A real-time polarization imaging method and system for APD laser radar

Abstract

A real-time polarization imaging system for active polarization laser radar (APD) lidar relates to the field of laser radar technology. To address the issues of insufficient image fusion accuracy and difficulty integrating with split-focal plane polarization imaging mechanisms in existing active polarization laser radar systems, a system based on a secondary imaging structure is provided. This system comprises a laser emission subsystem, a polarization imaging subsystem, and an APD detector. A micropolarizer array is positioned on the primary image plane and projected onto the APD array detector via a rear relay lens assembly, enabling simultaneous acquisition and pixel registration of polarization and range images. This system is suitable for high-contrast, real-time detection and imaging of camouflaged targets in complex environments.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a real-time polarization imaging method and system of an APD laser radar. Background Art

[0002] Laser detection and ranging (LiDAR) is an active remote sensing technology that transmits laser beams and receives their reflected echoes to obtain information such as target distance, shape, and motion. It is widely used in intelligent driving, remote sensing mapping, target identification, and military detection. In recent years, with the increasing complexity of detection mission environments and the increasing concealment of targets, traditional LiDAR faces problems such as insufficient recognition of weak and camouflaged targets and susceptibility to strong background light. Polarization imaging can improve the contrast of target images in complex environments and suppress the influence of stray light background, effectively enhancing the target recognition capabilities of traditional LiDAR. Therefore, LiDAR technology is gradually developing towards multi-dimensional perception, and the integration of intensity, distance, polarization, and other information has become a key trend in technological development.

[0003] In this context, active polarization imaging lidar has become a research hotspot. Unlike passive polarization imaging systems, active polarization lidar uses lasers with specific polarization states at the transmitter and extracts polarization information at the receiver, thereby enhancing the ability to identify target materials, surface structures, and other features. For example, some studies use rotating polarizers or liquid crystal polarization modulators in conjunction with CCD detectors to obtain images in different polarization states; other solutions integrate multiple polarization detection channels to achieve time-sharing or parallel imaging. In addition, the focus plane polarization imaging mechanism usually integrates a micro-polarizer array into the detector target position to obtain polarized light in four directions: 0°, 45°, 90°, and 135°, thereby obtaining polarization images of dynamic targets in real time, which is used for tasks such as camouflage target recognition, material classification, and surface roughness estimation.

[0004] However, existing active polarization lidar systems still have the following technical bottlenecks: First, most systems still use traditional CCD or CMOS cameras as detectors, which makes it difficult to achieve simultaneous acquisition of time-of-flight ranging and polarization imaging, resulting in insufficient image fusion accuracy; Second, although lidars using APDs (avalanche photodiodes) as detectors have single-photon detection capabilities, traditional polarization imaging lidars usually use a rotating polarizer at the laser transmitting end to obtain linearly polarized lasers in different directions, and perform secondary polarization modulation on the laser echo by rotating the polarizer at the receiving end to obtain target polarization information. This solution has poor real-time performance and is difficult to achieve real-time active polarization imaging requirements for dynamic targets. In addition, due to the limitations of the detector structure, it is difficult to achieve effective integration with the focal plane polarization imaging mechanism; Third, most existing micro-polarizer array devices require customized detector packaging, which is costly and inflexible, limiting their large-scale application in lidar systems.

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

[0006] To address the technical bottlenecks of insufficient image fusion accuracy and difficulty in achieving effective fusion with the split-focal plane polarization imaging mechanism in existing active polarization lidar systems, the present invention provides the following technical solutions:

[0007] An APD laser radar real-time polarization imaging system, comprising:

[0008] A laser emission subsystem, comprising a laser and a beam expander, wherein the laser is used to emit a pulsed laser signal, and the beam expander is arranged on the output optical path of the laser to collimate and expand the pulsed laser signal;

[0009] Polarization imaging subsystem, including filters, front objective lens group, micro-polarizer array module, rear relay lens group and APD detector;

[0010] The filter is arranged at the front end of the system and is used to filter out stray light in the pulse laser signal;

[0011] The front objective lens group is arranged on the outgoing light path of the filter, and is used to shape the received echo light beam and form a primary image;

[0012] The micro-polarizer array module is arranged at the image plane position of the primary image, and is used to modulate the polarization information of the primary image to obtain polarized light in multiple directions;

[0013] The rear relay lens group is arranged on the outgoing light path of the micro-polarizer array module, and is used to project the primary image to the secondary image plane position;

[0014] The APD detector is arranged at the secondary image plane position, and is used to receive the modulated polarization image and output raw data of intensity and time information.

[0015] Furthermore, a preferred embodiment is provided, which also includes a control and information processing subsystem for controlling the triggering timing of the laser and synchronizing it with the APD detector.

[0016] Furthermore, a preferred embodiment is provided, in which the control and information processing subsystem includes a signal generator and a main control computer, wherein 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 coordinate and control each component and perform image resolution and fusion processing on the received data.

[0017] Furthermore, a preferred embodiment is provided, wherein the micro-polarizer array module comprises 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.

[0018] Furthermore, a preferred embodiment is provided, wherein the micro-polarizer array module acquires polarization images in four directions: 0°, 45°, 90°, and 135°.

[0019] Furthermore, a preferred embodiment is provided, wherein the center wavelength of the filter is 1064 nm, the filtering bandwidth is ±1 nm, and the thickness is 3 mm.

[0020] Based on the same inventive concept, the present invention also provides an APD lidar real-time polarization imaging method, which is implemented based on the system described above and includes:

[0021] The step of sending a control signal to drive a signal generator to generate a pulse trigger signal;

[0022] The step of using the trigger signal to start the laser to emit 1064nm pulsed laser, and at the same time controlling the gate of the APD detector to open so as to keep it synchronized with the laser emission timing;

[0023] The laser signal is expanded and then irradiated to the target, and its echo signal is received. After the stray light outside the working band is filtered out by a filter, a primary image is formed through the front objective lens group;

[0024] Performing polarization information modulation on the primary image to obtain polarized light images in multiple directions, and projecting them onto a secondary image plane to form polarized image data;

[0025] The steps of collecting intensity and time raw data from the APD detector and receiving the data stream;

[0026] The steps of analyzing the raw data and calculating and generating corresponding intensity images, polarization images, distance images and three-dimensional images;

[0027] The step of performing an image fusion operation based on a pixel matching relationship between the polarization image and the range image to output a high-contrast fused image.

[0028] Based on the same inventive concept, the present invention also provides a computer storage medium for storing a computer program. When the computer program is read by a computer, the computer executes the method described above.

[0029] Based on the same inventive concept, the present invention also provides a computer, comprising a processor and a storage medium. When the processor reads the computer program stored in the storage medium, the computer executes the method described above.

[0030] Based on the same inventive concept, the present invention also provides a computer program product, which is a computer program. When the computer program is executed, the method described above is implemented.

[0031] Compared with the prior art, the technical solution provided by the present invention is beneficial in that:

[0032] By placing a micro-polarizer array module at the primary imaging plane of the optical system and combining it with a subsequent relay lens assembly for secondary imaging, this approach effectively integrates the APD lidar system with the split-focal plane polarization imaging mechanism. Compared to traditional designs that directly integrate micro-polarizers into the detector or place them at the end of the optical path, this solution modulates polarization information on the primary imaging plane before projecting the image. This not only avoids the APD structural mismatch issue but also retains its high temporal resolution. This allows for high-precision distance measurement while simultaneously acquiring polarization images, improving the system's ability to identify camouflaged targets.

[0033] By utilizing a standalone micro-polarizer array module, this approach overcomes the high cost and limited versatility inherent in existing technologies, which require integrated packaging of micro-polarizer array components with detectors. Composed of protective glass and micro-polarizers, this module offers excellent sealing and interchangeability, making it highly adaptable and suitable for use in any optical system with secondary imaging. Compared to existing solutions that rely on custom detector packaging, this structural design significantly enhances engineering flexibility and system versatility.

[0034] The system utilizes a 1064nm wavelength laser, coupled with a high-transmittance, low-stray-light filter and a high-quality front objective lens, resulting in excellent wavelength selectivity and image clarity for the incident echo signal. Compared to traditional systems that are unfiltered or use broadband filters, this solution effectively suppresses background light interference and improves the signal-to-noise ratio, enabling reliable imaging even in strong interference environments. This makes it particularly suitable for long-range detection missions in complex environments.

[0035] The use of a large-area array of APD detectors with single-photon sensitivity and an integrated microlens array structure in front of the target achieves a reception solution with high spatial resolution and high light energy utilization. Compared to traditional detectors using small-area APDs or without microlenses, this solution significantly improves the ability to capture weak echo signals without increasing the detector size, enabling the system to accurately detect weak, low-reflectivity targets. This is particularly suitable for applications at long distances or where the target is heavily camouflaged.

[0036] The control and information processing subsystem, coordinated through the main control computer and signal generator, ensures synchronization between laser emission and detector timing, enabling the system to simultaneously acquire intensity maps, polarization maps, distance maps, and 3D images within a single measurement cycle. Compared to existing systems that use time-sharing, multi-frame data acquisition, this solution significantly improves imaging efficiency and the temporal resolution of target capture. It also provides real-time dynamic target recognition capabilities, making it particularly suitable for emergency detection of high-speed or sudden targets.

[0037] This system supports pixel-level registration and fusion of polarization and range images, thanks to the simultaneous acquisition of both image data from the same array of APD detectors. Compared to systems that require image registration or multi-channel image fusion, this solution directly synthesizes high-contrast images through algorithms, fusing the high-contrast edge extraction of the target polarization image with the internal depth information of the range image. This enriches the target imaging details, significantly improves target feature recognition, and reduces image processing complexity and error rates.

[0038] It is suitable for real-time detection of camouflaged targets in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a structural diagram of an APD lidar real-time polarization imaging system.

[0040] Figure 2 Schematic diagram of the structure of the micro-polarizer array module.

[0041] Figure 3 Schematic diagram of polarization imaging principle of the micro-polarizer array

[0042] Figure 4 Schematic diagram of the micro-polarizer array structure.

[0043] Figure 5 The transmittance and extinction ratio curve of the micro-polarizer array is

[0044] Figure 6 It is a two-dimensional schematic diagram of the optical system structure of the polarization imaging subsystem.

[0045] Figure 7 Graph showing the modulation transfer function of the optical system of the polarization imaging subsystem.

[0046] Among them, 100 is the laser emission subsystem, 101 is the 1064nm laser, 102 is the beam expander, 200 is the polarization imaging subsystem, 201 is the 1064nm filter, 202 is the front objective lens group, 203 is the micropolarizer array module, 204 is the rear relay lens group, 205 is the APD detector, 1 is the circular protective glass, 2 is the micropolarizer array, 3 is the square protective glass, 4 is the metal layer, 5 is the intermediate layer, and 6 is the substrate. DETAILED DESCRIPTION

[0047] In order to make the advantages and benefits of the technical solution provided by the present invention more clearly reflected, the technical solution provided by the present invention is now further described in detail with reference to the accompanying drawings, specifically:

[0048] Embodiment 1: This embodiment provides an APD laser radar real-time polarization imaging system, including:

[0049] A laser emission subsystem, comprising a laser and a beam expander, wherein the laser is used to emit a pulsed laser signal, and the beam expander is arranged on the output optical path of the laser to collimate and expand the pulsed laser signal;

[0050] Polarization imaging subsystem, including filters, front objective lens group, micro-polarizer array module, rear relay lens group and APD detector;

[0051] The filter is arranged at the front end of the system and is used to filter out stray light in the pulse laser signal;

[0052] The front objective lens group is arranged on the outgoing light path of the filter, and is used to shape the received echo light beam and form a primary image;

[0053] The micro-polarizer array module is arranged at the image plane position of the primary image, and is used to modulate the polarization information of the primary image to obtain polarized light in multiple directions;

[0054] The rear relay lens group is arranged on the outgoing light path of the micro-polarizer array module, and is used to project the primary image to the secondary image plane position;

[0055] The APD detector is arranged at the secondary image plane position, and is used to receive the modulated polarization image and output raw data of intensity and time information.

[0056] It also includes a control and information processing subsystem for controlling the triggering timing of the laser and synchronizing it with the APD detector.

[0057] 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. The main control computer is used to coordinate and control various components and perform image resolution and fusion processing on the received data.

[0058] The micro-polarizer array module comprises 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.

[0059] The micro-polarizer array module acquires polarization images in four directions: 0°, 45°, 90°, and 135°.

[0060] The center wavelength of the filter is 1064 nm, the filtering bandwidth is ±1 nm, and the thickness is 3 mm.

[0061] A real-time polarization imaging method for an APD laser radar is also provided, which is implemented based on the system and includes:

[0062] The step of sending a control signal to drive a signal generator to generate a pulse trigger signal;

[0063] The step of using the trigger signal to start the laser to emit 1064nm pulsed laser, and at the same time controlling the gate of the APD detector to open so as to keep it synchronized with the laser emission timing;

[0064] The laser signal is expanded and then irradiated to the target, and its echo signal is received. After the stray light outside the working band is filtered out by a filter, a primary image is formed through the front objective lens group;

[0065] Performing polarization information modulation on the primary image to obtain polarized light images in multiple directions, and projecting them onto a secondary image plane to form polarized image data;

[0066] The steps of collecting intensity and time raw data from the APD detector and receiving the data stream;

[0067] The steps of analyzing the raw data and calculating and generating corresponding intensity images, polarization images, distance images and three-dimensional images;

[0068] The step of performing an image fusion operation based on a pixel matching relationship between the polarization image and the range image to output a high-contrast fused image.

[0069] Implementation Method 2: This implementation method further describes the technical solution provided in Implementation Method 1 in detail. Specifically:

[0070] A real-time polarization imaging system for an APD laser radar is described. The system primarily comprises a laser emission subsystem 100, a polarization imaging subsystem 200, and a control and information processing subsystem 300. The laser emission subsystem 100 provides an active laser illumination source; the polarization imaging subsystem 200 performs polarization modulation and imaging on the echo signal; and the control and information processing subsystem 300 coordinates and controls the operation of various components and performs image processing.

[0071] The laser emission subsystem 100 includes: a 1064 nm laser 101 and a beam expander 102 .

[0072] The 1064nm laser 101 is used to emit a laser signal with a central wavelength of 1064nm. The laser operates in a pulse mode, has excellent monochromaticity and thermal stability, and can achieve long-term stable emission.

[0073] The beam expander 102 is arranged on the outgoing optical path of the laser 101 and is used to collimate and expand the beam output by the laser. After beam expansion, the spot size covers 8×8 central pixels, meeting the requirements of long-distance target illumination.

[0074] The polarization imaging subsystem 200 includes: a 1064 nm 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 .

[0075] The 1064nm filter 201 is located at the front end of the system and is used to receive the echo light signal reflected by the target and filter out stray light outside the 1064nm wavelength, effectively improving the system signal-to-noise ratio. Preferably, the filter thickness is 3mm and the filter band is 1064±1nm.

[0076] The front objective lens group 202 is located after the filter 201 and is used to shape and reduce the incident light beam to form a primary image at its image plane. It is composed of five groups of spherical lenses and is made of H-ZF6 glass to optimize aberration control and improve image quality.

[0077] The micropolarizer array module 203 is positioned on the primary image plane and is used to modulate the polarization information of the formed primary image. From the object side to the image side, the micropolarizer array module 203 comprises, in order: a circular protective glass 1, a micropolarizer 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 micropolarizer array 2 from moisture and oxidation. The micropolarizer array 2 modulates the incident light to obtain polarized light components in four directions: 0°, 45°, 90°, and 135°. To enhance the system's transmittance and extinction ratio, the array surface is coated with a 1064nm infrared anti-reflection coating.

[0078] The structure of the micropolarizer array 2, from top to bottom, consists of a metal layer 4, an intermediate layer 5, and a substrate 6. The metal layer 4, which achieves linear polarization modulation, is preferably made of aluminum (Al). The intermediate layer 5 is made of silicon dioxide (SiO2), and the substrate 6 is made of K9 glass. The metal period P is 190 nm, the metal width L is 75 nm, the metal height H1 is 180 nm, the intermediate layer height H is 180 nm, and the substrate thickness HH is 1 mm. This structure achieves a transmittance of 84.37% at a wavelength of 1064 nm and an extinction ratio of 3199 dB.

[0079] The rear relay lens assembly 204, located after the micro-polarizer array module 203, is used to project the primary image onto the secondary image plane. Its design magnification is 1 to ensure a one-to-one correspondence between the micro-polarizer array and the APD detector pixels. The relay lens assembly consists of six groups of spherical lenses, ensuring high-resolution imaging capabilities.

[0080] The APD detector 205 is positioned at the secondary image plane, receiving the modulated polarization image and outputting raw data of intensity and time information. The APD detector is an array-type detector, preferably the GD5551 model from the 44th Institute of China Electronics Technology Group Corporation. The array size is 64×64, and it has single-photon detection sensitivity. A microlens array is integrated in front of the detection surface to increase light energy utilization to over 80%.

[0081] 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 synchronize it with the gate width of the APD detector 205. The main control computer 301 is responsible for coordinating the operation of the laser, APD detector, and signal generator, completing data acquisition and processing, and calculating the target's intensity image, polarization image, range image, and three-dimensional image. It can also perform image fusion processing of the polarization image and range image to generate a high-contrast fused image.

[0082] The system operates as follows: the main control computer 301 controls the signal generator 302 to output a trigger signal, causing the laser 101 to emit pulsed laser light. This pulsed laser light is then collimated and expanded by the beam expander 102 and directed toward a distant target. The target's reflected echo signal is filtered out by the filter 201 to remove stray light, and then enters the front objective lens assembly 202 to form a primary image. This primary image is polarized by the micro-polarizer array module 203 and then projected by the rear relay lens assembly 204 onto the secondary image plane where the APD detector 205 is located. The APD detector then outputs the received polarization image and time information to the main control computer 301 for image reconstruction and fusion processing, ultimately achieving the simultaneous acquisition of target intensity, polarization, distance, and three-dimensional information.

[0083] In terms of software:

[0084] First, the main control computer 301 initializes the hardware modules of the system, including the laser 101, the APD detector 205 and the signal generator 302, and sets relevant system parameters, such as the laser pulse frequency, the gate width, the frame rate and the fusion mode.

[0085] After initialization, the main control computer 301 sends a command to the signal generator 302, instructing it to output a pulse trigger signal. This trigger signal, on the one hand, activates the 1064nm laser 101 to emit a pulsed laser signal; on the other hand, it synchronously controls the opening time of the gate of the APD detector 205, so that its operating window precisely matches the arrival time of the laser echo.

[0086] After the laser signal is emitted, it is collimated and expanded by the beam expander 102 to form a uniform beam, which is then directed to the distant target surface. After the target reflects the return light signal, it enters the polarization imaging subsystem 200. First, the return light signal passes through the 1064nm filter 201 to filter out stray light in the non-target band, improving the system's signal-to-noise ratio. The beam then enters the pre-objective lens assembly 202, which completes beam shaping and focusing, forming an optical image of the target on the primary image plane.

[0087] A micro-polarizer array module 203 is positioned at the primary image plane. From the object side to the image side, this module comprises, in order, a circular protective glass 1, a micro-polarizer array 2, and a square protective glass 3. The micro-polarizer array 2 decomposes the primary image into four polarization patterns: 0°, 45°, 90°, and 135°. These polarized images are projected onto the secondary image plane via a post-relay lens assembly 204.

[0088] The array APD detector 205 located at the secondary image plane receives the image and records the intensity and time-of-flight information at each pixel. A microlens array is provided at the front end of the APD detector 205 to improve light energy collection efficiency.

[0089] The raw intensity and time data are transmitted via a data path to the main control computer 301 for processing. First, the software parses the time information to generate a range image, parses the intensity information to generate an intensity image, and constructs a polarization angle map and a polarization degree map using the four polarization components, thereby obtaining a polarization image and a three-dimensional image of the target.

[0090] Finally, the main control computer 301 invokes the image fusion module to fuse the polarization image and the range image based on a one-to-one pixel correspondence, generating a high-contrast fused image that improves the recognition of low-reflectivity or camouflaged targets. The fused image can then be output to the image analysis terminal, target recognition module, or display terminal for subsequent analysis.

[0091] Implementation Method 3: Combination Figure 1-7This embodiment further describes the above technical solution in detail through specific examples, specifically:

[0092] An APD laser radar real-time polarization imaging system, such as Figure 1 As shown, it includes: a laser emission subsystem 100, a polarization imaging subsystem 200 and a control and information processing subsystem 300.

[0093] The laser emission subsystem 100 includes: a 1064nm laser 101 and a beam expander 102;

[0094] The 1064nm laser 101 is used to emit a 1064nm laser signal, has good monochromaticity, high stability, works in a pulsed mode, has good heat dissipation measures, and can work for a long time.

[0095] The beam expander 102 is located on the outgoing optical path of the 1064nm laser 101 and is used to collimate and expand the laser light emitted by the 1064nm laser 101. After beam expansion, the laser light can illuminate a field of view of 8×8 central pixels, thereby illuminating a typical aerial target at a long distance.

[0096] The polarization imaging subsystem 200 includes: a 1064 nm 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 .

[0097] The 1064nm filter 201 is located at the front of the entire system and is used to filter out stray light outside the 1064nm band. The filter's filter band affects the system's signal-to-noise ratio. Excessive filter band width allows noise photons to enter, reducing the system's signal-to-noise ratio. Furthermore, the filter's thickness affects its filter band. Excessive thickness can cause the filter band to drift, resulting in reduced transmittance at 1064nm. Preferably, filter 201 is 3mm thick and has a filter band of 1064nm ± 1nm.

[0098] The front objective lens group 202 is located on the outgoing light path of the 1064nm filter 1, and is used to shape and shrink the light beam and form a primary image at the primary image plane position. The optical design of the front objective lens group 202 must ensure the collimation and imaging quality of the light beam.

[0099] The optical system structural parameters of the front objective lens group 202 are shown in Table 1.

[0100]

[0101] The micro-polarizer array module 203 is located at the primary image plane position after the light beam is shaped and reduced by the front objective lens group, and is composed of a circular protective glass 1, a micro-polarizer array 2 and a square protective glass 3 from the object side to the image side.

[0102] The protective glass is used to seal the micro-polarizer array 2 to prevent the micro-polarizer array 2 from being oxidized.

[0103] The micropolarizer array 2 modulates the polarization information of the light beam, producing polarized light at four angles: 0°, 45°, 90°, and 135°. To ensure the system's polarization extinction ratio, the micropolarizer array 2 is coated with a 1064nm infrared antireflection coating. Specifically, the pixel size and target surface area of ​​the micropolarizer array 2 should be consistent with those of the APD detector 205. Preferably, the pixel size of the micropolarizer array is 50μm, and the target surface area is 64×64.

[0104] like Figure 4 As shown, the micropolarizer array 2 is composed, from top to bottom, of a metal layer 4, an intermediate layer 5, and a base 6, 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 base height. The structural parameters of the micropolarizer array 2 are shown in Table 2.

[0105]

[0106] like Figure 5 As shown in the figure, 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.

[0107] 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 carving and packaging micro-polarizer arrays of ordinary detectors, is applicable to the focus plane polarization imaging requirements of any secondary imaging optical system, and has a high degree of freedom.

[0108] The micro-polarizer array 2 is required to achieve one-to-one matching with the target surface of the APD detector 205 at the pixel level 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.

[0109] The post-relay lens assembly 204 is located in the outgoing optical path of the micro-polarizer array module 203 and is used to project the primary image beam onto the secondary image plane. To achieve pixel matching between the micro-polarizer array 2 and the APD detector 205, the magnification of the post-relay lens assembly 204 is 1. The optical design of the relay lens assembly must ensure image clarity and resolution.

[0110] The optical system structural parameters of the rear relay lens assembly 204 are shown in Table 3.

[0111]

[0112] The optical system designed for 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 10 lp / mm at a wavelength of 1064 nm is above 0.9, which is close to the diffraction limit.

[0113] The APD detector 205 is located at the position where the primary image plane light beam is projected onto the secondary image plane through the rear relay lens group. It 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. To improve the utilization rate of light energy, a microlens array corresponding to its pixels 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, which can detect weak light signals. Because the system adopts a non-scanning imaging mechanism, the detector target surface scale should be as large as possible to obtain higher resolution. Specifically, the APD detector 205 is an array APD detector with an array scale of 64×64. As a preference, the APD detector 205 uses the GD5551 array APD detector of the 44th Institute of China Electronics Technology Group Corporation.

[0114] The control and information processing subsystem 300 includes: a main control computer 301 and a signal generator 302;

[0115] The signal generator 302 is used to control the triggering timing of the 1064 nm laser 101 and synchronize it with the gate width of the APD detector 205;

[0116] 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 acquire a target intensity image, a polarization image, a distance image and a three-dimensional image.

[0117] Since the polarization image and the range 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.

[0118] 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 to remove stray light other than the 1064nm narrowband wavelength. The front objective lens group forms a primary image at the primary image plane position, and the micro-polarizer array module modulates the polarization information of the light signal to obtain polarized light in four different directions. The secondary image is then formed at the array APD detector position through the rear relay lens group, and the received raw data of the intensity and time information is output to the main control computer. The target intensity image, polarization image, distance image and three-dimensional image are solved and obtained, 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.

[0119] The polarization imaging lidar provided in this application utilizes a secondary imaging mechanism, integrating a micro-polarizer array into the primary imaging plane of the optical system. This achieves the split-focal plane polarization imaging effect of the array APD detector, thereby simultaneously acquiring target intensity, polarization, distance, and three-dimensional information. This addresses the inability of traditional lidar and infrared passive polarization imaging to simultaneously detect both three-dimensional and two-dimensional polarization information of a target.

[0120] The above further describes the technical solution provided by the present invention in detail through several specific embodiments in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the several specific embodiments described above are not intended to limit the present invention. Any reasonable modification and improvement of the present invention, combination of embodiments and equivalent replacement based on the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An APD laser radar real-time polarization imaging system, characterized in that: include: A laser emission subsystem, comprising a laser and a beam expander, wherein the laser is used to emit a pulsed laser signal, and the beam expander is arranged on the output optical path of the laser to collimate and expand the pulsed laser signal; Polarization imaging subsystem, including filters, front objective lens group, micro-polarizer array module, rear relay lens group and APD detector; The filter is arranged at the front end of the polarization imaging subsystem to receive the echo light signal reflected by the target and filter out stray light; The front objective lens group is arranged on the outgoing light path of the filter, and is used to shape the received echo light beam and form a primary image; The micro-polarizer array module is arranged at the image plane position of the primary image, and is used to modulate 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, and is used to project the primary image to the secondary image plane position; The APD detector is arranged at the secondary image plane position, and is used to receive the modulated polarization image and output raw data of intensity and time information.

2. The APD laser radar real-time polarization imaging system according to claim 1, characterized in that: It also includes a control and information processing subsystem for controlling the triggering timing of the laser and synchronizing it with the APD detector.

3. The APD laser radar real-time polarization imaging system according to claim 2, characterized in that: 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. The main control computer is used to coordinate and control various components and perform image resolution and fusion processing on the received data.

4. The APD laser radar real-time polarization imaging system according to claim 1, characterized in that: The micro-polarizer array module comprises 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.

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

6. The APD laser radar real-time polarization imaging system 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 laser radar, characterized in that: The system according to claim 1 is implemented, comprising: 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 1064nm pulsed laser, and at the same time controlling the gate of the APD detector to open so as to keep it synchronized with the laser emission timing; The laser signal is expanded and then irradiated to the target, and its echo signal is received. After the stray light outside the working band is filtered out by a filter, a primary image is formed through the front objective lens group; Performing polarization information modulation on the primary image to obtain polarized light images in multiple directions, and projecting them onto a secondary image plane to form polarized image data; The steps of collecting intensity and time raw data from the APD detector and receiving the data stream; The steps of analyzing the raw data and calculating and generating corresponding intensity images, polarization images, distance images and three-dimensional images; The step of performing an image fusion operation based on a pixel matching relationship between the polarization image and the range image to output a high-contrast fused 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 according to 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 according to claim 7 .

10. A computer program product, being a computer program, characterized in that When the computer program is executed, the method according to claim 7 is implemented.

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