Spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery

Abstract

The application discloses a spectral and polarization coding device for hyperspectral and polarization spatial distribution recovery and a preparation method thereof. The spectral and polarization coding device is integrated with a multilayer curved film array based on a microlens array and an image sensor. The inner wall of the multilayer curved film array is arranged towards the image sensor. The multilayer curved film is composed of film layers of at least two materials which are alternately stacked. The outer wall of the multilayer curved film array is provided with a matching medium layer, and the refractive index of the matching medium layer matches that of the microlens array. Incident light is incident from the outer wall side of the multilayer curved film array, and after spectral and polarization coding of each multilayer curved film unit, a characteristic pattern is formed at the image sensor. The characteristic pattern is reconstructed to obtain spectral and polarization information at different spatial positions. The device has the advantages of small volume, relatively simple preparation process, flexible design and easy expansion, and can meet the diversified needs of hyperspectral imaging and vector light field detection in various application scenarios.

Description

Technical Field

[0001] This invention relates to the field of spectral and polarization detection, and in particular to the application and fabrication method of a spectral polarization encoding device for restoring hyperspectral and polarization spatial distribution in hyperspectral imaging and vector light field detection. Background Technology

[0002] Optical sensors have become an indispensable technology in daily life, scientific research, and industrial applications. With the rapid advancement of micro-nano fabrication technology and micro-nano optical devices, highly integrated miniature optical sensors have attracted widespread attention and achieved remarkable results in research and development. However, facing the ever-increasing sensing demands, especially for multi-dimensional optical field information sensing technologies that include spatial dimensions, such as hyperspectral imaging and vector light field detection, these have become key areas of focus for researchers.

[0003] Traditional spectral imaging techniques typically rely on spatial or wavelength scanning methods, which limits their ability to capture the spectral information of every pixel across the entire field of view in real time. Traditional polarization detection techniques are also limited by the need for physical mechanical components to drive the precise rotation of polarizers and waveplates, similarly hindering real-time detection. Furthermore, these techniques require relatively large equipment, making them inconvenient to carry. However, in recent years, researchers have proposed various miniaturized spectrometer and polarimeter designs based on spatial multiplexing coding devices combined with computational reconstruction schemes. These innovations pave the way for the practical application of miniaturized sensors for hyperspectral imaging and vector light field detection.

[0004] However, most existing high-performance spectral and polarization encoding devices have complex fabrication processes (such as metasurfaces). Therefore, there is a large research space for compact spectral and polarization encoding devices with simple structures and easy fabrication processes. Summary of the Invention

[0005] Based on this, the present invention addresses the problem of high cost of hyperspectral imaging and vector light field detection equipment by providing an application, design, and fabrication method of a spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery in hyperspectral imaging and vector light field detection.

[0006] This invention is achieved using the following technical solution:

[0007] A spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery includes a plurality of multilayer curved film arrays and an image sensor. The inner wall of the multilayer curved film array faces the image sensor. The multilayer curved film array is formed by arranging a plurality of multilayer curved film unit arrays, each of which is composed of alternating layers of at least two materials. The outer wall of the multilayer curved film array is provided with a matching medium layer, the refractive index of which is matched with that of the microlens array. Incident light enters from one side of the outer wall of the multilayer curved film array, forming a feature pattern at the image sensor behind each multilayer curved film unit. The feature pattern is reconstructed to obtain spectral and polarization information at different spatial locations.

[0008] The spectral and polarization encoding device of the present invention further includes a liquid crystal layer disposed outside the matching medium layer, which is used to acquire polarization information of the full Stokes parameters.

[0009] The liquid crystal in the liquid crystal layer has a fixed orientation, and the orientation distribution corresponds to the multilayer curved film unit. The liquid crystal layer above each multilayer curved film unit is divided into two regions. The liquid crystal molecules in the same region are arranged in the same direction, and the liquid crystal molecules in different regions are arranged in different directions.

[0010] The multi-layer curved film of the present invention can be a spherical or ellipsoidal surface, parabola, hyperboloid, or other non-spherical surface.

[0011] This invention first projects monochromatic light of different wavelengths onto a multilayer curved film array via an imaging lens group to obtain spectral calibration data of the multilayer curved film array; then projects polychromatic light of an actual object onto the multilayer curved film array via the imaging lens group to obtain a feature pattern; and reconstructs the feature pattern based on the spectral calibration data to obtain spectral information with different spatial distributions, thereby achieving hyperspectral imaging.

[0012] This invention first modulates monochromatic light of different wavelengths into different polarization states and collimates it into a multilayer curved film array to obtain spectral and polarization calibration data of the multilayer curved film array; then, a vector beam (which may contain broadband spectral information) with an unknown wavelength and unknown polarization state spatial distribution is collimated into the multilayer curved film array to obtain a feature pattern; the feature pattern is reconstructed based on the spectral and polarization calibration data to obtain spectral and polarization information with different spatial distributions, thereby realizing vector light field detection.

[0013] A method for designing and fabricating a spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery, comprising:

[0014] Multilayer curved film arrays were fabricated using microlens arrays as substrates;

[0015] A matching medium layer is obtained by covering a multilayer curved film array with a matching medium. The refractive index of the matching medium layer is matched with that of the microlens array, and the outer wall surface of the matching medium layer is planar.

[0016] A multi-layer curved film array covering a matching dielectric layer is integrated onto the surface of an image sensor.

[0017] The present invention integrates a liquid crystal layer on the outer surface of the matching medium layer.

[0018] The liquid crystal layer is prepared by adding a liquid crystal solution to a glass substrate with an alignment layer.

[0019] The multilayer curved film of this invention is designed with material selection and structural optimization based on the working band and modulation effect.

[0020] By employing the above-described technical solution, the technical solution provided by the present invention has at least the following advantages:

[0021] This invention achieves simultaneous encoding and sensing of spectral information and polarization states through the integrated application of material and structural design, combining the characteristics of curved surfaces with the interference modulation effect of multilayer films. Utilizing a simple array structure, this invention can efficiently complete hyperspectral imaging and vector light field detection tasks. The fabrication process of this device is based on mature technologies such as microlens arrays and coating processes, making it simple and suitable for large-scale production, thus offering significant practical advantages. Furthermore, this invention exhibits excellent design flexibility and scalability; by adjusting the film design or introducing liquid crystal layers, it can adapt to the needs of different wavelength bands, meeting the diverse requirements of hyperspectral imaging and vector light field detection in various application scenarios. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the basic structure of the spectral and polarization encoding device for hyperspectral imaging applications in Embodiment 1 of the present invention;

[0023] Figure 2 This is a cross-sectional schematic diagram of the multilayer curved film unit in the array in Embodiment 1 of the present invention;

[0024] Figure 3 This is a top view of the multilayer curved film in Embodiment 1 of the present invention and its representation in polar coordinates;

[0025] Figure 4 Comparison of the simulated transmission spectrum of the multilayer curved film array designed in Embodiment 3 of the present invention under normal incidence with the actual measurement results;

[0026] Figure 5 This is a schematic diagram of the basic structure of the spectral and polarization encoding device used for vector light field detection after adding a liquid crystal layer in Embodiment 2 of the present invention, which can realize the acquisition of polarization information of all Stokes parameters.

[0027] Figure 6 This is a schematic diagram of the liquid crystal layer used as an extension device in Embodiment 2 of the present invention;

[0028] Figure 7 and Figure 8 These are, respectively, the calibration optical path design diagram and the workflow diagram required to realize the hyperspectral imaging application in Embodiment 1 of the present invention;

[0029] Figure 9 and Figure 10 These are, respectively, the calibration optical path design diagram and the workflow diagram required to realize the vector light field detection application in Embodiment 2 of the present invention.

[0030] Figure label:

[0031] 1. Matching dielectric layer; 2. Multilayer curved film array; 21. TiO2 film layer; 22. SiO2 film layer; 3. Microlens array; 4. Image sensor; 5. Single curved substrate; 6. Liquid crystal layer; 61. Liquid crystals with different orientations. Detailed Implementation

[0032] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0033] Example 1: Hyperspectral Imaging Application

[0034] See Figure 1 This embodiment provides a spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery, including a matching medium layer 1, a multilayer curved film array 2, a microlens array 3, and an image sensor 4.

[0035] In this embodiment, a microlens array is used as the substrate of the multilayer curved film array. The bottom surface is flat, and the shape of the upper surface is not limited; it can be a part of a sphere, or a part of an aspherical surface such as an ellipsoid or parabola, with dimensions ranging from μm to mm. The microlens array is made of a wide-band high-transparency material, such as optical glasses like K9 glass, BK7 glass, or fused silica glass, or organic polymers like polymethyl methacrylate (PMMA). The refractive index of the matching medium layer is similar to that of the material used in the microlens array, and its outer surface is flat, enabling the encoding device to achieve optical characteristics similar to a parallel plate. The image sensor 4 is a planar image sensor located on the lower surface of the microlens array 3, used to read the feature patterns after spectral and polarization encoding.

[0036] See Figure 2 For each multilayer curved film unit in the array, the incident angle varies at different distances from the center of the sphere. Therefore, the optical path length experienced within the multilayer curved film varies, resulting in different interference modulation effects of the multilayer films. Consequently, the transmission spectral function differs at different distances from the center of the sphere. (See also...) Figure 3 Since the incident angles at non-center positions of the multilayer curved film unit are not zero, the transmission spectral functions of the multilayer curved film for S-waves and P-waves differ. Furthermore, when constructing polar coordinates in a top view, the polarization states of the incident light observed on the incident planes (OP1 and OP2 planes) corresponding to different polar angles differ. Therefore, the spectral response functions of two points (P1 and P2) with the same center distance but different polar angles also differ. Based on these characteristics, the multilayer curved film achieves spectral and polarization encoding of incident light. By arranging these units into an array structure, spectral and polarization information in different spatial dimensions can be acquired.

[0037] To realize the application of this spectral and polarization encoding device in hyperspectral imaging, this embodiment provides a spectral calibration optical path design, see [link to relevant documentation]. Figure 7 Specifically, it includes a computer, a monochromator, a multimode fiber, a collimating and expanding device, a polarization-depolarizing beam splitter, a power meter, an illumination optical path device, an imaging lens assembly, and the aforementioned spectral and polarization encoding device. Based on this, this embodiment provides a method for acquiring spectral calibration data, including the following steps:

[0038] Step A1: The computer-controlled monochromator outputs monochromatic light of a specific wavelength (polarized to natural light). After collimation and beam expansion, the beam is split by a depolarizing beam splitter. One beam is used to form uniform illumination on the imaging surface via an illumination optical path device, and then an image is formed on the surface of an image sensor integrated with a multi-layer curved film array by an imaging mirror. The feature pattern of the monochromatic light after spectral encoding by the multi-layer curved film array is recorded as spectral calibration data. The other beam uses a power meter to read the intensity of the monochromatic light. The above steps are repeated, changing the wavelength and intensity of the monochromatic light each time, while keeping the incident conditions of the monochromatic light in front of the encoding device basically unchanged. This allows the image sensor to obtain feature patterns formed by spectral encoding modulation of monochromatic light of different wavelengths. Since the wavelength of the monochromatic light is preset and is a known condition, and the intensity is obtained from the power meter, a correspondence can be established between the wavelength and intensity information of the monochromatic light within the operating band of the encoding device and the feature patterns of the monochromatic light after spectral encoding modulation.

[0039] Step A2: Based on the correspondence described in A1, the spectral calibration data of the encoding device within the working band range can be obtained, which is generally recorded in the form of a calibration matrix.

[0040] After spectral calibration, the spectral and polarization encoding device can be used to achieve hyperspectral imaging. For detailed workflow, please refer to [link to documentation]. Figure 8The object (such as an image from an LED display screen) is imaged onto the surface of an image sensor that integrates spectral and polarization encoding devices through an imaging lens group. The encoded feature pattern is obtained, and combined with the spectral calibration data obtained in the calibration step, a data cube containing three-dimensional information (two-dimensional intensity distribution information + spectral dimension information) is reconstructed using a neural network-based reconstruction algorithm.

[0041] Example 2: Vector Light Field Detection Application

[0042] The difference between this embodiment and Embodiment 1 is that a liquid crystal layer is added as an extension. See [link to embodiment 1]. Figure 5 For the structure of the liquid crystal layer, see [link to relevant documentation]. Figure 6 The liquid crystal orientation remains fixed, and its distribution corresponds to the multilayer curved film unit. The liquid crystal layer above each multilayer curved film unit is divided into two regions. Liquid crystal molecules within the same region align in the same direction, while the alignment of liquid crystal molecules differs between regions. Its main function is to introduce spatially distributed phase modulation, pre-modulating the spatial distribution of the polarization state of the incident light. The encoding device in Example 1 can only modulate the amplitude of the incident light, enabling only linear polarization detection. However, in this example, by introducing phase modulation of the liquid crystal layer, full Stokes parametric polarization detection can be achieved, making it suitable for complex vector light field detection.

[0043] Similarly, to realize the application of spectral and polarization encoding devices in vector light field detection, this embodiment provides a spectral and polarization calibration optical path design, see [link to relevant documentation]. Figure 9 Specifically, it includes a computer, a monochromator, a multimode fiber, a collimating and expanding device, a depolarizing beam splitter, a power meter, a spatial light modulator, polarizers fixed on a precision rotating stage, a half-wave plate, a quarter-wave plate (the desired polarization state is obtained by controlling the rotation angle of the polarizer and the wave plate), and the aforementioned spectral and polarization encoding device. Based on this, this embodiment provides a method for acquiring spectral and polarization calibration data, including the following steps:

[0044] Step B1: The computer-controlled monochromator outputs monochromatic light of a specific wavelength (polarized as natural light). After collimation and beam expansion, the beam is split by a depolarizing beam splitter. One path passes through a spatial light modulator and polarizers, half-wave plates, and quarter-wave plates to form a spatially uniformly distributed horizontal linearly polarized light collimated incident encoding device. An image sensor records the characteristic pattern after spectral and polarization encoding by a multilayer curved film array, which serves as spectral and polarization calibration data. The other path uses a power meter to read the light intensity corresponding to the monochromatic light.

[0045] Since the wavelength and polarization state of the monochromatic light are predetermined, they are known conditions. The light intensity is obtained from the power meter. Therefore, the wavelength, polarization state, and light intensity of the monochromatic light can all be correlated with the characteristic patterns corresponding to the monochromatic light.

[0046] Step B2: Repeat step B1, changing the wavelength and intensity of the monochromatic light each time. At the same time, the incident polarization state of the monochromatic light in front of the encoding device is kept basically unchanged by the precise rotation of the combination of polarizer, half-wave plate and quarter-wave plate. This allows the image sensor to obtain the feature pattern formed by the spectral and polarization encoding modulation of monochromatic light of different wavelengths with fixed polarization state, and obtain the correspondence between the monochromatic light information (wavelength and intensity) and the feature pattern under horizontal linear polarization incident.

[0047] Step B3: Change the rotation angles of the polarizer, half-wave plate, and quarter-wave plate so that the input polarization state of monochromatic light remains vertical linear polarization, 45° linear polarization, and right-hand circular polarization, respectively. Repeat step B2 to obtain the correspondence between the monochromatic light information (wavelength and intensity) and the feature pattern under the vertical linear polarization state, 45° linear polarization state, and right-hand circular polarization state. Combine this with the correspondence described in B2 to construct the correspondence between the full Stokes parameter information and the feature pattern of monochromatic light in the working band of the encoding device.

[0048] Based on the correspondence described in B2 and B3, the spectral and polarization calibration dataset of the encoding device within a certain spectral range can be obtained. The pattern of incident light with arbitrary spectral and polarization states after passing through the encoding device can be obtained by linear superposition of the feature patterns in the above calibration dataset.

[0049] For the specific workflow of the spectral and polarization encoding device for vector light field detection in this embodiment, please refer to [link to documentation]. Figure 10 It can be used Figure 9 The calibration optical path shown replaces the monochromator with a broadband light source. An unknown vector beam is generated by the modulation of a spatial light modulator and polarizers, half-wave plates, and quarter-wave plates. The beam is collimated and incident on the surface of an image sensor that integrates spectral and polarization encoding devices to obtain the encoded feature pattern. Combined with the spectral and polarization calibration data obtained in the calibration steps, a data cube containing three-dimensional information (the distribution information of polarization state in a two-dimensional plane + spectral dimension information) is reconstructed using a neural network-based reconstruction algorithm.

[0050] In particular, when the vector beam consists only of linearly polarized states, vector light field detection can be achieved without adding a liquid crystal layer.

[0051] Example 3: Fabrication of a Spectral and Polarization Encoding Device

[0052] Based on Example 1, this embodiment provides a method for designing and fabricating a spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery, specifically including the following steps:

[0053] Step S1: Select the material of the multilayer curved film and optimize the thickness of the multilayer curved film according to the required encoding modulation effect;

[0054] Step S2: Based on the optimized multilayer curved film results, deposit films of different materials sequentially and alternately on the curved surface of the microlens array 3; the deposition methods include, but are not limited to, physical vapor deposition methods such as magnetron sputtering, resistance thermal evaporation, electron beam evaporation, ion plating, and molecular beam epitaxy, as well as chemical vapor deposition methods such as low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, and photonic chemical vapor deposition.

[0055] Step S3: Fill the matching medium layer 1 above the multilayer curved film array 2. Depending on the refractive index of the material used in the microlens array, the matching medium can be microscope immersion oil, fiber optic refractive index matching liquid, polydimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA), etc. If a liquid matching medium is selected, a receiving cavity needs to be built above the multilayer curved film array 2 and the outer surface of the matching medium layer is sealed with a flat quartz glass plate.

[0056] Step S4: Place the image sensor 4 on the lower surface of the microlens array 3. The image sensor 4 can be a high-performance charge-coupled device image sensor (CCD) or complementary metal-oxide-semiconductor sensor (CMOS).

[0057] The structure of the spectral encoding device obtained based on the above steps is as follows: Figure 1 As shown.

[0058] In this embodiment, the multilayer film uses TiO2 and SiO2 as materials and is prepared by magnetron sputtering. The film has nine layers, and the specific structural parameters are shown in Table 1. The film quality of the multilayer film is also verified using the transmission spectrum function from 300 to 1100 nm. Specifically, the transmittance curve of the nine-layer film is simulated, and the transmittance curve of the multilayer film is directly detected using a Cary 5000 spectrometer. The detected transmittance curve of the multilayer film is compared with the simulation calculation results. (See Table 1 for details.) Figure 4 .Depend on Figure 4 It can be seen that the optical properties of the actual fabricated multilayer film are basically consistent with the simulation, indicating that the actual fabricated spectral and polarization encoding device based on multilayer curved film array can achieve the designed modulation effect, thereby ensuring good hyperspectral imaging and vector light field detection performance.

[0059] In addition, the matching medium in this embodiment is microscope oil immersion; the quartz glass, image sensor, microlens array and all the materials used above are commercially available and commonly purchased.

[0060] Table 1. Membrane Materials and Thicknesses

[0061] Material <![CDATA[TiO2]]> <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[SiO2]]> <![CDATA[TiO2 <!-- 5 -->]]> thickness 65nm 77nm 190nm 200nm 179nm 200nm 190nm 77nm 65nm

[0062] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0063] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0064] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery, characterized in that, The spectral polarization encoding device includes a multilayer curved film array based on a microlens array and an image sensor. The inner wall of the multilayer curved film array faces the image sensor. The multilayer curved film array is formed by arranging several multilayer curved film units, each composed of alternating layers of at least two materials. The outer wall of the multilayer curved film array is provided with a matching medium layer, the refractive index of which matches that of the microlens array. Incident light enters from one side of the outer wall of the multilayer curved film array, forming a feature pattern at the image sensor behind each multilayer curved film unit. The feature pattern is reconstructed to obtain spectral and polarization information at different spatial locations.

2. The spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 1, characterized in that, The spectral and polarization encoding device further includes a liquid crystal layer disposed outside the matching medium layer, which is used to acquire polarization information of the full Stokes parameters.

3. The spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 2, characterized in that, The liquid crystal in the liquid crystal layer has a fixed orientation, and the orientation distribution corresponds to the multilayer curved film unit. The liquid crystal layer above each multilayer curved film unit is divided into two regions. The liquid crystal molecules in the same region are arranged in the same direction, and the liquid crystal molecules in different regions are arranged in different directions.

4. The spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 1, characterized in that, The multi-layer curved film can be spherical or aspherical.

5. The spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 1, characterized in that, First, monochromatic light of different wavelengths is projected onto a multilayer curved film array through an imaging lens group to obtain spectral calibration data of the multilayer curved film array; then, polychromatic light of the actual object is projected onto the multilayer curved film array through an imaging lens group to obtain a feature pattern. Using spectral calibration data, the feature pattern is reconstructed to obtain spectral information with different spatial distributions, thus achieving hyperspectral imaging.

6. The spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 1, characterized in that, First, monochromatic light of different wavelengths is modulated into different polarization states and collimated and incident on a multilayer curved film array to obtain spectral and polarization calibration data of the multilayer curved film array. Then, a vector beam with an unknown wavelength and an unknown polarization state spatial distribution is collimated and incident on the multilayer curved film array to obtain a feature pattern. Using the spectral and polarization calibration data, the spectral and polarization information of different spatial distributions is reconstructed according to the spectral and polarization calibration data, thus realizing vector light field detection.

7. A method for preparing a spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery, characterized in that, include: Multilayer curved film arrays were fabricated using microlens arrays as substrates; A matching medium layer is obtained by covering a multilayer curved film array with a matching medium. The refractive index of the matching medium layer is matched with that of the microlens array, and the outer wall surface of the matching medium layer is planar. A multi-layer curved film array covering a matching dielectric layer is integrated onto the surface of an image sensor.

8. The method for preparing the spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 7, characterized in that, A liquid crystal layer is integrated on the outer surface of the matching medium layer.

9. The method for preparing the spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 8, characterized in that, The liquid crystal layer is prepared by adding a liquid crystal solution to a glass substrate with an alignment layer.

10. The method for preparing the spectral polarization encoding device for hyperspectral and polarization spatial distribution recovery according to claim 7, characterized in that, The multilayer curved film is designed with material selection and structural optimization based on the working band and modulation effect.

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