CN103472592A - Snapping type high-flux polarization imaging method and polarization imager - Google Patents

Abstract

The invention is a snapshot high-throughput polarization imaging method and a polarization imager. The polarization imager includes a front optical imaging system, a microlens array and an array polarization imaging detector. The microlens array is placed on the imaging surface of the front optical imaging system, and the array polarization imaging detector is placed on the focal plane of the microlens array. . The array polarized imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector pixel. The light emitted or reflected by the target in different directions is imaged on a microlens through the pre-optical imaging system, and the microlens disperses the received light of the target in different directions to each pixel of the array polarization imaging detector to form a sub-image , and finally obtain the images of each polarization angle of the target. The invention has the advantage of acquiring multiple polarization angle images of the target with one exposure, and can be applied to the monitoring and tracking of fast-changing or moving targets.

Description

A snapshot high-throughput polarization imaging method and polarization imager

technical field

The invention relates to optical imaging technology, in particular to a polarization imaging method and a polarization imager for realizing frame-style photography by using a light field imaging technology based on a microlens array and an array polarization imaging detector.

Background technique

Polarization imaging technology is the basis for obtaining the polarization information of the target image, and it is the premise of analyzing and identifying the target by using the polarization characteristics. At present, the polarization detection and analysis technology at home and abroad is mainly based on the Stokes vector analysis method. The polarization information detection based on this method needs to obtain at least three polarization angle images of the target. Different, polarization imaging technology is mainly divided into staring type and snapshot type. The staring polarization imaging technology realizes the acquisition of multiple polarization angle images of the target by switching the polarization element. It needs to stare at the target for a certain period of time to obtain different polarization image information through multiple exposures. It is required that the measured target and the instrument itself remain relatively still. The accuracy requirements are also high, and it is not suitable for the detection of moving or changing targets.

Snapshot polarization imaging technology refers to the acquisition of image information of multiple polarization angles of the target at the same time in one exposure, which has advantages in detecting moving or changing targets. Such techniques are mainly divided into: amplitude segmentation method, image plane segmentation method and aperture segmentation method. The amplitude division scheme is to use the light splitting element to divide the incident light to pass through different polarizers and be received by the corresponding detectors. Due to the use of multiple polarization imaging systems, this type of technology is costly and bulky, making it difficult to light and miniaturize. With the development of micro-processing technology, the image plane segmentation method has appeared. This method couples the polarizer array in front of the focal plane detector and directly images the target. This technology has an instantaneous field of view shift, and the accuracy of the polarization information is affected. The aperture division method is to use the subsequent optical system to form multiple target projection images, and make each image pass through different polarizers and then be received by the detector, so as to realize the detection of multiple polarization state information. The relay optical system of this system is complicated, which increases the design difficulty.

In recent years, a new type of computational imaging technology - light field imaging technology has emerged in the world. This technology combines the two-dimensional spatial distribution information of the target and the two-dimensional direction information of the geometric light propagation by adding a demodulation unit to the traditional optical imaging system. Recorded at the same time, the target information under different direction angles can be extracted, that is, the two-dimensional light intensity distribution of the target object, which has great advantages in information acquisition.

Literature [1] (R.Horstmeyer and et al., "Flexible multimodal camera using a light field architecture," International Conference on Computational Photography (2009)) uses pinhole arrays as modulation elements of light field imaging technology to combine multimodal filters The chip array is placed at the pupil of the front optical system, and the image information of different polarization angles of the target can be obtained in one shot. However, this technology has the following disadvantages: the luminous flux of the pinhole array is low, which increases the exposure time, and cannot be applied to fast-changing or moving targets; the physical diffraction spot of the pinhole array is large, and the utilization rate of the detector pixel is low.

Literature [2] (J.Tyo, "Hybrid division of aperture/division of a focal-plane polarimeter for real-time polarization imagery without an instantaneous field-of-view error," Optics Letter, 31(20), 2006) uses two A microlens array re-images the image on the imaging surface of the front optical system on the arrayed polarization imaging detector to obtain image information of different polarization angles of the target in real time. However, this technology has the following disadvantages: there is image crosstalk between adjacent picture elements; two microlens arrays are used, and the system complexity increases.

Contents of the invention

The technical problem to be solved by the present invention is to provide a snapshot-type high-throughput polarization imaging method and a polarization imager, which can obtain multiple polarization angle image information of a target in one shot, and be applied to the monitoring and tracking of rapidly changing or moving targets .

A snapshot type high-throughput polarization imager provided by the present invention includes a light field imaging mechanism based on a microlens array and an array polarization imaging detector, and the light field imaging mechanism includes a front optical imaging system and a microlens of the imaging system array. The front optical imaging system is composed of more than one lens; the microlens array is placed on the imaging surface of the front optical imaging system as a light field modulation unit; the array polarization imaging detector is placed on the focal plane of the microlens array, forming Light field imaging rear system. The array polarized imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector pixel.

A snapshot high-throughput spectral imaging method provided by the present invention includes step 1 to step 3.

Step 1, placing a microlens array on the imaging surface of the front optical imaging system; the F number of the microlenses in the micro lens array is equal to the equivalent F number of the front optical imaging system.

Step 2, place an array polarization imaging detector on the focal plane of the microlens array; the array polarization imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector image Yuan.

Step 3, the light emitted or reflected by the target in different directions is modulated by the pre-optical imaging system, and then imaged on a microlens on the microlens array. The microlens disperses the received light of the target in different directions into the array polarization Sub-images are formed on each pixel of the imaging detector, and finally a polarization angle image with a data cube size of (N _p , N _x , N _y ) is obtained, where N _p is the corresponding to the detector pixel covered by a microlens The number of polarization angles, (N _x , N _y ) is the obtained two-dimensional target resolution,

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

W _x and W _y are the length and width of the array polarization imaging detector, and d is the size of the microlens.

Each microlens in the microlens array in step 1 covers at least (M+2)×(M+2) picture elements, where 2M is the number of different polarization angles of the detection target.

Advantage and positive effect of the present invention are:

(1) The polarization imager and polarization imaging method of the present invention adopt a light field imaging mechanism based on a microlens array and an array polarization imaging detector, which has the advantage of obtaining multiple polarization angle images of the target with one exposure, and can be applied to rapid Monitoring and tracking of changing or moving targets.

(2) The polarization imager and polarization imaging method of the present invention use microlens arrays as light field modulation elements. Compared with small holes, microlenses have the advantages of high flux and low diffraction limit, which is conducive to improving the utilization rate of detector pixels , thereby improving the spatial resolution of the system.

(3) The polarization imager and polarization imaging method of the present invention use microlenses to cover multiple polarization detector pixels, avoiding the problem of image aliasing caused by diffraction and mechanical clamping and registration errors of adjacent microlenses.

Description of drawings

Fig. 1 is the schematic diagram of arrayed polarization imaging detector of the present invention;

Fig. 2 is the one-dimensional schematic diagram of the polarization imager of the present invention;

Fig. 3 is a schematic diagram of the positional relationship between the microlens and the detector;

FIG. 4 is a schematic flowchart of the polarization imaging method of the present invention.

Detailed ways

The present invention will be further described in detail with reference to the accompanying drawings and embodiments.

The present invention images the target on the plane where the microlens array is located through the front optical system, and each microlens corresponds to a pixel; each microlens images the aperture of the primary mirror onto the detector to form a macro pixel, and each pixel of the macro pixel Corresponding to a sampling sub-aperture of the lens, the detection result of each pixel is equivalent to the image formed by the target passing through the sampling sub-aperture; the detection result of the pixel coupled with polarizers with different polarization angles is equivalent to the image formed by the target passing through different polarization filters ; multiple microlenses corresponding to the same sub-aperture are coupled with the same polarizer angle, so that the image of a certain polarization angle of the target can be obtained by extracting the corresponding pixel. The invention has the advantage of completing data acquisition with one exposure, and the energy utilization rate of the microlens is much higher than that of the small hole, so it has the advantages of high flux and snapshot.

The snapshot high-throughput polarization imager provided by the present invention mainly includes a light field imaging mechanism based on a microlens array and an array polarization imaging detector. The light field imaging mechanism based on the microlens array includes a front optical system (main mirror) and a microlens array, and the microlens array is placed on the imaging surface of the front optical imaging system as a light field modulation unit. The array polarized imaging detector is composed of a CCD (Charge-coupled Device, charge-coupled device) detector array coupled with a linear polarizer array, each linear polarizer corresponds to a CCD detector pixel, as shown in Figure 1, the array The polarized imaging detector is placed on the focal plane of the microlens array to form a light field imaging rear system. As shown in Figure 1, a linear polarizer is arranged in front of each CCD detector pixel, and the polarization angle of the linear polarizer can be set by the user according to needs. The preferred setting method of the present invention is: each upper left, upper right The polarization angles of the four adjacent linear polarizers, the lower left and the lower right are 0 degree, 45 degree, 135 degree and 90 degree respectively.

In the embodiment of the present invention, the front optical imaging system is a transmission imaging system, which may also be realized by a reflection imaging system. As shown in Figure 2, it is a schematic diagram of the one-dimensional principle of the polarization imager of the present invention, the front optical imaging system is simplified as an ideal lens at the pupil of the front lens of the light field imaging mechanism, as shown in Figure 2 primary mirror. The target is imaged on a microlens on the microlens array through the pre-optical imaging system, and the microlens disperses the received light from different directions of the target to the pixel of the detector behind the microlens to form a sub-image , the target image acquired by each detector pixel corresponds to the light energy radiation of the target in different directions. Due to the modulation effect of the linear polarizer coupled to the detector, the light energy radiation of the target in different directions is modulated into light of a specific linear polarization angle, so each pixel of the detector obtains the light energy of a specific linear polarization angle of the target radiation. The polarization information of the target in different polarization directions can be obtained by coupling linear polarizers with different polarization directions (that is, micro-polarization filters) in front of the detector pixels. When the target expands to a two-dimensional target, it is imaged on the imaging surface where the microlens array is located through the pre-optical imaging system, and each microlens corresponds to a spatial unit of the target imaged, so the spatial two-dimensional information of the target can be obtained. At the same time, due to the modulation effect of the microlens, the pixel of the subsequent array polarization imaging detector acquires the radiation information of the light at different linear polarization angles in the spatial unit of the target, and extracts a certain value in the sub-image formed by each microlens. The pixel corresponding to the polarization angle can acquire the polarization image of the target at the polarization angle. By combining multiple images with different polarization angles, the complete polarization angle image information of the target can be obtained.

In the present invention, the F number of each microlens of the microlens array is equal to the effective F number of the front optical imaging system, and the detector is placed at the focal plane of the microlens array. As shown in Figure 2, L is the distance from the equivalent pupil of the front optical system to the image of the target, and f is the focal length of the microlens. The coverage imaging range d of the microlens on the detector is the diameter of the circular microlens or the width of the square microlens. For the design scheme of collecting four polarization angles, in order to effectively use the pixels of the detector and prevent aliasing between the sub-images generated by adjacent microlenses, the design scheme shown in Figure 1 is adopted, and only the microlenses are actually extracted. The four pixels covered by the central part of the lens are shown in Figure 3.

An embodiment of the imaging spectrometer of the present invention is shown in Figure 1, wherein the array type polarization imaging detector that the present invention adopts is placed at the focal plane of the microlens array, and the array type polarization imaging detector is composed of a plurality of different directions The linear polarizers are arranged according to a certain rule and then coupled with the CCD detector pixel. The arrangement is shown in Figure 1. In actual use, parameters such as the type, size, polarization angle and arrangement scheme of the array polarization imaging detector can be set according to needs. The arrangement scheme of the microlens array, the shape, size and focal length of the microlens are also set according to actual needs.

In the embodiment of the present invention, the microlens array is placed on the image plane where the target is imaged by the front optical imaging system, and one microlens in the microlens array corresponds to a pixel of the target imaged by the front optical imaging system, so The spatial resolution of an imaging spectrometer is determined by the number of microlenses in the microlens array, which is determined by the size of the detector and the size of the microlenses:

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>$

Among them, W _x and W _y are the length and width of the detector, d is the size of the microlens, if the microlens is circular, then d is the diameter of the microlens, if the microlens is square, then d is the diameter of the square microlens width. Finally, the resolution of the two-dimensional target obtained by the polarization imager is (N _x , N _y ).

As shown in Figure 4, the snapshot high-throughput spectral imaging method provided by the present invention is:

Step 1, placing a microlens array on the imaging surface of the front optical imaging system to form a light field imaging mechanism. The F number of the microlenses in the microlens array is equal to the equivalent F number of the front optical imaging system.

Step 2, placing an array polarization imaging detector on the focal plane of the microlens array. The array polarized imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector pixel.

Step 3, the light emitted or reflected by the target in different directions passes through the main mirror and is imaged on a microlens on the microlens array, and the microlens disperses the received light of the target in different directions to the array polarization imaging detector Sub-images with different polarization angles are formed on the pixels of the , and finally multiple target images with a size of (N _x , N _y ) and different polarization angles are obtained. in,

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

W _x and W _y are the length and width of the detector, and d is the size of the microlens.

Use three-dimensional cube data to represent the polarization angle image obtained, expressed as (N _p , N _x , N _y ), N _p is the number of polarization angles corresponding to the detector pixel covered by a microlens, for example, using the figure of the present invention In the embodiment shown in 1, N _p is 4, target images of 4 polarization angles can be obtained, and the resolution of each target image is (N _x , N _y ).

The present invention adopts each microlens to cover at least M×M picture elements, and 2M is the number of different polarization angles of the target detected by the system. Taking the 4 polarization angles in Fig. 1 as an example, the microlens covers at least 2×2 picture elements, such as Figure 3 shows. In order to avoid the aliasing of adjacent microlens images caused by errors such as mechanical installation, the present invention sets that each microlens covers at least (M+2)×(M+2) pixels, taking 4 polarization angles as an example, Microlenses cover at least 4×4 pixels.

Claims (5)

1. A snapshot high-throughput polarization imager, characterized in that it comprises a light field imaging mechanism based on a microlens array and an arrayed polarization imaging detector, and the light field imaging mechanism includes a front optical imaging system of an imaging system and Microlens array; the front optical imaging system is composed of more than one lens; the microlens array is placed on the imaging plane of the front optical imaging system as a light field modulation unit; the array polarized imaging detector is placed at the focal point of the microlens array On the plane, a light field imaging rear system is formed; the array polarization imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector pixel. 2. The snap-shot high-throughput polarization imager according to claim 1, characterized in that, in the linear polarizer array, four adjacent ones of each upper left, upper right, lower left and lower right are set The polarization angles of the linear polarizers are 0 degree, 45 degree, 135 degree and 90 degree respectively. 3. A snapshot high-throughput polarization imaging method, comprising the steps of: Step 1, placing a microlens array on the imaging surface of the front optical imaging system; the F number of the microlens in the microlens array is equal to the equivalent F number of the front optical imaging system; Step 2, place an array polarization imaging detector on the focal plane of the microlens array; the array polarization imaging detector is formed by coupling a CCD detector array and a linear polarizer array, and each linear polarizer corresponds to a CCD detector image Yuan; Step 3, the light emitted or reflected by the target in different directions is modulated by the pre-optical imaging system, and then imaged on a microlens on the microlens array. The microlens disperses the received light of the target in different directions into the array polarization Sub-images are formed on each pixel of the imaging detector, and finally a polarization angle image with a data cube size of (N _p , N _x , N _y ) is obtained, where N _p is the corresponding to the detector pixel covered by a microlens The number of polarization angles, (N _x , N _y ) is the obtained two-dimensional target resolution, $<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ W _x and W _y are the length and width of the array polarization imaging detector, and d is the size of the microlens. 4. The snapshot-type high-throughput polarization imaging method according to claim 3, characterized in that, in the linear polarizer array of the array polarization imaging detector placed in the step 2, each upper left and upper right The polarization angles of the four adjacent linear polarizers, the lower left and the lower right are 0 degree, 45 degree, 135 degree and 90 degree respectively. 5. The snapshot-type high-throughput polarization imaging method according to claim 3, characterized in that, in the microlens array in step 1, each microlens is set to at least cover (M+2)×(M +2) pixels, where 2M is the number of different polarization angles of the detection target.

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