental data, to implement voltage gradient compensation for the sub-wavelength units in the focused target area. According to the preset focusing size and the electrical characteristics of the sub-wavelength units, such as capacitance, resistance, etc., calculate the driving voltage of the sub-wavelength units in the focused target area; the change of the driving voltage will cause the orientation of the liquid crystal molecules in the sub-wavelength units to change, thereby changing their optical properties and realizing the adjustment of the effective size. By precisely controlling the voltage, the effective size of the sub-wavelength units can be gradually reduced to the target value.

[0088] Convert the calculated driving voltage value into an analog signal and output it to the electrodes of the sub-wavelength units in the focused target area, and synchronously update the phase distribution matrix. The change of the driving voltage will cause the orientation of the liquid crystal molecules in the sub-wavelength units to change, thereby changing their optical properties and realizing the adjustment of the effective size.

[0089] Perform boundary effect compensation on the updated phase distribution matrix. By applying a Gaussian weight window to the edge cells of the focused area, mitigate the diffraction effect caused by phase mutation, and output the adjusted new phase distribution matrix.

[0090] Based on the adjusted phase distribution matrix, perform imaging and imaging detection. During the imaging detection process, the quality assessment module analyzes the reconstructed image in real time and calculates the clarity index of the image. According to the clarity index, adopt a defocused phase plate design strategy, that is, on the basis of the original phase distribution, superimpose a quadratic phase correction term to dynamically adjust the phase distribution matrix;

[0091] Preferably, the specific steps for dynamically adjusting the phase distribution matrix include:

[0092] Obtain the clarity index of the image obtained by imaging the current phase distribution matrix. According to the actual application scenario and requirements, set a clarity threshold to determine whether the imaging quality is qualified. If the clarity index is less than the clarity threshold, it is determined that the imaging quality of the current phase distribution matrix is unqualified, and start the dynamic adjustment of the phase distribution matrix;

[0093] Please refer to Figure 3 , use the method of blind deconvolution to estimate the point spread function of the image obtained by imaging the current phase distribution matrix, and perform Gaussian fitting on the point spread function to obtain its full width at half maximum to calculate the target defocus amount, that is:

[0094] ;

[0095] where is the target defocus amount, is the optical wavelength, which determines the basic characteristics of light. When light of different wavelengths propagates in the metasurface grating, its phase change law is different. is the focal length of the optical system. In the far-field imaging system integrated in smart glasses, it reflects the ability of the metasurface grating to converge or diverge light. is the characteristic size of the sub-wavelength unit, such as the thickness of the liquid crystal molecule layer, which affects the optical path change when light propagates in the sub-wavelength unit, and thus affects the phase modulation effect. is the full width at half maximum of the point spread function, which reflects the spot size after imaging an ideal point light source by the imaging system. The smaller the full width at half maximum, the clearer the imaging. When calculating the optimal defocus amount, this value is used to quantify the imaging blur degree to determine the size of the defocus amount that needs to be compensated.

[0096] Set a defocus amount search range centered on the target defocus amount, and use the golden section algorithm to search within the search range. With maximizing the clarity index as the objective function, calculate the image clarity index based on the current defocus amount. By comparing the clarity indices at different defocus amounts, narrow down the search range to obtain the optimal defocus amount;

[0097] For each element in the phase distribution matrix, determine its corresponding position on the metasurface grating. Through the coordinate transformation formula, convert the row and column indices of the phase distribution matrix into two-dimensional coordinates on the metasurface grating;

[0098] Combine the optimal defocus amount with the metasurface grating coordinates to calculate the quadratic phase correction term corresponding to the element of the phase distribution matrix, that is:

[0099] ;

[0100] where, is the quadratic phase correction term corresponding to the th row and th column element of the phase distribution matrix, is the optimal defocus amount, is the metasurface grating coordinate corresponding to the th row and th column element of the phase distribution matrix;

[0101] Traverse each element in the phase distribution matrix, perform edge phase smoothing, and superimpose the calculated quadratic phase correction term value on the element at the corresponding position in the original phase distribution matrix to obtain the updated value of each element of the phase distribution matrix, and perform a modulo operation so that the value of each element of the phase distribution matrix is within the range of 0 - 2 ;

[0102] After completing the superposition adjustment of the quadratic phase correction term of the phase distribution matrix, obtain the updated phase distribution matrix, and automatically adjust the adjustment amplitude of the phase distribution matrix through an adaptive PID controller; the adaptive PID controller first calculates the error value between the current clarity index and the clarity threshold, and dynamically adjusts the proportional coefficient, integral coefficient, and differential coefficient according to the magnitude and change trend of the error value to calculate the adjustment amplitude of the phase distribution matrix.

[0103] After determining the adjustment amplitude of the phase distribution matrix through the adaptive PID controller, perform imaging acquisition again, evaluate the clarity of the image, calculate the clarity index, and compare the adjusted clarity index with the index before adjustment. The comparison method can be to directly calculate the difference between the two, or calculate the ratio of the two. If the difference or ratio exceeds the preset threshold, it is considered that the adjustment effect is significant; otherwise, it is considered that the adjustment effect is not significant;

[0104] If the adjustment effect is significant, continue to adjust the phase distribution matrix through the adaptive PID controller, re-adjust the PID parameters according to the newly calculated error value, and determine the adjustment amplitude of the new phase distribution matrix, so that the phase distribution matrix is continuously optimized to further improve the image clarity until the target clarity is reached or other stop conditions are met.

[0105] If the adjustment effect is not significant, recalculate the quadratic phase correction term, perform superposition adjustment on the phase distribution matrix, and perform a new round of phase distribution matrix adjustment.

[0106] Configure the iteration threshold, count the number of superposition adjustments. If the number of superposition adjustments is greater than the iteration threshold, an abnormal warning for superposition adjustment is given. To inform that there is an abnormality in the superposition adjustment of the phase distribution matrix, indicating that the current imaging system cannot effectively improve the imaging quality, it is necessary to further check whether the system hardware status and parameter settings are reasonable, or consider replacing other imaging optimization methods.

[0107] The compressive sensing acquisition module is used to collect the light modulated by the metasurface grating after the metasurface modulation module completes the adjustment of the phase distribution matrix, and sample the far-field information of the target scene according to the principle of compressive sensing.

[0108] Please refer to Figure 4 , preferably, the specific steps for obtaining the far-field information of the target scene include:

[0109] When the focused target area is recognized and the phase distribution matrix of the hyperplane grating is adjusted, configure the initial sampling rate, which can be adjusted according to user requirements and scene complexity;

[0110] Use the random number generation algorithm to generate a binary matrix that is exactly the same shape as the sampling area according to the configured initial sampling rate, and use it as the first sampling mask. During the process of generating this sampling mask, in order to prevent the continuous sampling points from being too concentrated and having an adverse impact on the sampling effect, effective methods such as Poisson disk sampling are used to verify and adjust the generated mask. The specific verification process is to analyze the generated mask and count the number of continuous sampling points and their concentration degree. If these indicators exceed the preset threshold, discard the currently generated mask, re-execute the random number generation algorithm, generate a new mask again and perform verification, and so on, until the generated mask meets the preset requirements.

[0111] Determine the user's focused target area, configure the buffer ratio, expand outward according to the configured buffer ratio with the focused target area as the center to form a buffer area, and define the remaining part of the sampling area as the background area. During the division process, it is necessary to ensure that there is no overlap between each area and the entire sampling area is covered.

[0112] Set the sampling rate increase thresholds, including the upper increase threshold and the lower increase threshold, and the upper increase threshold is greater than the lower increase threshold. Based on the initial sampling rate and the upper increase threshold, set the sampling rate for the focused target area, and based on the initial sampling rate and the lower increase threshold, set the sampling rate for the buffer area;

[0113] Respectively adopt the same random number generation algorithm and Poisson disk sampling verification adjustment method as the first sampling mask, and generate the second sampling mask and the third sampling mask according to the increased sampling rate;

[0114] Perform a logical OR operation on the first sampling mask, the second sampling mask, and the third sampling mask. For the elements at the corresponding positions in the three masks, as long as one of them is 1, the operation result is 1; only when all three elements are 0, the operation result is 0. Through this operation, the sampling number corresponding to each sampling area can be obtained, and this sampling number reflects the number of samplings that should be performed for each sampling area based on comprehensive consideration of different area characteristics and the initial sampling rate.

[0115] According to the sampling number of each sampling area and the shape and size of the area, divide each sampling area into several sub-areas with similar sampling numbers, so that the deviation of the sampling numbers of each sub-area is within the preset deviation range;

[0116] After completing the sub-area division, synchronously carry out the sampling work for each sub-area to obtain the far-field information of the target scene, that is, the light-related information after being modulated by the metasurface grating, including the intensity information and phase information of the light.

[0117] The image reconstruction module reconstructs the target scene image based on the acquired far-field information of the target scene, combined with the imaging requirements, and based on the reconstruction algorithm, and gradually approaches the real image of the target object through continuous iterative optimization.

[0118] Preferably, the specific steps for updating the target scene image include:

[0119] Perform real-time monitoring on the received far-field information, configure the monitoring time window, and within the monitoring time window, calculate the real-time change rate of the acquired far-field information. For example, for the received far-field light intensity information, calculate the extreme value change within its monitoring time window as its real-time change rate;

[0120] Set the change rate threshold. If the real-time change rate of the far-field information is less than the change rate threshold, it is determined that the far-field information is stable and image reconstruction is started; otherwise, continuous monitoring is carried out;

[0121] If the image reconstruction algorithm is started, based on the built-in reconstruction algorithm, such as the iterative shrinkage threshold algorithm based on compressive sensing, reconstruct the initial reconstructed image. This algorithm utilizes the sparsity of the signal and approaches the real image through continuous iteration.

[0122] Set the parameters of the reconstruction algorithm, including the number of iterations, step size, and regularization parameter. These parameters will affect the convergence speed and reconstruction accuracy of the algorithm and need to be adjusted according to the actual situation.

[0123] Obtain the real-time far-field information after stabilizing the far-field information and perform normalization processing. Specifically, it includes normalizing the light intensity information to the interval [0, 1] and normalizing the light phase information to the interval [0, 2 interval;

[0124] Input the normalized far-field information into the reconstruction algorithm and output the initial reconstructed image through operations;

[0125] Please refer to Figure 5 , after obtaining the initial reconstructed image, continuously receive subsequent far-field information and obtain new far-field light intensity and phase information.

[0126] Compare the subsequent far-field information with the far-field information used for the current reconstructed image and calculate the update change amount. Specifically, for the light intensity, calculate the difference in intensity values at each corresponding position to obtain the intensity change amount; for the phase, calculate the phase difference to obtain the phase change amount;

[0127] Determine the image update strategy according to the magnitude of the update change amount, that is, according to the calculated intensity change amount and phase change amount;

[0128] Configure the update change threshold, including the upper update change threshold and the lower update change threshold, and the upper update change threshold is greater than the lower update change threshold. If the update change threshold is less than the lower update change threshold, then adopt an interpolation-based update strategy. The specific operation is to substitute the calculated change amount into the interpolation formula and fine-tune the pixel values at the corresponding positions in the initial reconstructed image to generate the updated target scene image.

[0129] If the update change threshold is greater than the upper update change threshold, then re-perform image reconstruction according to the new far-field light intensity and phase information; otherwise, select a reconstruction algorithm more suitable for large change amounts, such as the model-based total variation reconstruction algorithm. Take the initial reconstructed image and the new far-field information as inputs and run the total variation reconstruction algorithm to generate the updated target scene image.

[0130] After completing the update of the target scene image, continue to monitor the far-field information and repeat the above image update process to maintain the consistency between the image and the actual scene.

[0131] The quality assessment module is used to evaluate the quality of the reconstructed target scene image when generating the target scene image and calculate the image clarity index of the target scene image;

[0132] Preferably, the specific steps of calculating the image clarity index of the target scene image include:

[0133] The target scene image is converted into a grayscale image and denoised using a filtering algorithm to simplify the subsequent calculation process. It can also effectively retain the main structure and brightness information of the image, laying the foundation for subsequent clarity calculations.

[0134] Construct horizontal and vertical gradient operators, calculate the gradient values ​​of each pixel of the grayscale image in the horizontal and vertical directions. The gradient value reflects the rate of change of the pixel in the corresponding direction, and calculate the gradient amplitude of each pixel; the gradient amplitude represents the intensity of the image edge at the pixel. The larger the gradient amplitude, the more drastic the image change at that point, that is, the more obvious the edge of the image, which provides a key data basis for the subsequent clarity index calculation.

[0135] According to the division of the acquisition area, the gradient amplitudes of the pixel points in each sampling area are accumulated, and normalized based on the number of pixels in each sampling area to obtain the image clarity index of each sampling area, eliminating the influence of the area size on the clarity index and making the clarity indexes of different areas comparable.

[0136] The image clarity index of the focused target area is used as the basic clarity index. Since the focused target area is usually the core part of the user's attention, its clarity plays an important role in the overall image quality assessment. The relative deviation of the image clarity index of the focused target area and other areas is calculated respectively. The relative deviation intuitively reflects the degree of deviation of the clarity index of other areas compared with the clarity index of the focused target area in the form of percentage, which helps to evaluate the difference in clarity between different areas. The basic clarity index is weighted and adjusted based on the relative deviation of the image clarity index, so as to obtain an index that can more comprehensively and accurately reflect the overall clarity of the target scene image, providing a reliable basis for image quality assessment and subsequent image processing.

[0137] The feedback display module is used to display the target scene image to the user so that the user can detect and mark the target scene image;

[0138] The target scene image is displayed on the imaging terminal in a clear and intuitive way, supporting multiple display modes, such as color display, grayscale display, etc., to meet the needs of different users. In addition to the target scene image, other imaging-related information such as imaging parameters, quality assessment results, etc. will also be displayed. By displaying this information, users can better understand the imaging process and results, providing a reference for subsequent analysis and decision-making.

[0139] The feedback display module has a user interaction function, allowing users to operate on the displayed target scene image, such as zooming in, zooming out, rotating, marking, etc., to facilitate the user's detection and analysis of the target scene based on the displayed information and imaging results.

[0140] Embodiment 2

[0141] A metasurface grating is composed of sub-wavelength units. The sub-wavelength units include liquid crystal molecules and transparent electrodes. By driving the rotation of the liquid crystal molecules with voltage, the optical path difference is changed to perform continuous phase modulation on light.

[0142] The metasurface grating is integrated with an environmental temperature sensor, which can obtain environmental temperature data in real time and call the pre-stored temperature-refractive index mapping relationship. This mapping relationship is fitted from a large amount of experimental data and can accurately reflect the corresponding relationship between temperature and refractive index, so as to correct the refractive index of the metasurface grating. Based on the geometric phase theory, a target wavefront function is constructed by combining the corrected refractive index, and the target wavefront function is discretized to generate an initial phase distribution matrix matching the arrangement structure of the sub-wavelength units.

[0143] The metasurface grating works in cooperation with an eye movement tracking sensor. The eye movement tracking sensor monitors the user's line of sight direction in real time. When the user's line of sight focuses on a specific area, according to the layout of the metasurface grating and the specific area provided by the eye movement tracking, a corresponding focused target area on the metasurface is divided. For this focused target area, a local high-density phase modulation mode is activated. Based on the voltage-phase model, according to the focusing requirements and the performance of the metasurface grating, voltage gradient compensation is implemented for the sub-wavelength units in this area. By precisely controlling the voltage, the orientation of the liquid crystal molecules in the sub-wavelength units is changed, and then the phase distribution matrix in this area is adjusted.

[0144] During the imaging process, the metasurface grating drives the sub-wavelength units through the transparent electrodes based on the adjusted phase distribution matrix to regulate the wavefront of light, image the light modulated by the metasurface grating, and obtain a target scene image. The quality evaluation module analyzes the target scene image, calculates the image clarity index and gives feedback. The metasurface grating, according to this feedback, adopts a defocused phase plate design strategy. By calculating the target defocus amount, a quadratic phase correction term is superimposed on the original phase distribution matrix to dynamically adjust the phase distribution matrix to improve the imaging quality. At the same time, boundary effect compensation is performed on the updated phase distribution matrix. By applying a Gaussian weight window to the edge units of the focused area, the diffraction effect caused by phase mutation is alleviated to ensure the stability and accuracy of the imaging effect.

[0145] Embodiment 3

[0146] An imaging terminal includes a far-field imaging system, and also includes a display device, a central processing unit, an optical regulation system, a data acquisition component, an eye movement interaction device, a power management system, and a communication device;

[0147] The display device uses a high-resolution display screen, has good display performance, can display the reconstructed target scene image in real time, and at the same time supports multiple display modes to meet the needs of different users. In addition, the display device can also synchronously display information related to imaging, including the image clarity index of the target scene image, imaging parameters, etc., which is convenient for users to intuitively understand the imaging process and results.

[0148] The central processing unit integrates a high-performance processor, memory, and storage device, and has data processing capabilities. During the imaging process, the central processing unit receives the image clarity index feedback by the quality assessment module, and dynamically adjusts the phase distribution matrix of the metasurface regulation module according to the actual application scenario and requirements to optimize the imaging effect. At the same time, based on the change amount of the far-field information obtained by the data acquisition component, the reconstructed target scene image is refreshed in real time to ensure that the image is consistent with the actual scene.

[0149] The optical regulation system includes a sub-wavelength liquid crystal unit array, a transparent electrode driving circuit, and a temperature sensor. The temperature sensor monitors the ambient temperature in real time, corrects the refractive index change of the liquid crystal material through the pre-stored mapping relationship between temperature and refractive index, and ensures that the metasurface grating can maintain stable optical performance at different ambient temperatures. Based on the geometric phase theory, combined with the corrected refractive index, a target wavefront function is constructed to generate an initial phase distribution matrix, and according to the user's gaze area feedback by the eye movement interaction device, the corresponding area of the metasurface grating is activated to the local high-density phase regulation mode, and the phase distribution matrix is dynamically adjusted to realize flexible regulation of the light wavefront and meet different imaging requirements.

[0150] The data acquisition component configures an optical signal sensor, an analog-to-digital conversion circuit, and a random number generator. After the metasurface modulation module completes the adjustment of the phase distribution matrix, the optical signal sensor collects the light rays modulated by the metasurface grating. According to the principle of compressive sensing, a binary matrix with the same shape as the sampling area is generated by the random number generator as the sampling mask, and effective methods such as Poisson disk sampling are used to verify and adjust the sampling mask to ensure the rationality of the sampling point distribution. According to the user's focused target area and the set buffer ratio, the buffer area and the background area are divided, the sampling rates of different areas are set, the sampling masks corresponding to each area are generated respectively, the sampling numbers corresponding to each sampling area are obtained through logical OR operation, each sampling area is divided into several sub-areas with similar sampling numbers, and the sampling work is carried out synchronously for each sub-area to obtain the far-field information of the target scene, including the intensity information and phase information of the light rays, and the optical signal is converted into a digital signal through the analog-to-digital conversion circuit and transmitted to the central processing unit for subsequent processing.

[0151] The eye movement interaction device includes an infrared camera, an eyeball feature recognition chip, and a three-dimensional attitude sensor. The infrared camera collects the user's line-of-sight direction data at a fixed frequency, including the horizontal and vertical angle information of the eyeball and the pupil position. The eyeball feature recognition chip analyzes and processes the collected data to determine whether the user's line of sight is focused. When the user's line of sight is focused, the line-of-sight focused area is mapped to the metasurface grating according to the layout of the metasurface grating, and the focused target area is divided. At the same time, the three-dimensional attitude sensor monitors the three-dimensional attitude of the user's head in real time and compensates for the imaging deviation that may be caused by head movement to improve the imaging accuracy. The eye movement interaction device also supports the gesture recognition function. The user can interact with the imaging terminal through simple gesture operations such as zooming in, zooming out, rotating, and marking, which is convenient for detecting and analyzing the target scene image.

[0152] The power management system is responsible for providing stable power supply for each module of the imaging terminal. A rechargeable battery is adopted and equipped with a charging management circuit, which has a dynamic power consumption control function. It can reasonably allocate power according to the working state of each module, reduce the overall power consumption, and extend the battery life. At the same time, it supports fast charging technology and can replenish the battery power in a short time to meet the user's usage requirements.

[0153] The communication device integrates wireless communication modules such as Bluetooth and Wi-Fi, supports multiple wireless communication protocols, and can realize data transmission and remote control between the imaging terminal and other devices. Through the wireless communication module, the imaging terminal can transmit data such as the collected raw data, the reconstructed image, and the quality assessment result to other devices, which is convenient for the user to perform further processing and analysis. At the same time, it can also receive the instructions and configuration information sent by other devices to realize remote control of various functions of the imaging terminal, improving the convenience and flexibility of use.

[0154] Working principle and its effects:

[0155] The working principle and its effects of a far-field imaging system, a metasurface grating, and an imaging terminal are as follows:

[0156] When the user issues an instruction, the far-field imaging system initializes immediately. It reads the ambient temperature, corrects the refractive index of the metasurface grating according to the pre-stored relationship, constructs and discretizes the target wavefront function, generates the initial phase distribution matrix, and improves the phase modulation accuracy of the optical signal at different temperatures. With the help of the eye movement interaction device, it collects the user's line-of-sight direction data in real time. After determining the focusing area, it demarcates the sub-wavelength units according to the layout of the metasurface grating and divides the focusing target area. It sets the focusing size, uses the voltage gradient compensation technology to regulate the driving voltage of the sub-wavelength units, changes the optical path difference, optimizes the phase distribution matrix, and improves the imaging clarity of the key area. After completing the adjustment of the phase distribution matrix, it divides the buffer and background areas centered on the focusing target area, optimizes the sampling frequency according to the regional characteristics, generates the sampling mask, determines the sampling number of each area and divides the sub-areas, and synchronously samples to obtain the far-field information of the target scene, reducing data redundancy and improving the information acquisition efficiency of the key area. It monitors the change rate of the far-field information in real time. If the information is stable, it reconstructs the image of the normalized far-field information using the built-in algorithm. Then it continuously compares the new and old far-field information, and flexibly selects interpolation, re-reconstruction, or total variation reconstruction strategies to update the image according to the update change amount to ensure consistency with the actual scene. After imaging, it converts the image to grayscale and denoises it, constructs a gradient operator to calculate the pixel gradient value and amplitude, accumulates and normalizes them by region, and obtains the overall clarity index based on the clarity index of the focusing area. If the imaging quality does not meet the standard, the system calculates the secondary phase correction term according to the clarity index, superimposes it on the phase distribution matrix, and dynamically adjusts it by means of adaptive PID control until the imaging quality is qualified.

[0157] The metasurface grating corrects the refractive index and generates the phase distribution matrix according to the temperature data and the mapping relationship, dynamically adjusts the phase in combination with the user's line of sight, controls the driving voltage of the sub-wavelength units according to the phase for imaging, and then optimizes the phase distribution matrix according to the image clarity feedback to ensure accurate phase modulation and high-quality imaging. Each component of the imaging terminal works in coordination. The display device presents the image and the clarity index. The central processing unit adjusts the phase distribution matrix and refreshes the image according to the index and the far-field information. The optical regulation system is responsible for the generation of the phase distribution matrix and temperature compensation. The data acquisition component performs sampling and information acquisition. The eye movement interaction device realizes line-of-sight tracking and gesture recognition. The power management system provides power consumption control and charging. The communication device ensures data transmission and remote control, creating an efficient, intelligent, and stable far-field imaging experience for users and promoting the application of intelligent terminals in multiple fields.

[0158] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A far-field imaging system, characterized in that: include: Receive user instructions for initialization, read ambient temperature data, call the temperature and refractive index mapping relationship to correct the metasurface grating refractive index and construct a target wavefront function, and discretize the target wavefront function into an initial phase distribution matrix corresponding to the metasurface grating; Divide the focus target area of ​​the metasurface grating in combination with the user's line of sight direction data, set the focus size, and perform local high-density phase control on the focus target area to obtain an adjusted phase distribution matrix; After adjusting the metasurface grating based on the phase distribution matrix, the buffer area and the background area of ​​the sampling area are divided with the focus target area as the center; Configure and optimize the sampling frequency, generate a sampling mask for each sampling area, obtain the sampling number of each sampling area and divide it into sub-areas, and synchronously sample each of the sub-areas to obtain the far-field information of the target scene; Setting a monitoring time window and calculating the change rate of the far-field information of the target scene to determine whether the far-field information is stable, and if stable, reconstructing the initial reconstructed image, and determining an image update strategy based on the far-field information update change amount to update the target scene image; Based on the image clarity index of the target scene image, determine whether the imaging quality is qualified. If it is unqualified, obtain the secondary phase correction term based on the image clarity index, and superimpose the secondary phase correction term value on the element at the corresponding position in the phase distribution matrix to dynamically adjust the phase distribution matrix until the imaging quality is qualified.

2. A far-field imaging system as claimed in claim 1, characterized in that: The specific steps of adjusting the phase distribution matrix include: Collect the user's sight direction data, configure the focus time window, calculate the change of each sight direction data within the focus time window, and judge whether the user's sight is focused according to the change; If the user's line of sight is focused, the line of sight focusing area is mapped onto the metasurface grating to determine the sub-wavelength units of the metasurface grating covered by the line of sight focusing area, so as to divide the focusing target area of ​​the metasurface grating; Setting a focus size, performing voltage gradient compensation on the sub-wavelength units in the focus target area based on the focus size, and calculating a driving voltage of the sub-wavelength units in the focus target area; Convert the driving voltage value into an analog signal, output it to the sub-wavelength unit electrode of the focusing target area, and synchronously update the phase distribution matrix; The updated phase distribution matrix is ​​compensated for boundary effects, and an adjusted phase distribution matrix is ​​output.

3. A far-field imaging system as claimed in claim 1, characterized in that: The specific steps of dynamically adjusting the phase distribution matrix include: Obtaining the clarity index of the image acquired by the current phase distribution matrix imaging, and setting a clarity threshold, and judging whether the clarity index is less than the clarity threshold, so as to judge whether the current phase distribution matrix imaging quality is qualified; If the imaging quality of the current phase distribution matrix is ​​judged to be unqualified, the dynamic adjustment of the phase distribution matrix is ​​started, that is: Obtaining the point spread function of the image acquired by the current phase distribution matrix imaging, and performing Gaussian fitting on the point spread function to obtain its half-height and half-width to calculate the target defocus amount; A defocus search interval is set with the target defocus as the center. Within the search interval, the maximization of the clarity index is used as the objective function. The image clarity index is calculated according to the current defocus. By comparing the clarity indexes under different defocus amounts, the search interval is narrowed to obtain the optimal defocus.

4. A far-field imaging system as claimed in claim 3, characterized in that: The specific steps of dynamically adjusting the phase distribution matrix also include: Converting the row and column indices of the phase distribution matrix into two-dimensional coordinates on the metasurface grating; Combining the optimal defocus amount with the metasurface grating coordinates, the quadratic phase correction term corresponding to the phase distribution matrix element is calculated; Traverse each element in the phase distribution matrix, superimpose the calculated secondary phase correction term value on the element at the corresponding position in the original phase distribution matrix, obtain each element value updated by the phase distribution matrix, and automatically adjust the adjustment amplitude of the phase distribution matrix through the controller to obtain an updated phase distribution matrix; After the phase distribution matrix is ​​dynamically adjusted, imaging acquisition is performed to obtain the image clarity index, and the clarity index after adjustment is compared with the index before adjustment to determine whether the adjustment effect is significant; If the adjustment effect is significant, continue to adjust the phase distribution matrix; if the adjustment effect is not significant, recalculate the secondary phase correction term and perform superimposed adjustment on the phase distribution matrix; Configure the iteration threshold and count the number of superposition adjustments. If the number of superposition adjustments is greater than the iteration threshold, a superposition adjustment abnormality warning is issued.

5. A far-field imaging system as claimed in claim 1, characterized in that: The specific steps of obtaining the far-field information of the target scene include: Configure an initial sampling rate, and generate a binary matrix having the same shape as the sampling area based on the initial sampling rate as a first sampling mask; Determine the user's focus target area, configure the buffer ratio, take the focus target area as the center, expand outward according to the configured buffer ratio to form a buffer area, and use the remaining part of the sampling area as the background area; Setting a sampling rate increase threshold, and based on the initial sampling rate and the sampling rate increase threshold, respectively setting the sampling rates of the focus target area and the buffer area, and generating a second sampling mask and a third sampling mask; Performing a logical OR operation on the first sampling mask, the second sampling mask, and the third sampling mask to obtain the number of samples corresponding to each sampling area; According to the number of samples in each sampling area, each sampling area is divided into multiple sub-areas, and each sub-area is sampled synchronously to obtain the far-field information of the target scene.

6. A far-field imaging system as claimed in claim 1, characterized in that: The specific steps of updating the target scene image include: Perform real-time monitoring on the received far-field information, configure the monitoring time window, and calculate the real-time change rate of the collected far-field information within the monitoring time window; Set the change rate threshold. If the real-time change rate of the far-field information is less than the change rate threshold, the far-field information is considered stable and image reconstruction is started, that is: The real-time far-field information is obtained after the far-field information is stabilized, normalized, and input into the built-in reconstruction algorithm to reconstruct the initial reconstructed image and output the initial reconstructed image.

7. A far-field imaging system as claimed in claim 6, characterized in that: The specific steps of updating the target scene image also include: After obtaining the initial reconstructed image, the far-field information is continuously received and compared with the far-field information of the current reconstructed image to calculate the updated change; According to the size of the update change, determine the image update strategy, that is: Configure update change thresholds, including the upper update change threshold and the lower update change threshold; If the update change threshold is less than the update change lower threshold, an interpolation-based update strategy is used to update the pixel value at the corresponding position in the initial reconstructed image, thereby generating an updated target scene image; If the update change threshold is greater than the update change upper threshold, the image is reconstructed based on the new far-field information to generate an updated target scene image; Otherwise, a total variation-based reconstruction algorithm is used, taking the initial reconstructed image and the new far-field information as input to generate an updated target scene image; After completing the target scene image update, continue to monitor the far-field information and update the target scene image.

8. A far-field imaging system as claimed in claim 1, characterized in that: The specific calculation steps of the image clarity index include: Convert the target scene image into a grayscale image and use a filtering algorithm to remove noise; Construct horizontal and vertical gradient operators, calculate the horizontal and vertical gradient values ​​of each pixel of the grayscale image, and calculate the gradient amplitude of each pixel; According to the division of the acquisition area, the gradient amplitude of the pixel points in each sampling area is accumulated, and normalized based on the number of pixels in each sampling area to obtain the image clarity index of each sampling area; The image clarity index of the focused target area is taken as the basic clarity index, and the relative deviations of the image clarity indexes of the focused target area and other areas are calculated respectively. The basic clarity index is weightedly adjusted based on the relative deviations of the image clarity indexes to obtain the image clarity index of the target scene image.

9. A metasurface grating, applied to a far-field imaging system according to any one of claims 1 to 8, wherein the metasurface grating is composed of subwavelength units, wherein the subwavelength units include liquid crystal molecules and transparent electrodes, and the liquid crystal molecules are driven by voltage to rotate to change the optical path difference, thereby continuously phase modulating the light, characterized in that: The metasurface grating, based on the ambient temperature sensor data, calls the temperature and refractive index mapping relationship to correct the metasurface grating refractive index, so as to construct a target wavefront function and generate an initial phase distribution matrix; Dividing the focus target area of ​​the metasurface grating in combination with the user's line of sight direction data to adjust the phase distribution matrix of the focus target area; The driving voltage of the sub-wavelength unit of the metasurface grating is regulated based on the phase distribution matrix to perform imaging and obtain an image of the target scene; Based on the image clarity index feedback of the target scene image, the phase distribution matrix is ​​dynamically adjusted by superimposing a secondary phase correction term.

10. An imaging terminal, comprising a far-field imaging system according to any one of claims 1 to 8, characterized in that: It also includes a display device, a central processing unit, an optical control system, a data acquisition component, an eye movement interaction device, a power management system, and a communication device; The display device is used to display the reconstructed target scene image and its image clarity index in real time; The central processing unit dynamically adjusts the phase distribution matrix according to the image clarity index and realizes real-time image refresh based on the change amount of far-field information; The optical control system includes a sub-wavelength liquid crystal unit array, a transparent electrode driving circuit and a temperature sensor to generate a dynamic phase distribution matrix and perform temperature compensation; The data acquisition component is configured with an optical signal sensor, an analog-to-digital conversion circuit, and a random number generator to perform compressed sensing sampling and far-field information acquisition; The eye-movement interaction device includes an infrared camera, an eye feature recognition chip, and a three-dimensional posture sensor to achieve eye tracking and gesture recognition; The power management system is used to provide power consumption control and charging functions; The communication device is used to realize data transmission and remote control.

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