APD laser radar real-time polarization imaging method and system

Abstract

The invention discloses an APD laser radar real-time polarization imaging system, and relates to the technical field of laser radars. In order to solve the problems that an existing active polarization laser radar system is insufficient in image fusion precision and difficult to fuse with a focal plane polarization imaging mechanism, the invention provides a system based on a secondary imaging structure. The system comprises a laser emission subsystem, a polarization imaging subsystem and an APD (avalanche photo diode) detector, a micro-polaroid array is arranged on a primary image surface and is projected to the APD array detector through a rear relay lens group, and synchronous acquisition and pixel registration of a polarization image and a distance image are realized. The method is suitable for high-contrast real-time detection and imaging application of a camouflage target in a complex environment.

Description

Technical Field

[0001] It relates to the field of lidar technology, and particularly to a real-time polarization imaging method and system for APD lidar. Background Technique

[0002] Lidar (LiDAR) is an active remote sensing technology that obtains information such as the distance, shape, and motion of a target by emitting a laser beam and receiving its reflected echo, and is widely used in fields such as intelligent driving, remote sensing mapping, target recognition, and military detection. In recent years, with the complication of the detection task environment and the enhancement of target concealment, traditional lidar faces problems such as insufficient recognition ability for weak targets and camouflaged targets and being easily affected by strong background light. The polarization imaging mechanism can improve the imaging contrast of the target in a complex environment and can suppress the influence of the stray light background, and can effectively improve the target recognition ability of traditional lidar. Therefore, lidar technology is gradually developing towards multi-dimensional perception, and integrating information such as intensity, distance, and polarization has become an important trend in technology development.

[0003] In this context, active polarization imaging lidar has become one of the research hotspots. Different from passive polarization imaging systems, active polarization lidar uses a laser with a specific polarization state at the transmitting end and extracts polarization information at the receiving end, thereby enhancing the recognition ability of target material, surface structure and other characteristics. For example, some studies use a rotating polarizer or a liquid crystal polarization modulator in cooperation with a CCD detector to obtain images of different polarization states; some other schemes integrate multiple polarization detection channels to achieve time-sharing or parallel imaging. In addition, the split focal plane polarization imaging mechanism usually integrates a micro-polarizer array into the detector target surface position to obtain polarized light in four directions of 0°, 45°, 90°, and 135°, so as to obtain the polarization image of a dynamic target in real time for tasks such as camouflaged target recognition, material classification, and surface roughness estimation.

[0004] However, the existing active polarization lidar systems still have the following technical bottlenecks: First, most systems still use traditional CCD or CMOS cameras as detectors, making it difficult to synchronously obtain time-of-flight ranging and polarization imaging, resulting in insufficient image fusion accuracy; Second, although lidar using APD (avalanche photodiode) as a detector has single-photon detection ability, traditional polarization imaging lidar usually uses the method of setting a rotating polarizer at the laser transmitting end to obtain linearly polarized lasers in different directions, and performs secondary polarization modulation on the laser echo through a rotating polarizer at the receiving end to obtain target polarization information. This scheme has poor real-time performance and is difficult to meet the real-time active polarization imaging requirements of dynamic targets. Moreover, limited by the detector structure, it is difficult to effectively integrate with the split focal plane polarization imaging mechanism; Third, most of the existing micro-polarizer array devices need to customize the detector package, with high cost and poor flexibility, which limits their large-scale application in lidar systems.

[0005] Therefore, how to achieve the efficient integration of the APD lidar system and the split focal plane polarization imaging mechanism, and simultaneously obtain the intensity image, polarization image, distance image and three-dimensional image while ensuring high temporal and spatial resolutions, so as to improve the real-time recognition ability of camouflaged targets in complex backgrounds, has become a key technical problem urgently to be solved in this field. Summary of the Invention

[0006] To solve the technical bottleneck problems of insufficient image fusion accuracy in the existing active polarization lidar system and the difficulty in achieving effective integration with the split focal plane polarization imaging mechanism, the technical solution provided by the present invention is as follows: An APD lidar real-time polarization imaging system, comprising: A laser emission subsystem, including a laser and a beam expander. The laser is used to emit pulsed laser signals, and the beam expander is arranged on the outgoing light path of the laser for collimating and expanding the pulsed laser signals. A polarization imaging subsystem, including a filter, a front objective lens group, a micro-polarizer array module, a rear relay lens group and an APD detector; The filter is arranged at the front end of the system for filtering out stray light in the pulsed laser signals; The front objective lens group is arranged on the outgoing light path of the filter for shaping the received echo beam and forming a primary image; The micro-polarizer array module is arranged at the image plane position of the primary image for modulating the polarization information of the primary image to obtain polarized light in multiple directions; The rear relay lens group is arranged on the outgoing light path of the micro-polarizer array module for projecting the primary image to the secondary image plane position; The APD detector is arranged at the secondary image plane position for receiving the modulated polarization image and outputting the original data of intensity and time information.

[0007] Furthermore, a preferred embodiment is provided, which further includes a control and information processing subsystem for controlling the trigger timing of the laser and synchronizing with the APD detector.

[0008] Furthermore, a preferred embodiment is provided. The control and information processing subsystem includes a signal generator and a main control computer. The signal generator is used to control the trigger timing of the laser and synchronize with the APD detector, and the main control computer is used to coordinately control each component and perform image calculation and fusion processing on the received data.

[0009] Further, a preferred embodiment is provided, where the micro-polarizer array module includes a circular protective glass, a micro-polarizer array, and a square protective glass, which are arranged in sequence from the object side to the image side.

[0010] Further, a preferred embodiment is provided, where the micro-polarizer array module acquires polarization images in four directions of 0°, 45°, 90°, and 135°.

[0011] Further, a preferred embodiment is provided, where the central wavelength of the filter is 1064 nm, the filtering bandwidth is ±1 nm, and the thickness is 3 mm.

[0012] Based on the same inventive concept, the present invention also provides a method for real-time polarization imaging of an APD lidar, which is implemented based on the described system and includes: The step of sending a control signal to drive a signal generator to generate a pulse trigger signal; The step of using the trigger signal to start the laser to emit 1064 nm pulsed laser, and at the same time controlling the opening of the gating of the APD detector to keep it synchronized with the laser emission timing; The step of expanding the laser signal and irradiating it onto the target, receiving its echo signal, filtering out stray light in non-working wavelength bands through a filter, and forming a primary image through a front objective lens group; The step of performing polarization information modulation on the primary image, acquiring polarization light images in multiple directions, and projecting them onto a secondary image plane to form polarization image data; The step of collecting the intensity and time raw data from the APD detector and receiving the data stream; The step of analyzing the raw data and calculating and generating corresponding intensity images, polarization images, distance images, and three-dimensional images; The step of performing image fusion operation according to the pixel matching relationship between the polarization image and the distance image and outputting a high-contrast fusion image.

[0013] Based on the same inventive concept, the present invention also provides a computer storage medium for storing a computer program, and when the computer program is read by a computer, the computer executes the described method.

[0014] Based on the same inventive concept, the present invention also provides a computer, which includes a processor and a storage medium, and when the processor reads the computer program stored in the storage medium, the computer executes the described method.

[0015] Based on the same inventive concept, the present invention also provides a computer program product, which is a computer program, and when the computer program is executed, the described method is implemented.

[0016] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: By arranging the micro-polarizer array module at the position of the primary image plane of the optical system and combining it with the subsequent relay lens group for secondary imaging, the integration of the APD lidar system and the split focal plane polarization imaging mechanism is effectively achieved. Compared with the traditional design method of directly integrating the micro-polarizer into the detector or placing it at the end of the optical path, this solution performs imaging projection after modulating the polarization information at the primary image plane, not only avoiding the problem of inadaptability of the APD structure, but also retaining the high time resolution characteristic, so as to achieve high-precision distance measurement while obtaining the polarization image, and improving the system's recognition ability for camouflaged targets.

[0017] By adopting the micro-polarizer array module in an independent packaging form, the problems of high cost and low versatility brought by the need to integrate and package the micro-polarization array device with the detector in the prior art are solved. This module is composed of a protective glass and a micro-polarizer, has good sealing performance and replaceability, strong adaptability, and can be widely used in any optical system with a secondary imaging structure. Compared with the existing solutions that rely on customized packaging of detectors, this structural design greatly improves the flexibility of engineering implementation and the system versatility.

[0018] The system uses a 1064nm wavelength laser in cooperation with a filter with high transmittance and low stray light and a high-quality front objective lens group, so that the incident echo signal has good wavelength selectivity and imaging clarity. Compared with the traditional system without filtering or using a broadband filter, this solution effectively suppresses the interference of background light, improves the signal-to-noise ratio, and enables the system to still have reliable imaging ability under a strong interference background, especially suitable for long-range detection tasks in complex environments.

[0019] An array APD detector with a large area array and single-photon level sensitivity is selected, and a micro-lens array structure is integrated in front of its target surface, realizing a receiving scheme with high spatial resolution and high light energy utilization rate. Compared with the traditional detectors using small area APDs or without micro-lens structures, this solution significantly improves the ability to capture weak echo signals without increasing the volume of the detector, enabling the system to have the ability to accurately detect weak and low-reflectivity targets, especially suitable for application scenarios with long distances or strong target camouflage.

[0020] The control and information processing subsystem ensures the timing synchronization of the laser emission and the detector through the coordinated control of the main control computer and the signal generator, so that the system can simultaneously obtain the intensity map, polarization map, distance map and three-dimensional image within a single measurement cycle. Compared with the existing systems that use the time-sharing multi-frame method for data acquisition, this solution significantly improves the imaging efficiency and the time resolution of target capture, has the ability to identify real-time dynamic targets, and is especially suitable for emergency detection of high-speed or sudden targets.

[0021] This system supports pixel - level registration and fusion of polarization images and distance images, thanks to the fact that both types of image data are synchronously acquired by the same array APD detector. Compared with systems that require image registration or multi - channel image fusion, this solution can directly synthesize high - contrast images through algorithms, fuse the high - contrast edge extraction effect of the target polarization image with the internal depth information of the distance image, enrich the imaging details of the target, significantly improve the recognition effect of target features, and reduce the complexity and error rate of image processing.

[0022] It is applicable to the real - time detection requirements of camouflaged targets in complex environments. Brief Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of an APD lidar real - time polarization imaging system.

[0024] Figure 2 It is a schematic structural diagram of the micro - polarizer array module.

[0025] Figure 3 It is the schematic principle diagram of polarization imaging of the micro - polarizer array Figure 4 It is a schematic structural diagram of the micro - polarizer array.

[0026] Figure 5 It is the curve graph of the transmittance and extinction ratio of the micro - polarizer array Figure 6 It is a two - dimensional schematic structural diagram of the optical system of the polarization imaging sub - system.

[0027] Figure 7 It is the modulation transfer function graph of the optical system of the polarization imaging sub - system.

[0028] Among them, 100 is the laser emission sub - system, 101 is a 1064nm laser, 102 is a beam expander, 200 is the polarization imaging sub - system, 201 is a 1064nm filter, 202 is a front objective lens group, 203 is a micro - polarizer array module, 204 is a rear relay lens group, 205 is an APD detector, 1 is a circular protective glass, 2 is a micro - polarizer array, 3 is a square protective glass, 4 is a metal layer, 5 is an intermediate layer, and 6 is a substrate. Detailed Embodiments

[0029] To make the advantages and beneficial effects of the technical solutions provided by the present invention more clearly manifested, the technical solutions provided by the present invention are further described in detail below with reference to the accompanying drawings. Specifically: Embodiment 1. This embodiment provides an APD lidar real - time polarization imaging system, including: The laser emission subsystem includes a laser and a beam expander. The laser is used to emit pulsed laser signals, and the beam expander is arranged on the outgoing light path of the laser to collimate and expand the pulsed laser signals. The polarization imaging subsystem includes a filter, a front objective lens group, a micro-polarizer array module, a rear relay lens group, and an APD detector. The filter is arranged at the front end of the system to filter out stray light in the pulsed laser signals. The front objective lens group is arranged on the outgoing light path of the filter to shape the received echo beam and form a primary image. The micro-polarizer array module is arranged at the image plane position of the primary image to modulate the polarization information of the primary image and obtain polarized light in multiple directions. The rear relay lens group is arranged on the outgoing light path of the micro-polarizer array module to project the primary image to the secondary image plane position. The APD detector is arranged at the secondary image plane position to receive the modulated polarization image and output the original data of intensity and time information.

[0030] It further includes a control and information processing subsystem for controlling the trigger timing of the laser and synchronizing with the APD detector.

[0031] The control and information processing subsystem includes a signal generator and a main control computer. The signal generator is used to control the trigger timing of the laser and synchronize with the APD detector, and the main control computer is used to coordinately control each component and perform image resolution and fusion processing on the received data.

[0032] The micro-polarizer array module includes a circular protective glass, a micro-polarizer array, and a square protective glass, which are arranged in sequence from the object side to the image side.

[0033] The micro-polarizer array module acquires polarization images in four directions of 0°, 45°, 90°, and 135°.

[0034] The center wavelength of the filter is 1064 nm, the filtering bandwidth is ±1 nm, and the thickness is 3 mm.

[0035] It also provides an APD lidar real-time polarization imaging method implemented based on the above system, including: The step of sending a control signal to drive the signal generator to generate a pulsed trigger signal. The step of using the trigger signal to start the laser to emit 1064 nm pulsed laser, and at the same time controlling the opening of the gating of the APD detector to keep it synchronized with the laser emission timing. The step of expanding the laser signal and irradiating it onto the target, and receiving its echo signal. After filtering out the stray light in non-working wavelength bands through a filter, forming a primary image through a front objective lens group; The step of performing polarization information modulation on the primary image, obtaining polarization light images in multiple directions, and projecting them onto a secondary image plane to form polarization image data; The step of collecting the original intensity and time data from the APD detector and receiving this data stream; The step of analyzing the original data and calculating to generate corresponding intensity images, polarization images, distance images, and three-dimensional images; The step of performing image fusion operation according to the pixel matching relationship between the polarization image and the distance image and outputting a high-contrast fusion image.

[0036] Embodiment 2: This embodiment is a further detailed description of the technical solution provided in Embodiment 1. Specifically: An APD lidar real-time polarization imaging system, which mainly includes: a laser emission subsystem 100, a polarization imaging subsystem 200, and a control and information processing subsystem 300. Among them, the laser emission subsystem 100 is used to provide an active laser illumination source; the polarization imaging subsystem 200 is used to perform polarization modulation and imaging on the echo signal; the control and information processing subsystem 300 is used to coordinately control the operation of each component and perform image solution processing.

[0037] The laser emission subsystem 100 includes: a 1064nm laser 101 and a beam expander 102.

[0038] The 1064nm laser 101 is used to emit a laser signal with a central wavelength of 1064nm. The laser operates in pulse mode, has excellent monochromaticity and thermal stability, and can achieve long-term stable emission.

[0039] The beam expander 102 is arranged on the output optical path of the laser 101 and is used to collimate and expand the beam output by the laser. The spot size after expansion covers 8×8 central pixels, meeting the illumination requirements for distant targets.

[0040] The polarization imaging subsystem 200 includes: a 1064nm filter 201, a front objective lens group 202, a micro-polarizer array module 203, a rear relay lens group 204, and an APD detector 205.

[0041] The 1064nm filter 201 is located at the front end of the system and is used to receive the echo optical signal reflected by the target and filter out the stray light outside the 1064nm wavelength, effectively improving the signal-to-noise ratio of the system. Preferably, the thickness of the filter is 3mm, and the filtering wavelength band is 1064±1nm.

[0042] The front objective lens group 202 is located behind the filter 201 and is used to shape and reduce the incident light beam to form a primary image at its image plane position. It consists of five groups of spherical lenses and is made of H-ZF6 glass material to optimize aberration control and improve imaging quality.

[0043] The micro-polarizer array module 203 is arranged at the primary image plane position and is used to modulate the polarization information of the formed primary image. The micro-polarizer array module 203 sequentially includes from the object side to the image side: a circular protective glass 1, a micro-polarizer array 2, and a square protective glass 3. The circular protective glass 1 and the square protective glass 3 form a sealed structure to protect the micro-polarizer array 2 and prevent it from being affected by moisture and oxidation. The micro-polarizer array 2 modulates the incident light to obtain the polarization light components in four directions of 0°, 45°, 90°, and 135° respectively. To enhance the system transmittance and extinction ratio, an infrared anti-reflection film with a wavelength of 1064nm is coated on the surface of the array film.

[0044] The structure of the micro-polarizer array 2 sequentially includes from top to bottom: a metal layer 4, an intermediate layer 5, and a substrate 6. Among them, the metal layer 4 is used to achieve linear polarization modulation, preferably made of aluminum (Al) material, the intermediate layer 5 is silicon dioxide (SiO2), and the substrate 6 is K9 glass. The metal period P is 190nm, the metal width L is 75nm, the metal height H1 is 180nm, the intermediate layer height H is 180nm, and the substrate thickness HH is 1mm. The transmittance of this structure at a wavelength of 1064nm can reach 84.37%, and the extinction ratio reaches 3199dB.

[0045] The rear relay lens group 204 is arranged behind the micro-polarizer array module 203 and is used to project the primary image to the secondary image plane position. Its designed magnification is 1 to ensure a one-to-one correspondence between the micro-polarizer array and the APD detector pixels. The relay lens group consists of six groups of spherical lenses, ensuring high-resolution imaging ability.

[0046] The APD detector 205 is arranged at the secondary image plane position and is used to receive the modulated polarization image and output the original data of intensity and time information. The APD detector is an array type, preferably the GD5551 type of the 44th Institute of China Electronics, with an array scale of 64×64, having single-photon detection sensitivity, and integrating a micro-lens array in front of the detector surface to increase the light energy utilization rate to more than 80%.

[0047] The control and information processing subsystem 300 includes a main control computer 301 and a signal generator 302. The signal generator 302 is used to control the trigger timing of the laser 101 and keep it synchronized with the gating width of the APD detector 205. The main control computer 301 is responsible for coordinating the work of the laser, the APD detector and the signal generator, completing data acquisition and processing, calculating the intensity image, polarization image, distance image and three-dimensional image of the target, and performing image fusion processing on the polarization map and distance map to generate a high-contrast fusion image.

[0048] The system working process is as follows: The main control computer 301 controls the signal generator 302 to output a trigger signal, so that the laser 101 emits pulsed laser light, which is collimated and expanded by the beam expander 102 and irradiated onto a distant target. The target echo signal enters the front objective lens group 202 to form a primary image after the stray light is filtered by the filter 201. After the polarization information of the primary image is modulated by the micro-polarizer array module 203, it is projected by the rear relay lens group 204 to the position of the secondary image plane where the APD detector 205 is located. The APD detector outputs the received polarization image and time information to the main control computer 301 for image reconstruction and fusion processing, and finally realizes the synchronous acquisition of the target intensity, polarization, distance and three-dimensional information.

[0049] In terms of software: First of all, the main control computer 301 initializes each hardware module of the system, including the laser 101, the APD detector 205 and the signal generator 302, and at the same time sets relevant system parameters, such as the laser pulse frequency, gating width, frame rate and fusion mode.

[0050] After the initialization is completed, the main control computer 301 issues an instruction to the signal generator 302 to control it to output a pulsed trigger signal. On the one hand, this trigger signal starts the 1064nm laser 101 to emit pulsed laser signals; on the other hand, it synchronously controls the opening time of the gating of the APD detector 205 to make its working window match the arrival time of the laser echo exactly.

[0051] After the laser signal is emitted, it is collimated and expanded by the beam expander 102 to form a uniform light beam, which is irradiated onto the surface of a distant target. After the target reflects the optical signal, it enters the polarization imaging subsystem 200. First, the reflected optical signal passes through the 1064nm filter 201 to filter out the stray light in non-target bands and improve the signal-to-noise ratio of the system. Subsequently, the light beam enters the front objective lens group 202 to complete beam shaping and focusing, and form an optical image of the target on the primary image plane.

[0052] A micro-polarizer array module 203 is arranged at the position of the first image plane. This module sequentially includes a circular protective glass 1, a micro-polarizer array 2, and a square protective glass 3 from the object side to the image side. Among them, the micro-polarizer array 2 is used to decompose the first image into polarization maps in four directions of 0°, 45°, 90°, and 135°. This polarized image is projected onto the second image plane through the rear relay lens group 204.

[0053] The array APD detector 205 arranged at the position of the second image plane receives the said image and records the corresponding intensity and time-of-flight information at each pixel. A micro-lens array is arranged at the front end of the APD detector 205, which can improve the light energy collection efficiency.

[0054] The original data of the intensity and time are transmitted through the data path to the main control computer 301 for processing. First, the software analyzes the time information to generate a distance image, analyzes the intensity information to generate an intensity image, and constructs a polarization angle map and a polarization degree map through four-direction polarization components, and then obtains the polarization image and three-dimensional image of the target.

[0055] Finally, the main control computer 301 calls the image fusion module to perform fusion processing on the polarization image and the distance image based on the one-to-one correspondence of pixels, generates a high-contrast fusion image, and improves the recognition effect on low-reflectivity or camouflaged targets. The fused result can be further output to the image analysis end, the target recognition module, or the display terminal for subsequent analysis.

[0056] Embodiment 3. Combination Figure 1-7 To illustrate this embodiment, this embodiment further describes the above-provided technical solution in detail through specific embodiments. Specifically: An APD lidar real-time polarization imaging system, as Figure 1 shown, includes: a laser emission subsystem 100, a polarization imaging subsystem 200, and a control and information processing subsystem 300.

[0057] The laser emission subsystem 100 includes: a 1064nm laser 101 and a beam expander 102; The 1064nm laser 101 is used to emit a 1064nm laser signal. Its monochromaticity is good enough, its stability is high, its working mode is pulsed, and it has good heat dissipation measures and can work for a long time.

[0058] The beam expander 102 is located on the outgoing light path of the 1064nm laser 101 and is used to collimate and expand the laser emitted by the 1064nm laser 101. After expansion, the laser can illuminate a field of view of 8×8 central pixels and can achieve illumination of typical air targets at a long distance; The polarization imaging sub-system 200 includes: a 1064nm filter 201, a front objective lens group 202, a micro-polarizer array module 203, a rear relay lens group 204, and an APD detector 205.

[0059] The 1064nm filter 201 is located in front of the entire system and is used to filter out stray light outside the 1064nm band. The filtering band of the filter affects the signal-to-noise ratio of the system. An overly large filtering band allows noise photons to enter, thereby reducing the system's signal-to-noise ratio. At the same time, the thickness of the filter affects its filtering band, and an overly large thickness can cause the filtering band to drift, resulting in a decrease in the transmittance of 1064nm light. Preferably, the thickness of the filter 201 is 3mm, and the filtering band is 1064nm ± 1nm.

[0060] The front objective lens group 202 is located on the outgoing light path of the 1064nm filter 1 and is used to shape and reduce the beam, and form a primary image at the position of the primary image plane. The optical design of the front objective lens group 202 needs to ensure the collimation and imaging quality of the beam.

[0061] The optical system structure parameters of the front objective lens group 202 are shown in Table 1.

[0062]

[0063] The micro-polarizer array module 203 is located at the position of the primary image plane formed after the beam is shaped and reduced by the front objective lens group, and consists of a circular protective glass 1, a micro-polarizer array 2, and a square protective glass 3 in sequence from the object side to the image side.

[0064] The protective glass is used to seal the micro-polarizer array 2 to prevent the micro-polarizer array 2 from oxidizing.

[0065] The micro-polarizer array 2 is used to modulate the polarization information of the beam to obtain polarized light in four directions of 0°, 45°, 90°, and 135° respectively. To ensure the polarization extinction ratio of the system, the micro-polarizer array 2 is coated with an infrared antireflection film of 1064nm. Specifically, the pixel size and target surface scale of the micro-polarizer array 2 should be consistent with those of the APD detector 205. Preferably, the pixel size of the micro-polarizer array is 50μm, and the target surface scale is 64×64.

[0066] As Figure 4 shown, the structure of the micro-polarizer array 2 consists of a metal layer 4, an intermediate layer 5, and a substrate 6 from top to bottom in sequence, where L is the metal width, H1 is the metal height, P is the metal period, H is the intermediate layer height, and HH is the substrate height. The structure parameters of the micro-polarizer array 2 are shown in Table 2.

[0067]

[0068] AsFigure 5 As shown, the designed transmittance of the obtained micro-polarizer array can reach 91.86% in the 1064nm band, and the extinction ratio can reach 4370.2dB.

[0069] The micro-polarizer array module 203 is characterized in that it adopts an independent module packaging method, which solves the problem of difficulty and high cost in engraving and packaging micro-polarizer arrays of ordinary detectors, is suitable for the focus plane polarization imaging needs of any secondary imaging optical system, and has a high degree of freedom.

[0070] The micro-polarizer array 2 is required to achieve a one-to-one pixel-level match with the target surface of the APD detector 205 at the primary image plane position, and the axial, meridian and sagittal errors are as small as possible so as not to affect the imaging quality of the entire system.

[0071] The rear relay lens group 204 is located on the outgoing light path of the micro-polarizer array module 203, and is used to project the primary image plane light beam to the secondary image plane. In order to achieve the effect of pixel matching between the micro-polarizer array 2 and the APD detector 205, the magnification of the rear relay lens group 204 is 1. The optical design of the relay lens group needs to ensure the clarity and resolution of the imaging.

[0072] The optical system structural parameters of the rear relay lens group 204 are shown in Table 3.

[0073]

[0074] The optical system designed by the polarization imaging subsystem 200 is as follows Figure 5 As shown, the technical indicators are: focal length: 120mm, entrance pupil diameter: 30mm, field of view: 3.05°, operating wavelength: 1064nm. Figure 6 As shown, the MTF of the optical system designed for the polarization imaging subsystem 200 at the Nyquist frequency of 10lp / mm at a wavelength of 1064nm is above 0.9, which is close to the diffraction limit.

[0075] The APD detector 205 is located at the position where the primary image plane light beam is projected to the secondary image plane through the rear relay lens group, and is used to receive the light signal carried by the light beam and output the intensity and time information raw data to the control and information processing subsystem 300. In order to improve the utilization rate of light energy, a microlens array corresponding to its pixel is integrated in front of the detector target surface. After the microlens array converges, the light energy utilization rate is increased to more than 80%; its bandwidth is high enough to detect narrow pulse signals; its sensitivity can reach the single photon level, and it can detect weak light signals. Since the system adopts a non-scanning imaging mechanism, the scale of the detector target surface should be as large as possible to obtain a higher resolution. Specifically, the APD detector 205 is an array APD detector with an array scale of 64×64. Preferably, the APD detector 205 uses the GD5551 array APD detector of China Electronics 44 Institute.

[0076] The control and information processing 300 subsystem includes: a main control computer 301 and a signal generator 302; The signal generator 302 is used to control the trigger timing of the 1064nm laser 101 and synchronize the gate width of the APD detector 205; The main control computer 301 is used to simultaneously control the laser 101, the APD detector 205 and the signal generator 302, and calculate and obtain the target intensity image, polarization image, distance image and three-dimensional image.

[0077] Since the polarization image and the distance image are acquired simultaneously by the same detector, a one-to-one pixel matching relationship can be achieved. Therefore, this relationship can be used to perform image algorithm fusion to obtain a high-contrast image of the target.

[0078] The working process is as follows: the main control computer controls the signal generator to provide an electrical signal, triggering the laser to emit a 1064nm laser signal, which is collimated and expanded by a beam expander. After being incident on a distant target, the reflected echo light signal enters the polarization imaging subsystem, and is filtered out through a 1064nm filter except for the 1064nm narrowband wavelength. The light is imaged at the primary image plane position through the front objective lens group, and the polarization information of the light signal is modulated by the micro-polarizer array module to obtain polarized light in four different directions. The light is then imaged at the array APD detector position through the rear relay lens group, and the received raw data of intensity and time information is output to the main control computer. The target intensity image, polarization image, distance image and three-dimensional image are calculated and acquired, and then the target polarization image and distance image are fused through the image fusion algorithm to obtain a high-contrast fused image of the target.

[0079] The polarization imaging lidar provided by this application adopts a secondary imaging mechanism, integrates the micro-polarizer array to the position of the primary image plane of the optical system, realizes the split focal plane polarization imaging effect of the array APD detector, and thus simultaneously obtains the intensity information, polarization information, distance information and three-dimensional information of the target. It fills the gap that traditional lidar and infrared passive polarization imaging cannot simultaneously detect the three-dimensional information and two-dimensional polarization information of the target.

[0080] The technical solutions provided by the present invention are further described in detail through several specific embodiments above to highlight the advantages and beneficial effects of the technical solutions provided by the present invention. However, the several specific embodiments described above are not used as limitations to the present invention. Any reasonable modifications and improvements to the present invention, combinations of embodiments, equivalent substitutions, etc. within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. An APD lidar real-time polarization imaging system, characterized in that Comprising: A laser emission subsystem, including a laser and a beam expander. The laser is used to emit pulsed laser signals, and the beam expander is arranged on the outgoing light path of the laser for collimating and expanding the pulsed laser signals. A polarization imaging subsystem, including a filter, a front objective lens group, a micro-polarizer array module, a rear relay lens group, and an APD detector. The filter is arranged at the front end of the system for filtering out stray light in the pulsed laser signals. The front objective lens group is arranged on the outgoing light path of the filter for shaping the received echo beam and forming a primary image. The micro-polarizer array module is arranged at the image plane position of the primary image for modulating the polarization information of the primary image to obtain polarized light in multiple directions. The rear relay lens group is arranged on the outgoing light path of the micro-polarizer array module for projecting the primary image to the secondary image plane position. The APD detector is arranged at the secondary image plane position for receiving the modulated polarization image and outputting the original data of intensity and time information.

2. The real-time polarization imaging system of an APD lidar according to claim 1, characterized in that It further includes a control and information processing subsystem for controlling the trigger timing of the laser and synchronizing with the APD detector.

3. The real-time polarization imaging system of an APD lidar according to claim 1, wherein The control and information processing subsystem includes a signal generator and a main control computer. The signal generator is used to control the trigger timing of the laser and synchronize with the APD detector, and the main control computer is used to coordinately control each component and perform image resolution and fusion processing on the received data.

4. The real-time polarization imaging system of an APD lidar according to claim 1, characterized in that, The micro-polarizer array module includes a circular protective glass, a micro-polarizer array, and a square protective glass, arranged in sequence from the object side to the image side.

5. The real-time polarization imaging system of an APD lidar according to claim 1, characterized in that, The micro-polarizer array module acquires polarization images in four directions of 0°, 45°, 90°, and 135°.

6. The real-time polarization imaging system of an APD lidar according to claim 1, characterized in that, The center wavelength of the filter is 1064 nm, the filtering bandwidth is ±1 nm, and the thickness is 3 mm.

7. A real-time polarization imaging method for APD lidar, characterized in that, Implemented based on the system described in claim 1, including: The step of sending a control signal to drive the signal generator to generate a pulsed trigger signal. The step of using the trigger signal to start the laser to emit 1064 nm pulsed laser, and at the same time controlling the opening of the gating of the APD detector to keep it synchronized with the laser emission timing. The step of expanding the laser signal and irradiating it to the target, and receiving its echo signal. After filtering out the stray light in the non-working wavelength band by the filter, forming a primary image through the front objective lens group. The step of performing polarization information modulation on the primary image, acquiring polarization light images in multiple directions, and projecting them to the secondary image plane to form polarization image data. The step of collecting the original data of intensity and time from the APD detector and receiving the data stream. The step of analyzing the original data and calculating to generate corresponding intensity images, polarization images, distance images, and three-dimensional images. The step of performing image fusion operation according to the pixel matching relationship between the polarization image and the distance image and outputting a high-contrast fusion image.

8. A computer storage medium for storing a computer program, characterized in that, When the computer program is read by a computer, the computer executes the method described in claim 7.

9. A computer, comprising a processor and a storage medium, characterized in that, When the processor reads the computer program stored in the storage medium, the computer executes the method described in claim 7.

10. A computer program product, as a computer program, characterized in that When the computer program is executed, the method described in claim 7 is implemented.

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