A compact distributed field-of-view stitching laser radar system for all-time thousand-beam long-distance three-dimensional detection

Abstract

The application provides a compact distributed field-of-view splicing laser radar system for all-day long-distance three-dimensional detection of kilo-beam, and belongs to the technical field of laser radar. The system comprises an IPC, a plurality of tunable, narrow-linewidth, nanosecond pulse width fiber lasers, a collimating beam-splitting emission optical system, an off-axis three-mirror receiving optical system, a pull-tower type array fiber-array beam-splitting system, a precise imaging lens group, an ultranarrow-band light filtering system, a trigger and temperature control module and a small facet array SPAD. The system performs all-day, large field-of-view, high-precision three-dimensional imaging on high-speed moving targets, and the working principle is that the laser emission system synchronously emits N*N (not less than 32*32) small divergence angle laser beams to cover a large area in front of the radar, and the included angle between the laser beams is M*M degrees; at the same time, based on the time of flight, the receiving system synchronously detects N*N laser echo signals for narrow field-of-view single-photon detection, and inversely calculates the three-dimensional point cloud imaging information of the target at the corresponding distance.

Description

Technical Field

[0001] This invention belongs to the field of lidar technology, and particularly relates to a compact distributed field-of-view stitching lidar system for all-weather, thousand-beam, long-range, three-dimensional detection. Background Technology

[0002] LiDAR, based on laser ranging technology, acquires a 3D image of a target by covering the target surface with an emitted laser beam and fusing the echo signals scattered by the target features. The pulse-time-of-flight method is the simplest and most typical method for target mapping. It uses a narrow-pulse laser as the light source, emitting the beam through an optical system. A receiving telescope calculates the laser's flight time by receiving the time difference between the emitted laser and the target's scattered echo signals, thus obtaining the longitudinal depth information of the illuminated target features. It can be used with a laser scanning module to achieve 3D imaging of targets to the north, or it can simultaneously emit multiple laser pulses and combine them with linear or area array photodetectors to achieve 3D imaging of the overall shape and features of the target. The longitudinal resolution of the imaging is determined by the laser pulse width, the size of the imaging area depends on the scanning range, the focal length of the optical system, and the size of the photodetector's photosensitive surface.

[0003] Currently, imaging lidar can be classified into three types according to its working method: single-point scanning type, linear array scanning type, and area array staring type.

[0004] The dot matrix lidar uses a single-point beam and unit detector to achieve single-point detection. Combined with a two-dimensional scanning galvanometer module, it completes two-dimensional field-of-view coverage scanning of the target, obtains a dense dot matrix image, and inverts the target's three-dimensional image by integrating the single-point ranging information.

[0005] Linear array lidar emits laser beams in a linear array, and the receiving end uses a linear array detector or a small area array detector, so that the system can simultaneously obtain the distance information of multiple target points in the linear array direction. With the help of a one-dimensional scanning galvanometer, the linear array beam can achieve two-dimensional point coverage of the detected target. Similarly, by combining the single-point distance information, a three-dimensional image of the target can be obtained.

[0006] The staring laser radar array is designed to emit lasers in a two-dimensional plane array through an output optical system, thereby achieving multi-beam coverage of the two-dimensional space of the target. The receiving end uses a large array detector with the same number of pixels as the laser beam to receive the lasers synchronously one-to-one, and inverts the image to achieve three-dimensional imaging of the target.

[0007] The technical defects existing in the prior art include:

[0008] A dot matrix lidar contains only a single beam. To acquire an N×N resolution 3D image, it needs to be combined with a complex 2D precision scanning system. The system is complex, has poor stability, and takes a lot of time to scan and cover the entire target, making it inefficient and unsuitable for accurate imaging of moving targets.

[0009] Linear array lidar: It can simultaneously emit N (1×N) linear array laser beams, but still requires a one-dimensional precision scanning system to achieve a large field of view coverage of the target. The system structure is complex and the stability is poor. It also requires a certain amount of time to complete the target feature scanning coverage. The efficiency is still relatively low and it is not suitable for accurate imaging of fast relative moving targets. When using a linear array detector for detection, under the condition of fixed system aperture and focal length, the size of the linear array detector is limited by the one-dimensional field of view. Compared with dot array lidar, the emitted laser energy needs to be increased by N times to meet the imaging effect of the same detection distance.

[0010] A staring laser radar array uses an optical system to collimate and emit an incident laser beam with a large divergence angle, covering a large area of ​​targets in front. It achieves wide field-of-view coverage of targets without the need for an integrated scanning module. Using an aberration-correcting optical system with a certain focal length, the array detector can clearly detect targets and provide real-time, high-precision imaging of moving targets. However, it has the following drawbacks: With limited focal lengths in the optical system (especially long-focal-length optical systems), its detection field of view is limited by the size of the detector array. Ultra-large array detectors have not yet been developed, so the total detection field of view remains relatively small. Compared to a dot-array laser radar, the laser energy needs to be increased by N×N times for the same detection distance; compared to a linear array laser radar, the emitted laser energy needs to be increased by N times. To achieve detection at longer distances, the array detector is generally operated in Geiger mode for single-photon sensitivity detection. This is because large array single-photon detection... The development of such devices is currently difficult. On the other hand, large-area SPADs bring high signal crosstalk and low operating frame rate, which is not conducive to point cloud imaging of highly dynamic targets. In addition, large field of view conditions introduce extremely large background photon noise, and background noise suppression during the daytime is extremely difficult. Traditional narrowband interference filters can meet the requirements of large field of view during the daytime, but their bandwidth is limited and the filtering effect is not good. The ultra-narrowband filtering technology using filters and Fabry-Perot etalon cascades can achieve narrowband filtering, but it cannot meet the requirements of large field of view operation. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention proposes a compact distributed field-of-view stitched lidar system for all-weather, thousand-beam, long-range, three-dimensional detection.

[0012] This invention provides a compact distributed field-of-view stitched lidar system for all-weather, thousand-beam, long-range, three-dimensional detection. The system includes: an IPC (Integrated Photonic Array), multiple tunable narrow-linewidth nanosecond fiber lasers, a collimating beam-splitting emission optical system, an off-axis three-mirror receiving optical system, a tapered array fiber-array beam splitting system, a precision imaging lens group, an ultra-narrowband filter system, a triggering and temperature control module, and a small-area SPAD (Special Optical Array). Wherein:

[0013] The multi-channel tunable narrow-linewidth nanosecond fiber laser uses a semiconductor single-frequency fiber laser with a wavelength tunable within a certain range as a seed source. After three stages of pre-amplification (each stage's output includes optical isolators, filters, pump sources, and other optical devices), it enters the EOPM for phase modulation. Then, it passes through a 50:50 beam splitter, splitting one optical path into two paths of equal power before entering the main amplification system. Each stage of the three pre-amplification stages includes an optical isolator, filter, and pump source.

[0014] The collimating and beam-splitting optical system collimates and expands the fiber beam and splits it into two-dimensional beams for emission. The collimating and beam-splitting optical system consists of an off-axis aspherical mirror and a DOE element. The off-axis aspherical mirror is used to collimate the fiber beam and compress the divergence angle of the emitted beam. The DOE is used to emit the collimated beam into two-dimensional space according to the principle of equal energy distribution. At the same time, the divergence angle of the split beam is consistent with that of the incident beam to achieve long-distance and large field-of-view coverage.

[0015] The off-axis three-mirror receiving optical system consists of an aspherical off-axis primary mirror, a receiving aperture, and an off-axis correcting mirror, which is used to correct edge field-of-view phase aberration, and the edge field-of-view blur is smaller than the core diameter of the multimode fiber.

[0016] The tapered array fiber-to-array beam splitter system is used to connect off-axis three-mirror receiving optical systems and precision imaging lens groups. The fiber used is gradient refractive index multimode fiber with a core / cladding ratio of 50 / 125. One end is tapered and acid-etched to make the core / cladding ratio 30 / 45.

[0017] The precision imaging lens assembly is used to connect the subarray end of the small area array single-photon detector and the tapered array fiber-to-array beam splitter system.

[0018] The ultra-narrowband filter system consists of an IF and an FPI connected in series in the optical path, with the center wavelengths of the IF and FPI being consistent with the emitted laser.

[0019] The triggering and temperature control modules provide triggering for the laser and the small area array SPAD, and control the center wavelength of the ultra-narrow band filter system to prevent the center wavelength of the ultra-narrow band filter system from drifting due to external environmental fluctuations. The triggering and temperature control modules are controlled in real time by the IPC through the serial port.

[0020] The small area array SPAD consists of J channels. Each channel performs photon-level sensitivity detection on the corresponding sub-array fiber signal and outputs the three-dimensional point cloud of the spatial region corresponding to the sub-array fiber. The J-channel small area array SPAD outputs the corresponding J-channel region point cloud data and transmits it to the IPC.

[0021] IPC stitches together the measured point cloud data of each SPAD array according to the corresponding spatial regions to complete the inversion output of the total field of view 3D point cloud image.

[0022] The system proposed according to the present invention is for multi-channel tunable narrow-linewidth nanosecond fiber lasers:

[0023] The operating wavelength is 1550nm, used for synchronous emission of multiple laser pulses, and the fiber optic transmission path is K;

[0024] The main amplification system is a two-stage amplification system. The first-stage main amplifier uses 12 / 250PM erbium-ytterbium co-doped fiber to amplify the power to the required 5% energy, and then splits the beam into the second-stage main amplification system. The second-stage main amplifier uses large-mode-field erbium-ytterbium co-doped active fiber. Through appropriate coiling and encapsulation technology, the fiber mode and beam quality are controlled within the target range.

[0025] It emits narrow pulses with a time scale of nanosecond pulse width, less than or equal to 3 nanoseconds; the laser wavelength is tunable in frequency, with a tuning accuracy of picometers; and the output linewidth is less than 50 picometers.

[0026] According to the system proposed in this invention, for a collimating beam-splitting optical system:

[0027] Off-axis aspherical mirrors are used to collimate fiber beams and compress the divergence angle of the emitted beam to no more than 0.15 mrad.

[0028] The divergence angle of the split beam is consistent with that of the incident beam to achieve long-distance large field of view coverage. The angle between the beams is φ / N-1, where φ is the detection field of view angle of the system.

[0029] The collimating and beam-splitting optical system consists of K off-axis mirrors and a DOE (Diffraction Optical Array), with each path individually connected to a single output laser fiber. Each path covers a field of view of [missing information]. K paths are spliced ​​together to cover N×N points and regions, with the angle between the optical axes of each path being φ / N-1.

[0030] According to the system proposed in this invention, an aspherical off-axis primary mirror is used in an off-axis three-reflector receiving optical system to achieve high-efficiency optical reception with a large field of view of a large-area fiber array under the requirements of fixed receiving optical aperture and long focal length. The single-beam output light divergence angle is 0.15mrad, and the single-beam receiving field of view is 0.2mrad.

[0031] According to the system proposed in this invention, for a tapered array fiber-to-array beam splitting system, the receiving end is connected to an off-axis three-mirror receiving optical system. The non-tapered end is an N×N array, and the output end splits the N×N array into J sub-arrays, where J = N×N / A, and A is the number of surface elements of a single small area detector. Each sub-array is generated by the tapered end. The fiber spacing in the sub-array is 50µm.

[0032] According to the system proposed in this invention, a multi-lens design is adopted for the precision imaging lens group to correct edge field aberrations, and each fiber image is aligned with the surface element; at the same time, the intermediate optical path adopts a collimation design to compress the total divergence angle of the sub-array fiber and loads an ultra-narrowband filter system. The precision imaging lens group consists of J groups of optical systems with the same parameters.

[0033] According to the system proposed in this invention, for an ultra-narrowband filter system, the IF bandwidth is 350 pm and the FPI bandwidth is 50 pm.

[0034] In summary, this invention provides a compact distributed field-of-view stitching lidar system for long-range 3D detection with thousands of beams. It employs N×N beams with narrow linewidth and small divergence angle laser emission to cover a large area of ​​the scene at a long distance. It uses a high off-axis three-reflector optical system and a tapered fiber array-fiber beam splitter system to achieve precise point-to-point reception of N×N beams. It combines ultra-narrowband filtering to suppress background light noise during the daytime. It achieves high signal-to-noise ratio and long-range independent detection of sub-fields of view through multiple small area array SPADs and point-to-point clear imaging optical modules. Finally, it uses a computer to stitch together the sub-field of view imaging results of multiple detectors according to their positions to achieve long-range large field-of-view 3D imaging.

[0035] Compared with the prior art, the technical advantages of this invention are as follows:

[0036] 1. Real-time thousand-beam wide-field staring coverage and high-precision 3D point cloud acquisition of high-speed moving targets. There is currently no related design system, which is a significant breakthrough in the field of ultra-wide field of view long-distance single-photon detection.

[0037] 2. Achieve long-range, wide-field-of-view, all-day long-range detection based on small array SPADs.

[0038] 3. Based on off-axis three-mirror and tapered fiber array-fiber beam splitter design, the contradiction between long focal length and large field of view detection is resolved, and synchronous, high-precision and high-efficiency coupling reception of thousand-beam photonic signals is achieved.

[0039] 4. Based on narrow linewidth light sources, we will carry out ultra-narrowband filtering technology and tapered fiber array-fiber beam splitting design and optimization to solve the problems of single-photon sensitivity detection and effective background light noise suppression under all-day conditions with large array and large field of view, and improve the signal-to-noise ratio.

[0040] 5. Based on fiber optic structured system design, the system is more compact, miniaturized, and integrated.

[0041] 6. Small-area SPADs are used for stitched field of view coverage, which effectively reduces the high crosstalk between signals of each element in photoelectric detection and the high dark count rate of the detector when using large-area SPADs. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram illustrating the principle of synchronous transmission and reception detection of N×N small divergence angle laser beams according to an embodiment of the present invention.

[0044] Figure 2 A schematic diagram of a compact distributed field-of-view stitched lidar system for all-weather, thousand-beam, long-range three-dimensional detection according to an embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of a 32×32 beam lidar system according to an embodiment of the present invention;

[0046] Figure 4 This is a schematic diagram of the composition of a 32×32 beam long-range three-dimensional detection optical field-of-view stitching lidar system according to an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Definitions of abbreviations and key terms:

[0049] Industrial Personal Computer (IPC);

[0050] Diffractive optical elements (DOE)

[0051] Single Photon Detectors: SPAD;

[0052] Interference filter (IF);

[0053] Fabry-Perot Interferometer (FPI)

[0054] Laser Control Unit (LCU)

[0055] Avalanche Photo Diode (APD)

[0056] Geiger Mode (GM)

[0057] This invention focuses on accurate 3D imaging of fast-moving targets around the clock, improving the detection field of view and detection range. It proposes a compact, distributed field-of-view stitched lidar system for long-range 3D detection using a thousand beams. At the laser emission end, a tunable, narrow-linewidth, nanosecond fiber laser is selected for simultaneous amplification of multiple pulse energy channels and fiber optic output, meeting the energy requirements for long-range, large-field-of-view detection.

[0058] After passing through the beam-expanding optical system, each optical fiber is split and emitted by its own diffractive optical element, realizing single-beam single-path laser with small divergence angle, high energy, and array emission; multiple array beams are spliced ​​in space in two dimensions to achieve two-dimensional coverage of a large spatial area and needle-shaped beams.

[0059] The receiver of the tapered array fiber-to-array beam splitter performs small field-of-view reception of spatial needle beams with one-to-one precise fiber-to-beam matching. The receiver is connected to an off-axis three-mirror optical system to achieve long focal length, large field of view, and high image quality imaging. It meets the requirements of high optical efficiency signal photon coupling into each fiber, completes single-beam laser narrow field-of-view reception, reduces daytime background noise, and provides efficient reception coverage of a large two-dimensional spatial area to increase the detection field of view.

[0060] The tapered array fiber-to-array beam splitter splits the output end into multiple sub-fiber arrays. The fiber used is graded-index multimode fiber. One end of the fiber is cladding etched and tapered. The fibers are tightly packed at the end of the sub-fiber array to achieve efficient transmission of photonic signals while reducing the total effective output area of ​​the sub-fiber array. This ensures high peak transmittance and narrow bandwidth for subsequent ultra-narrowband filter design.

[0061] Each sub-fiber array is connected to a precision imaging mirror group. The imaging mirror group is designed with high image quality to ensure a one-to-one correspondence between the fiber image points of the image terminal fiber array and the detector surface elements. At the same time, the imaging mirror group is designed with a beam-expanding and collimating optical path in the middle to achieve optical divergence angle compression. Ultra-narrowband filter devices can be embedded to achieve narrowband suppression of background light noise and improve the detection signal-to-noise ratio.

[0062] The narrowband filter adopts a series combination of IF and FPI based on a center working wavelength of 1550nm to achieve ultra-narrow bandwidth. The FPI adopts a multi-channel design with the number of channels matching the number of sub-fiber arrays. Combined with a tapered array fiber-array beam splitter, it achieves ultra-narrowband filtering with a large field of view and suppresses external environmental background noise.

[0063] Each sub-fiber array is detected one-to-one by a small-area single-photon detector, operating in Geiger mode. It has the sensitivity of single-photon response and, compared with large-area SPAD, has a lower dark count rate and a higher frame rate, which can further improve the signal-to-noise ratio of the echo signal, increase the detection distance and the quality of the 3D point cloud.

[0064] Finally, the point cloud data from the small-area single-photon detector is stitched together to achieve all-weather, large-field-of-view, long-distance three-dimensional point cloud imaging.

[0065] The above solutions address the limitations of all-weather, long focal length, and ultra-wide field of view conditions, enabling high-precision real-time three-dimensional imaging of distant, high-speed moving targets by a thousand-beam lidar.

[0066] First Embodiment

[0067] like Figure 1 As shown, the compact distributed field-of-view stitching lidar system for long-range 3D detection with thousands of beams is used for all-weather, large field-of-view, and high-precision 3D imaging of high-speed moving targets. Its working principle is that the laser emission system synchronously emits N×N beams (not less than 32×32 beams) of small divergence angle laser beams to cover a large area of ​​space in front of the radar, with the angle between the laser beams being M×M degrees; at the same time, based on the time-of-flight transmission, the receiving system synchronously detects the N×N laser echo signals in real time to perform narrow field-of-view single-photon detection, and retrieves the 3D point cloud imaging information of the target at the corresponding distance.

[0068] like Figure 2 As shown, the system mainly consists of the following components: IPC, multi-channel tunable, narrow linewidth, nanosecond pulse width fiber laser, collimating beam splitting emission optical system, off-axis three-mirror receiving optical system, tapered array fiber-array beam splitting system, precision imaging lens group, ultra-narrowband filter system, triggering and temperature control module, and small area array SPAD.

[0069] The multi-channel tunable, narrow-linewidth, nanosecond pulse width fiber laser described in this invention is required to operate at a wavelength of 1550nm, which is eye-safe and within the atmospheric window band. It must also have high repetition rate, high energy, and multi-channel synchronous laser pulse emission capabilities (the fiber optic transmission path is K) to ensure that the echo signal has a sufficient signal-to-noise ratio under large field-of-view conditions. The fiber laser primarily uses a semiconductor single-frequency fiber laser with a tunable wavelength within a certain range as the seed source. After three stages of pre-amplification (each stage's output includes optical isolators, filters, pump sources, and other optical components), it enters the EOPM for phase modulation. Then, it passes through a 50:50 beam splitter, splitting the optical path into two paths of equal power for the main amplification system. The main amplification system consists of two stages. The first stage uses 12 / 250PM erbium-ytterbium co-doped fiber to amplify the power to the required 5% energy, before splitting the beam again and entering the second stage main amplifier. This second stage uses large-mode-field erbium-ytterbium co-doped active fiber. Through appropriate coiling and encapsulation techniques, the fiber mode and beam quality are controlled within a good range. In terms of time scale, it requires narrow pulse emission with nanosecond pulse widths. This invention aims to achieve decimeter-level imaging resolution, typically selecting a pulse width of 3 nanoseconds or less. In terms of frequency, this invention requires that the fiber laser wavelength be tunable with a tuning accuracy of picometers; at the same time, it should have narrow linewidth output with an output linewidth of less than 50 picometers (i.e., less than the bandwidth of a narrowband filter system).

[0070] The collimating and beam-splitting optical system described in this invention is used to collimate and expand an optical fiber beam and to split the beam in two-dimensional space. In this invention, the collimating and beam-splitting optical system consists of an off-axis aspherical mirror and a DOE element. The off-axis aspherical mirror is used to collimate the optical fiber beam and compress the divergence angle of the emitted beam; in this invention, the divergence angle is required to be no greater than 0.15 mrad. The DOE is used to emit the collimated beam in two-dimensional space according to the principle of equal energy distribution. Simultaneously, the divergence angle of the split beam is consistent with that of the incident beam. To achieve long-distance, large field-of-view coverage, the beam angle in this invention is φ / N-1, where φ is the system's detection field of view angle. The collimating and beam-splitting optical system consists of K off-axis mirrors and DOEs, each individually connected to an emitted laser fiber, and each covering a specific field of view area. K paths are spliced ​​together to cover N×N points and regions, with the angle between the optical axes of each path being φ / N-1.

[0071] The off-axis three-mirror receiving optical system described in this invention requires the off-axis three-mirror receiving optical components to consist of an aspherical off-axis primary mirror, a receiving aperture, and an off-axis correcting mirror, correcting edge field-of-view aberrations, with the edge field-of-view blur spot smaller than the multimode fiber core diameter. This is used to solve the problem of large-field-of-view, high-efficiency optical reception of large-area fiber arrays under fixed receiving optical aperture and long focal length requirements. In this invention, the divergence angle of the single-beam output light is 0.15 mrad, therefore the corresponding single-beam receiving field of view cannot be too large; 0.2 mrad is sufficient.

[0072] A tapered array fiber-optic beam splitter module is used to connect an off-axis three-mirror receiving telescope and a precision imaging lens group, solving the problems of dividing the total field of view into separate detection areas and the secondary compact spatial arrangement of the array fiber. The fiber used in this invention is a gradient refractive index multimode fiber (core / cladding 50 / 125), with one end tapered and acid-etched to 30 / 45 (core / cladding), reducing the core and cladding diameter while ensuring high transmission efficiency. The receiving end is connected to the off-axis three-mirror (N×N array at the non-tapered end), and the output end splits the N×N array into J subarrays, where J = N×N / A, and A is the number of surface elements of a single small area detector. Each subarray is formed by the tapered end... The fiber spacing between the sub-arrays is 50µm.

[0073] The precision imaging lens assembly connects the small-area array single-photon detector to the subarray end of the tapered array fiber-to-array beam splitter module. It employs a multi-lens design to correct edge field-of-view aberrations, ensuring precise and clear fiber images in the edge regions, with each fiber image aligned with its corresponding area element. Simultaneously, the central optical path is collimated to compress the total divergence angle of the subarray fibers and accommodate an ultra-narrowband filter system. The precision imaging lens assembly consists of J sets of optical systems with identical parameters.

[0074] The ultra-narrowband filter system consists of an inductance filter (IF) and an optical pulse filter (FPI) connected in series in the optical path. The center wavelengths of the IF and FPI are consistent with the emitted laser. In this invention, the bandwidth of the IF is approximately 350 pm, and the bandwidth of the FPI is approximately 50 pm.

[0075] The triggering and temperature control modules provide timed triggering for the laser and the small-area SPAD array, respectively. The temperature control module is used to stabilize the center wavelength of the ultra-narrowband filter system, preventing it from drifting due to external environmental fluctuations. Both modules are controlled in real-time by the IPC via a serial port.

[0076] The small area array SPAD consists of J channels. Each channel performs photon-level sensitivity detection on the corresponding sub-array fiber signal and outputs the three-dimensional point cloud of the spatial region corresponding to the sub-array fiber. The J-channel small area array SPAD outputs the point cloud data of their respective J-channel regions and transmits it to the IPC.

[0077] IPC stitches together the measured point cloud data of each SPAD array according to the corresponding spatial regions to complete the inversion output of the total field of view 3D point cloud image.

[0078] Second Embodiment

[0079] like Figure 3 As shown, a compact distributed field-of-view stitched lidar system with 32×32 beams (array beam spacing 20m, covering a 620m×620m area at a detection distance of 10km) is used as an example. Figure 4 As shown, the 32×32 beam long-range three-dimensional detection optical field-of-view stitching lidar system mainly includes the following components: IPC; 4-channel synchronous fiber-fiber tunable, narrow-linewidth, nanosecond pulse fiber lasers; 4-channel collimating beam splitter emission optical components; off-axis three-mirror receiving optical components; tapered array fiber-array beam splitter waveguide components; ultra-narrowband filter components; precision imaging optical components; and 4-channel 16×16 SPADs.

[0080] A 10kHz tunable pulsed fiber laser synchronously emits high-energy pulsed lasers with a center wavelength of 1550nm from its four fiber output ports. The pulse width is 3ns, the single-pulse energy is not less than 50uJ, the linewidth is less than 50pm, and the tuning accuracy is less than 20pm. These pulses are used to match the center wavelength of the narrowband filter components in the system. The four fiber beams are collimated by off-axis mirrors to compress the field of view to 0.15mrad. Each collimated beam enters a DOE diffraction element to achieve 16×16 beam splitting (each beam has a divergence angle of 0.15mrad and an included angle of 2mrad). The four-beam splitting system achieves a 32×32 beam wide field of view coverage through spatial pointing control (see...). Figure 3A 327mm focal length off-axis three-mirror optical system achieves precise imaging of a 32×32 needle-shaped beam onto the focal plane, exhibiting excellent imaging quality at the edge of the field of view, with the edge field of view blur being significantly smaller than the multimode fiber core diameter of the array fiber placed at the focal plane. The tapered array fiber-array beam splitter assembly consists of simple refractive index multimode fiber. One end of the graded refractive index fiber is tapered and acid-etched, resulting in a 45µm end face and 30µm core diameter. The non-tapered ends of the fibers are arrayed in a 32×32 pattern. Combined with the off-axis three-mirror optical system, this achieves a single-fiber receiving field of view slightly larger than the divergence angle of the emitted beam, ensuring that the receiving optical coverage of the single emitted beam and that each receiving field of view coincides with the optical axis of the emitted beam. The other end of the assembly is split into four 16×16 fiber arrays, each closely spaced with a 50µm spacing, minimizing the total emitting area of ​​the output fiber array. Each 16×16 fiber optic array is connected to a precision imaging lens group, which then precisely couples the fiber optics to the SPAD focal plane at a 1:1 ratio. Adjusting the fiber optic angles ensures a precise one-to-one correspondence between the array fibers and SPAD elements. The central optical path of the precision imaging lens group is a collimated optical path with an effective aperture of 25.4mm. This collimated beam is used to load an ultra-narrowband filter to suppress background photon noise during the day. The ultra-narrowband filter system consists of an inductance filter (IF) and a photosensitive interpolation filter (FPI). The IF has an effective aperture of one inch and a bandwidth of 350pm. The FPI consists of four channels with identical parameters (bandwidth 50pm, FSR 1nm, effective aperture one inch, center wavelength consistent with the laser), integrated onto two integral fused silica glass lenses through coating. Controlling the stability of the two fused silica glass lenses ensures that the four channels maintain the same transmittance parameters at all times. The combination of IF and FPI achieves ultra-narrow bandwidth spectral transmission in the collimated optical path. The entire rear optical path is precisely temperature-controlled by a temperature control module to ensure a stable center wavelength. Four SPADs simultaneously detect the echo photons of each laser pulse, forming their own point cloud images. These images are then stitched together by an IPC (based on the detection area of ​​each SPAD) to form a complete large-field-of-view point cloud stitched image.

[0081] In summary, this invention provides a compact distributed field-of-view stitching lidar system for long-range 3D detection with thousands of beams. It employs N×N beams with narrow linewidth and small divergence angle laser emission to cover a large area of ​​the scene at a long distance. It uses a high off-axis three-reflector optical system and a tapered fiber array-fiber beam splitter system to achieve precise point-to-point reception of N×N beams. It combines ultra-narrowband filtering to suppress background light noise during the daytime. It achieves high signal-to-noise ratio and long-range independent detection of sub-fields of view through multiple small area array SPADs and point-to-point clear imaging optical modules. Finally, it uses a computer to stitch together the sub-field of view imaging results of multiple detectors according to their positions to achieve long-range large field-of-view 3D imaging.

[0082] Compared with the prior art, the technical advantages of this invention are as follows:

[0083] 1. Real-time thousand-beam wide-field staring coverage and high-precision 3D point cloud acquisition of high-speed moving targets. There is currently no related design system, which is a significant breakthrough in the field of ultra-wide field of view long-distance single-photon detection.

[0084] 2. Achieve long-range, wide-field-of-view, all-day long-range detection based on small array SPADs.

[0085] 3. Based on off-axis three-mirror and tapered fiber array-fiber beam splitter design, the contradiction between long focal length and large field of view detection is resolved, and synchronous, high-precision and high-efficiency coupling reception of thousand-beam photonic signals is achieved.

[0086] 4. Based on narrow linewidth light sources, we will carry out ultra-narrowband filtering technology and tapered fiber array-fiber beam splitting design and optimization to solve the problems of single-photon sensitivity detection and effective background light noise suppression under all-day conditions with large array and large field of view, and improve the signal-to-noise ratio.

[0087] 5. Based on fiber optic structured system design, the system is more compact, miniaturized, and integrated.

[0088] 6. Small-area SPADs are used for stitched field of view coverage, which effectively reduces the high crosstalk between signals of each element in photoelectric detection and the high dark count rate of the detector when using large-area SPADs.

[0089] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A compact distributed field-of-view stitching lidar system for all-weather kilo-beam long-range 3D probing, characterized in that, The system comprises: an IPC, a multi-channel tunable narrow linewidth nanosecond fiber laser, a collimating beam-splitting emission optical system, an off-axis three-mirror receiving optical system, a tapered array fiber-array beam-splitting system, a precise imaging lens group, an ultranarrow-band filter system, a trigger and temperature control module, and a facet array SPAD; wherein: The multi-channel tunable narrow linewidth nanosecond fiber laser uses a semiconductor single-frequency fiber laser with a tunable wavelength in a certain range as a seed source, is pre-amplified in three stages, each stage of output is provided with an optical isolator and a filter and a pump source, then enters an EOPM for phase modulation, and then passes through a 50:50 beam splitter, the light path is split into two paths with equal power, and enters a main amplification system; wherein, each stage of output in the three-stage pre-amplification comprises an optical isolator and a filter and a pump source; The collimating beam-splitting emission optical system collimates and expands the fiber beam and performs two-dimensional spatial beam splitting; the collimating beam-splitting emission optical system is composed of an off-axis aspheric mirror and a DOE element, the off-axis aspheric mirror is used for collimating the fiber beam and compressing the divergence angle of the emitted beam, and the DOE is used for two-dimensional spatial emission of the collimated beam according to the principle of equal energy division, and meanwhile, the divergence angle of the split beam is consistent with the incident beam, so as to realize long-distance large-field coverage; The off-axis three-mirror receiving optical system is composed of an aspheric off-axis main mirror, a receiving diaphragm mirror and an off-axis correction mirror, and is used for correcting the difference of the edge field of view and making the edge field of view diffraction spot smaller than the core diameter of the multimode fiber; The tapered array fiber-array beam-splitting system is used for connecting the off-axis three-mirror receiving optical system and the precise imaging lens group, the fiber used is a gradient refractive index multimode fiber, the core / cladding is 50 / 125, and one end is processed by tapering and acid etching to make the core / cladding 30 / 45; The precise imaging lens group is used for connecting the facet array single-photon detector and the subarray end of the tapered array fiber-array beam-splitting system; The ultranarrow-band filter system is composed of an IF and an FPI connected in series in the light path, and the center wavelengths of the IF and the FPI are consistent with the emitted laser; The trigger and temperature control module provides triggering for the laser and the facet array SPAD respectively, controls the center wavelength of the ultranarrow-band filter system, and makes the center wavelength of the ultranarrow-band filter system not drift due to external environment fluctuation, and the trigger and temperature control module is controlled in real time by the IPC through a serial port; The facet array SPAD is composed of J paths, each path separately detects the photon level sensitivity of the corresponding subarray fiber signal, outputs the three-dimensional point cloud of the corresponding space region of the subarray fiber, and transmits the corresponding J-path region point cloud data of each facet array SPAD to the IPC; The IPC splices the measured point cloud data of each facet array SPAD according to the corresponding space region, and completes the inversion output of the total field of view three-dimensional point cloud image.

2. The compact distributed field-of-view stitching laser radar system for all-weather kilometric beam three-dimensional probing according to claim 1, characterized in that For the multi-channel tunable narrow linewidth nanosecond fiber laser: The working wavelength is 1550 nm, and is used for synchronously emitting multi-channel laser pulses, and the fiber emission beam is K; The main amplification system is a two-stage amplification system, wherein the first-stage main amplifier adopts 12 / 250 PM erbium-ytterbium co-doped optical fiber to amplify power to 5% of required energy, and then the power is split to enter another stage of main amplification system; the second-stage main amplifier adopts large-mode-area erbium-ytterbium co-doped active fiber, and through appropriate coil and packaging technology, the mode and beam quality of the optical fiber are controlled within the target level range; The narrow pulse has a nanosecond pulse width in the time scale, and the pulse width is less than or equal to 3 nanoseconds; the laser wavelength is tunable in the frequency, and the tuning accuracy is picometer; and the output line width is less than 50 picometers.

3. The compact distributed field-of-view stitching laser radar system for all-weather kilometric-beam three-dimensional probing according to claim 2, characterized in that, For the collimation beam-splitting emission optical system: The off-axis aspheric mirror is used to collimate the optical fiber beam and compress the divergence angle of the outgoing beam, and the divergence angle is not greater than 0.15 mrad; The divergence angle of the split beam is consistent with the incident beam to realize long-distance large-field coverage, and the included angle between the beams is φ / N-1, and φ is the system detection field angle. The collimating beam-splitting emission optical system is composed of K off-axis mirrors and DOEs, each of which is connected with a laser fiber for emission, and each covers a field of view area of K paths are spliced together to cover N x N points and areas, and the included angle between the optical axes of each path is φ / N-1.

4. The compact distributed field-of-view stitching laser radar system for all-weather kilometric beam three-dimensional probing according to claim 3, characterized in that, For the off-axis three-mirror receiving optical system, the aspheric off-axis main mirror is used to realize large-field high-efficiency optical receiving of a large-area fiber array under the requirements of fixed receiving optical aperture and long focal length, the divergence angle of a single outgoing beam is 0.15 mrad, and the single beam receiving field angle is 0.2 mrad.

5. The compact distributed field-of-view stitching laser radar system for all-weather kilometric-beam three-dimensional probing according to claim 4, characterized in that, For the tapered array fiber-array beam splitting system, the receiving end is connected with the off-axis three-mirror receiving optical system, the non-tapered end is N×N array, and the exit end splits the N×N array into J beam sub-arrays, wherein J=N×N / A, A is the number of single facet array detector elements, each sub-array is arranged by the tapered end with a sub-array fiber spacing of 50um.

6. The compact distributed field-of-view stitching laser radar system for all-weather kilometric-beam three-dimensional probing according to claim 5, characterized in that, For the precise imaging lens group, a multi-lens design is adopted to correct the edge field aberration, and each fiber image is aligned with the unit area; meanwhile, the collimation design is adopted in the middle light path to compress the total divergence angle of the sub-array fiber, and the super-narrow band filter system is loaded; the precise imaging lens group is composed of J groups of optical systems with the same parameters.

7. A compact distributed field-of-view stitching lidar system for all-weather kilometric beam three-dimensional probing according to claim 6, characterized in that, For the super-narrow band filter system, the IF bandwidth is 350 pm, and the FPI bandwidth is 50 pm.

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