CN115265781B - System and method for rapidly acquiring plane array polarized spectrum image - Google Patents

Abstract

A fast array polarization spectrum image acquisition system and method, belonging to the field of optoelectronic imaging technology, in order to solve the problems existing in the prior art, the system is composed of a beam reduction unit, a collimating compensating mirror, a microlens array, a correction lens group, a filter, an isolation plate, a focal plane polarization detector and an image processing module; the beam reduction unit, the collimating compensating mirror, the microlens array, the correction lens group, the filter, the isolation plate, the focal plane polarization detector are coaxially arranged in sequence, and the focal plane polarization detector is electrically connected to the image processing module; the present invention divides the light field into 16 parts through the microlens array, each corresponding to a spectrum segment, and then uses the focal plane polarization detector to quickly collect the target image, so that the polarization images under 16 spectrum segments can be obtained at the same time by taking a picture, and the two-dimensional image information of the detection target can be directly and quickly obtained by using the array imaging method. It is more suitable for high-speed motion missile-borne platforms with strict requirements on volume, weight and power consumption.

Description

A fast area array polarization spectrum image acquisition system and method

Technical Field

The invention belongs to the technical field of photoelectric imaging, and in particular relates to a fast array polarization spectrum image acquisition system and method.

Background technique

The seeker is the core component of precision-guided weapons. Precision-guided weapons measure the deviation parameters of the weapon from the ideal motion trajectory through the rangefinder, gyroscope or electronic stabilization device installed on the seeker, use the deviation parameters to form control instructions, and transmit the instructions to the actuator on the missile to control and stabilize the flight of the missile, ultimately achieving precision strikes.

The seeker follows the missile at a fast speed, with limited space and high time resolution requirements. In order to obtain target position information, a fast array polarization spectral image acquisition method is urgently needed. The existing spectral polarization imaging mechanisms mainly include two categories in terms of time resolution: time-sharing and simultaneous. The time-sharing system mainly uses rotating polarizing elements, acousto-optic tunable filters, liquid crystals and other mechanisms, which have poor target observation effects on moving platforms. In the traditional simultaneous acquisition method, although the time resolution is met, the system size is large and the power consumption is high, which is not suitable for the guidance device. At present, there is no fast array polarization spectral image acquisition method suitable for the seeker proposed at home and abroad.

Summary of the invention

In order to solve the problems existing in the prior art, the present invention proposes a fast array polarization spectrum image acquisition system and method. The method does not require moving parts and complex solution methods, which improves the reliability and stability of the system. The present invention uses the fast array polarization spectrum image acquisition method based on light field segmentation coding to enable an optical seeker to quickly acquire target position information to achieve positioning and tracking.

A method for acquiring a fast planar array polarization spectrum image, characterized in that the method comprises the following steps:

Step 1: Build the system, coaxially arrange the beam reduction unit, collimation compensation mirror, microlens array, correction lens group, filter, isolation plate, and focal plane polarization detector, and electrically connect the focal plane polarization detector to the image processing module.

Step 2: The beam reduction unit composed of the Cassegrain system compresses the light. The Cassegrain primary mirror compresses the large-aperture incident light by a certain factor, and the Cassegrain secondary mirror collimates the compressed small-aperture light to obtain small-aperture parallel light.

Step 3: The 4×4 microlens array receives the small-aperture parallel light beam and performs light field segmentation on the small-aperture parallel light beam to form 16 beams of light with the same aperture and converge them.

Step 4: The center of the 4×4 spectral array coincides with the optical axis of the 4×4 microlens array. After the splitting, each beam of light passes through the corresponding filter. The filtering ranges of the 16 filters are different, thus obtaining 16 spectral channels.

Step 5: The light beam of each spectral channel is focused onto different areas of the focal plane detector, and the detector is used to obtain the corresponding 0°, 45°, 90°, and 135° linear polarization images and angular polarization images under different spectral channels.

Step 6: Use the image processing module to solve the polarization image and obtain the polarization degree map and polarization angle map of the detection target.

A fast area array polarization spectrum image acquisition system, which consists of a beam reduction unit, a collimating compensation mirror, a microlens array, a correction mirror group, a filter, an isolation plate, a focal plane polarization detector and an image processing module; the beam reduction unit, the collimating compensation mirror, the microlens array, the correction mirror group, the filter, the isolation plate, and the focal plane polarization detector are coaxially arranged in sequence, and the focal plane polarization detector is electrically connected to the image processing module;

The target light beam is incident on the beam reduction unit to compress the light beam and then emit a small-aperture parallel light beam through the collimating compensation mirror. The microlens array receives the small-aperture parallel light beam and performs light field splitting on it to divide it into 16 small-aperture light beams; the light path is then corrected and the aberration is reduced through the correction lens group. The filter performs spectral filtering on the 16 small-aperture light beams to generate 16 spectral channels. The center of each filter coincides with the optical axis of the microlens array lens group to ensure the coaxial structure. Finally, it is focused on the corresponding 16 areas on the focal plane polarization detector. The focal plane polarization detector is used to simultaneously obtain information in the four polarization directions of 0°, 45°, 90°, and 135°, so that the image processing module can be used to solve 16 polarization images of different spectral bands in real time.

Beneficial effects of the present invention:

The present invention divides the light field into 16 parts through a microlens array, each part corresponds to a spectral band, and then uses a split-focus plane polarization detector to quickly collect the target image, so as to obtain polarization images in 16 spectral bands at the same time in one shot, and uses a planar array imaging method to directly and quickly obtain two-dimensional image information of the detection target.

The present invention does not require moving parts and complex solution methods, which improves the reliability and stability of the system. The system has a compact structure, uses a single detector to obtain multi-dimensional methods and improves the speed of data processing. Compared with traditional systems, it does not require multi-dimensional information de-aliasing.

The imaging of the present invention is highly real-time and can ensure that the tracked target is not lost, and has better tracking stability. Secondly, the system has little loss in resolution, which improves the recognition of target details. The system completes the collection of the light beam reflected by the target object and the light beam emitted by the target itself, realizes the real-time acquisition of polarization spectrum images, and finally processes the acquired polarization spectrum images. Therefore, the fast array polarization spectrum image acquisition mechanism is more suitable for high-speed moving missile-borne platforms with strict requirements on volume, weight, and power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described below with reference to the accompanying drawings and specific embodiments:

FIG. 1 is a schematic diagram showing the composition of a fast planar array polarization spectrum image acquisition system of the present invention.

FIG. 2 is a diagram of a microlens array according to the present invention.

FIG. 3 is a structural diagram of the correction lens assembly of the present invention.

FIG. 4 is a schematic diagram of spectral channel coding of the filter array according to the present invention.

FIG. 5 is a diagram showing an actual detector pixel usage area according to the present invention.

FIG. 6 is a flowchart of a method for acquiring a fast planar array polarization spectrum image according to the present invention.

In Figure 1: 1. beam reduction unit, 2. collimating compensation mirror, 3. microlens array, 4. correction lens group, 5. filter, 6. isolation plate, 7. focal plane polarization detector, 8. image processing module.

Detailed ways

The present invention is further described below in conjunction with the accompanying drawings.

As shown in FIG1 , a fast area array polarization spectrum image acquisition system is composed of a beam reduction unit 1, a collimating compensation mirror 2, a microlens array 3, a correction lens group 4, a filter 5, an isolation plate 6, a focal plane polarization detector 7 and an image processing module 8; the beam reduction unit 1, the collimating compensation mirror 2, the microlens array 3, the correction lens group 4, the filter 5, the isolation plate 6, and the focal plane polarization detector 7 are coaxially arranged in sequence, and the focal plane polarization detector 7 is electrically connected to the image processing module 8;

The beam reduction unit 1 is composed of a Cassegrain system, and the surface shapes of the Cassegrain primary mirror and the secondary mirror are both hyperbolic. The primary mirror compresses the large-diameter beam into a small-diameter beam with a compression ratio of 6.8 times, and the secondary mirror collimates the small-diameter beam to obtain a small-diameter parallel beam.

The collimating compensating lens 2 is a double-cemented lens, and all the surfaces of the double-cemented lens are spherical. The collimating compensating lens is used to compensate for the aberration of a small-aperture parallel light beam and reduce the influence of the fairing on the imaging quality of the subsequent system.

As shown in FIG2 , the microlens array 3 is arranged in 4×4, and every two adjacent microlenses are equally spaced. The parameters of each microlens are consistent with the surface shape, and all are plano-convex lenses. The microlens array performs light field splitting on the incident small-aperture parallel light beam to obtain 16 beams of uniform aperture, with a beam aperture of 1.38 mm. The light field splitting forms 16 beams of light and performs imaging separately to achieve simultaneous acquisition of multiple images.

As shown in FIG3 , the correction mirror 1 4-1 of the correction mirror group is a convex-concave lens with a spherical surface. The correction mirror 2 4-2 is a convex-concave lens with a spherical surface. The correction mirror 3 4-3 is a double convex lens with a spherical surface. The functions of the correction mirror 1 4-1, the correction mirror 2 4-2 and the correction mirror 3 4-3 are: first, to correct the optical path so that each microlens can form a corresponding image; second, to correct aberrations. The aberrations corresponding to each channel of the microlens array are not consistent, so a correction lens is needed to correct the aberrations so that the aberrations of each channel are controlled within an acceptable range; and also to compensate for the optical focal length. The optical focal lengths of the correction mirror 1 4-1, the correction mirror 2 4-2 and the correction mirror 3 4-3 compensate each other to ensure the total optical focal length of the entire system.

The filter 5 is a 4×4 filter array, corresponding to the front 4×4 microlens array. The filter array is coaxial with each channel of the microlens array. Each channel of the filter array is coated with 16 thin films with different spectral bands to generate 16 spectral channels, as shown in FIG4 .

The isolation plate 6 is used to physically isolate the focal plane polarization detector 7. As shown in Figure 5, there will be a gap of 100 pixels between the detector areas corresponding to each channel. In order to avoid imaging aliasing between channels, it is necessary to design an isolation plate 6 to isolate each area of the focal plane polarization detector 7. The isolation plate is in a mesh shape, with a width of 100 pixels and a height of 5 mm.

In order to focus the 16 beams on the detector without image aliasing, the focal plane polarization detector 7 needs to be designed to ensure that there is a 100-pixel space between the 16 regions on the focal plane polarization detector 7; the detector target surface is divided into 4 equal parts horizontally and vertically, and each spectrum segment occupies 400×400 pixels. The actual detector pixel usage area is shown in Figure 5 below.

The target light beam is incident on the beam reduction unit 1 to compress the light beam and then pass through the collimating compensation mirror 2 to emit a small-aperture parallel light beam. The microlens array 3 receives the small-aperture parallel light beam and performs light field splitting on it, dividing it into 16 small-aperture light beams. Then the correction lens group 4 corrects the optical path and reduces the aberration. The filter 5 performs spectral filtering on the 16 small-aperture light beams to generate 16 spectral channels. The center of each filter 5 coincides with the optical axis of the microlens array lens group 4 to ensure the coaxial structure. Finally, it is focused on the corresponding 16 areas on the focal plane polarization detector 7. The focal plane polarization detector 7 is used to simultaneously obtain information on the four polarization directions of 0°, 45°, 90°, and 135°, so that the image processing module 8 can be used to solve the polarization images of 16 different spectral bands in real time.

Embodiment: A fast array polarization spectrum image acquisition system has an operating band of 450-706nm, which can be used for an optical seeker to quickly obtain target position information to achieve positioning and tracking. Since the system is used for an optical seeker, a fairing is added to the front end of the entire system. The fairing surface is spherical, and the two surfaces of the fairing have the same curvature radius and a caliber of 160mm. It is used to ensure the aerodynamic layout of the warhead, and on the premise of ensuring the optical performance of the system, it greatly improves the aerodynamic performance of the high-speed flying warhead, improves the environmental adaptability of the optical system, and meets the requirements of supersonic flight.

Normalizing the focal length to 1, the optical system structural parameters are shown in Table 1:

Table 1 Optical structure parameters

Technical indicators:

The system entrance pupil diameter is 100mm. The wavelength range of light passing through the Cassegrain system is 450-706nm and the output light is required to be parallel light. The total focal length of the system is 175mm, the half field of view angle is 0.057°, the microlens array is 4×4 units, and there are 16 channels in total. The wavelength range of the output light of the Cassegrain system is divided into 16 equal parts and incident on 16 channels, and each channel corresponds to a wavelength width of 16nm.

The microlens array 3 is used to realize the segmentation of the light field, and the microlens array is placed in the parallel light path. Therefore, in order to ensure that the light beam passing through the microlens array corresponds to the imaging area of the polarization detector, the size of the microlens array is required to be equivalent to the size of the detector target surface, and the size of each microlens unit is required to correspond to the size of each imaging area of the detector.

In addition, since the microlens has the function of focusing, the curvature of each microlens unit needs to be molded according to the optical design results. Each microlens corresponds to 400×400 pixels, and each pixel is 3.45um, so the aperture of each microlens unit is about 2mm. According to the 4×4 layout, considering the structural gap between the microlens units, the size of the microlens array is about 10mm×10mm, which is equivalent to the size of the detector target surface.

The filter array adopts a 4×4 layout, with a total of 16 channels, and the spectrum covers the visible light band of 450-706nm. The width of each spectral channel is 16nm. Each spectral channel needs to be encoded to obtain spectral images of 16 different spectral bands at the same time. The size of the filter array is comparable to that of the microlens array, about 10mm×10mm.

The bottom surface in Figure 4 is the detector surface, and the relationship between the filter code, spectrum band and corresponding pixel coordinates is shown in the following table.

Table 2 Spectral channel encoding

Serial number Spectrum Corresponding detector pixel coordinates 1 450nm～466nm X(100～500), Y(100～500) 2 466nm～482nm X(600～1000), Y(100～500) 3 482nm～498nm X(1100～1500), Y(100～500) 4 498nm～514nm X(1600～2000), Y(100～500) 5 514nm～530nm X(100～500), Y(600～1000) 6 530nm～546nm X(600～1000), Y(600～1000) 7 546nm～562nm X(1100～1500), Y(600～1000) 8 562nm～578nm X(1600～2000), Y(600～1000) 9 578nm～594nm X(100～500), Y(600～1000) 10 594nm～610nm X(600～1000), Y(100～500) 11 610nm～626nm X(1100～1500), Y(100～500) 12 626nm～642nm X(1600～2000), Y(100～500) 13 642nm～658nm X(100～500), Y(100～500) 14 658nm～674nm X(600～1000), Y(100～500) 15 674nm～690nm X(1100～1500), Y(100～500) 16 690nm～706nm X(1600～2000), Y(100～500)

As shown in FIG6 , a method for acquiring a fast planar array polarization spectrum image includes the following steps:

Step 1: Build the system, coaxially arrange the beam reduction unit, collimation compensation mirror, microlens array, correction lens group, filter, isolation plate, and focal plane polarization detector, and electrically connect the focal plane polarization detector to the image processing module.

Step 2: The beam reduction mirror group composed of the Cassegrain system uses a large-aperture primary mirror to collect target information, and then compresses the light. The Cassegrain primary mirror compresses the large-aperture incident light by a certain ratio, and the Cassegrain secondary mirror collimates the compressed small-aperture light to obtain small-aperture parallel light.

Step 3: The 4×4 microlens array receives the small-aperture parallel light beam and performs light field segmentation on the small-aperture parallel light beam to form 16 beams of light with the same aperture and converge them.

Step 4: The center of the 4×4 spectral array coincides with the optical axis of the 4×4 microlens array. After the splitting, each beam of light passes through the corresponding filter. The filtering ranges of the 16 filters are different, thus obtaining 16 spectral channels.

Step 5: The light beam of each spectral channel is focused onto different areas of the focal plane detector, and the detector is used to obtain the corresponding 0°, 45°, 90°, and 135° linear polarization images and angular polarization images under different spectral channels.

Step 6: Use the image processing module to solve the polarization image and obtain the polarization degree map and polarization angle map of the detected target. The image processing unit is used to automatically and quickly find the image with the most obvious target contrast from the 96 images of polarization degree maps of 16 spectral channels and polarization angle maps of 16 spectral channels and polarization maps of four linear polarization directions corresponding to each spectral channel, and accurately identify and extract the target through the fast fusion reconstruction enhancement algorithm, thereby improving the target detection rate in complex battlefield environments.

Claims (6)

1. The rapid area array polarization spectrum image acquisition system is characterized by comprising a fairing, a beam shrinking unit, a collimation compensation mirror, a micro lens array, a correction mirror group, an optical filter, a separation plate, a focal plane polarization detector and an image processing module; the beam shrinking unit, the collimation compensation mirror, the micro lens array, the correction mirror group, the optical filter, the isolation plate and the focal plane polarization splitting detector are coaxially arranged in sequence, and the focal plane polarization splitting detector is electrically connected with the image processing module; the beam shrinking unit consists of a blocking lattice Lin Jitong, and both the blocking lattice Lin Zhujing and the secondary mirror are hyperboloid surfaces; the correcting lens group comprises a correcting lens I, a correcting lens II and a correcting lens III;

the target light beam is incident into the beam shrinking unit to compress the light beam and then the light beam passes through the collimation compensation mirror to emit a small-caliber parallel light beam, and the micro lens array receives the small-caliber parallel light beam and carries out light field light splitting on the small-caliber parallel light beam to divide the light field into 16 small-caliber light beams; correcting the optical path through a correction lens group, reducing aberration, performing spectral filtering on 16 small-caliber light beams by using optical filters to generate 16 spectral channels, and enabling the center of each optical filter to coincide with the optical axis of the micro lens array lens group so as to ensure the coaxial structure; utilizing a reticular isolation plate to physically isolate each region of the focal plane polarization detector; finally, focusing on 16 corresponding areas on the focal plane polarization detector, and simultaneously acquiring information of four polarization directions of 0 degree, 45 degrees, 90 degrees and 135 degrees by using the focal plane polarization detector, so that 16 polarized images in different spectral bands are calculated in real time by using an image processing module; automatically and quickly searching an image with the most obvious target contrast, and accurately identifying and extracting the target through a quick fusion reconstruction enhancement algorithm, so that the target detection rate in a complex battlefield environment is improved;

the optical parameters of the system are as follows:

2. the system of claim 1, wherein the primary mirror compresses the large-caliber light beam into a small-caliber light beam, and the secondary mirror collimates the small-caliber light beam to obtain a small-caliber parallel light beam.

3. The system of claim 1, wherein the collimation compensation lens is a double-cemented lens, and all surface forms of the double-cemented lens are spherical surfaces; the collimation compensation mirror is used for compensating aberration of the small-caliber parallel light beam, and reducing influence of the fairing on imaging quality of a subsequent system.

4. The rapid area array polarized light spectrum image acquisition system according to claim 1, wherein the microlens array is arranged in a 4 x 4 arrangement, and every two adjacent microlenses are equally spaced; each micro lens has the same parameters as the surface shape and is a plano-convex lens; the micro lens array performs light field splitting on the incident small-caliber parallel light beams to obtain 16 light beams with the same caliber, and the 16 light beams are formed by the light field splitting to respectively image so as to realize simultaneous acquisition of a plurality of images.

5. The system of claim 1, wherein the filter is a 4 x 4 array of filters corresponding to a front 4 x 4 array of microlenses; the filter array is coaxial with each channel of the microlens array; each channel of the filter array is respectively plated with 16 films with different spectral ranges to generate 16 spectral channels.

6. The rapid area array polarized spectral image acquisition system of claim 1, wherein 16 areas on the split focal plane polarization detector are spaced apart by 100 pixels; the detector target surface is divided into 4 parts in the transverse direction and the longitudinal direction, and each spectrum occupies 400×400 pixels.