Polarization imaging device and polarization analysis method based on single-frame polarization collinear holography

Abstract

The invention discloses a polarization imaging device and a polarization analysis method based on single-frame polarization collinear holography, and relates to the field of polarization imaging.According to the polarization imaging device, through combination of optical elements such as a half-wave plate, a Wollaston prism and a CCD camera, spatial multiplexing of a detector plane is carried out, and the polarization collinear holography is obtained. And four polarization collinear holograms can be simultaneously acquired by a single frame. According to the polarization analysis method, a Fourier transform auxiliary angular spectrum method is adopted to analyze an intensity distribution diagram of a polarization collinear hologram to estimate initial wavefront distribution, and an iterative finite support constraint selection method is adopted to solve the problem of twin images in the polarization collinear hologram. And further quantizing a complete Jones matrix and a complete Stokes parameter from the finally reconstructed complex amplitude information. The invention solves the problems of high complexity and long processing time caused by independent reconstruction of amplitude, phase and polarization in the traditional polarization holographic technology, and effectively solves the problem that the traditional off-axis polarization holographic imaging system limits the size of an imaging field of view.

Description

Technical Field

[0001] The present invention relates to the field of polarization imaging, and particularly to a polarization imaging device and a polarization analysis method based on single-frame polarization collinear holography. Background Art

[0002] Polarization imaging has become increasingly important in modern imaging as it provides additional contrast mechanisms and characterization capabilities beyond traditional intensity-based techniques. In biological imaging, polarization-based microscopes play a crucial role in non-invasive and non-destructive molecular structure analysis. Although polarization characterization techniques have been around for decades, recent advancements (such as high-performance polarization optical elements, interferometric methods, and high-resolution, high-speed polarization cameras) have renewed interest in Jones matrix and Stokes parameter extraction. These techniques have found wide applications in fields such as biomedical imaging, spectroscopy, polarization microscopy, chemistry, soft matter physics, and metamaterials. The state-of-the-art polarization imaging systems typically employ complex experimental designs, including off-axis and in-line interferometry, for single-shot polarization component detection. However, their reliance on complex setups, computationally intensive matrix extraction, and expensive optical components limits their practicality for real-time or in vivo imaging.

[0003] In contrast, digital in-line holography (DIH) has made new progress in recent years, leveraging advanced digital signal processing for complex amplitude reconstruction and compact system design. These advantages offer new opportunities to extend DIH to polarization measurements through polarization-sensitive in-line holography. However, developing a robust polarization image processing framework remains a challenge, particularly for the automatic quantification of simultaneously extracting orthogonal polarization components, Jones matrix elements, and Stokes parameters from in-line holograms. Achieving this goal requires high-speed and high-precision computational tools for amplitude, phase, and polarization reconstruction. Further progress in such quantitative methods is crucial for the widespread adoption of polarization in-line holography in biomedical imaging and characterization.

[0004] Existing polarization techniques mainly rely on off-axis polarization interferograms or holograms to reconstruct the complex amplitude information of orthogonal polarization components and extract Jones matrix elements, usually using multiple or single acquisition schemes. Some methods combine dual-source illumination with off-axis interferometry to achieve single-shot recording of multiple polarization components. In digital reconstruction, these off-axis techniques typically use Fourier-transform-based fringe analysis, which introduces a spatial bandwidth product limitation and reduces the effective field of view. Due to multiple polarization components and conjugate spectra, single-frame methods are further affected by spectral overlap in the frequency domain, leading to challenges such as accurate central peak selection, high spatial frequency loss, and increased computational complexity. To alleviate these problems, some methods incorporate additional computational techniques, such as the Kramers-Kronig relations, to improve imaging quality and overcome bandwidth limitations. Recent progress has explored digital polarization online holography, but the synchronous complex amplitude reconstruction from multiple polarization holograms and real-time Jones matrix extraction are still immature, presenting a key opportunity for innovation. Summary of the Invention

[0005] An object of this application is to propose a polarization imaging device and a polarization analysis method based on single-frame polarization collinear holography for the above-mentioned technical problems.

[0006] In a first aspect, the present invention provides a polarization imaging device based on single-frame polarization collinear holography, comprising a laser light source, a spatial filter, a collimating lens, a first half-wave plate, a Wollaston prism, a 4-f lens group, a second half-wave plate, a beam displacer, and a camera, which are sequentially arranged along the optical axis direction; a sample to be measured is placed between the second half-wave plate and the beam displacer. The beam emitted by the laser light source is filtered and expanded by passing through the spatial filter and the collimating lens in sequence to obtain a plane wave; the plane wave is incident on the first half-wave plate to rotate the plane wave into a linearly polarized light at 45°, and the linearly polarized light at 45° is then incident on the Wollaston prism to split the linearly polarized light at 45° into corresponding horizontally polarized light beam and vertically polarized light beam according to a separation angle of 1°, and then passes through the 4-f lens group and the second half-wave plate in sequence. The horizontally polarized light beam and the vertically polarized light beam obtained by separation are converged by the 4-f lens group, and the horizontally polarized light beam and the vertically polarized light beam are respectively converted into a linearly polarized light beam at +45° and a linearly polarized light beam at -45° by the second half-wave plate; the linearly polarized light beam at +45° and the linearly polarized light beam at -45° are simultaneously irradiated on the sample to be measured to obtain a transmitted light beam corresponding to the linearly polarized light beam at +45° and a transmitted light beam corresponding to the linearly polarized light beam at -45°. The transmitted light beam corresponding to the linearly polarized light beam at +45° and the transmitted light beam corresponding to the linearly polarized light beam at -45° pass through the beam displacer, and the transmitted light beam corresponding to the linearly polarized light beam at +45° and the transmitted light beam corresponding to the linearly polarized light beam at -45° are respectively separated into corresponding horizontal polarization components and vertical polarization components, generating four spatially multiplexed polarization beams carrying sample information and propagating to the plane of the camera to generate corresponding spatially multiplexed polarization collinear holograms.

[0007] Preferably, the laser light source adopts a vertically polarized coherent light source with a wavelength of 632.8 nm, and the camera adopts a CCD camera.

[0008] Preferably, the principal axes of the first half-wave plate and the second half-wave plate form an angle of 22.5° with the vertical direction.

[0009] Preferably, the focal length of the collimating lens is 200 mm, the focal lengths of the two lenses in the 4-f lens group are both 150 mm, and a reflecting mirror is further included. The reflecting mirror is arranged between the collimating lens and the first half-wave plate and is used to change the direction of the plane wave from horizontal to vertical.

[0010] Preferably, the spatially multiplexed polarization collinear hologram includes polarization collinear holograms corresponding to four polarization directions, and the four polarization directions include the horizontal polarization direction and the vertical polarization direction of the transmitted light beam corresponding to the linearly polarized light beam at +45° and the horizontal polarization direction and the vertical polarization direction of the transmitted light beam corresponding to the linearly polarized light beam at -45°.

[0011] In a second aspect, the present invention provides a polarization analysis method based on single-frame polarization collinear holography, which uses a polarization imaging device based on single-frame polarization collinear holography according to any one of the first aspect, and includes the following steps:

[0012] S1. Obtain the intensity distribution map of the spatially multiplexed polarization collinear hologram, separate and register it, and obtain the intensity distribution maps of four polarization collinear holograms with individual polarization directions.

[0013] S2. For the intensity distribution map of each polarization collinear hologram with an individual polarization direction, calculate the initial wavefront distribution on the plane of the polarization collinear hologram with the individual polarization direction through the angular spectrum method according to the intensity distribution map of the polarization collinear hologram with the individual polarization direction.

[0014] S3. Use the iterative finite support constraint selection method to propagate the initial wavefront distribution back and forth between the first reconstruction plane at a distance of +z from the polarization collinear hologram plane and the second reconstruction plane at a distance of -z from the polarization collinear hologram plane until convergence, and obtain the finally reconstructed complex amplitude information.

[0015] S4. Traverse the intensity distribution maps of all polarization collinear holograms with individual polarization directions, and repeat steps S2 - S3 to obtain the finally reconstructed complex amplitude information corresponding to each polarization direction.

[0016] S5. Calculate the Jones matrix and Stokes parameters corresponding to the sample to be measured by using the finally reconstructed complex amplitude information corresponding to the four polarization directions.

[0017] Preferably, calculating the initial wavefront distribution on the plane of the polarization collinear hologram with an individual polarization direction through the angular spectrum method according to the intensity distribution map of the polarization collinear hologram with the individual polarization direction specifically includes:

[0018] Perform a fast Fourier transform on the intensity distribution map of the polarization collinear hologram with an individual polarization direction to obtain the frequency domain distribution of the intensity distribution map of the polarization collinear hologram with the individual polarization direction.

[0019] Initialize the optical parameters of the polarization imaging device and obtain the transfer function.

[0020] Multiply the frequency domain distribution of the intensity distribution map of the polarization collinear hologram with an individual polarization direction by the transfer function to obtain a multiplication result, and perform an inverse fast Fourier transform on the multiplication result to obtain the initial wavefront distribution on the plane of the polarization collinear hologram with the individual polarization direction.

[0021] Preferably, step S3 specifically includes:

[0022] Propagate the initial wavefront distribution to the first reconstruction plane to obtain the true image in the first reconstruction plane of the first round; perform the iterative process of the current round on the true image in the first reconstruction plane of the first round;

[0023] In the iterative process of the current round, filter the true image in the first reconstruction plane of the current round according to the support region and size specification of the sample to be measured to obtain the separated finite region;

[0024] Replace the complex field value of the separated finite region with the average value of the complex field values of the regions outside the finite region to obtain the reconstructed complex amplitude information of the current round; propagate the reconstructed complex amplitude information of the current round to the second reconstruction plane to obtain the virtual image in the second reconstruction plane of the current round;

[0025] In the iterative process of the next round, use the virtual image in the second reconstruction plane of the current round as the true image in the first reconstruction plane of the next round, calculate the reconstructed complex amplitude information of the next round, and repeat the above steps until convergence. The reconstructed complex amplitude information of the last round is used as the finally reconstructed complex amplitude information.

[0026] Preferably, the elements of the Jones matrix are given by the following formula:

[0027] ;

[0028] where, and represent the parameters of the transmitted beam corresponding to the linearly polarized +45° beam and the parameters of the transmitted beam corresponding to the linearly polarized -45° beam, both of which are constant real numbers, 、 、 and represent the elements of the Jones matrix, represents the finally reconstructed complex amplitude information obtained by the nth iteration corresponding to the mth polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized +45° beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized -45° beam respectively, represents the spatial coordinate.

[0029] Preferably, the expressions of the Stokes parameters are as follows:

[0030] ;

[0031] where, 、 、 and respectively represent the total light intensity, horizontal / vertical linearly polarized components, + / -45° linearly polarized components, and right-handed / left-handed circularly polarized components, represent the spatial coordinates, represent the imaginary unit, , represents the complex amplitude information of the finally reconstructed nth iteration corresponding to the mth polarization direction, represents the complex conjugate of the complex amplitude information of the finally reconstructed nth iteration corresponding to the mth polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and vertical polarization direction of the transmitted beam corresponding to the linearly polarized beam of +45° and the horizontal polarization direction and vertical polarization direction of the transmitted beam corresponding to the linearly polarized beam of -45°, respectively.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The polarization imaging device based on single-frame polarization collinear holography proposed by the present invention uses a Wollaston prism, a beam displacer, and a CCD camera to achieve spatial multiplexing and concurrent detection of four polarization collinear holograms, and can simultaneously generate orthogonally polarized beams, thereby allowing different polarization collinear holograms to be formed for each polarization direction.

[0034] (2) The polarization analysis method based on single-frame polarization collinear holography proposed by the present invention uses the Fourier transform-assisted angular spectrum method to process the intensity distribution map of the spatially multiplexed polarization collinear hologram to estimate the initial wavefront distribution, and then uses the iterative finite support constraint selection method to eliminate the defocused repeated images in the polarization collinear hologram, and can automatically quantify the complete Jones matrix and Stokes parameters from the reconstructed complex amplitude distribution, enhancing its applicability to in vivo imaging and characterization.

[0035] (3) The polarization analysis method based on single-frame polarization collinear holography proposed by the present invention has the ability to obtain complex amplitude information by single exposure, can simultaneously extract the Jones matrix and Stokes parameters with high precision, thereby significantly shortening the processing time, making real-time biological imaging more efficient and accurate, and effectively solving the problem of the limitation of the imaging field of view size for traditional off-axis polarization holographic imaging systems for the design and application of polarization collinear holographic imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 Optical path diagram of the polarization imaging device based on single-frame polarization collinear holography according to an embodiment of the present application;

[0038] Figure 2 Schematic flow chart of the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0039] Figure 3 Flow block diagram of the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0040] Figure 4 Spatial multiplexing polarization component detection results on the CCD camera plane in the sample-free state of the polarization imaging device based on single-frame polarization collinear holography according to an embodiment of the present application;

[0041] Figure 5 Intensity distribution diagram of the polarization collinear hologram corresponding to a known anisotropic object (polarizer with a 45° cross mark with respect to the horizontal axis) in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0042] Figure 6 Amplitude (first row) and phase (second row) distribution diagrams of specific polarization components extracted from the polarization collinear hologram corresponding to a known anisotropic object (polarizer with a 45° cross mark with respect to the horizontal axis) in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0043] Figure 7 Amplitude (first row) and phase (second row) distribution diagrams of the polarization matrix elements reconstructed from the polarization collinear hologram corresponding to a known anisotropic object (polarizer with a 45° cross mark with respect to the horizontal axis) in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0044] Figure 8 Intensity distribution diagram of the polarization collinear hologram corresponding to the birefringence resolution test target in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0045] Figure 9 Represents the amplitude distribution diagram of the elements of the Jones matrix extracted from the polarization collinear hologram corresponding to the standard birefringence resolution test target in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0046] Figure 10 Phase distribution diagram of the elements of the Jones matrix extracted from the polarization collinear hologram corresponding to the standard birefringence resolution test target in the polarization analysis method based on single-frame polarization collinear holography according to an embodiment of the present application;

[0047] Figure 11 Intensity distribution diagram of the polarization collinear hologram of the insect wing sample in the polarization analysis method based on single-frame polarization collinear holography according to the embodiment of the present application;

[0048] Figure 12 Amplitude distribution diagram of the elements of the Jones matrix extracted from the intensity distribution diagram of the polarization collinear hologram of the insect wing sample in the polarization analysis method based on single-frame polarization collinear holography according to the embodiment of the present application;

[0049] Figure 13 Phase distribution diagram of the elements of the Jones matrix extracted from the intensity distribution diagram of the polarization collinear hologram of the insect wing sample in the polarization analysis method based on single-frame polarization collinear holography according to the embodiment of the present application;

[0050] Reference numerals: 1, laser light source; 2, spatial filter; 3, collimating lens; 4, mirror; 5, first half-wave plate; 6, Wollaston prism; 7, 4-f lens group; 8, second half-wave plate; 9, sample to be measured; 10, beam displacer; 11, camera. Detailed implementation manners

[0051] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] Figure 1Disclosed is a polarization imaging device provided by an embodiment of the present application based on single-frame polarization collinear holography, including a laser light source 1, a spatial filter 2, a collimating lens 3, a first half-wave plate 5, a Wollaston prism 6, a 4-f lens group 7, a second half-wave plate 8, a beam displacer 10, and a camera 11 arranged in sequence along the optical axis direction; a sample to be measured 9 is placed between the second half-wave plate 8 and the beam displacer 10. The beam emitted by the laser light source 1 passes through the spatial filter 2 and the collimating lens 3 in sequence for filtering and beam expansion to obtain a plane wave. The plane wave is incident on the first half-wave plate 5 to rotate the plane wave into a linearly polarized light at 45°. The linearly polarized light at 45° is then incident on the Wollaston prism 6 to split the linearly polarized light at 45° into corresponding horizontally polarized beam and vertically polarized beam according to a 1° separation angle, and then passes through the 4-f lens group 7 and the second half-wave plate 8 in sequence. The 4-f lens group 7 converges the separated horizontally polarized beam and vertically polarized beam, and the second half-wave plate 8 converts the horizontally polarized beam and the vertically polarized beam into a linearly polarized beam at +45° and a linearly polarized beam at -45° respectively. The linearly polarized beam at +45° and the linearly polarized beam at -45° irradiate the sample to be measured 9 simultaneously to obtain a transmitted beam corresponding to the linearly polarized beam at +45° and a transmitted beam corresponding to the linearly polarized beam at -45°. The transmitted beam corresponding to the linearly polarized beam at +45° and the transmitted beam corresponding to the linearly polarized beam at -45° pass through the beam displacer 10 to separate the transmitted beam corresponding to the linearly polarized beam at +45° and the transmitted beam corresponding to the linearly polarized beam at -45° into corresponding horizontal polarization components and vertical polarization components respectively, generating four spatially multiplexed polarization beams carrying sample information and propagating to the plane of the camera 11 to generate a corresponding spatially multiplexed polarization collinear hologram.

[0053] In a specific embodiment, the laser light source 1 uses a vertically polarized coherent light source with a wavelength of 632.8 nm, and the camera 11 uses a CCD camera.

[0054] In a specific embodiment, the principal axes of the first half-wave plate 5 and the second half-wave plate 8 form an angle of 22.5° with the vertical direction.

[0055] In a specific embodiment, the focal length of the collimating lens 3 is 200 mm, the focal lengths of the two lenses in the 4-f lens group 7 are both 150 mm, and a reflecting mirror 4 is further included. The reflecting mirror 4 is arranged between the collimating lens 3 and the first half-wave plate 5 and is used to change the direction of the plane wave from horizontal to vertical.

[0056] Specifically, the polarization imaging device in the embodiments of the present application adopts a compact single-exposure polarization coaxial holographic optical path, integrating optical elements such as a Wollaston prism 6 (WP), a beam displacer 10 (BD), and a half-wave plate (HWP). Through the combination of the Wollaston prism 6 (WP), a 4-f lens group 7, and the half-wave plate (HWP), specific linearly polarized illumination beams (+45° and -45°) can be generated for the detection of the sample to be measured 9. This device can simultaneously generate orthogonal polarization beams, thereby forming independent polarization collinear holograms for each polarization component. By using the beam displacer 10 (BD) and a CCD camera to achieve spatial multiplexing, four polarization collinear holograms can be synchronously detected.

[0057] As Figure 1 shown, this polarization coaxial holographic optical path uses a vertically polarized coherent light source with a wavelength of 632.8 nm. After the beam emitted by the light source passes through a spatial filter 2 and a collimating lens 3 with a focal length of 200 mm for filtering and beam expansion, a plane wave is obtained. This plane wave adjusts the optical path direction through a mirror 4 to make the optical path structure more reasonable. After adjusting the optical path direction, the plane wave passes through a first half-wave plate 5 with an angle of 22.5° between the main optical axis and the vertical direction to rotate the vertically polarized incident beam into a linearly polarized light of 45°, and then enters the Wollaston prism 6 (WP). The Wollaston prism 6 (WP) divides the linearly polarized light of 45° into corresponding horizontally polarized beam and vertically polarized beam according to a separation angle of 1°. The 4-f lens group 7 composed of two lenses with the same focal length (150 mm) re-converges the separated polarization beams onto the surface of the sample to be measured 9. Before illuminating the sample to be measured 9, by placing a second half-wave plate 8 with an angle of 22.5° between the main optical axis and the vertical direction, these polarization beams are respectively converted into linearly polarized beams of +45° and linearly polarized beams of -45°. Finally, the sample to be measured 9 is simultaneously illuminated by the linearly polarized beam of +45° and the linearly polarized beam of -45°, meeting the necessary conditions for single-exposure detection. The single-exposure detection scheme is achieved through the combination of a polarization-sensitive beam displacer 10 (BD) and a CCD camera. The beam displacer 10 (BD) separates the transmitted beam corresponding to the linearly polarized beam of +45° and the transmitted beam corresponding to the linearly polarized beam of -45° into corresponding horizontally polarized components and vertically polarized components, thereby generating four spatially multiplexed polarization beams carrying sample information. These spatially multiplexed polarization beams carrying sample information propagate to the imaging plane of the CCD camera to generate corresponding polarization collinear holograms. The camera detection area is divided into four quadrants, corresponding to the polarization collinear holograms of a single polarization direction respectively, ensuring efficient synchronous acquisition.

[0058] In a specific embodiment, the spatially multiplexed polarization collinear hologram includes polarization collinear holograms corresponding to four polarization directions, and the four polarization directions include the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly -45° polarized beam.

[0059] Specifically, the spatially multiplexed polarization collinear hologram includes polarization collinear holograms respectively corresponding to four polarization directions; the four polarization directions correspond to the four quadrants of the camera detection area, which are the horizontal polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam, the horizontal polarization direction of the transmitted beam corresponding to the linearly -45° polarized beam, and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam. Subsequently, the spatially multiplexed polarization collinear hologram collected is further subjected to polarization analysis to analyze and obtain polarization information of the sample 9 to be measured, etc.

[0060] Further referring to Figure 2 a method embodiment of polarization analysis based on single-frame polarization collinear holography is provided in the present application. This method embodiment uses Figure 1 the polarization imaging device based on single-frame polarization collinear holography shown.

[0061] Referring to Figure 2 a method of polarization analysis based on single-frame polarization collinear holography is proposed in the embodiment of the present application. Using the above-mentioned polarization imaging device based on single-frame polarization collinear holography, it includes the following steps:

[0062] S1. Obtain the intensity distribution map of the spatially multiplexed polarization collinear hologram, perform separation and registration, and obtain the intensity distribution maps of the polarization collinear holograms of four individual polarization directions.

[0063] Specifically, the intensity distribution map corresponding to the spatially multiplexed polarization collinear hologram obtained by the above-mentioned polarization imaging device can be obtained, and the intensity distribution map is separated and registered to obtain the intensity distribution maps of the polarization collinear holograms of four individual polarization directions , m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly -45° polarized beam respectively.

[0064] S2. For the intensity distribution map of the polarization collinear hologram of each individual polarization direction, calculate the initial wavefront distribution on the plane of the polarization collinear hologram of the individual polarization direction according to the intensity distribution map of the polarization collinear hologram of the individual polarization direction by the angular spectrum method.

[0065] In a specific embodiment, the initial wavefront distribution on the plane of the polarization collinear hologram in a single polarization direction is calculated by the angular spectrum method according to the intensity distribution diagram of the polarization collinear hologram in a single polarization direction, specifically including:

[0066] Perform a fast Fourier transform on the intensity distribution diagram of the polarization collinear hologram in a single polarization direction to obtain the frequency domain distribution of the intensity distribution diagram of the polarization collinear hologram in a single polarization direction;

[0067] Initialize the optical parameters of the polarization imaging device and obtain the transfer function;

[0068] Multiply the frequency domain distribution of the intensity distribution diagram of the polarization collinear hologram in a single polarization direction by the transfer function to obtain a multiplication result, and perform an inverse fast Fourier transform on the multiplication result to obtain the initial wavefront distribution on the plane of the polarization collinear hologram in a single polarization direction.

[0069] Specifically, referring to Figure 3 , the intensity distribution diagrams of the polarization collinear holograms in each single polarization direction are processed to reconstruct the complex amplitude information on the plane of the sample to be measured. This complex amplitude information includes an amplitude distribution and a phase distribution. It can be seen from the corresponding intensity distribution formula that each intensity distribution is a combination of zero-order terms, which helps to form virtual images and real images. Therefore, there is a problem of defocused double images with splash overlap in the digital reconstruction of spatially multiplexed polarization collinear holograms. The polarization analysis method proposed in the embodiments of the present application uses the angular spectrum method to numerically solve the Rayliegh - Sommerfield integral and adopts a finite support constraint selection method to eliminate spatially overlapping twin images.

[0070] Specifically, the execution of the angular spectrum method starts from initializing the optical parameters of the polarization imaging device, and the transfer function is calculated using the optical parameters of the polarization imaging device. The calculation process of the transfer function is an existing method and will not be elaborated here. Perform a fast Fourier transform on the intensity distribution diagram of the polarization collinear hologram in a single polarization direction, and the corresponding frequency domain distribution can be obtained. Multiply this frequency domain distribution by the transfer function, and then perform an inverse fast Fourier transform to obtain the initial wavefront distribution on the plane of the polarization collinear hologram in a single polarization direction.

[0071] S3. Iteratively use the finite support constraint selection method to propagate the initial wavefront distribution back and forth between a first reconstruction plane at a distance of +z from the plane of the polarization collinear hologram and a second reconstruction plane at a distance of -z from the plane of the polarization collinear hologram until convergence, and obtain the finally reconstructed complex amplitude information.

[0072] In a specific embodiment, step S3 specifically includes:

[0073] Propagate the initial wavefront distribution to the first reconstruction plane to obtain the true image in the first reconstruction plane of the first round; perform the iterative process of the current round on the true image in the first reconstruction plane of the first round;

[0074] During the iterative process of the current round, filter the true image in the first reconstruction plane of the current round according to the support region and size specification of the sample to be measured to obtain the separated finite region;

[0075] Replace the complex field value of the separated finite region with the average value of the complex field values of the regions outside the finite region to obtain the reconstructed complex amplitude information of the current round; propagate the reconstructed complex amplitude information of the current round to the second reconstruction plane to obtain the virtual image in the second reconstruction plane of the current round;

[0076] In the iterative process of the next round, use the virtual image in the second reconstruction plane of the current round as the true image in the first reconstruction plane of the next round, calculate the reconstructed complex amplitude information of the next round, and repeat the above steps until convergence. The reconstructed complex amplitude information of the last round is used as the finally reconstructed complex amplitude information.

[0077] Specifically, propagate the initial wavefront distribution to the first reconstruction plane at a distance of +z from the polarization collinear hologram plane to obtain the true image, and then perform the iterative process of the finite support constraint selection method on this true image. During this iterative process, separate the finite region, and by replacing the complex field value of this finite region with the average value of the complex field values of the external region (i.e., the region outside the finite region), the true image information can be filtered out to obtain the reconstructed complex amplitude information. Propagate this reconstructed complex amplitude information to the first reconstruction plane at a distance of -z from the polarization collinear hologram plane to obtain the virtual image. In the cyclic iterative process, replace the virtual image with the true image, and reconstruct the complete complex amplitude information by propagating back and forth between the two reconstruction planes until the reconstructed image finally converges. This finite support constraint selection method locates the virtual image and the true image of the sample to be measured on the two reconstruction planes, and filters out the true image in one of the planes according to the set support constraints to obtain the separated finite region. The finite size of the sample to be measured makes the true image only appear in the selected finite region.

[0078] S4. Traverse the intensity distribution diagrams of all polarization collinear holograms of individual polarization directions, and repeat steps S2 and S3 to obtain the finally reconstructed complex amplitude information corresponding to each polarization direction.

[0079] Specifically, the above steps S2 and S3 are repeated for the intensity distribution diagrams of all the polarization collinear holograms with a single polarization direction. Thus, the final reconstructed complex amplitude information corresponding to each polarization direction can be obtained, and this final reconstructed complex amplitude information can be used to characterize or image the polarization state and polarization characteristics of the anisotropic sample to be measured.

[0080] S5. Calculate the Jones matrix and Stokes parameters corresponding to the sample to be measured by using the final reconstructed complex amplitude information corresponding to four polarization directions.

[0081] In a specific embodiment, the elements of the Jones matrix are given by the following formula:

[0082] ;

[0083] where and represent the parameters of the transmitted beam corresponding to the linearly polarized beam of +45° and the parameters of the transmitted beam corresponding to the linearly polarized beam of -45°, both of which are constant real numbers. 、 、 and represent the elements of the Jones matrix. represents the final reconstructed complex amplitude information obtained from the nth iteration corresponding to the mth polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and vertical polarization direction of the transmitted beam corresponding to the linearly polarized beam of +45° and the horizontal polarization direction and vertical polarization direction of the transmitted beam corresponding to the linearly polarized beam of -45°, respectively. represents the spatial coordinates.

[0084] In a specific embodiment, the expression of the Stokes parameters is as follows:

[0085] ;

[0086] where 、 、 and represent the total light intensity, the horizontal / vertical linear polarization component, the +45° / -45° linear polarization component, and the right-handed / left-handed circular polarization component, respectively. represents the spatial coordinates. represents the imaginary unit. , represents the final reconstructed complex amplitude information obtained from the nth iteration corresponding to the mth polarization direction. Denote the complex conjugate of the finally reconstructed complex amplitude information obtained from the n-th iteration corresponding to the m-th polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized +45° beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized -45° beam respectively.

[0087] Specifically, the polarization imaging or characterization of the sample to be measured is accomplished by calculating the elements of the complete Jones matrix from the finally reconstructed complex amplitude information. The elements of this Jones matrix carry the polarization information of the anisotropic object to be measured. Further, the Stokes parameters can be calculated using the finally reconstructed complex amplitude information, and these Stokes parameters are used to describe the polarization characteristics of the sample to be measured.

[0088] The technical solution of the present application will be further described below through specific embodiments.

[0089] The polarization imaging device of the embodiment of the present application can synchronously detect the intensity distributions of polarization collinear holograms in four polarization directions during a single exposure process. Figure 4 Show the spatial multiplexing polarization component detection results of the transmitted beams corresponding to the linearly polarized +45° beam and the -45° beam on the CCD camera plane in the state without a sample. This detection data is used for the initial calibration of the beam and determining the positioning coordinates of each polarization direction in the detector. To verify the imaging ability of the polarization analysis method, the researchers recorded the polarization collinear holograms corresponding to a known anisotropic object (a polarizer with a 45° cross mark with respect to the horizontal axis), and its intensity distribution is as Figure 5 shown. These polarization collinear holograms are processed using the polarization analysis method based on single-frame polarization collinear holography proposed in the embodiment of the present application, and the corresponding finally reconstructed complex amplitude information is successfully reconstructed. Figure 6 Show the reconstructed amplitude and phase distributions of the anisotropic sample at the sample plane. By obtaining the complex amplitude information corresponding to a specific polarization direction, the polarization matrix elements (the elements of the Jones matrix) of the sample can be flexibly extracted. Figure 7 Present the extraction results of the amplitude and phase distributions of the elements of the sample Jones matrix, which are in complete agreement with the theoretical values.

[0090] In addition, by extracting the polarization matrix elements of a standard birefringence resolution test target, the imaging ability of this method is further verified. The intensity distribution of the recorded polarization collinear hologram is as Figure 8 shown. The complete polarization matrix elements reconstructed using the polarization analysis method based on single-frame polarization collinear holography proposed in the embodiment of the present application are as Figure 9 and 10 shown, where Figure 9 is the amplitude distribution, Figure 10It is the phase distribution corresponding to the elements of the extracted Jones matrix. In the diagonal and off-diagonal components of the elements of the extracted Jones matrix, the birefringence characteristics of the resolution target (showing reverse brightness values) can be clearly observed, which is completely consistent with the polarization characteristics of this birefringent resolution test target.

[0091] In addition, an embodiment of the present application also uses an actual object, an insect wing, as a sample to be measured to verify the implementation effect of this imaging method. Figure 11 It shows the intensity distribution diagram of the spatially multiplexed polarization collinear hologram recorded when using an insect wing as a sample. The polarization matrix elements extracted by the polarization analysis method based on single-frame polarization collinear holography proposed in the embodiment of the present application are as Figure 12 and 13 shown, where Figure 12 is the amplitude distribution of the elements of the Jones matrix, and Figure 13 is the corresponding phase distribution.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polarization imaging device based on single-frame polarization collinear holography, characterized in that It includes a laser light source, a spatial filter, a collimating lens, a first half-wave plate, a Wollaston prism, a 4-f lens group, a second half-wave plate, a beam displacer and a camera, which are arranged in sequence along the optical axis direction; the sample to be measured is placed between the second half-wave plate and the beam displacer, and the beam emitted by the laser light source passes through the spatial filter and the collimating lens in sequence for filtering and beam expansion to obtain a plane wave; the plane wave is incident on the first half-wave plate to rotate the plane wave into a linearly polarized light at 45°, and the linearly polarized light at 45° is then incident on the Wollaston prism to split the linearly polarized light at 45° into corresponding horizontally polarized beam and vertically polarized beam according to a separation angle of 1°, and then passes through the 4-f lens group and the second half-wave plate in sequence. The horizontally polarized beam and the vertically polarized beam separated by the 4-f lens group are converged, and the horizontally polarized beam and the vertically polarized beam are respectively converted into a linearly polarized light at +45° and a linearly polarized light at -45° through the second half-wave plate; the linearly polarized light at +45° and the linearly polarized light at -45° are simultaneously irradiated on the sample to be measured to obtain a transmitted beam corresponding to the linearly polarized light at +45° and a transmitted beam corresponding to the linearly polarized light at -45°. The transmitted beam corresponding to the linearly polarized light at +45° and the transmitted beam corresponding to the linearly polarized light at -45° pass through the beam displacer, and the transmitted beam corresponding to the linearly polarized light at +45° and the transmitted beam corresponding to the linearly polarized light at -45° are respectively separated into corresponding horizontal polarization components and vertical polarization components, generating four spatially multiplexed polarization beams carrying sample information and propagating to the plane of the camera to generate a corresponding spatially multiplexed polarization collinear hologram.

2. The polarization imaging device based on single-frame polarization collinear holography according to claim 1, characterized in that The laser light source adopts a vertically polarized coherent light source with a wavelength of 632.8 nm, and the camera adopts a CCD camera.

3. The polarization imaging device based on single-frame polarization collinear holography according to claim 1, characterized in that The main optical axes of the first half-wave plate and the second half-wave plate both have an angle of 22.5° with the vertical direction.

4. The polarization imaging device based on single-frame polarization collinear holography according to claim 1, characterized in that The focal length of the collimating lens is 200 mm, the focal lengths of the two lenses in the 4-f lens group are both 150 mm, and it further includes a reflector, which is arranged between the collimating lens and the first half-wave plate and is used to change the direction of the plane wave from horizontal to vertical.

5. The polarization imaging device based on single-frame polarization collinear holography according to claim 1, characterized in that The spatially multiplexed polarization collinear hologram includes polarization collinear holograms corresponding to four polarization directions, and the four polarization directions include the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized light at +45° and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly polarized light at -45°.

6. A polarization analysis method based on single-frame polarization collinear holography, using the polarization imaging device based on single-frame polarization collinear holography according to any one of claims 1-5, characterized in that It includes the following steps: S1, obtaining the intensity distribution diagram of the spatially multiplexed polarization collinear hologram, separating and registering it to obtain the intensity distribution diagrams of the polarization collinear holograms of four individual polarization directions; S2, for the intensity distribution diagram of the polarization collinear hologram of each individual polarization direction, calculating the initial wavefront distribution on the plane of the polarization collinear hologram of the individual polarization direction through the angular spectrum method according to the intensity distribution diagram of the polarization collinear hologram of the individual polarization direction; S3. Use the iterative finite support constraint selection method to propagate the initial wavefront distribution back and forth between the first reconstruction plane at +z from the polarization collinear hologram plane and the second reconstruction plane at -z from the polarization collinear hologram plane until convergence, to obtain the finally reconstructed complex amplitude information; S4. Traverse the intensity distribution diagrams of all polarization collinear holograms of individual polarization directions, and repeat steps S2 - S3 to obtain the finally reconstructed complex amplitude information corresponding to each polarization direction; S5. Calculate the Jones matrix and Stokes parameters corresponding to the sample to be measured by using the finally reconstructed complex amplitude information corresponding to four polarization directions.

7. The polarization analysis method based on single-frame polarization collinear holography according to claim 6, characterized in that The initial wavefront distribution on the polarization collinear hologram plane of an individual polarization direction is calculated by the angular spectrum method according to the intensity distribution diagram of the polarization collinear hologram of the individual polarization direction, specifically including: Perform a fast Fourier transform on the intensity distribution diagram of the polarization collinear hologram of the individual polarization direction to obtain the frequency domain distribution of the intensity distribution diagram of the polarization collinear hologram of the individual polarization direction; Initialize the optical parameters of the polarization imaging device and obtain the transfer function; Multiply the frequency domain distribution of the intensity distribution diagram of the polarization collinear hologram of the individual polarization direction by the transfer function to obtain a multiplication result, and perform an inverse fast Fourier transform on the multiplication result to obtain the initial wavefront distribution on the polarization collinear hologram plane of the individual polarization direction.

8. The polarization analysis method based on single-frame polarization collinear holography according to claim 6, characterized in that Step S3 specifically includes: Propagate the initial wavefront distribution to the first reconstruction plane to obtain the real image in the first reconstruction plane of the first round; perform the iterative process of the current round on the real image in the first reconstruction plane of the first round; During the iterative process of the current round, filter the real image in the first reconstruction plane of the current round according to the support region and size specification of the sample to be measured to obtain the separated finite region; Replace the complex field value of the separated finite region with the average value of the complex field values of the regions outside the finite region to obtain the reconstructed complex amplitude information of the current round; propagate the reconstructed complex amplitude information of the current round to the second reconstruction plane to obtain the virtual image in the second reconstruction plane of the current round; In the iterative process of the next round, use the virtual image in the second reconstruction plane of the current round as the real image in the first reconstruction plane of the next round, calculate the reconstructed complex amplitude information of the next round, repeat the above steps until convergence, and use the reconstructed complex amplitude information of the last round as the finally reconstructed complex amplitude information.

9. The polarization analysis method based on single-frame polarization collinear holography according to claim 6, characterized in that The elements of the Jones matrix are given by the following formula: ； Among them, and represent the parameters of the transmitted beam corresponding to the linearly +45° polarized light beam and the parameters of the transmitted beam of the -45° polarized light, both of which are constant real numbers, 、 、 and represent the elements of the Jones matrix, represents the finally reconstructed complex amplitude information obtained by the nth iteration corresponding to the mth polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized light beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly -45° polarized light beam, represents the spatial coordinates.

10. The polarization analysis method based on single-frame polarization collinear holography according to claim 6, characterized in that The expressions of the Stokes parameters are as follows: ； Among them, , , and represent the total light intensity, horizontal / vertical linearly polarized components, + / -45° linearly polarized components, and right-handed / left-handed circularly polarized components, respectively, represents the spatial coordinates, represents the imaginary unit, , represents the complex amplitude information of the finally reconstructed complex amplitude obtained by the nth iteration corresponding to the mth polarization direction, represents the complex conjugate of the complex amplitude information of the finally reconstructed complex amplitude obtained by the nth iteration corresponding to the mth polarization direction, where m = 1, 2, 3, 4, corresponding to the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly +45° polarized beam and the horizontal polarization direction and the vertical polarization direction of the transmitted beam corresponding to the linearly -45° polarized beam, respectively.

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