Single-exposure birefringence imaging system and method based on four-state metasurface coding

Abstract

The invention discloses a single-exposure birefringence quantitative imaging system and method based on four-state metasurface coding. The system comprises a circularly polarized light source module, a sample scanning module, a four-state metasurface mask, an area array detector and a calculation processing unit. Left-hand circularly polarized light is adopted to irradiate a sample, emergent light of the sample is transmitted freely and then enters a four-state metasurface mask, the mask is formed by randomly arranging four functional units including a vertical wire grid, a horizontal wire grid, a transparent substrate and a metal film at equal probability, and a statistical independent equivalent modulation mask is formed for two orthogonal polarization components. After the modulated light field is freely propagated, an area array detector records an intensity image through single exposure, a calculation processing unit reconstructs Jones vector complex amplitude by adopting a constrained complex total variation regularization and accelerated near-end gradient descent algorithm, and then phase delay and an optical axis azimuth angle are extracted. The total axial length of the system is smaller than 10 mm, discrete components such as a lens beam splitter are not needed, and ultra-compact integration is achieved.

Description

Technical Field

[0001] This invention relates to the fields of optical imaging and computational imaging technology, and in particular to a single-exposure birefringence imaging system and method based on four-state metasurface coding. Background Technology

[0002] Birefringence is an inherent property of optically anisotropic materials and is widely found in biological tissues and engineering materials. By quantitatively measuring birefringence parameters—phase retardation and optical axis azimuth—markerless and non-destructive testing of material microstructures can be achieved, which has important applications in pathological diagnosis, materials testing, and optical metrology.

[0003] Existing birefringence measurement techniques face the challenge of balancing measurement speed, system compactness, and information integrity. One type of method relies on time-series acquisition, such as the rotating polarizer method and the liquid crystal compensator method, which calculates Stokes parameters or Jones matrices after acquiring multiple polarization images through multiple exposures. While these methods can obtain complete polarization information, they require multiple mechanical or electronic modulations, limiting measurement speed and making it difficult to meet the real-time imaging requirements of dynamic processes. Furthermore, the systems typically contain multiple discrete optical components, resulting in a large size. Another type of method uses a focal plane polarization camera, achieving single-exposure polarization measurement by integrating a micro-polarizer array at the sensor pixel level. However, this type of method has a fundamental drawback: the spatial resolution is reduced to one-quarter of the original due to the superpixel structure, and it can only acquire linear polarization Stokes parameters, failing to obtain the phase information of the Jones vector, thus limiting its ability to fully characterize birefringent samples. Summary of the Invention

[0004] To address the shortcomings of existing technologies, such as difficulty in simultaneously acquiring complete Jones vector information of birefringent samples under single-exposure conditions, complex system structures, and difficulty in achieving ultra-compact integration, this invention provides a single-exposure birefringent imaging system and method based on four-state metasurface encoding.

[0005] On the one hand, a single-exposure birefringence imaging system based on four-state metasurface coding is provided, including a circularly polarized light source module, a sample scanning module, a four-state metasurface mask, an area array detector, and a computing processing unit; The circularly polarized light source module is used to generate left-handed circularly polarized illumination light to illuminate the birefringent sample under test. The sample scanning module is used to carry the birefringent sample to be tested and to realize two-dimensional precision displacement scanning of the sample relative to the illumination spot. The four-state metasurface mask is placed at a first distance behind the sample and is used to independently spatially modulate the two orthogonal polarization components of the sample's emitted light field. The area array detector is placed at a second distance behind the four-state metasurface mask and is used to record an intensity image in a single exposure. The computational processing unit is connected to the area array detector and is used to receive the intensity image and reconstruct the complex amplitude of the two polarization components from the intensity image simultaneously based on an optimization algorithm, thereby extracting the birefringence parameters of the sample.

[0006] On the other hand, a single-exposure birefringence imaging method based on four-state metasurface coding is provided, including: The birefringent sample under test is illuminated with circularly polarized light, and the sample is scanned in two dimensions. The light field output by the sample reaches the four-state metasurface mask after propagating through the first free space segment. The two orthogonal polarization components are independently spatially modulated by the four-state metasurface mask. After the mask-modulated light field travels a second free space propagation distance, it reaches the area array detector, which records an intensity image in a single exposure. The computational processing unit receives the intensity image and uses the accelerated proximal gradient descent algorithm to solve an optimization problem that includes an amplitude domain data fidelity term and a constrained complex total variation regularization term, thereby reconstructing the complex amplitudes of the two polarization components simultaneously from the single intensity image. Extract the birefringence parameters of the sample.

[0007] The above technical solution has the following advantages or beneficial effects: This invention employs a four-state metasurface mask to statistically independently and randomly encode two orthogonal polarization components. Combined with a computational reconstruction algorithm, it achieves quantitative acquisition of the complete Jones vector (amplitude and phase) of a birefringent sample under a single exposure condition, overcoming the technical bottleneck of traditional methods that require multiple time-series acquisitions or sacrifice spatial resolution. The system uses a four-state encoding scheme combining a subwavelength metal wire grid with a transparent substrate and a metal film. The average transmittance of the two equivalent masks is approximately 50%, and the spatial cross-correlation is close to zero, mathematically guaranteeing the complete and independent acquisition of dual polarization channel information. The system's total axial length is less than 10 mm, eliminating the need for discrete optical components such as lenses, beam splitters, and analyzers. It consists only of a metasurface mask and an area array detector, achieving ultra-compact integration. Attached Figure Description

[0008] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0009] Figure 1 This is a schematic diagram of the optical path of a single-exposure birefringence imaging system based on four-state metasurface coding, as described in Example 1. Figure 2This is a schematic diagram of the four functional unit structures of the four-state metasurface mask in Example 1; Figure 3 The two equivalent polarization masks formed by the four-state metasurface encoding in Example 1 and Schematic diagram; Figure 4 The flowchart of the algorithm in the computational processing unit of Embodiment 1 Figure 5 The results are used to verify the data simulation. Detailed Implementation

[0010] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0011] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the invention. The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0012] Furthermore, to facilitate a clear description of the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0013] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0014] All data acquisition in this embodiment is carried out in accordance with laws and regulations and with user consent, and the data is used legally.

[0015] Example 1 This embodiment provides a single-exposure birefringence quantitative imaging system based on four-state metasurface coding. The system employs a four-state metasurface mask, which consists of four functional units randomly arranged: a vertical linear grid, a horizontal linear grid, a transparent substrate, and a metal film. Independent spatial amplitude modulation is applied to the two orthogonal polarization components. The modulated light field propagates through a second free-space segment and is then used by an area array detector to record an intensity image in a single exposure. The computational processing unit reconstructs the complex amplitude distribution of the Jones vector using constrained complex total variational regularization and an accelerated near-end gradient descent algorithm, ultimately achieving quantitative imaging of the sample's birefringence parameters. This system features the advantages of acquiring complete Jones vector information in a single exposure, an ultra-compact structure with a total axial length of less than 10 mm, no need for discrete components such as lenses and beam splitters, and high reconstruction accuracy, enabling high-resolution quantitative imaging of the multi-dimensional polarization characteristics of samples.

[0016] like Figure 1 The system includes a circularly polarized light source module, a sample scanning module, a four-state metasurface mask, an area array detector, and a computing processing unit.

[0017] The circularly polarized light source module is used to generate left-handed circularly polarized illumination light to illuminate the birefringent sample under test. The sample scanning module is used to carry the birefringent sample to be tested and to realize two-dimensional precision displacement scanning of the sample relative to the illumination spot.

[0018] The four-state metasurface mask is placed behind the sample at a first distance. The four-state metasurface mask is composed of four functional units arranged in random space, including a first-direction subwavelength metal grid that transmits the x-polarization component and blocks the y-polarization component, a second-direction subwavelength metal grid that transmits the y-polarization component and blocks the x-polarization component, a transparent substrate region that transmits both x and y polarization components, and a continuous metal film region that blocks both x and y polarization components. The array detector is placed behind the four-state metasurface mask at a distance of... This location is used to record an intensity image in a single exposure; The computational processing unit is connected to the area array detector and is used to receive the intensity image and reconstruct the complex amplitude of the two polarization components from the intensity image simultaneously based on an optimization algorithm, thereby extracting the birefringence parameters of the sample.

[0019] The total axial length of the system is d1+d2, which is less than 10mm under typical parameters (d1= 5-7 mm, d2= 2-4 mm), achieving ultra-compact integration. The system does not require traditional optical components such as lenses, beam splitters, and analyzers, and consists of only two core components: a metasurface mask and an area array detector.

[0020] Furthermore, the circularly polarized light source module outputs the Jones vector as follows: Left-handed circularly polarized light is used to excite the two orthogonally polarized components of the sample with equal weight.

[0021] Furthermore, the sample scanning module includes a high-precision displacement platform and its drive controller, which enables the illumination spot to traverse all imaging areas of the sample through point-by-point or line-by-line scanning. The sample applies a Jones matrix transformation to the incident light, and the output field is a Jones vector. ,in, and These are the complex amplitude fields for the x and y polarization components, respectively, containing the amplitude and polarization information of the sample.

[0022] Furthermore, such as Figure 2 As shown, the four-state metasurface mask is composed of four functional units arranged in a random spatial arrangement: S1 state (V-Grating): A vertical subwavelength metal wire grid on a SiO2 substrate that transmits the x-polarization component and blocks the y-polarization component. S2 state (H-Grating): A horizontal subwavelength metal wire grid on a SiO2 substrate that transmits the y-polarization component and blocks the x-polarization component. S3 state (Aperture): A bare substrate region that simultaneously transmits both x and y polarization components; S4 state (Metal): A continuous metal film covering region on a SiO2 substrate that blocks both x and y polarization components; The four functional units are arranged in a random distribution with equal probability, each occupying approximately 25% of the area. Based on this, two equivalent binary amplitude mask functions are defined. and , here It is a spatial coordinate, the equivalent mask for the x-polarization component. It is 1 at positions S1 and S3, and 0 at positions S2 and S4; the equivalent mask for the y-polarization component. It is 1 at positions S2 and S3, and 0 at positions S1 and S4, that is:

[0023]

[0024] like Figure 3 As shown, since the four states are equally probable random distributions, and Their average transmittance is approximately 50%. Both values ​​being 1 only occur in the S3 state, while both being 0 occur almost simultaneously in the S4 state. (Calculations...) and The spatial cross-correlation coefficient between them approaches zero, providing a mathematical basis for the separation of information from the dual polarization channels. For the sake of brevity, the following text is omitted. ,remember , .

[0025] After mask modulation, the x-polarization component becomes The y-polarization component becomes ,in, The distance is Angular spectral propagation operator, It is the component of the optical field (complex amplitude) in two orthogonal polarization directions.

[0026] Furthermore, based on EMT theoretical analysis and FDTD numerical optimization, the final structural parameters of the metasurface are determined as shown in Table 1. The grating period Λ = 150 nm is approximately 1 / 3.4 of the operating wavelength λ0 = 517 nm, satisfying the subwavelength condition and ensuring that higher-order diffraction is cut off. The linewidth w = 45 nm corresponds to a fill factor f = 0.30, achieving a good trade-off between extinction ratio and transmission efficiency.

[0027] Table 1. Parameters of the four-state metasurface structure

[0028] Rigorous full-wave electromagnetic simulations of the four-state metasurface were performed using the open-source FDTD software Meep. Simulation model settings: the computational domain consisted of a single wire-grating periodic cell (150 nm × 150 nm), with periodic boundary conditions in the x / y directions and a perfectly matched layer (PML, 1.0 μm thickness) in the z direction. The spatial resolution was 100 pts / μm (grid spacing 10 nm). The light source was a Gaussian pulsed plane wave covering the 450-600 nm band, and two independent simulations were performed for x-polarization and y-polarization. Transmittance and reflectance were normalized relative to the bare SiO2 substrate.

[0029] The FDTD simulation results at the design wavelength λ0 = 517 nm are shown in Table 2.

[0030] Table 2. FDTD simulation results of the four-state metasurface at λ0 = 517 nm

[0031] Both V-Grating and H-Grating exhibit extinction ratios of 25.3 dB and high polarization transmittance of 0.997, while their blocking polarization transmittance is only 0.003, approaching ideal binary polarization modulation. Energy conservation verification of the metal state (T + R + A = 0.007 + 0.749 + 0.244 = 1.000) confirms the physical consistency of the simulation. Broadband analysis shows that V-Grating and H-Grating maintain high extinction ratios in the 450-600 nm visible light band, with polarization transmittance remaining above 0.95, verifying the excellent broadband polarization selectivity of the metasurface design.

[0032] Furthermore, since there is no interference between the two orthogonal polarization vectors after mask modulation, the intensity recorded by the detector is an incoherent superposition of the two component intensities:

[0033] in, and For the forward operator of two channels, where and The complex amplitude distributions in the x and y polarization directions are defined as follows: ; In the formula, crop is the cropping operator. and The distance is and Angular spectrum propagation operator.

[0034] The detector's measurement model is a highly underdetermined nonlinear inverse problem—4N² real unknowns need to be recovered from N² real intensity measurements. and (Each polarization channel has its own amplitude and phase), with an underdetermined ratio of 4:1. The nonlinearity originates from the modulus-square operation of the intensity measurement. The two polarization channels are incoherently superimposed on the detector, further increasing the difficulty of information decoupling.

[0035] Furthermore, the computing and processing unit is connected to the area array detector and is used to receive the single intensity image and perform the following operations: The birefringence parameter reconstruction problem is modeled as an optimization problem that includes amplitude domain data fidelity terms and constrained complex total variation regularization terms; The optimization problem is solved using an accelerated proximal gradient descent algorithm. Extract birefringence parameters from the reconstructed Jones vector; The phase delay distribution and optical axis orientation distribution of the output sample.

[0036] Specifically, the birefringence parameter reconstruction problem is modeled as an optimization problem including amplitude domain data fidelity terms and constrained complex total variational regularization terms, including:

[0037] in, This involves substituting the current model (or the currently estimated object / wavefield parameters) into the forward imaging model to obtain the predicted detection intensity, which is then compared with the measured intensity. For measuring intensity; λ is the regularization parameter. The first term... For the amplitude domain data fidelity term, the amplitude difference is used. The 2-norm, rather than the intensity difference, is used because the objective function landscape in the amplitude domain is flatter, which is beneficial for the convergence of the gradient descent algorithm. (Second term) For the complex total variation (CCTV) regularization term, the TV of a complex-valued field U is defined as: Where x and y correspond to two dimensions, and It is a finite difference operator; like Figure 4 As shown, the Accelerated Proximal Gradient (APG) algorithm is used to solve the above optimization problem. The specific iterative process is as follows: S1, Calculation data fidelity item regarding and Wirtinger gradient:

[0038]

[0039] in , , To predict the intensity for the model; For measuring strength; , and They are respectively and The adjoint operator; The specific form of the adjoint operator is:

[0040]

[0041] in, It is pixel-by-pixel multiplication. It is a complex input on the detector plane (ROI region). The input variables; zeropad is the zero-padding operation (accompanying crop), where For the angular spectrum backpropagation operator, It is from the object surface to the mask surface; It's from the mask surface to the detector surface. It is an adjoint operator Input variables; S2, gradient descent step: The calculated Wirtinger gradient (i.e., the derivative with respect to the conjugate) is multiplied by the step size in the negative direction and then used to update the current variable to reduce the error of the data fidelity term;

[0042]

[0043] This step updates the estimate along the negative gradient direction, where γ is the step size parameter and K is the total number of iterations.

[0044] S3, the proximal step, applies a TV regularization constraint to the gradient descent result, and then uses Nesterov momentum to accelerate convergence.

[0045]

[0046] in, Here, k is the TV near-end operator, and k is the current iteration number.

[0047] S4, Momentum Acceleration: Benefit The changing trend Perform an extrapolation to generate "forward points". This is used for the next gradient calculation, thereby accelerating convergence.

[0048] S5. Dynamically adjust the regularization parameter λ using a sigmoid curve annealing strategy, starting from the initial value according to the sigmoid curve. Gradually decrease to the final value ,

[0049] in It is the current iteration number. It is the total number of iterations. These are the annealing iteration parameters. The larger the size, the faster the annealing: Repeat iterative steps S1-S5 200-400 times until convergence.

[0050] The extraction of birefringence parameters from the reconstructed Jones vector specifically involves: Birefringence parameters include phase delay δ and optical axis azimuth angle θ;

[0051]

[0052] in, The complex parameter (complex ratio) is constructed from the reconstructed Jones vector components and is used to map Jones information (amplitude + phase) to birefringence parameters. This algorithm directly utilizes the complex value information (amplitude and phase) of the Jones vector, avoiding the singular value problem in the Stokes parameter-based method.

[0053] Furthermore, this embodiment provides specific parameter configurations and numerical simulation verification results for the above-mentioned imaging system to demonstrate the feasibility and expected beneficial effects of the technical solution of the present invention.

[0054] Table 3 Numerical Simulation System Parameters The imaging system parameters used in this embodiment are shown in Table 3.

[0055]

[0056] The birefringence test samples were generated using a Modified Shepp-Logan phantom to simulate spatially varying birefringence parameter distributions. The phase delay was set to δ = π / 2 (corresponding to a quarter-wave plate, uniformly distributed), and the optical axis azimuth θ was spatially distributed within the range of [0, π / 4] using the grayscale values ​​of the phantom image. This setup simulates anisotropic materials with spatially varying optical axis azimuth angles, such as liquid crystal devices or biological tissue slices. 1% root-mean-square (RMS) additive white Gaussian noise was added during the measurement process to simulate detector noise.

[0057] In the simulation, the diffraction intensity pattern recorded by the area array detector is as follows: Figure 5 As shown in (a), a typical spatial structure of coaxial holographic diffraction fringes and four-state metasurface mask-coded modulation is presented. After 400 iterations of the CCTV-APG algorithm, the Jones vector components... and Amplitude distribution and arg( ) and arg( The phase distribution of ) such as Figure 5 As shown in (b), the reconstruction results are compared with the ground truth (GT). The normalized root mean square error of the amplitude is 3.2%. The normalized root mean square error of the amplitude is 1.7%, and both amplitude and phase are visually recovered with high fidelity.

[0058] Birefringence parameters were extracted from the reconstructed Jones vector. The reconstructed phase retardation δ showed a near-uniform π / 2 distribution (MAE = 3.61°), and the spatial variation pattern of the optical axis azimuth angle θ was highly consistent with that of the Shepp-Logan phantom (MAE = 2.30°). The boundaries of each elliptical structure were clearly distinguishable, such as... Figure 5 As shown in (c), the cross-sectional contrast curve along the horizontal line at the center of the image is as follows: Figure 5 As shown in (d), including and The reconstructed values ​​(red dashed lines) of the amplitude cross section and the birefringence parameter cross sections of δ and θ show a high degree of agreement with the true values ​​(blue solid lines) across all four physical quantities, verifying the reliability of this method in terms of quantitative accuracy. A summary of the quantitative reconstruction errors is shown in Table 4.

[0059] Table 4. Quantitative Error Analysis of Numerical Simulation (1% Noise Level)

[0060] Example 2 This embodiment provides a single-exposure birefringence quantitative imaging method based on four-state metasurface coding, including the following steps: The birefringent sample under test is illuminated with circularly polarized light, and the sample is scanned in two dimensions. The light field output by the sample reaches the four-state metasurface mask after propagating through the first free space segment. The two orthogonal polarization components are independently spatially modulated by the four-state metasurface mask. After the mask-modulated light field travels a second free space propagation distance, it reaches the area array detector, which records an intensity image in a single exposure. The computational processing unit receives the intensity image and uses the accelerated proximal gradient descent algorithm to solve an optimization problem that includes an amplitude domain data fidelity term and a constrained complex total variation regularization term, thereby reconstructing the complex amplitude of two polarization components simultaneously from the single intensity image. Extract the birefringence parameters of the sample.

Claims

1. A single-exposure birefringence quantitative imaging system based on four-state metasurface coding, characterized in that, It includes a circularly polarized light source module, a sample scanning module, a four-state metasurface mask, an area array detector, and a computing and processing unit; The circularly polarized light source module is used to generate left-handed circularly polarized illumination light to illuminate the birefringent sample under test. The sample scanning module is used to carry the birefringent sample to be tested and to realize two-dimensional precision displacement scanning of the sample relative to the illumination spot. The four-state metasurface mask is placed at a first distance behind the sample and is used to independently spatially modulate the two orthogonal polarization components of the sample's emitted light field. The area array detector is placed at a second distance behind the four-state metasurface mask and is used to record an intensity image in a single exposure. The computational processing unit is connected to the area array detector and is used to receive the intensity image and reconstruct the complex amplitude of the two polarization components from the intensity image simultaneously based on an optimization algorithm, thereby extracting the birefringence parameters of the sample.

2. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 1, characterized in that, The four-state metasurface mask is composed of four functional units arranged in random space, including a first-direction subwavelength metal grid that transmits the x-polarization component and blocks the y-polarization component, a second-direction subwavelength metal grid that transmits the y-polarization component and blocks the x-polarization component, a transparent substrate region that transmits both x and y polarization components, and a continuous metal film region that blocks both x and y polarization components.

3. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 2, characterized in that, The four-state metasurface mask defines two equivalent binary amplitude masks. and Among them, the equivalent mask for the x-polarization component It is 1 at positions S1 and S3, and 0 at positions S2 and S4; the equivalent mask for the y-polarization component. It is 1 at the S2 and S3 states, and 0 at the S1 and S4 states.

4. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 1, characterized in that, The computing and processing unit is connected to the area array detector and is used to receive the single intensity image and perform the following operations: Model the birefringence parameter reconstruction problem into an optimization problem; The optimization problem is solved using an accelerated proximal gradient descent algorithm. Extract birefringence parameters from the reconstructed Jones vector; The phase delay distribution and optical axis azimuth distribution of the output sample.

5. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 4, characterized in that, The optimization problem includes an amplitude domain data fidelity term and a constrained complex total variational regularization term.

6. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 4, characterized in that, The computational processing unit uses an accelerated proximal gradient descent algorithm to solve the optimization problem, and the iterative process includes: Calculate the Wirtinger gradient of the data fidelity term with respect to the complex amplitudes of the two polarization components; Update the current estimate along the negative gradient direction with a set step size to obtain the gradient descent step; Apply TV regularization constraints to the gradient descent results, and then use Nesterov momentum to accelerate convergence to obtain the proximal step; Extrapolate based on the changing trend of the results of two adjacent iterations to generate look-ahead points for the next gradient calculation; The regularization parameters are dynamically adjusted using a sigmoid curve annealing strategy. Repeat the above steps until convergence.

7. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 1, characterized in that, The birefringence parameters include phase delay and optical axis azimuth.

8. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 1, characterized in that, The circularly polarized light source module outputs a Jones vector. Left-handed circularly polarized light is used to excite the two orthogonally polarized components of the sample with equal weight.

9. The single-exposure birefringence quantitative imaging system based on four-state metasurface coding according to claim 1, characterized in that, The sample scanning module includes a high-precision displacement platform and its drive controller, which enables the illumination spot to traverse each imaging area of ​​the sample through point-by-point or line-by-line scanning.

10. A single-exposure birefringence quantitative imaging method based on four-state metasurface coding, employing the system described in any one of claims 1-9, characterized in that, include: The birefringent sample under test is illuminated with circularly polarized light, and the sample is scanned in two dimensions. The light field output by the sample reaches the four-state metasurface mask after propagating through the first free space segment. The two orthogonal polarization components are independently spatially modulated by the four-state metasurface mask. After the mask-modulated light field travels a second free space propagation distance, it reaches the area array detector, which records an intensity image in a single exposure. The computational processing unit receives the intensity image and uses the accelerated proximal gradient descent algorithm to solve an optimization problem that includes an amplitude domain data fidelity term and a constrained complex total variation regularization term, thereby reconstructing the complex amplitude of two polarization components simultaneously from the single intensity image. Extract the birefringence parameters of the sample.

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