Snapshot Mueller matrix polarization imaging device and method based on photo-oriented liquid crystal chip

Abstract

The invention discloses a snapshot Mueller matrix polarization imaging device and method based on a photo-oriented liquid crystal chip. The device comprises a light source unit, a polarization modulation unit based on the photo-alignment liquid crystal chip, a sample measurement unit, a polarization demodulation unit based on the photo-alignment liquid crystal chip, a light detector unit and a computer. According to the invention, the light source unit and the polarization modulation unit generate polarized light which is distributed in a specific mode in a space in a polarization state, the polarized light generates signal light after acting similarly, and after the signal light passes through the polarization demodulation unit, the signal light can be subjected to one-time photographing exposure through the light detector to acquire a signal image. And calculating the spatial distribution of all Mueller matrix elements of the to-be-detected sample through a computer. Measurement can be completed only through single exposure of the light detector, and the measurement speed is high; meanwhile, mechanical rotating elements, electric adjustable elements and the like are not needed, and the structure is simple and compact; the device has the advantages of high spatial resolution, high measurement precision and low manufacturing cost.

Description

Technical Field

[0001] The present invention belongs to the field of polarization optical measurement, and in particular relates to a snapshot Mueller matrix polarization imaging device and method based on a light-oriented liquid crystal chip. Background Art

[0002] Mueller matrix polarization imaging technology detects objects by measuring the spatial distribution of the Mueller matrix elements of the target object, which can provide hidden information that traditional imaging technology cannot obtain. The Mueller matrix is ​​a 4×4 matrix that can fully describe the polarization changes after the interaction between light and objects, including birefringence, dichroism, depolarization and other characteristics. Therefore, Mueller matrix polarization imaging technology can obtain the most complete polarization information of the target object, which not only has important scientific significance, but also has broad application prospects in biomedicine, industrial testing, environmental monitoring and other fields.

[0003] Mueller matrix polarization imaging technology is mainly divided into two categories: time-sharing type and snapshot type. The time-sharing technology collects multiple photos through timing-controlled mechanical or electrically adjustable elements to reconstruct the Mueller matrix. Although the principle is simple and the spatial resolution is high, the sampling time is long and multiple measurements affect the accuracy of the results. It is only suitable for the analysis of static or time-varying samples. Snapshot technology generally uses the method of polarization spatial modulation, and only needs to use a single detector for one exposure to complete the sampling, and then obtain the spatial distribution of the Mueller matrix. It has a fast measurement speed and a compact structure, which has significant advantages. Existing solutions mainly include snapshot Mueller matrix polarization imaging technology based on polarization gratings or birefringent crystals and snapshot Mueller matrix polarization imaging technology based on optical metasurfaces, but they generally have problems such as low spatial resolution, low measurement accuracy, high processing cost, and complex structure. Therefore, their practical application is greatly limited. Summary of the invention

[0004] The purpose of the present invention is to provide a snapshot Mueller matrix polarization imaging device and method based on a photo-oriented liquid crystal chip to address the deficiencies of the prior art. Compared with other snapshot Mueller matrix polarization imaging technologies, the device has the advantages of high spatial resolution, high measurement accuracy, low cost, and a simple and compact structure.

[0005] The technical solution for achieving the purpose of the present invention is as follows: A snapshot Mueller matrix polarization imaging device based on a photo-oriented liquid crystal chip, comprising a light source unit, a polarization modulation unit, a sample measurement unit, a polarization demodulation unit, a light detector unit and a computer; The light source unit, polarization modulation unit, sample measurement unit, polarization demodulation unit and light detector unit are arranged in sequence along the light path direction; The light source unit is provided with a monochromatic light source and a first lens in sequence along the light path; the polarization modulation unit is provided with a first polarizer and a first liquid crystal chip in sequence along the light path; the light source unit and the polarization modulation unit generate polarized light whose polarization state is distributed in a specific manner in space; The sample measurement unit is provided with a second lens, a sample stage and a third lens in sequence along the optical path direction, and the sample is placed on the sample stage; The polarization demodulation unit is provided with a second liquid crystal chip and a second polarizer in sequence along the optical path; the light detector unit is provided with a fourth lens and a light detector in sequence along the optical path; the polarization demodulation unit and the light detector unit perform full Stokes polarization imaging on the signal light emitted by the sample measurement unit; In the direction along the light path, the first liquid crystal chip, the sample, the second liquid crystal chip and the photosensitive surface of the light detector are in an optical conjugate position; in the direction perpendicular to the light path, each sub-pixel of the first liquid crystal chip and each super-pixel of the second liquid crystal chip are in an optical conjugate position; The computer is connected to the photodetector to collect the signal image detected by the photodetector; based on the image collected by the photodetector in one exposure, the computer calculates the spatial distribution of all Mueller matrix elements of the sample to achieve snapshot Mueller matrix polarization imaging.

[0006] The optical path of the device is defined in a right-hand rectangular coordinate system XYZ, wherein the principal optical axis is parallel to the Z axis, the positive direction of the Z axis is the light propagation direction, and the light transmission axis of the first polarizer is parallel to the X axis.

[0007] The first liquid crystal chip and the second liquid crystal chip are both liquid crystal boxes with microstructures that are infused with nematic liquid crystals and are made using liquid crystal light-controlled orientation technology. The microstructures of the first liquid crystal chip and the second liquid crystal chip are both composed of superpixels that are periodically repeated in space, and each superpixel is divided into at least four sub-pixels of equal area. In each sub-pixel, the nematic liquid crystal is uniformly oriented along a specific direction, and the orientation directions of the liquid crystals are different in different sub-pixels.

[0008] In the device, the microstructures of the first liquid crystal chip and the second liquid crystal chip are composed of super pixels that are periodically repeated in space, and each super pixel is divided into four sub pixels with equal areas; in each sub pixel, the liquid crystal is uniformly oriented, and the director n is parallel to the surface, and for the first liquid crystal chip and the second liquid crystal chip, the angle between the liquid crystal director n in the sub pixel i and the X axis is i 1 =51.69°, the angle between the liquid crystal director n and the X axis in sub-pixel ii is i 2 =164.88°, the angle between the liquid crystal director n and the X axis in sub-pixel iii is i3 =128.31°, the angle between the liquid crystal director n and the X axis in sub-pixel iv is i 4 =15.12°; the phase delay introduced by the first liquid crystal chip 202 and the second liquid crystal chip 401 is 228.19°.

[0009] The light detector is an area array image sensor capable of capturing a complete two-dimensional image of signal light within one exposure cycle.

[0010] A measurement method using the snapshot Mueller matrix polarization imaging device based on a light-oriented liquid crystal chip, comprising the steps of calculating the spatial distribution of all Mueller matrix elements of the sample from the image collected by the light detector through a single exposure: In the XYZ coordinate system, the Mueller matrix of the first polarizer is assumed to be M P1 , the Mueller matrix of the second polarizer is M P2 , the Mueller matrix of each sub-pixel of the first liquid crystal chip is , the Mueller matrix of each sub-pixel of the second liquid crystal chip is , j =1,2,3,…,n, the Mueller matrix of the sample is M sample , the Stokes parameter of the light emitted by the monochromatic light source is S 0 , the light emitted from the sample is conjugated to the first liquid crystal chip i The Stokes parameter of the sub-pixel light is , i =1,2,3,…,m, incident on the photosensitive surface of the photodetector conjugate to the second liquid crystal chip j The Stokes parameter of the light of a sub-pixel is , 𝑗=1,2,3,…,n; The first element is I (j) , which can be measured by a light detector; ;set up The first behavior ,remember ; Then the Mueller matrix of the sample is M sample , the light intensity I measured by the light detector (j) , j =1,2,3,…,n, calculated by the following formula ; in, yes MPSG The Moore-Penrose pseudoinverse, ; yes M PSA The Moore-Penrose pseudoinverse.

[0011] Beneficial effects of the present invention: (1) The snapshot Mueller matrix polarization imaging device based on the photo-oriented liquid crystal chip provided by the present invention can complete the sampling by only one exposure using a single light detector, and then calculate the spatial distribution of all Mueller matrices of the sample. It has a fast measurement speed and is suitable for the observation of dynamic samples.

[0012] (2) The use of photo-oriented liquid crystal chips to achieve structured polarized illumination and full-Stokes polarization imaging not only has a flexible spatial modulation method and can significantly reduce the measurement matrix condition number by optimizing the liquid crystal orientation pattern, significantly improving the system measurement accuracy, but also greatly reduces the processing difficulty and cost compared to the optical metasurface solution, and improves the processing efficiency.

[0013] (3) The optical path structure design in which the liquid crystal chip is conjugated with the sample to be tested is adopted. This design does not involve diffraction and spatial spectrum analysis while keeping the system structure simple and compact. It has high light energy utilization and camera format utilization, and the spatial resolution of the imaging can reach the theoretical maximum value of the snapshot type solution.

[0014] Of course, any technical solution of the present invention may not be able to achieve all of the above beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of an embodiment of the device of the present invention.

[0016] Figure 2 It is a schematic diagram of the structure of a liquid crystal chip in an embodiment of the device of the present invention.

[0017] In the figure, there are a light source unit 1, a polarization modulation unit 2, a sample measurement unit 3, a polarization demodulation unit 4, a light detector unit 5, a computer 6, a white light source 101, a color filter 102, a first lens 103, a first polarizer 201, a first liquid crystal core 202, 301, a sample stage 302, a third lens 303, a second liquid crystal chip 401, a second polarizer 402, a fourth lens 501, and a light detector 502. DETAILED DESCRIPTION

[0018] With reference to the accompanying drawings, the present invention will be further described in detail below in conjunction with specific embodiments.

[0019] In an exemplary embodiment, Figure 1 As shown, a snapshot Mueller matrix polarization imaging device based on a light-oriented liquid crystal chip is provided, comprising a light source unit 1, a polarization modulation unit 2, a sample measurement unit 3, a polarization demodulation unit 4, a light detector unit 5 and a computer 6 which are sequentially connected along an optical path.

[0020] In the light source unit 1, a monochromatic light source composed of a white light source 101 and a color filter 102, and a first lens 103 are sequentially arranged along the light path direction. The polarization modulation unit 2 is sequentially arranged with a first polarizer 201 and a first liquid crystal chip 202 along the light path direction. The light source unit 1 and the polarization modulation unit 2 generate polarized light whose polarization state is distributed in a specific manner in space. The sample measurement unit 3 is sequentially arranged with a second lens 301, a sample stage 302 and a third lens 303 along the light path direction, and the sample is placed on the sample stage 302. The polarization demodulation unit 4 is sequentially arranged with a second liquid crystal chip 401 and a second polarizer 402 along the light path direction. The light detector unit 5 is sequentially arranged with a fourth lens 501 and a light detector 502 along the light path direction. The polarization demodulation unit 4 and the light detector unit 5 perform full Stokes polarization imaging on the signal light emitted by the sample measurement unit 3. The computer 6 is connected to the light detector 502 to collect the signal image detected by the light detector 502.

[0021] The optical path of the device is defined in a right-hand rectangular coordinate system XYZ, wherein the principal optical axis is parallel to the Z axis (the positive direction of the Z axis is the light propagation direction), the light transmission axis of the first polarizer 201 is parallel to the X axis, and the angle between the light transmission axis of the second polarizer 402 and the X axis is 0°.

[0022] The first liquid crystal chip 202 and the second liquid crystal chip 401 are both liquid crystal cells with microstructures made by using liquid crystal light-controlled orientation technology and filled with E7 nematic liquid crystals. The thickness of liquid crystals in each place of the liquid crystal cell is equal. The microstructures of the first liquid crystal chip 202 and the second liquid crystal chip 401 are both composed of super-pixels that are periodically repeated in space. Each super-pixel is divided into four sub-pixels of equal area, such as Figure 2 As shown. In each sub-pixel, the liquid crystal is uniformly oriented, and the director n is parallel to the surface. For the first liquid crystal chip 202 and the second liquid crystal chip 401, the angle between the liquid crystal director n in the sub-pixel i and the X-axis is (counterclockwise is positive) i 1 =51.69°, the angle between the liquid crystal director n and the X axis in sub-pixel ii is i 2 =164.88°, the angle between the liquid crystal director n and the X axis in sub-pixel iii is i 3 =128.31°, the angle between the liquid crystal director n and the X axis in sub-pixel iv is i 4=15.12°. The phase delay introduced by the first liquid crystal chip 202 and the second liquid crystal chip 401 is 228.19°.

[0023] In the direction along the optical axis, the photosensitive surfaces of the first liquid crystal chip 202, the sample, the second liquid crystal chip 401 and the light detector 502 are in optically conjugate positions; in the direction perpendicular to the optical axis, each sub-pixel of the first liquid crystal chip 202 and each super-pixel of the second liquid crystal chip 401 are in optically conjugate positions.

[0024] The light detector 502 may be a black and white camera. The image collected by the light detector 502 in one exposure can be used to calculate the spatial distribution of all Mueller matrix elements of the sample by the following method: In the XYZ coordinate system, the Mueller matrix of the first polarizer 201 is assumed to be M P1 , the Mueller matrix of the second polarizer 402 is M P2 , the Mueller matrix of each sub-pixel of the first liquid crystal chip 202 is , the Mueller matrix of each sub-pixel of the second liquid crystal chip 401 is , ( j =1,2,3,…,n), the Mueller matrix of the sample is M sample , the Stokes parameter of the light emitted by the monochromatic light source is S 0 , the light emitted from the sample is conjugated to the first liquid crystal chip 202 i The Stokes parameter of the sub-pixel light is (i=1,2,3,…,n), the light incident on the photosensitive surface of the light detector 502 is conjugate to the second liquid crystal chip 401 j The Stokes parameter of the light of a sub-pixel is (𝑗=1,2,3,…,n); The first element is I (j) , which can be detected by the light detector 502; ;set up The first behavior ,remember ; Then the Mueller matrix of the sample is M sample , the light intensity I can be measured by the light detector 502 (j) ( j =1,2,3,…,n) is calculated by the following formula ; in, yes M PSGThe Moore-Penrose pseudoinverse, ; yes M PSA The Moore-Penrose pseudoinverse.

[0025] The device only needs to use a single light detector for one exposure to complete sampling, and then calculate the spatial distribution of all Mueller matrices of the sample, with a fast measurement speed. The spatial resolution of the imaging of the measurement device is excellent, which can reach the theoretical upper limit of snapshot Mueller matrix polarization imaging technology (reducing the spatial resolution of the linear dimension by 4 times and increasing the measurement speed by 16 times). At the same time, M PSG and M PSA The condition numbers are all 1.73, so the measuring device has excellent measurement accuracy.

[0026] The embodiments described above can be further combined or replaced, and the embodiments are only descriptions of preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various changes and improvements made by ordinary technicians in this field to the technical solution of the present invention belong to the protection scope of the present invention. The protection scope of the present invention is given by the attached claims and any equivalents thereof.

Claims

1. A snapshot Mueller matrix polarization imaging device based on a light-oriented liquid crystal chip, characterized in that: It includes a light source unit, a polarization modulation unit, a sample measurement unit, a polarization demodulation unit, a light detector unit and a computer; The light source unit, polarization modulation unit, sample measurement unit, polarization demodulation unit and light detector unit are arranged in sequence along the light path direction; The light source unit is provided with a monochromatic light source and a first lens in sequence along the light path; the polarization modulation unit is provided with a first polarizer and a first liquid crystal chip in sequence along the light path; the light source unit and the polarization modulation unit generate polarized light whose polarization state is distributed in a specific manner in space; The sample measurement unit is provided with a second lens, a sample stage and a third lens in sequence along the optical path direction, and the sample is placed on the sample stage; The polarization demodulation unit is provided with a second liquid crystal chip and a second polarizer in sequence along the optical path; the light detector unit is provided with a fourth lens and a light detector in sequence along the optical path; the polarization demodulation unit and the light detector unit perform full Stokes polarization imaging on the signal light emitted by the sample measurement unit; In the direction of the optical path, the photosensitive surfaces of the first liquid crystal chip, the sample, the second liquid crystal chip and the photodetector are in optically conjugate positions; In a direction perpendicular to the optical path, each sub-pixel of the first liquid crystal chip and each super-pixel of the second liquid crystal chip are in an optically conjugate position; The computer is connected to the photodetector to collect the signal image detected by the photodetector; based on the image collected by the photodetector in one exposure, the computer calculates the spatial distribution of all Mueller matrix elements of the sample to achieve snapshot Mueller matrix polarization imaging.

2. The device according to claim 1, characterized in that The optical path of the device is defined in a right-hand rectangular coordinate system XYZ, wherein the principal optical axis is parallel to the Z axis, the positive direction of the Z axis is the light propagation direction, and the light transmission axis of the first polarizer is parallel to the X axis.

3. The device according to claim 1 or 2, characterized in that: The first liquid crystal chip and the second liquid crystal chip are both liquid crystal boxes with microstructures that are infused with nematic liquid crystals and are made using liquid crystal light-controlled orientation technology. The microstructures of the first liquid crystal chip and the second liquid crystal chip are both composed of superpixels that are periodically repeated in space, and each superpixel is divided into at least four sub-pixels of equal area. In each sub-pixel, the nematic liquid crystal is uniformly oriented along a specific direction, and the orientation directions of the liquid crystals are different in different sub-pixels.

4. The device according to claim 3, characterized in that The microstructures of the first liquid crystal chip and the second liquid crystal chip are composed of superpixels that are periodically repeated in space. Each superpixel is divided into four subpixels of equal area. In each subpixel, the liquid crystal is uniformly oriented, and the director n is parallel to the surface. For the first liquid crystal chip and the second liquid crystal chip, the angle between the liquid crystal director n in subpixel i and the X-axis is θ 1=51.69°, the angle between the liquid crystal director n and the X axis in sub-pixel ii is θ 2=164.88°, the angle between the liquid crystal director n and the X axis in sub-pixel iii is θ 3 = 128.31°, the angle between the liquid crystal director n and the X axis in sub-pixel iv is θ 4=15.12°; the phase delay introduced by the first liquid crystal chip 202 and the second liquid crystal chip 401 is 228.19°.

5. The device according to claim 1, characterized in that The light detector is an area array image sensor capable of capturing a complete two-dimensional image of signal light within one exposure cycle.

6. A measurement method using the snapshot Mueller matrix polarization imaging device based on a light-aligned liquid crystal chip as claimed in claim 1 or 2, characterized in that: The method comprises the steps of calculating the spatial distribution of all Mueller matrix elements of the sample using an image collected by the light detector through a single exposure: In the XYZ coordinate system, the Mueller matrix of the first polarizer is assumed to be M P1 , the Mueller matrix of the second polarizer is M P2 , the Mueller matrix of each sub-pixel of the first liquid crystal chip is , the Mueller matrix of each sub-pixel of the second liquid crystal chip is , j =1,2,3,…,n, the Mueller matrix of the sample is M sample , the Stokes parameter of the light emitted by the monochromatic light source is S 0 , the light emitted from the sample is conjugated to the first liquid crystal chip i The Stokes parameter of the sub-pixel light is , i =1,2,3,…,m, incident on the photosensitive surface of the photodetector conjugate to the second liquid crystal chip j The Stokes parameter of the light of a sub-pixel is , 𝑗=1,2,3,…,n; The first element is I (j) , which can be measured by a light detector; ;set up The first behavior ,remember ; Then the Mueller matrix of the sample is M sample , the light intensity I measured by the light detector (j) , j =1,2,3,…,n, calculated by the following formula ； in, yes M PSG The Moore-Penrose pseudoinverse, ； yes M PSA The Moore-Penrose pseudoinverse.

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