Micro-nano polarization imaging spectrometer based on aperture segmentation

Abstract

The application discloses a kind of micro-nano polarization imaging spectrometer based on aperture segmentation, belong to polarization imaging spectrometer technical field.The application includes front group first imaging objective lens, field stop, front group eyepiece, optical filter, micro-nano polarizer, sub-aperture lens group array, focusing mirror and detector in order along optical path.The field stop is placed at the image plane of front group first imaging objective lens, and is used to adjust the peripheral shape of primary image, and the peripheral shape is adjusted to rectangle.The front group eyepiece is used to collimate the image from field stop into parallel light.The front group first imaging objective lens, field stop and front group eyepiece jointly constitute front group common aperture system, the aperture segmentation technology in polarization detection is introduced in the polarization imaging spectrometer in the application, optical filter and micro-nano polarizer are respectively inserted in each aperture, and the image containing same spatial information, different spectral information and polarization information is obtained in one exposure process, with the advantages of high time resolution, high compactness and strong anti-interference ability.

Description

Technical Field

[0001] This invention belongs to the field of polarization imaging spectrometer technology, and relates to a micro-nano polarization imaging spectrometer based on aperture segmentation. Background Technology

[0002] With the continuous development of science and technology, fields such as space remote sensing, military reconnaissance, and environmental monitoring have placed higher demands on the accuracy of target detection and identification. Spectral imaging technology is capable of simultaneously acquiring both spatial and spectral information of a target. By acquiring spectral images of the target scene and then performing spectral analysis, target identification can be achieved. However, spectral resolution and spatial resolution are inversely related; therefore, increasing spectral resolution to improve the probability of target identification inevitably leads to a decrease in spatial resolution. Thus, combining polarization imaging with spectral imaging has become a new approach for target detection and identification. Polarization imaging can acquire detailed information about the target, compensating for the spatial resolution sacrificed by spectral imaging to improve spectral resolution. Polarization imaging spectral detection technology has become a new research hotspot.

[0003] Currently, common polarization imaging spectral detection systems can be divided into two categories: time-division polarization imaging spectral detection systems and amplitude-division polarization imaging spectral detection systems. Time-division polarization imaging spectral detection systems mostly acquire different polarization images of the target scene by rotating polarizers, which significantly reduces the system's temporal resolution. Amplitude-division polarization imaging spectral detection systems are generally large and heavy, making them inconvenient to carry during observation.

[0004] In 2023, patent CN 116295837A proposed a snapshot-type Fourier transform Stokes polarization imaging spectrometer. By employing a high-order phase retarder based on a birefringent crystal for polarization modulation, all Stokes parameters of the incident light field are modulated into the light intensity signal. Simultaneously, it utilizes multi-lens array-based multiple imaging technology and multi-level micromirror spatial phase modulation technology to achieve simultaneous acquisition of light intensity information at all interference orders of the target scene, obtaining a three-dimensional data cube of the interferometric image array. Through interferogram extraction, channel filtering, and Fourier transform, snapshot measurements of the target image, spectrum, and polarization are achieved. However, the entire system's optical path is a cross-shaped path, resulting in a less compact overall system structure, which is not conducive to reducing the size and weight of the optical system. Furthermore, interferometric systems have high requirements for the accuracy of the optical path difference between the reference and measurement optical paths, making the system more susceptible to external interference. Summary of the Invention

[0005] To address the shortcomings of existing technologies: (1) they require a Michelson interferometer-type cross-shaped optical path, resulting in an overall structure that is not compact enough, which is not conducive to reducing the size and weight of the optical system; (2) they have high requirements for the accuracy of the optical path difference between the reference optical path and the measurement optical path, making them susceptible to external interference. This invention provides a micro-nano polarization imaging spectrometer based on aperture segmentation. By introducing aperture segmentation technology from polarization detection into the polarization imaging spectrometer, and inserting filters and micro-nano polarizers into each aperture, an image containing the same spatial information, different spectral information, and polarization information can be obtained in a single exposure process. This has the advantages of high temporal resolution, high compactness, and strong anti-interference ability.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] The present invention discloses a micro-nano polarization imaging spectrometer based on aperture segmentation, which includes, in sequence along the optical path, a front primary imaging objective, a field stop, a front eyepiece, a filter, a micro-nano polarizer, a sub-aperture lens array, a focusing lens, and a detector.

[0008] The front primary imaging objective lens is used to image the target object in one pass.

[0009] The field stop is positioned at the image plane of the front primary imaging objective lens and is used to adjust the outer shape of the primary image, shaping it into a rectangle. The center of the field stop is a rectangular aperture for adjusting the outer shape of the primary image; the size of the central light-transmitting rectangular area is determined by the coordinates of the edge image points on the primary image plane. The field stop has a protrusion for engaging with the lens barrel groove, ensuring that the edge of the resulting rectangular image is parallel to the detector target surface. The center of the rectangular aperture of the field stop should be located on the optical axis of the front primary imaging objective lens and the front eyepiece lens.

[0010] The front eyepiece is used to collimate the image transmitted from the field stop into parallel light.

[0011] The front primary imaging objective, field stop, and front eyepiece together form the front common aperture system. The aperture of the incident parallel light is adjusted through the front common aperture system, providing sufficient space for the mechanical installation of filters, micro / nano polarizers, and sub-aperture lens arrays.

[0012] The filter contains N 2 A slice is used to select the spectral range of different channels to generate N. 2 One spectral channel. N at the front end of the filter. 2 A mechanical pressure ring is used to achieve aperture segmentation for the micro / nano polarization imaging spectrometer.

[0013] The micro / nano polarizer contains N 2 The pieces are located at N. 2After each filter, each micro / nano polarizer allows light from each spectral channel to be polarized into four different states. The entire micro / nano polarization imaging spectrometer obtains light containing 4N... 2 Polarization spectrum images of various states.

[0014] Preferably, when four filters are used, they are symmetrically positioned around the optical axis, creating four spectral channels. Four mechanical retaining rings at the front of the filters achieve aperture segmentation for the micro / nano polarization imaging spectrometer. Four micro / nano polarizers are positioned after the four filters, each allowing light from each spectral channel to generate four polarization states. The entire micro / nano polarization imaging spectrometer obtains polarization spectral images containing 16 states.

[0015] Preferably, when the filter array comprises nine filters, these nine filters are arranged in a 3x3 grid, distributed across the nine cells of the grid, producing nine spectral channels. Nine mechanical retaining rings at the front of the filters achieve aperture segmentation for the micro / nano polarization imaging spectrometer. Nine micro / nano polarizers are located after the nine filters, and each micro / nano polarizer allows light from each spectral channel to generate four polarization states. The entire micro / nano polarization imaging spectrometer obtains polarization spectral images containing 36 states.

[0016] The sub-aperture lens array is used to adjust the position of the image after the filter is segmented.

[0017] The focusing lens is used to adjust the size of the image formed by the sub-aperture lens array, and to match the size of the image formed by the sub-aperture lens array with the target surface size of the detector.

[0018] The detector is used to receive image information.

[0019] The present invention discloses a working method for a micro / nano polarization imaging spectrometer based on aperture segmentation, comprising the following steps:

[0020] The light emitted from the target object passes sequentially through the front primary imaging objective lens. The field stop adjusts the outer shape of the primary image, shaping it into a rectangle. This rectangular primary image then exits through the front eyepiece as square parallel beams. These beams strike a filter and are split into N... 2Each sub-spectral channel contains multiple spectral channels. Light containing the same spatial information but different spectral information passes through micro / nano polarizers located in each sub-spectral channel. The polarization state of the incident light is modulated by the micro / nano polarizers. The light, containing the same spatial information but different spectral and polarization information, continues to propagate after passing through the micro / nano polarizers. The propagation direction is adjusted by a sub-aperture lens array and a focusing lens, so that the image planes of the sub-channels, after being stitched together, completely cover the entire detector target surface. By solving the image obtained from the entire detector target surface, images with the same spatial information but different spectral and polarization information of the target object are obtained, thus achieving the capture of multiple polarization spectral images in a single exposure.

[0021] Preferably, the micro / nano polarization structure achieves polarization modulation through a metal wire grating structure. A metal wire grating is a grating with many parallel metal strips distributed on a transparent substrate. The TE-polarized light is the component polarized in the same direction as the grating, while the TM-polarized light is the component polarized perpendicular to the grating. When the grating period is much smaller than the incident light wavelength, TE light passing through the metal wire grating generates electrons that oscillate freely along the grating direction, causing the TE light to be reflected. However, the TM light can directly pass through the metal wire grating medium, achieving polarization modulation.

[0022] Polarization spectral image processing is achieved using Stokes vector theory. The Stokes vector consists of four parameters, where:

[0023] S0=<|E x | 2 >+<|E y | 2 > (1)

[0024] S1=<|E x | 2 >-<|E y | 2 > (2)

[0025] S2=<2·E x ·E y ·cosδ> (3)

[0026] S3=<2·E x ·E y sinδ> (4)

[0027] In the formula, <> represents the average value of the time parameter, E x E represents the electric field strength in the x-direction. y δ represents the electric field intensity in the y-direction, and δ represents the amplitude E. x E yThe phase difference. Physical quantity S0 represents the total light intensity, physical quantity S1 represents the intensity difference between the 0° polarization direction vector and the 90° polarization direction vector, physical quantity S2 represents the intensity difference between the 45° polarization direction vector and the 135° polarization direction vector, and physical quantity S3 represents the intensity difference between right-handed and left-handed circularly polarized light.

[0028] The first three parameters (S0, S1, S2) of the incident light Stokes vector can be extracted from the acquired image. These three parameters can be calculated using the following formula:

[0029] S0=I0+I 90 (5)

[0030] S1=I0I 90 (6)

[0031] S2=I 45 -I 135 (7)

[0032] Where I0 represents the polarization vector intensity of the light passing through the 0° linear polarizer, I 45 I represents the vector intensity of polarized light passing through a 45° linear polarizer. 90 I represents the vector intensity of polarized light passing through a 90° linear polarizer. 135 This represents the vector intensity of polarized light passing through a 135° linear polarizer. I0 and I2 are directly read from the detector image. 45 I 90 and I 135 Substituting these values ​​into formulas (1)-(7) yields the polarization-related parameter E. x E y And δ. By combining the spectral range selection function of different channels of the filter, polarization spectral image processing can be realized.

[0033] Beneficial effects:

[0034] 1. This invention discloses a micro / nano polarization imaging spectrometer based on aperture segmentation. Through aperture segmentation, it enables the acquisition of images containing the same spatial information, different spectral information, and different polarization information using only a single detector, reducing the system's size and weight, and lowering its cost.

[0035] 2. This invention discloses a micro / nano polarization imaging spectrometer based on aperture segmentation. By combining the polarization modulation function of micro / nano polarization structures and the spectral range selection function of different channels of filters with the aperture segmentation method, the system's target recognition probability is significantly improved. Simultaneously, it enables the acquisition of all required images in a single exposure, improving the system's temporal resolution. Attached Figure Description

[0036] Figure 1A schematic diagram of a micro / nano polarization imaging spectrometer based on aperture segmentation is provided for an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a micro-nano polarizer in a micro-nano polarization imaging spectrometer based on aperture segmentation is provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of image processing results for a micro / nano imaging spectrometer based on aperture segmentation, provided as an embodiment of the present invention.

[0039] In the figure: 1-Target object, 2-Front primary imaging objective lens, 3-Field stop, 4-Front eyepiece lens, 5-Filter, 6-Micro-nano polarizer, 7-Sub-aperture lens array, 8-Focusing lens, 9-Detector. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment discloses a micro-nano polarization imaging spectrometer based on aperture segmentation, including a target object 1, a front primary imaging objective lens 2, a field stop 3, a front eyepiece 4, a filter 5, a micro-nano polarizer 6, a sub-aperture lens array 7, a focusing lens 8, and a detector 9.

[0043] The function of the front primary imaging objective 2 is to form an intermediate image plane. A field stop 3 is inserted into this intermediate image plane to adjust it into a rectangle. The front primary imaging objective 2, the field stop 3, and the front eyepiece 4 together form the front common aperture system, adjusting the aperture of the incident parallel light and providing sufficient space for the mechanical mounting of the filter 5, the micro / nano polarizer 6, and the sub-aperture lens array 7.

[0044] The field stop 3 is a coin-shaped aperture, and the size of the central light-transmitting rectangular area is determined by the coordinates of the edge image points at the primary image plane. The field stop 3 is not a regular coin shape; it has a protrusion at the top to cooperate with the lens tube, ensuring that the edge of the formed rectangular image is parallel to the detector target surface. The center of the rectangular light-transmitting aperture of the field stop 3 should be located on the optical axis of the front primary imaging objective lens 2 and the front eyepiece lens 4.

[0045] The filter 5 comprises four filters symmetrically distributed in four quadrants. The retaining ring on its front surface serves as the system's aperture stop, dividing the system's detection target surface into four regions. Each region contains different spectral information, achieved by coating different films on the filter surface, allowing the four regions to obtain spectral information at different wavelengths.

[0046] The micro / nano polarizer 6 comprises four pieces, corresponding to the four filters. Each micro / nano polarizer is further divided into four parts. The micro / nano polarizer is designed so that the image plane regions corresponding to the four parts of the micro / nano polarizer receive light vector intensities with polarization degrees of 0°, 45°, 90°, and 135°, respectively. A schematic diagram of the designed metal wire grid type micro / nano polarizer is shown below. Figure 2 As shown. In addition, due to the adjustment of the front primary imaging objective lens 2 and the front eyepiece lens 4, the incident light on the micro-nano polarizer 6 is approximately parallel, so the spatial information contained in the image formed in each region is the same.

[0047] The sub-aperture lens array 7 includes four lens groups, which are located directly behind the filter 5 and the micro / nano polarizer 6. They converge and image the light passing through the filter 5 and the micro / nano polarizer 6, and make the convergence point of the edge field of view of the four regions near the optical axis of the front primary imaging objective 2 and the front eyepiece 4 located on the optical axis of the front primary imaging objective 2 and the front eyepiece 4.

[0048] The focusing lens 8 adjusts the size and position of the image formed by the sub-aperture lens array 7 so that the image formed by the sub-aperture lens array 7 can fall exactly on the target surface of the detector 9 and fill the entire target surface.

[0049] The detector 9 is used to receive image information.

[0050] Polarization spectral image processing is achieved using Stokes vector theory. A schematic diagram of the resulting polarization spectral image is shown below. Figure 3 As shown.

[0051] The connection relationships between the above-mentioned components are as follows:

[0052] The pupils of the front primary imaging objective 2 and the front eyepiece 4 are matched and share the same optical axis. The field stop 3 is located on the primary image plane of the front primary imaging objective 2. This structure is collectively referred to as the front common aperture system, and they all share the same optical axis. The purpose of the front-end optical structure is to generate parallel light of a suitable aperture size. The filter 5, micro / nano polarizer 6, and sub-aperture lens array 7 each contain four sub-sections, which share the same optical axis and are symmetrically distributed around the optical axis of the front common aperture system. The focusing lens 8 and detector 9 are located at the rearmost end and share the same optical axis as the front common aperture system.

[0053] The working method of a micro / nano polarization imaging spectrometer based on aperture segmentation disclosed in this embodiment is as follows:

[0054] A target object 1 is defined. The light emitted from target object 1 passes sequentially through the front single-image objective lens 2, the field stop 3, and the front eyepiece 4, becoming a square parallel beam. This beam then strikes filter 5, splitting into four beams containing the same spatial information but different spectral information. After passing through a micro / nano polarizer 6, polarization modulation is achieved. Following adjustments to the size of the lens array 7 and the focusing lens 8, the beam can completely cover the entire detector target surface. By processing the resulting image, an image containing the same spatial information, different spectral information, and different polarization information of target object 1 can be obtained.

[0055] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A micro-nano polarization imaging spectrometer based on aperture segmentation, characterized by: The optical path sequentially comprises a front group of primary imaging objective lens (2), a field diaphragm (3), a front group of eyepiece (4), a filter (5), a micro-nano polarizer (6), a sub-aperture lens group array (7), a focusing mirror (8) and a detector (9); The front group of primary imaging objective lens (2) is used for primary imaging of the target object (1); The field diaphragm (3) is arranged at the image plane of the front group of primary imaging objective lens (2) and is used for adjusting the peripheral shape of the primary image into a rectangle; the middle part of the field diaphragm (3) is a rectangular hole for adjusting the peripheral shape of the primary image, and the size of the central light transmission rectangular region is determined by the coordinates of the edge image points at the primary image plane; the field diaphragm (3) is provided with a protrusion for cooperating with the barrel groove, and the barrel groove and the protrusion of the field diaphragm (3) make the edges of the rectangular image parallel to the target surface of the detector (9); the center of the rectangular light transmission aperture of the field diaphragm (3) should be located on the optical axis of the front group of primary imaging objective lens (2) and the front group of eyepiece (4); The front group of eyepiece (4) is used for collimating the image from the field diaphragm (3) into parallel light; The front group of primary imaging objective lens (2), the field diaphragm (3) and the front group of eyepiece (4) jointly form a front group of common aperture system, which adjusts the aperture of the incident parallel light and provides sufficient space for the mechanical installation of the filter (5), the micro-nano polarizer (6) and the sub-aperture lens group array (7); The filter (5) comprises N 2 pieces, for spectral range selection of different channels, generating N 2 spectral channels; N 2 mechanical pressure rings in front of the filter (5), realizing aperture segmentation of the micro-nano polarization imaging spectrometer; The micro-nano polarizer (6) contains N 2 pieces, respectively behind N 2 pieces of filters (5); each micro-nano polarizer (6) can allow light in each spectral channel to produce four polarization states, respectively; the entire micro-nano polarization imaging spectrometer obtains a polarization spectral image containing 4N 2 states. The sub-aperture lens group array (7) is used for adjusting the image position after the image is divided by the filter (5); The focusing mirror (8) is used for adjusting the size of the image formed by the sub-aperture lens group array (7) to match the size of the target surface of the detector (9); The detector (9) is used for receiving image information.

2. The aperture division based micro / nano polarization imaging spectrometer according to claim 1, wherein: When the filter (5) contains 4 pieces, the four filters (5) are symmetrically arranged around the optical axis to generate 4 spectral channels; the 4 mechanical compression rings at the front end of the filter (5) realize the aperture segmentation of the micro-nano polarization imaging spectrometer; the micro-nano polarizer (6) contains 4 pieces and is arranged behind the 4 filters (5), and each micro-nano polarizer (6) can generate four polarization states for the light of each spectral channel; the entire micro-nano polarization imaging spectrometer obtains polarization spectral images containing 16 states.

3. The aperture-splitting-based micro / nano polarization imaging spectrometer according to claim 1, wherein: When the filter (5) contains 9 pieces, the 9 filters (5) are arranged in a nine-square grid and distributed in the nine squares of the nine-square grid to generate 9 spectral channels; the 9 mechanical compression rings at the front end of the filter (5) realize the aperture segmentation of the micro-nano polarization imaging spectrometer; the micro-nano polarizer (6) contains 9 pieces and is arranged behind the 9 filters (5), and each micro-nano polarizer (6) can generate four polarization states for the light of each spectral channel; the entire micro-nano polarization imaging spectrometer obtains polarization spectral images containing 36 states.

4. The aperture-splitting-based micro / nano polarization imaging spectrometer according to claim 1, 2 or 3, characterized in that: The light emitted by the target object (1) passes through the front group of primary imaging objective lens (2) in turn, and the peripheral shape of the primary image is adjusted to be rectangular through the field diaphragm (3). The primary image with rectangular shape is emitted by the front group of eyepiece (4) as square parallel light, which is incident on the filter (5) and is divided into N 2 spectral channels. The light containing the same spatial information and different spectral information passes through the micro-nano polarizer (6) in each sub-spectral channel, and the polarization state of the incident light is modulated based on the micro-nano polarizer (6). The light containing the same spatial information, different spectral information and different polarization information continues to propagate after passing through the micro-nano polarizer (6). The propagation direction is adjusted through the sub-aperture lens group array (7) and the focusing mirror (8), so that the sub-channel image plane is spliced and completely covers the entire detector (9) target surface. By solving the image obtained by the entire detector (9) target surface, an image with the same spatial information, different spectral information and different polarization information of the target object (1) is obtained, that is, a single exposure captures multiple polarized spectral images.

5. The aperture-splitting-based micro / nano polarization imaging spectrometer according to claim 4, characterized in that: Micro-nano polarization structure realizes polarization modulation through metal wire grid structure; the metal wire grid is a grating with many parallel metal bars distributed on a transparent substrate; the TE direction of polarized light is the same as the polarization component of the grating direction, and the TM wave is the polarization component perpendicular to the grating direction; when the grating period is much smaller than the wavelength of the incident light, the TE light will produce electrons that can freely oscillate along the grating direction when passing through the metal wire grid, and the TE light will be reflected, but the TM light can directly pass through the metal wire grid medium, thereby realizing polarization modulation; Through the Stokes vector theory, the polarization spectrum image is solved; the Stokes vector is composed of four parameters, wherein: S0 = <|E x | 2 >+<|E y | 2 > (1) S1 = <|E x | 2 - <|E y | 2 > (2) S2 = <2 · E x · E y · cos δ > (3) S3 = <2 · E x · E y · sin δ > (4) wherein < > indicates an average value of a time parameter, E x represents an electric field intensity in the x direction, E y represents an electric field intensity in the y direction, and δ represents an amplitude E x , E y ; the physical quantity S0 represents a total light intensity value, the physical quantity S1 represents an intensity difference between a 0° polarization direction vector and a 90° polarization direction vector, the physical quantity S2 represents an intensity difference between a 45° polarization direction vector and a 135° polarization direction vector, and the physical quantity S3 represents a difference between right-handed light and left-handed light intensities in circularly polarized light; The first three parameters (S0, S1, S2) of the incident light Stokes vector can be extracted from the obtained image; the three parameters are calculated by the following formula: S0 = I0 + I 90 (5) S1 = I0 - I 90 (6) S2 = I 45 - I 135 (7) Where I0 represents the polarization vector intensity of the light passing through the 0° linear polarizer, I 45 I represents the vector intensity of polarized light passing through a 45° linear polarizer. 90 I represents the vector intensity of polarized light passing through a 90° linear polarizer. 135 This represents the polarization vector intensity of light passing through a 135° linear polarizer; I0 and I are directly read from the image obtained by the detector (9). 45 I 90 and I 135 Substituting these values ​​into formulas (1)-(7) yields the polarization-related parameter E. x E y And δ; combined with the spectral range selection function of different channels of filter (5), polarization spectrum image calculation is realized.

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