A single-photon three-dimensional imaging system and method based on an area array detector

Abstract

The application discloses a single-photon three-dimensional imaging system based on surface array detection, which comprises a multi-beam laser point array module, a common-aperture scanning transceiver module, a synchronous control module, an image processing module and a transceiver coupling registration module, and provides a system registration method to solve the great difficulty in transceiver matching of a single-photon three-dimensional imaging system using multi-beam emission and array detector; the multi-beam laser point array module and the common-aperture scanning transceiver module are controlled by the synchronous control module to realize high-sensitivity detection and fast imaging of a target based on multi-beam two-dimensional laser point array scanning, and an image processing algorithm based on sub-pixel scanning and calculation imaging can effectively improve the lateral resolution of long-distance imaging under a limited divergence angle. The system and method of the application realize accurate matching of multi-beam illumination and array detection in long-distance single-photon three-dimensional imaging, greatly improve energy efficiency and measurement speed, and obtain a longer detection distance and higher imaging quality.

Description

Technical Field

[0001] This invention relates to the field of laser three-dimensional imaging technology, and in particular to a single-photon three-dimensional imaging system and registration method based on multi-beam array detection. Background Technology

[0002] 3D imaging has numerous applications, including machine vision, security surveillance, and autonomous driving. Currently, long-range obstacle detection methods include radar, vision cameras, and 3D LiDAR. Radar is primarily used for long-range target detection and tracking, but it has blind spots at closer ranges and insufficient detection capability for small targets. Vision cameras are advantageous in acquiring target contour features, but they are highly susceptible to ambient lighting conditions and have insufficient ranging capabilities. 3D LiDAR combines the characteristics of radar waves and optics, acquiring not only the distance and orientation information of targets but also the 3D contour information of the targets themselves for target detection and recognition. It effectively compensates for the shortcomings of radar and vision camera obstacle detection technologies, and due to its superior 3D scene perception capabilities, it has been widely applied to various platforms.

[0003] Linear probe lidar distinguishes echo signals from noise by setting a threshold level in the echo detection circuit. However, due to the low gain of linear detectors, the echo signal needs to contain at least several hundred photons to ensure a good signal-to-noise ratio, thus requiring high single-pulse energy of the emitted laser and high transceiver efficiency of the optical system. In wide-field-of-view lidar applications, it is difficult to detect distant targets. Compared to linear probe lidar, single-photon lidar uses highly sensitive single-photon detectors and employs a high-repetition-rate, low-pulse-energy detection mechanism, which is significant for improving the system's effective range.

[0004] Single-photon lidar can be categorized into two types based on its detection method: single-point scanning and area array imaging. Single-point scanning lidar, limited by its single-point scanning imaging mode, has a slower 3D imaging speed, making it unsuitable for applications requiring large fields of view and rapid imaging. To further improve the speed of single-photon imaging and expand the imaging field of view and resolution, it is necessary to use area array single-photon detection devices. Gm-APD arrays are one type of area array single-photon detection device. Currently, large-scale Gm-APD array fabrication technology in China is not yet mature; the highest pixel size of the developed Gm-APD arrays is 64×64, which is insufficient to meet the detection requirements of large fields of view and high resolution. Therefore, it is necessary to combine scanning imaging technology and point cloud image processing to achieve expanded imaging field of view and resolution.

[0005] On the other hand, for lidar using array detectors, flood illumination is a common method in the transmitting optical system. However, flood illumination requires the emitted beam to illuminate the entire field of view, thus placing strict requirements on the laser emission energy and resulting in low laser energy utilization. If the fill factor of the array detector is not high, microlens alignment is also required for laser echo reception. Therefore, to further improve the utilization efficiency of laser pulse energy, it is necessary to study multi-beam imaging schemes based on pulse beam splitting.

[0006] However, while multi-beam illumination and array detector imaging techniques can effectively improve the energy efficiency of single-photon 3D imaging systems, achieving precise one-to-one matching between each illumination beam and its corresponding detector pixel remains a very difficult challenge. Failure to achieve precise matching can lead to a sharp decline in energy efficiency due to mismatched transmit and receive fields of view. Therefore, an effective and easily implemented method is needed to achieve precise matching between the two. Summary of the Invention

[0007] The main objective of this invention is to provide a single-photon three-dimensional imaging system and method based on multi-beam array detection. By combining multi-beam laser illumination, system registration, control scanning, and array detector imaging with image processing methods, it is possible to achieve rapid imaging of the spatial position of distant targets and reconstruction of their three-dimensional shape.

[0008] The technical solution adopted in this invention is:

[0009] A single-photon three-dimensional imaging system based on area array detection is provided, comprising:

[0010] A multi-beam laser array module is used to generate a multi-beam two-dimensional laser array for measurement, including a laser, a beam expander, a Damman grating and a focusing lens group connected in sequence;

[0011] The common aperture scanning transceiver module enables the common aperture scanning transmission and reception of multi-beam two-dimensional laser array and target echo signals. It includes an array detector and a field stop, a hollow mirror, a transmitting mirror group, and a light wedge scanning unit arranged in sequence. The array detector is set on the focal plane of the transmitting mirror group.

[0012] The synchronization control module is connected to the laser, array detector and optical wedge scanning unit. It is used to control the multi-beam two-dimensional laser array to emit probe light and the array detector to receive synchronization signals. It also provides optical wedge scanning unit control signals to the common aperture scanning transceiver module.

[0013] The image processing module, connected to the synchronization control module, is used to transform and process the photon time-of-flight data to complete the three-dimensional imaging of the target.

[0014] The transceiver coupling registration module enables a one-to-one correspondence between the two-dimensional laser dot matrix and the array detector pixels on the intermediate image plane. It includes an infrared illumination source, an off-axis parabolic mirror, an attenuator, and a focal plane detector. The attenuator is located in front of the focal plane detector, and the photosensitive surface of the focal plane detector coincides with the focal plane of the off-axis parabolic mirror.

[0015] According to the above technical solution, the beam expanding unit is a telescope system with a beam expanding ratio of 10, and the Daman grating has a beam splitting angle of 1.2 mrad and a size of 10×10 mm.

[0016] Following the above technical solution, the focal length of the focusing lens group is 43.4mm, and the focal length range of the transmitting lens group is 162.2mm.

[0017] Following the above technical solution, the hollow reflector is a duplex reflector with a small hole with a diameter of less than 26mm at the center.

[0018] A single-photon three-dimensional imaging method based on area array detection is provided. This measurement method is based on the aforementioned single-photon three-dimensional imaging system based on area array detection, and specifically includes the following steps:

[0019] S1. Adjusting the divergence angle of the expanded laser: Set the multi-beam laser array module and the transceiver coupling registration module to be on the same optical axis, and remove the Dammann grating and focusing lens group of the multi-beam laser array module; The laser generated by the laser passes through the beam expanding unit and is incident on the off-axis parabolic mirror, and converges onto the focal plane detector at the focal plane of the off-axis parabolic mirror. Adjust the spacing of each optical component of the beam expanding unit so that the light spot on the focal plane detector is smaller than the specified value, and obtain the beam divergence angle required for measurement;

[0020] S2, Intermediate image plane two-dimensional laser dot matrix adjustment;

[0021] S3. Confocal adjustment of the focusing lens group and the transmitting lens group: Based on the optical path of S1, the focusing lens group and the common aperture scanning transceiver module are installed in the common optical path between the beam expander unit and the transceiver coupling and registration module; the focal length and transfer function of the transmitting lens group of the common aperture scanning transceiver module are measured, and the spacing between each lens of the transmitting lens group is adjusted to meet the design requirements for focal length and imaging quality; the laser emitted by the laser, after passing through the beam expander group, the focusing lens group and the transmitting lens group, illuminates the off-axis parabolic mirror and converges onto the photosensitive surface of the focal plane detector at the focal plane of the off-axis parabolic mirror; the spacing between the focusing lens group and the transmitting lens group is adjusted to minimize the focused spot.

[0022] S4. Adjustment of two-dimensional laser dot matrix distribution on the focal plane of the off-axis parabolic lens;

[0023] S5. Registration of the two-dimensional laser dot array and the array detector: Based on the optical path of S4, the array detector is placed on the focal plane of the emitting mirror group, while the laser is turned off and the array detector is illuminated by an infrared illumination source; the position of the array detector is adjusted so that the focal plane detector can clearly image the array detector, and compared with the two-dimensional laser dot array distribution image recorded in step S4. It is found that the two-dimensional laser dot array and the array detector are basically superimposed, and the one-to-one correspondence registration of the two-dimensional laser dot array and the array detector pixels is completed.

[0024] S6. Target 3D Imaging: Based on the optical path system already registered in S5, the transceiver coupling registration module is removed, and a synchronization control module and an image processing module are installed to form a single-photon 3D imaging system based on area array detection. In this system, the synchronization control module controls the laser to emit high-repetition-rate pulsed laser light and simultaneously emits a measurement synchronization signal, realizing the emission of a multi-beam two-dimensional laser array and target surface scanning measurement. The image processing module transforms the photon time-of-flight data and recovers the target's 3D image from extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging.

[0025] Following the above technical solution, step S2, the adjustment of the intermediate image plane two-dimensional laser dot array, refers to installing a Damman grating and focusing lens group in the common optical path between the beam expansion unit and the transceiver coupling registration module based on the optical path of S1. At the same time, the off-axis parabolic mirror is removed, and the attenuator and focal plane detector are adjusted to the focal plane of the focusing lens group to ensure that the photosensitive surface of the focal plane detector and the focal plane of the focusing lens group coincide. The spacing between each lens of the focusing lens group is adjusted so that the distribution of the two-dimensional laser dot array is strictly consistent with the pixel distribution of the array detector.

[0026] Following the above technical solution, the adjustment of the two-dimensional laser dot matrix distribution on the focal plane of the off-axis parabolic mirror in step S4 refers to installing a Dammann grating in the common optical path between the beam expander and the focusing lens group, based on the optical path in S3. The laser emitted by the laser is formed into multi-beam light through the beam expander and the Dammann grating, and then illuminates the off-axis parabolic mirror after passing through the focusing lens group and the common aperture scanning transceiver module. The beams then converge onto the photosensitive surface of the focal plane detector at the focal plane of the off-axis parabolic mirror to clearly image the two-dimensional laser dot matrix. The direction of the Dammann grating is adjusted to adjust the two-dimensional laser dot matrix to a horizontal position, and the image of the two-dimensional laser dot matrix distribution at this time is recorded.

[0027] According to the above technical solution, in step S6, the synchronous control module controls the laser to emit a high-repetition pulsed laser, which refers to a laser beam with a single pulse energy of not less than 0.5mJ, a repetition frequency of not less than 10kHz, and a beam quality of 1.5.

[0028] Following the above technical solution, in step S6, the synchronization control module controls the laser to emit a high-repetition-rate pulsed laser while simultaneously sending a measurement synchronization signal. This enables the emission of a multi-beam two-dimensional laser array and target surface scanning measurement. The synchronization control module controls the laser to emit a laser pulse while simultaneously sending a synchronization signal to the array detector, synchronously generating a START timing start pulse signal. After a fixed delay, the START signal generates a distance-gated signal EN, which serves as the start signal for the high-frequency clock counter TDC in each pixel of the array detector. When the laser pulse echo signal returns to the photosensitive surface of the array detector, the photosensitive pixel will generate a Geiger avalanche signal. After the threshold discrimination circuit detects the avalanche signal, it generates a voltage pulse STOP to stop the high-frequency clock counter TDC of the pixel. Then, after the EN signal ends, the TDC count value of each pixel is output serially.

[0029] Following the above technical solution, in step S6, the image processing module transforms the photon time-of-flight data and recovers the three-dimensional image of the target from the extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging. This includes the following steps:

[0030] S61. Obtain a transient image of the spatiotemporal distribution based on the current input photon counting data;

[0031] S62. Background noise photons are reduced through preprocessing;

[0032] S63. Solve the optimization function by convex optimization global minimization to obtain the penalized maximum likelihood estimate of the optimization function;

[0033] S64. Reconstruct a three-dimensional image of the target area.

[0034] The beneficial effects of this invention are as follows: This invention provides a single-photon 3D imaging system based on area array detection. It utilizes a synchronous control module to control a multi-beam laser array module and a common-aperture scanning transceiver module to achieve high-sensitivity detection and rapid imaging of targets based on a multi-beam 2D ​​laser array. Simultaneously, it provides a single-photon 3D imaging system and registration method to solve the significant difficulties in transceiver matching in single-photon 3D imaging systems using array detectors. The image processing algorithm based on sub-pixel scanning and computational imaging can effectively improve the lateral resolution of long-distance imaging under limited divergence angles. The system and method of this invention achieve precise matching of multi-beam illumination and array detection in long-distance single-photon 3D imaging, greatly improving energy efficiency and measurement speed, and obtaining greater detection distances and higher imaging quality. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a single-photon three-dimensional imaging system based on area array detection according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the beam-expanding laser divergence angle adjustment according to an embodiment of the present invention;

[0038] Figure 3 This is a flowchart of a single-photon three-dimensional imaging method based on area array detection according to an embodiment of the present invention;

[0039] Figure 4 This is an image processing flowchart of a single-photon three-dimensional imaging method based on area array detection according to an embodiment of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] This invention provides a single-photon three-dimensional imaging system based on area array detection, comprising:

[0042] Multi-beam laser dot matrix module 1 is used to generate a multi-beam two-dimensional laser dot matrix for measurement, such as... Figure 1 As shown, it includes a laser 101, a beam expander 102, a Damman grating 103, and a focusing lens group 104 connected in sequence.

[0043] The beam expander 102 is used to control the laser divergence angle. For the multi-beam illumination mode of the single-photon three-dimensional imaging system, the duty cycle of the illumination laser dot array is determined by the laser divergence angle and the separation angle of the beam splitting system composed of the Damman grating 103 and the focusing lens group 104. Due to the limitation of the long-distance photon flight time, the duty cycle determines the maximum distance of long-distance single-photon detection. The beam splitting system composed of the Damman grating 103 and the focusing lens group 104 is used to generate the illumination laser dot array, that is, the array-distributed light spots that appear on the intermediate image plane.

[0044] The common aperture scanning transceiver module 2 enables common aperture scanning transmission and reception of multi-beam two-dimensional laser array and target echo signals, such as... Figure 1As shown, it includes an array detector 205 and a field stop 201, a hollow mirror 202, a emitting mirror group 203, and a light wedge scanning unit 204 arranged in sequence. The array detector 205 is disposed on the focal plane of the emitting mirror group.

[0045] By setting the intermediate image plane field stop 201, stray light from the beam splitting system can be filtered out. On the other hand, the conjugation of the intermediate image plane of the common aperture scanning transceiver module 2 is realized, which enables the field of view of the receiving optical system and the field of view of the transmitting optical system to be completely matched. That is, the array detector 205 pixels are matched one-to-one with the far-field laser two-dimensional dot matrix. This geometric alignment relationship is fixed and will not change with the distance of the target.

[0046] The hollow reflector 202 uses a duplex reflector as the system's beam-splitting element to couple the transmitting and receiving optical paths. Its central opening reduces energy loss and beam quality degradation caused by traditional reflectors, and further suppresses stray light in the transmitting path, avoiding any impact on image quality. The opening area is very small, and the echo energy entering the laser through it is extremely weak, posing no threat to laser performance. The small opening area also does not significantly reduce the effective aperture of the receiving optical path. The optical wedge scanning unit 204 projects a two-dimensional laser dot array onto the target area at a set speed and angle, and receives the diffuse reflection echo signal from the target.

[0047] The synchronization control module 3, connected to the laser 101, array detector 205, and optical wedge scanning unit 204, controls the multi-beam two-dimensional laser array to emit probe light and the array detector 205 to receive synchronization signals, providing control signals for the optical wedge scanning unit 204 to the common aperture scanning transceiver module 2. Under the control of the synchronization control module 3, the optical wedge scanning unit 204 deflects and projects the incident two-dimensional laser array at a specified angle and speed.

[0048] Image processing module 4, connected to the synchronization control module, is used to transform and process photon time-of-flight data to complete target three-dimensional imaging.

[0049] Image processing module 4 transforms the photon count data and recovers the target's three-dimensional information from the extremely weak photon count data at a distance using a reconstruction algorithm based on subpixel scanning and computational imaging.

[0050] The transceiver coupling registration module 5 enables a one-to-one correspondence between the two-dimensional laser dot matrix and the array detector pixels on the intermediate image plane, such as... Figure 2 As shown, it includes an infrared illumination source 501, an off-axis parabolic mirror 502, an attenuator 503, and a focal plane detector 504. The attenuator 503 is disposed in front of the focal plane detector 504, and the photosensitive surface of the focal plane detector 504 coincides with the focal plane of the off-axis parabolic mirror 502.

[0051] In a preferred embodiment, the beam expander 102 is a telescope system with a beam expansion ratio of 10, and the Dammann grating 103 has a beam splitting angle of 1.2 mrad (0.066°) and a size of 10 × 10 mm. In order to prevent adjacent laser beams from overlapping and to ensure that they are smaller than the field of view of the detector pixels during long-distance detection, the beam is expanded by the telescope system with a beam expansion ratio of 10, outputting a laser beam with a divergence angle of 0.158 mrad and a beam diameter of 10 mm. The beam splitting system based on the Dammann grating 103 generates a 64 × 64 far-field projected laser beam, which is then focused by the focusing lens group 104 to generate an array of laser dots on the central image plane.

[0052] In a preferred embodiment, the focal length of the focusing lens group is 43.4 mm, and the focal length of the emitting lens group ranges from 162.2 mm.

[0053] In a preferred embodiment, the hollow reflector 202 is a duplex reflector with a small hole of 25.5 mm in diameter at its center. The area of ​​the hole is very small, and the echo energy entering the laser through the hole is very weak and will not harm the performance of the laser. The small area of ​​the hole will also not significantly reduce the effective aperture of the receiving optical path.

[0054] This invention provides a single-photon three-dimensional imaging method based on area array detection. This measurement method is based on the aforementioned single-photon three-dimensional imaging system based on area array detection, and specifically includes the following steps:

[0055] S1, Adjustment of the beam-expanding laser divergence angle, such as Figure 2 As shown, the multi-beam laser array module 1 and the transceiver coupling and registration module 5 are set to coaxial orientation, and the Damman grating 103 and focusing lens group 104 of the multi-beam laser array module 1 are removed. The laser generated by the laser 101 is incident on the off-axis parabolic mirror 502 after passing through the beam expander unit 102, and converges onto the focal plane detector 504 at the focal plane of the off-axis parabolic mirror 502. The spacing of each optical component in the beam expander unit is adjusted so that the light spot on the focal plane detector 504 is smaller than a specified value, thereby obtaining the beam divergence angle required for measurement. For a 6m off-axis parabolic mirror, it should be less than 0.99mm.

[0056] In a specific embodiment, the beam expander 102 is a telescope system with a beam expansion ratio of 10, and the Damman grating 103 has a beam splitting angle of 1.2 mrad (0.066°) and a size of 10 × 10 mm. In order to prevent adjacent laser beams from overlapping and to ensure that they are smaller than the detector pixel field of view during long-distance detection, the beam is expanded by a telescope system with a beam expansion ratio of 10, outputting a laser beam with a divergence angle of 0.158 mrad and a beam diameter of 10 mm.

[0057] S2, Adjustment of the two-dimensional laser dot matrix in the intermediate image plane.

[0058] S3. Confocal adjustment of the focusing lens group and the transmitting lens group: Based on the optical path of S1, the focusing lens group 104 and the common aperture scanning transceiver module 2 are installed in the common optical path between the beam expander unit 102 and the transceiver coupling and registration module 5; the focal length and transfer function of the transmitting lens group 203 of the common aperture scanning transceiver module 2 are measured, and the spacing between the lenses of the transmitting lens group 203 is adjusted to meet the design requirements for focal length and imaging quality; the laser emitted by the laser 101, after passing through the beam expander group, the focusing lens group 104, and the transmitting lens group 203, illuminates the off-axis parabolic mirror 502 and converges onto the photosensitive surface of the focal plane detector 504 at the focal plane of the off-axis parabolic mirror 502; the spacing between the focusing lens group 104 and the transmitting lens group 203 is adjusted to minimize the focused spot. At this time, the intermediate image plane is simultaneously located on the focal planes of the focusing lens group 104 and the transmitting lens group 203.

[0059] The Gm-APD array detector achieves conjugation of the intermediate image plane in the transmitting and receiving optical systems, ensuring a perfect match between the field of view of the receiving and transmitting optical systems. The Gm-APD array detector has a pixel size of 50 μm, a photosensitive target size of 3.2 × 3.2 mm, a Damman grating with a 103 beam splitting angle of 1.2 mrad, and a focusing lens focal length of 43.4 mm. In this configuration, the diameter of each focused spot is 13.7 μm, smaller than the pixel photosensitive surface size of 43.7 μm.

[0060] The common aperture scanning transceiver module 2 is used to project and detect laser signals, achieving common aperture transmission and scanning. Due to the perfect matching of the transmitting and receiving fields of view, the instantaneous field of view corresponding to a single pixel is 0.308 mrad. The focal length of the transmitting mirror group 203 is 162.2 mm, and the instantaneous field of view for each imaging is 1.13° (1.6° diagonally). The two-dimensional laser dot array is projected onto the target surface through the optical wedge scanning unit 204. After diffuse reflection from the target surface, the echo signal of the transmitted laser beam is focused by the receiving optical system and finally projected onto the photosensitive surface of the Gm-APD array detector through the hollow reflector 202, thereby obtaining the round-trip flight time of the laser beam and calculating the target distance information.

[0061] S4. Adjustment of two-dimensional laser dot distribution on the focal plane of the off-axis parabolic lens.

[0062] S5. Registration of the two-dimensional laser dot matrix and array detector: Based on the optical path of S4, the array detector 205 is placed on the focal plane of the emitting mirror group 203, while the laser 101 is turned off. The array detector 205 is illuminated by the infrared illumination source 501. The position of the array detector 205 is adjusted so that the focal plane detector 504 can clearly image the array detector 205. The image is compared with the two-dimensional laser dot matrix distribution image recorded in step S4. It is found that the two-dimensional laser dot matrix and the array detector 205 are basically superimposed, and the one-to-one correspondence registration of the two-dimensional laser dot matrix and the array detector 205 pixels is completed.

[0063] In practice, the laser 101 and infrared light source 501 are repeatedly used to illuminate the two-dimensional laser dot array. The direction of the two-dimensional laser dot array is adjusted by the Damman grating 103. The horizontal (vertical) displacement is adjusted by the spatial position of the array detector 205. Since S2 ensures that the two-dimensional laser dot array and the array detector 205 are strictly consistent in size, after repeated adjustments, the two-dimensional laser dot array and the array detector 205 pixels are registered in a one-to-one correspondence.

[0064] S6. Target 3D Imaging: Based on the optical path system already registered in S5, the transceiver coupling registration module is removed, and a synchronization control module and an image processing module are installed to form a single-photon 3D imaging system based on area array detection. In this system, the synchronization control module controls the laser to emit high-repetition-rate pulsed laser light and simultaneously emits a measurement synchronization signal, realizing the emission of a multi-beam two-dimensional laser array and target surface scanning measurement. The image processing module transforms the photon time-of-flight data and recovers the target's 3D image from extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging.

[0065] Before performing 3D imaging, the system is calibrated. After calibration, a single-photon 3D imaging system based on area array detection is assembled to perform 3D imaging of the target, eliminating the need to calibrate the system for each measurement.

[0066] As the preferred embodiment, the intermediate image plane two-dimensional laser dot array adjustment in step S2 refers to installing a Damman grating 103 and a focusing lens group 104 in the common optical path between the beam expander unit 102 and the transceiver coupling registration module 5 based on the optical path in S1. At the same time, the off-axis parabolic mirror 502 is removed, and the attenuator 503 and the focal plane detector 504 are adjusted to the focal plane of the focusing lens group 104 to ensure that the photosensitive surface of the focal plane detector 504 and the focal plane of the focusing lens group 104 coincide. The spacing between the lenses of the focusing lens group 104 is adjusted so that the distribution of the two-dimensional laser dot array is strictly consistent with the pixel distribution of the array detector 205.

[0067] The array detector 205 uses a Gm-APD array, and the divergence angle of the laser beam is matched with the beam splitting angle of the Damman grating 103, which meets the matching requirements of the duty cycle of the array detector 205. The fill factor of the Gm-APD array detector (China Electronics Technology Group Corporation) is 60%.

[0068] As the preferred embodiment, the adjustment of the two-dimensional laser dot matrix distribution on the focal plane of the off-axis parabolic mirror in step S4 refers to the installation of a Dammann grating 103 in the common optical path between the beam expander 102 and the focusing lens group 104, based on the optical path in S3. The laser emitted by the laser 101 forms a multi-beam light through the beam expander 102 and the Dammann grating 103, and after passing through the focusing lens group 104 and the common aperture scanning transceiver module 2, it illuminates the off-axis parabolic mirror 502, and then converges onto the photosensitive surface of the focal plane detector 504 at the focal plane of the off-axis parabolic mirror 502 to clearly image the two-dimensional laser dot matrix. The direction of the Dammann grating 103 is adjusted to adjust the two-dimensional laser dot matrix to a horizontal position, and the image of the two-dimensional laser dot matrix distribution at this time is recorded.

[0069] In the preferred embodiment, the high-repetition pulsed laser controlled by the synchronization control module in step S6 refers to a laser beam with a single pulse energy of not less than 0.5 mJ, a repetition frequency of not less than 10 kHz, and a beam quality of 1.5.

[0070] Laser 101 generates a high-peak-energy, narrow-pulse-width laser beam, providing a good active light source for long-distance ranging. The single-pulse energy is 0.5 mJ, the repetition frequency is 10 kHz, and the beam quality is 1.5. Beam expander 102 collimates and expands the laser beam from laser 101, matching the divergence angle of the laser beam with the beam-splitting angle of the Damman grating 103, thus meeting the duty cycle matching requirements with the array detector. The fill factor of the Gm-APD array detector (China Electronics Technology Group Corporation) is 60%, and the beam-splitting angle of the Damman grating (Holo / Or) is 1.2 mrad. (0.066°), with dimensions of 10×10mm, to ensure that adjacent laser beams do not overlap and are smaller than the detector pixel's field of view during long-distance detection, a telescope system with a beam expansion ratio of 10 is used to expand the beam, outputting a laser beam with a divergence angle of 0.158mrad and a beam diameter of 10mm. A beam-splitting system based on a Damman grating 103 generates a 64×64 far-field projected laser beam, which is converged by a focusing lens group 104 to generate an array of laser dots on the intermediate image plane. This dot array achieves conjugation of the intermediate image plane of the transmitting and receiving optical systems with the Gm-APD array detector, ensuring that the field of view of the receiving optical system and the field of view of the transmitting optical system are perfectly matched. The Gm-APD array detector has a pixel size of 50μm, a photosensitive target size of 3.2×3.2mm, a Damman grating beam splitting angle of 1.2mrad, and a focal length of 43.4mm for the focusing lens. At this time, the diameter of each focused spot is 13.7μm, which is smaller than the pixel photosensitive surface size of 43.7μm.

[0071] The common aperture scanning transceiver module 2 is used to project and detect the laser light signal to achieve common aperture transmission and scanning. A hollow reflector 202 couples the transmitting and receiving optical paths. Due to the perfect matching of the transmitting and receiving fields of view, the instantaneous field of view angle corresponding to a single pixel is 0.308 mrad, the focal length of the projection lens is 162.2 mm, and the instantaneous field of view angle for each imaging is 1.13° (1.6° diagonally). The two-dimensional laser dot array is projected onto the target surface through the scanning system. After diffuse reflection from the target surface, the echo signal of the emitted laser beam is focused by the common aperture scanning transceiver module 2 and finally projected onto the photosensitive surface of the Gm-APD array detector via the hollow reflector 202, thereby obtaining the round-trip flight time of the laser beam and calculating the target distance information.

[0072] In the preferred embodiment, in step S6, the synchronization control module 3 controls the laser 101 to emit a high-repetition-rate pulsed laser and simultaneously emits a measurement synchronization signal. This enables the emission of a multi-beam two-dimensional laser array and target surface scanning measurement. Specifically, the synchronization control module 3 controls the laser 101 to emit a laser pulse while simultaneously sending a synchronization signal to the array detector 205, which synchronously generates a START timing start pulse signal. After a fixed delay, the START signal generates a distance-gated signal EN, which serves as the start signal for the high-frequency clock counter TDC in each pixel of the array detector. When the laser pulse echo signal returns and reaches the photosensitive surface of the array detector, the photosensitive pixel will generate a Geiger avalanche signal. After the threshold discrimination circuit detects the avalanche signal, it generates a voltage pulse STOP to stop the high-frequency clock counter TDC of the pixel. Then, after the EN signal ends, the TDC count value of each pixel is output serially.

[0073] As a specific embodiment, the TDC counter is 12-bit, with a time resolution of 1.25 ns, and the gate is set to a maximum cutoff time of 5.12 μs, with a distance detection range of 768 m.

[0074] In the preferred embodiment, step S6 involves the image processing module transforming the photon time-of-flight data and reconstructing the three-dimensional image of the target from extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging. This includes the following steps:

[0075] S61. Obtain a transient image of the spatiotemporal distribution based on the current input photon counting data;

[0076] S62. Background noise photons are reduced through preprocessing;

[0077] S63. Solve the optimization function by convex optimization global minimization to obtain the penalized maximum likelihood estimate of the optimization function;

[0078] S64. Reconstruct a three-dimensional image of the target area.

[0079] Based on the registered single-photon 3D imaging system using area array detection, the imaging process of the measured target is as follows: A laser beam is output from laser 101; the pulsed laser emitted by laser 101 has its divergence angle controlled by beam expander 102, and then incident on a beam splitting system based on Damman grating 103 to generate a two-dimensional parallel laser beam array. This array is then converged by focusing lens group 104, resulting in a two-dimensional laser dot array on the intermediate image plane. The two-dimensional laser dot array is projected onto the target surface through the hollow reflector 202 and optical wedge scanning unit 204 of the common aperture scanning transceiver module 2. The echo signal formed by the diffuse reflection of the emitted laser beam from the target surface is focused by the receiving optical system and finally projected onto the photosensitive surface of array detector 205 through the hollow reflector 202, thus obtaining the round-trip flight time of the laser beam. The photon counting data is transformed by image processing module 4, and the three-dimensional information of the target is recovered from the extremely weak photon counting data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging.

[0080] Understandably, currently available laser 3D imaging systems often employ single-point scanning with varying apertures, resulting in slow scanning speeds, low resolution, and issues with transmit / receive registration. The few single-photon 3D imaging systems that use array detectors also primarily employ flood illumination due to significant difficulties in transmit / receive matching. When imaging distant targets, they are limited by energy efficiency and struggle to achieve good results.

[0081] To address the technical problem this invention aims to solve, the present invention provides a single-photon three-dimensional imaging system and registration method based on multi-beam array illumination and array detector. This simplifies the transmit / receive matching by employing a conjugated method between the intermediate image planes of the shared aperture multi-beam illumination array and the array detector pixels. A corresponding registration method is proposed, achieving precise matching of multi-beam illumination and array detector in long-distance single-photon three-dimensional imaging, significantly improving energy efficiency, achieving longer detection distances, and higher imaging quality.

[0082] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0083] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A single-photon three-dimensional imaging system based on area array detection, characterized in that, include: The multi-beam laser array module includes a laser, a beam expander, a Damman grating, and a focusing lens group connected in sequence; The common aperture scanning transceiver module includes an array detector and a field stop, a hollow mirror, a transmitting mirror group, and a light wedge scanning unit arranged in sequence. The array detector is located on the focal plane of the transmitting mirror group. Synchronization control module; Image processing module; The transceiver coupling and registration module includes an infrared illumination source, an off-axis parabolic mirror, an attenuator, and a focal plane detector. The attenuator is located in front of the focal plane detector, and the photosensitive surface of the focal plane detector coincides with the focal plane of the off-axis parabolic mirror. The registration process of this single-photon 3D imaging system includes the following steps: S1. Adjusting the divergence angle of the expanded laser: Set the multi-beam laser array module and the transceiver coupling registration module to be on the same optical axis, and remove the Dammann grating and focusing lens group of the multi-beam laser array module; The laser generated by the laser passes through the beam expanding unit and is incident on the off-axis parabolic mirror, and converges onto the focal plane detector at the focal plane of the off-axis parabolic mirror. Adjust the spacing of each optical component of the beam expanding unit so that the light spot on the focal plane detector is smaller than the specified value, and obtain the beam divergence angle required for measurement; S2, Intermediate image plane two-dimensional laser dot matrix adjustment; S3. Confocal adjustment of the focusing lens group and the transmitting lens group: Based on the optical path of S1, the focusing lens group and the common aperture scanning transceiver module are installed in the common optical path between the beam expander unit and the transceiver coupling and registration module; the focal length and transfer function of the transmitting lens group of the common aperture scanning transceiver module are measured, and the spacing between each lens of the transmitting lens group is adjusted to meet the design requirements for focal length and imaging quality; the laser emitted by the laser, after passing through the beam expander group, the focusing lens group and the transmitting lens group, illuminates the off-axis parabolic mirror and converges onto the photosensitive surface of the focal plane detector at the focal plane of the off-axis parabolic mirror; the spacing between the focusing lens group and the transmitting lens group is adjusted to minimize the focused spot. S4. Adjust the two-dimensional laser dot matrix distribution on the focal plane of the off-axis parabolic lens to be horizontal, and record the image of the two-dimensional laser dot matrix distribution at this time. S5. Registration of the two-dimensional laser dot array and the array detector: Based on the optical path adjusted in S4, the array detector is placed on the focal plane of the emitting mirror group, while the laser is turned off and the array detector is illuminated by an infrared illumination source; the position of the array detector is adjusted so that the focal plane detector can clearly image the array detector, and compared with the two-dimensional laser dot array distribution image recorded in step S4, and it is found that the two-dimensional laser dot array and the array detector are basically superimposed, thus completing the one-to-one correspondence registration of the two-dimensional laser dot array and the array detector pixels. S6. Target 3D Imaging: Based on the optical path system already registered in S5, the transceiver coupling registration module is removed, and a synchronization control module and an image processing module are installed to form a single-photon 3D imaging system based on area array detection. In this system, the synchronization control module controls the laser to emit high-repetition-rate pulsed laser light and simultaneously emits a measurement synchronization signal, realizing the emission of a multi-beam two-dimensional laser array and target surface scanning measurement. The image processing module transforms the photon time-of-flight data and recovers the target's 3D image from extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging.

2. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, The beam expander is a telescope system with a beam expansion ratio of 10, and the Damman grating has a beam splitting angle of 1.2 mrad and a size of 10 × 10 mm.

3. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, The focal length of the focusing lens group is 43.4 mm, and the focal length of the emitting lens group ranges from 162.2 mm.

4. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, The hollow reflector is a duplex reflector with a small hole with a diameter of less than 26mm at the center.

5. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, The intermediate image plane two-dimensional laser dot array adjustment in step S2 refers to installing a Damman grating and focusing lens group in the common optical path between the beam expander unit and the transceiver coupling registration module based on the optical path in S1, while removing the off-axis parabolic mirror, and adjusting the attenuator and focal plane detector to the focal plane of the focusing lens group to ensure that the photosensitive surface of the focal plane detector and the focal plane of the focusing lens group coincide, and adjusting the spacing of each lens in the focusing lens group so that the distribution of the two-dimensional laser dot array is strictly consistent with the pixel distribution of the array detector.

6. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, The adjustment of the two-dimensional laser dot matrix distribution on the focal plane of the off-axis parabolic mirror in step S4 refers to the installation of a Dammann grating in the common optical path between the beam expander and the focusing lens group, based on the optical path in S3. The laser emitted by the laser is formed into multi-beam light through the beam expander and the Dammann grating, and then illuminates the off-axis parabolic mirror after passing through the focusing lens group and the common aperture scanning transceiver module. The beams then converge onto the photosensitive surface of the focal plane detector at the focal plane of the off-axis parabolic mirror to clearly image the two-dimensional laser dot matrix. The direction of the Dammann grating is adjusted to adjust the two-dimensional laser dot matrix to a horizontal position, and the image of the two-dimensional laser dot matrix distribution at this time is recorded.

7. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, In step S6, the synchronization control module controls the laser to emit a high-repetition-rate pulsed laser, which refers to a laser beam with a single pulse energy of not less than 0.5 mJ, a repetition frequency of not less than 10 kHz, and a beam quality of 1.

5.

8. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, In step S6, the synchronization control module controls the laser to emit high-repetition pulsed laser light and simultaneously sends a measurement synchronization signal to realize the emission of the multi-beam two-dimensional laser array and target surface scanning measurement. This means that the synchronization control module controls the laser to emit a laser pulse while simultaneously sending a synchronization signal to the array detector, and synchronously generates a START timing start pulse signal. After a fixed delay, the START signal generates a distance gate signal EN, which serves as the start signal for the high-frequency clock counter TDC in each pixel of the array detector. When the laser pulse echo signal returns to the photosensitive surface of the array detector, the photosensitive pixel will generate a Geiger avalanche signal. After the threshold discrimination circuit detects the avalanche signal, it generates a voltage pulse STOP to stop the high-frequency clock counter TDC of the pixel. Then, after the EN signal ends, it serially outputs the TDC count value of each pixel.

9. The single-photon three-dimensional imaging system based on area array detection according to claim 1, characterized in that, In step S6, the image processing module transforms the photon time-of-flight data and recovers the three-dimensional image of the target from extremely weak photon count data at a long distance using a reconstruction algorithm based on sub-pixel scanning and computational imaging. This includes the following steps: S61. Obtain a transient image of the spatiotemporal distribution based on the current input photon counting data; S62. Background noise photons are reduced through preprocessing; S63. Solve the optimization function by convex optimization global minimization to obtain the penalized maximum likelihood estimate of the optimization function; S64. Reconstruct a three-dimensional image of the target area.

Images