Compact distributed view field splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection

Abstract

The invention provides a compact distributed view field splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection, and belongs to the technical field of laser radars. The system comprises an IPC, a multi-path tunable narrow linewidth nanosecond pulse width fiber laser, a collimation beam splitting emission optical system, an off-axis three-mirror receiving optical system, a tapering array fiber-array beam splitting system, an accurate imaging lens group, an ultra-narrow band filtering system, a trigger and temperature control module and a small area array SPAD. The system performs all-day, large-view-field and high-precision three-dimensional imaging on a high-speed moving target, and the working principle of the system is as follows: the laser emitting system synchronously emits N * N (not less than 32 * 32) small-divergence-angle laser beams to cover a large-area area of a space in front of a radar, and the included angle between the laser beams is M * M degrees; and meanwhile, N * N laser echo signals are synchronously detected in real time based on the flight time transmitting and receiving system to carry out narrow-field single-photon detection, and three-dimensional point cloud imaging information of the target at the corresponding distance is inverted.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser radars, and in particular relates to a compact distributed field of view splicing laser radar system for all-day, thousand-beam, long-distance, three-dimensional detection. Background Art

[0002] LiDAR is based on laser ranging technology. It covers the target surface with an outgoing laser spot, receives the echo signal scattered by the target features for fusion inversion, and obtains a three-dimensional image of the target. Among them, the pulse flight time method is the most concise and typical method for mapping the target. The principle is to use a narrow pulse laser as the light source, and then emit a laser beam through the optical system. The receiving telescope calculates the laser flight time by receiving the time difference between the outgoing laser and the target scattered echo signal, and obtains the longitudinal depth information of the corresponding features of the illuminated target. It can be used in conjunction with the laser scanning module to achieve three-dimensional imaging of the north target, or it can simultaneously emit multiple laser pulse beams and combine with linear or planar array photoelectric detectors to achieve three-dimensional imaging of the overall shape characteristics of the target. The longitudinal resolution of the imaging is determined by the laser pulse width, and the size of the imaging area depends on the scanning range, the focal length of the optical system, and the size of the photosensitive surface of the photoelectric detector.

[0003] At present, imaging lidar can be divided into the following three categories according to its working mode: single-point scanning type, linear array scanning type and area array staring type.

[0004] The dot matrix laser radar uses a single-point beam and a unit detector to achieve single-point detection, and combines it with a two-dimensional scanning galvanometer module to complete the two-dimensional field of view coverage scan of the target, obtain a dense dot matrix map, and invert the single-point ranging information to obtain a three-dimensional image of the target.

[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, and cooperate with a one-dimensional scanning galvanometer to achieve two-dimensional point coverage of the detected target by the linear array beam. Similarly, combined with single-point distance information, the three-dimensional image of the target can be inverted.

[0006] The area array staring lidar designs an output optical system to emit the output laser in an array within a two-dimensional plane, completing multi-beam coverage of the two-dimensional space of the detection target. The receiving end uses a large area array detector with the same number of pixels as the laser beam for one-to-one synchronous reception, and inversion realizes three-dimensional imaging of the target.

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

[0008] The dot-matrix laser radar only contains a single beam. To achieve three-dimensional image acquisition with N×N resolution, it needs to be combined with a complex two-dimensional precision scanning system. The system is complex, unstable, and takes a lot of time to scan and cover the entire target. It is inefficient and not suitable for accurate imaging of moving targets.

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

[0010] The array staring laser radar uses the optical system to collimate the incident laser beam with a large divergence angle to cover a large area of ​​targets in front. It can achieve a large field of view coverage of the targets in front without the need for an integrated scanning module. The array detector uses a certain focal length aberration-free optical system to achieve clear detection of targets, and can image moving targets in real time with high precision. However, there are the following shortcomings: when the focal length of the optical system is limited (especially the long focal length optical system), 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 is still small; compared with the point array laser radar, the laser energy needs to be increased by N×N times under the same detection distance. Compared with the linear array laser radar, the output laser energy needs to be increased by N times; in order to achieve detection at a longer distance, the array detector is generally operated in the Geiger mode for single-photon sensitivity detection. On the one hand, large array single-photon detection On the other hand, large-array SPADs bring higher signal crosstalk and lower operating frame rate, which is not conducive to point cloud imaging of highly dynamic targets. In addition, a large background photon noise is introduced under large field of view conditions, and it is extremely difficult to suppress background noise with a large field of view during the day. During the day, traditional narrow-band interference filters can meet the large field of view filtering needs, but their bandwidth is limited and the filtering effect is poor. The ultra-narrow-band filtering technology that uses filters and Fabry-Perot etalon cascades can achieve narrow-band filtering, but it cannot meet the working needs of a large field of view. Summary of the invention

[0011] In response to the above technical problems, the present invention proposes a compact distributed field of view splicing lidar system for all-day, thousand-beam, long-distance three-dimensional detection.

[0012] The present invention provides a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection, the system comprising: IPC, multi-channel tunable narrow linewidth nanosecond fiber laser, collimated beam splitting emission optical system, off-axis three-reflection receiving optical system, tapered array fiber-array beam splitting system, precise imaging lens group, ultra-narrow band filtering system, trigger and temperature control module, small array SPAD; wherein:

[0013] The multi-channel tunable narrow-linewidth nanosecond fiber laser uses a semiconductor single-frequency fiber laser with a tunable wavelength within a certain range as a seed source. After three-stage pre-amplification (the output of each stage is equipped with optical isolators, filters, pump sources and other optical devices), it enters the EOPM for phase modulation, and then passes through a 50:50 optical splitter. The optical route is divided into two equal-power routes and enters the main amplification system. Among them, each output of the three-stage pre-amplification includes an optical isolator, filter, and pump source.

[0014] The collimated beam splitting emission optical system collimates and expands the optical fiber beam and emits it in two-dimensional space; the collimated beam splitting emission optical system consists of an off-axis aspheric mirror and a DOE element. The off-axis aspheric mirror is used to collimate the optical fiber beam and compress the divergence angle of the emitted beam. The DOE is used to emit the collimated beam in two dimensions in space according to the principle of equal energy division. 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 aspheric off-axis primary mirror, a receiving aperture mirror, and an off-axis correcting mirror, which is used to correct the edge field of view aberration, and the edge field of view dispersion spot is smaller than the core diameter of the multimode optical fiber;

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

[0017] The precise imaging mirror set is used to connect the small-array single-photon detector and the sub-array end of the tapered array fiber-array beam splitting system;

[0018] The ultra-narrowband filtering system consists of IF and FPI connected in series in the optical path, and the central wavelength of IF and FPI is consistent with the output laser;

[0019] The trigger and temperature control modules provide triggers for the laser and small array SPAD respectively, and control the central wavelength of the ultra-narrowband filter system so that the central wavelength of the ultra-narrowband filter system does not fluctuate due to external environmental fluctuations. The trigger and temperature control modules are controlled in real time by the IPC through the serial port;

[0020] The small array SPAD is composed of J channels, each of which performs photon-level sensitivity detection on the corresponding sub-array fiber signal and outputs a three-dimensional point cloud of the spatial area corresponding to the sub-array fiber. The J-channel small array SPAD outputs the corresponding J-channel area point cloud data to the IPC;

[0021] IPC stitches the measured point cloud data of each array SPAD according to the corresponding spatial area to complete the inversion output of the three-dimensional point cloud image of the total field of view.

[0022] According to the system proposed by the present invention, for multi-channel tunable narrow linewidth nanosecond fiber laser:

[0023] The working wavelength is 1550nm, which is used to synchronously transmit multiple laser pulses, and the optical fiber transmission path is K;

[0024] The main amplification system is a two-stage amplification system, in which 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 another stage of the main amplification system. The other stage of the main amplifier uses large-mode-field erbium-ytterbium co-doped active fiber. Through appropriate coiling and packaging technology, the fiber mode and beam quality are controlled within the target level range.

[0025] On the time scale, it has a narrow pulse emission with a pulse width of nanoseconds, which is less than or equal to 3 nanoseconds; the laser wavelength is tunable in frequency with a tuning accuracy of picometers; and the output line width is less than 50 picometers.

[0026] According to the system proposed by the present invention, for the collimated beam splitting emission optical system:

[0027] The off-axis aspheric mirror is used to collimate the fiber beam and compress the divergence angle of the outgoing 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 and large field of view coverage. The angle between the beams is φ / N-1, where φ is the detection field of view of the system.

[0029] The collimated beam splitting emission optical system consists of K off-axis mirrors and DOEs. Each channel is connected to an output laser fiber separately. Each channel covers a field of view of K channels are spliced ​​together to cover N×N points and areas, and the angle between the optical axes of each channel is φ / N-1.

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

[0031] According to the system proposed in the present invention, for the tapered array fiber-array splitting system, the receiving end is connected to the 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 beam sub-arrays, where J=N×N / A, A is the number of facets of a single small array detector, and each sub-array is split by the tapered end. The sub-array optical fiber spacing is 50um.

[0032] According to the system proposed in the present invention, a multi-lens design is adopted for the precise imaging mirror group to correct the edge field aberration, and each fiber image is aligned with the surface element one by one; at the same time, the intermediate optical path adopts a collimation design to compress the total divergence angle of the sub-array optical fiber and load the ultra-narrow band filtering system. The precise imaging mirror group is composed of J groups of optical systems with the same parameters.

[0033] According to the system proposed by the present invention, for the ultra-narrowband filtering system, the IF bandwidth is 350pm and the FPI bandwidth is 50pm.

[0034] In summary, the present invention provides a compact distributed field of view stitching lidar system for thousand-beam long-distance three-dimensional detection, which adopts N×N beam narrow linewidth and small divergence angle laser emission to cover a large range of scenes at a long distance, adopts a high off-axis three-reflection optical system and a tapered fiber array-fiber splitting system to achieve point-to-point precise reception of N×N light beams, combines ultra-narrow band filtering to achieve background light noise suppression during daytime, and achieves high signal-to-noise ratio and long-distance independent detection of sub-fields through multiple small array SPADs and point-to-point clear imaging optical modules. Finally, the sub-field imaging results of multiple detectors are stitched by computer according to position to achieve long-distance large-field three-dimensional imaging.

[0035] Compared with the prior art, the present invention has the following technical effects:

[0036] 1. Real-time thousand-beam large-field-of-view staring coverage and high-precision three-dimensional point cloud acquisition of high-speed moving targets are achieved. There is currently no relevant design system, which is a breakthrough of great significance in the field of ultra-large-field-of-view long-distance single-photon detection.

[0037] 2. Based on small array SPAD, long-distance, large field of view and all-day long-distance detection can be achieved.

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

[0039] 4. Based on narrow linewidth light sources, ultra-narrowband filtering technology and tapered fiber array-fiber splitting design and optimization are carried out to solve the problem of single-photon sensitivity detection and effective background light noise suppression in large arrays and large fields of view under all-day conditions, and improve the signal-to-noise ratio.

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

[0041] 6. Small-array SPADs are used for splicing field coverage, effectively reducing the high crosstalk between the signals of each element in photoelectric detection and the high dark count rate of the detector when using large-array SPADs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 Schematic diagram of the principle of synchronous transmission, reception and detection of N×N small divergence angle laser beams according to an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of the composition of a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection according to an embodiment of the present invention;

[0045] Figure 3 32×32 beam laser radar system according to an embodiment of the present invention;

[0046] Figure 4 Schematic diagram of the composition of a 32×32 beam optical field stitching laser radar system for long-distance three-dimensional detection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work 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: Diffractive Optical Elements, DOE;

[0051] Single photon detector: Single Photon Avalanche Diodes, SPAD;

[0052] Interference filter: Interference Filter, IF;

[0053] Fabry-Perot Interferometer: Fabry-Perot Interferometer, FPI;

[0054] Laser Control Unit: Laser Control Unit, LCU;

[0055] Avalanche Photo Diode: Avalanche Photo Diode, APD;

[0056] Geiger Mode:Geiger Mode,GM.

[0057] The present invention starts from the accurate 3D imaging of fast-moving targets all day long, improves the detection field of view and detection distance, and proposes a compact distributed field of view splicing laser radar system for thousand-beam long-distance 3D detection. At the laser output end, a tunable, narrow linewidth, nanosecond fiber laser is selected for multi-channel pulse energy synchronous amplification and fiber output to meet the energy requirements of long-distance and large field of view detection.

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

[0059] The receiving end of the tapered array fiber-array beam splitter is used to perform small-field-of-view and one-to-one precise fiber-beam matching reception of the spatial needle-shaped light beam. The receiving end is connected to an off-axis three-mirror optical system to achieve long focal length, large field-of-view, and high-quality imaging, meet the requirements of high optical efficiency signal photon coupling into each optical fiber, complete single-beam laser narrow-field-of-view reception, reduce daytime background noise, and efficiently receive and cover a large two-dimensional spatial area to increase the detection field of view.

[0060] Tapered fiber array - The output end of the array beam splitter is divided into multiple sub-fiber arrays. The optical fiber used is a graded-index multimode optical fiber. One end of the optical fiber is clad and taper-treated. The optical fibers at the end of the sub-fiber array are closely arranged to achieve efficient transmission of photon signals while reducing the total effective light output area of ​​the sub-fiber array, ensuring the high peak transmittance and narrow bandwidth function of the subsequent ultra-narrowband filtering design.

[0061] Each fiber array is connected to a precise imaging lens group. The imaging lens group is designed for high image quality to ensure a one-to-one correspondence between the fiber image points of the terminal fiber array and the detector element. At the same time, a beam expansion and collimation optical path design is performed in the middle of the imaging lens group to achieve optical divergence angle compression. An ultra-narrowband filter device can be embedded to achieve narrowband suppression of sky-high 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 the central working wavelength of 1550nm to achieve ultra-narrow bandwidth of the filter. FPI adopts a multi-channel design, and the number of channels is consistent with the number of sub-fiber arrays. Combined with the tapered array fiber-array beam splitter, it can achieve large-field ultra-narrowband filtering and suppress external environmental background noise.

[0063] Each sub-fiber array uses a small-array single-photon detector for one-to-one detection, working in Geiger mode, with the sensitivity of single-photon response. At the same time, compared with the large-array SPAD, it has a lower dark count rate and a higher frame rate, which can further improve the signal-to-noise ratio of the echo signal, and improve the detection distance and the quality of the three-dimensional point cloud.

[0064] Finally, the point cloud data of the small array single-photon detectors are processed by field-of-view stitching to achieve three-dimensional point cloud imaging of targets at all times, with a large field of view and at long distances.

[0065] The above solution can solve the problem of high-precision real-time three-dimensional imaging of long-distance and high-speed moving targets by thousand-beam lidar under the constraints of all-day, long focal length and ultra-large field of view.

[0066] First embodiment

[0067] like Figure 1 As shown in the figure, the compact distributed field-of-view stitching lidar system for thousand-beam long-distance three-dimensional detection is used for all-day, large-field-of-view, high-precision three-dimensional 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 laser beams to cover a large area in front of the radar, and the angle between the laser beams is M×M degrees; at the same time, based on the time-of-flight emission, the receiving system synchronously detects the N×N beams of laser echo signals in real time to perform narrow-field-of-view single-photon detection, and inverts the three-dimensional point cloud imaging information of the target at the corresponding distance.

[0068] like Figure 2 As shown, the system mainly includes the following components: IPC, multi-channel tunable, narrow linewidth, nanosecond pulse fiber laser, collimated beam splitting emission optical system, off-axis three-reflection receiving optical system, tapered array fiber-array beam splitting system, precise imaging mirror group, ultra-narrow band filtering system, trigger and temperature control module, and small array SPAD.

[0069] The multi-channel tunable, narrow linewidth, nanosecond pulse width fiber laser described in the present invention requires an operating wavelength of 1550nm human eye safety, atmospheric window band, and has high repetition rate, high energy, multi-channel laser pulse synchronous emission function (the fiber emission beam is K), ensuring that the echo signal has a sufficient signal-to-noise ratio under large field of view conditions. Among them, the fiber laser mainly uses a semiconductor single-frequency fiber laser with a tunable wavelength in a certain range as a seed source, and enters the EOPM for phase modulation after three-stage pre-amplification (the output of each stage is equipped with optical isolators, filters, pump sources and other optical devices), and then passes through a 50:50 optical splitter. The optical route is divided into two equal-power routes, and the main amplification system is performed. The main amplification is composed of a two-stage amplification system, one of which uses 12 / 250PM erbium-ytterbium co-doped optical fiber to amplify the power to the required 5% energy, and then splits into another stage of the main amplifier. The other stage of the main amplifier uses a large-mode field erbium-ytterbium co-doped active fiber. Through appropriate coiling and packaging technology, the mode and beam quality of the optical fiber are controlled within a good level range. On the time scale, it is required to have a narrow pulse emission with a nanosecond pulse width. The present invention requires obtaining a decimeter-level imaging resolution, and generally selects a pulse width of less than or equal to 3 nanoseconds. In terms of frequency, the present invention requires that the fiber laser wavelength has a tunable function with a tuning accuracy of picometers; at the same time, it has a narrow linewidth output with an output linewidth of less than 50 picometers (i.e., less than the bandwidth of a narrowband filtering system).

[0070] The collimated beam splitting emission optical system described in the present invention is used to collimate and expand the optical fiber light beam and to split and emit it in two-dimensional space. In the present invention, the collimated beam splitting emission optical system is composed of an off-axis aspheric mirror and a DOE element. The off-axis aspheric mirror is used to collimate the optical fiber light beam and compress the divergence angle of the output light beam. The divergence angle in the present invention is required to be no more than 0.15 mrad; the DOE is used to emit the collimated light beam in two dimensions in space according to the principle of equal energy division. At the same time, the divergence angle of the split light beam is consistent with the incident light beam. In order to achieve long-distance and large field of view coverage, the angle between the light beams of the present invention is φ / N-1, where φ is the system detection field of view angle; the collimated beam splitting emission optical system is composed of K off-axis mirrors and DOEs, each of which is separately connected to an output laser optical fiber, and each covers the field of view area K channels are spliced ​​together to cover N×N points and areas, and the angle between the optical axes of each channel is φ / N-1.

[0071] The off-axis three-mirror receiving optical system described in the present invention requires that the off-axis three-mirror receiving optical component is composed of an aspheric off-axis primary mirror, a receiving aperture mirror, and an off-axis corrective mirror, and the edge field of view phase difference is corrected, and the edge field of view dispersion spot is smaller than the core diameter of the multimode optical fiber. It is used to solve the large field of view and high-efficiency optical reception of a large-array optical fiber array under the requirements of a fixed receiving optical aperture and a long focal length. In the present invention, the divergence angle of a single beam of emitted light is 0.15mrad, and the corresponding single beam of light receiving field of view angle cannot be too large, and 0.2mrad meets the requirement.

[0072] The tapered array optical fiber-array splitting module is used to connect the off-axis three-mirror receiving telescope and the precise imaging lens group, solving the problem of dividing the total field of view into regions for separate detection and the secondary tight arrangement of the array optical fiber space. The optical fiber used in the present invention is a gradient refractive index multimode optical fiber (core / cladding is 50 / 125), one end of which is tapered and acid-etched to 30 / 45 (core / cladding), reducing the core and cladding diameters while ensuring high transmission efficiency. The receiving end is connected to the off-axis three-mirror (the non-tapered end is an N×N array), and the output end splits the N×N array into J beam sub-arrays, where J=N×N / A, A is the number of facets of a single small array detector, and each sub-array is tapered at the tapered end. Arrangement, the sub-array optical fiber spacing is 50um.

[0073] The precision imaging mirror set is used to connect the small array single photon detector and the sub-array end of the tapered array fiber-array beam splitter module. The multi-lens design is used to correct the edge field aberration to meet the requirements of accurate and clear fiber images in the edge area, and each fiber image is aligned with the facet element one by one; at the same time, the middle optical path is collimated to compress the total divergence angle of the sub-array fiber and load the ultra-narrowband filtering system. The precision imaging mirror set consists of J groups of optical systems with the same parameters.

[0074] The ultra-narrowband filtering system is composed of IF and FPI connected in series in the optical path. The central wavelengths of IF and FPI are consistent with the emitted laser. In the present invention, the IF bandwidth is about 350pm and the FPI bandwidth is about 50pm.

[0075] The trigger and temperature control modules provide timing triggers for the laser and small array SPAD respectively. The temperature control module is used to control the stability of the central wavelength of the ultra-narrowband filter system so that the central wavelength does not drift due to external environmental fluctuations. The trigger and temperature control modules are controlled in real time by the IPC through the serial port.

[0076] The small array SPAD is composed of J channels, each of which performs photon-level sensitivity detection on the corresponding sub-array optical fiber signal and outputs a three-dimensional point cloud of the spatial area corresponding to the sub-array optical fiber. The J-channel small array SPAD outputs the corresponding J-channel area point cloud data and transmits them to the IPC.

[0077] IPC stitches the measured point cloud data of each array SPAD according to the corresponding spatial area to complete the inversion output of the three-dimensional point cloud image of the total field of view.

[0078] Second embodiment

[0079] like Figure 3 As shown in the figure, a 3D detection compact distributed field of view stitching LiDAR system with 32×32 beams (array beam spacing is 20m, covering a range of 620m×620m at a detection distance of 10km) is taken as an example. Figure 4 As shown, the 32×32 beam optical field of view stitching lidar system for long-distance three-dimensional detection mainly includes the following components: IPC; 4-way synchronous fiber-optic tunable, narrow-linewidth, nanosecond pulse fiber laser; 4-way collimated beam splitting emission optical component; off-axis three-reflection receiving optical component; tapered array fiber-array beam splitting waveguide component; ultra-narrow band filtering component; precise imaging optical component; 4-way 16×16 SPAD.

[0080] The 4-way fiber output port of the 10KHz tunable pulse fiber laser synchronously emits high-energy central wavelength 1550nm pulse laser with a pulse width of 3ns, a single pulse energy of not less than 50uJ, a line width of less than 50pm, and a tuning accuracy of less than 20pm, which is used to match the central wavelength of the system narrowband filter component; the 4-way fiber beams are collimated by off-axis reflectors to achieve a field of view compression of 0.15mrad, and each collimated beam enters the DOE diffractive optical element to achieve 16×16 beam splitting emission (the divergence angle of each beam is 0.15mrad, and the angle of each beam is 2mrad). The 4-way beam splitting system achieves a large field of view coverage of 32×32 beams through spatial pointing control (see Figure 3). An off-axis three-mirror optical system with a focal length of 327mm can accurately image a 32×32 needle-shaped light beam on the focal plane. It has excellent imaging quality in the edge field of view, and the edge field of view dispersion spot is much smaller than the multimode fiber core diameter of the array fiber placed at the focal plane. The tapered array fiber-array beam splitting waveguide component is composed of a simple refractive index multimode optical fiber. One end of the gradient refractive index fiber is tapered and acid-etched, so that the end face size of the tapered end fiber is 45um and the core is 30um. The non-tapered end of the optical fiber is arrayed in 32×32, and the off-axis three-mirror optical system is used to achieve a single fiber receiving field of view that is slightly larger than the divergence angle of the outgoing beam, so that the receiving optical coverage of the single outgoing beam and the coincidence of each receiving field of view with the optical axis of the outgoing beam are achieved. The other end of the component is divided into 4 16×16 fiber arrays. Each fiber array is closely arranged with a spacing of 50um, which minimizes the total luminous area of ​​the array fiber at the outgoing end. Each 16×16 fiber array is connected to a precision imaging mirror group, and is precisely coupled to the SPAD focal plane in a 1:1 ratio through the imaging mirror group. The fiber angle is adjusted to achieve a one-to-one precise correspondence between the array fiber and the SPAD facet. The middle optical path of the precision imaging mirror group is a collimated optical path. The effective aperture of the collimated beam is 25.4mm, which is used to load ultra-narrowband filter components to suppress background photon noise during the day. The ultra-narrowband filter system consists of IF and FPI. The IF has an effective aperture of one inch and a bandwidth of 350pm. The FPI consists of four channels with the same parameters (bandwidth of 50pm, FSR1nm, effective aperture of one inch, and the central wavelength is consistent with the laser). It is integrated on two integral fused quartz glass lenses through coating. The stability of the two fused quartz glasses is controlled to ensure that the four channels always maintain the same transmittance parameters. The ultra-narrow bandwidth spectrum in the collimated optical path is transmitted through the combination of IF and FPI. The temperature of the entire rear optical path is precisely controlled by the temperature control module to ensure the stability of the central wavelength. The 4-channel SPADs synchronously detect the echo photons of each laser pulse to form their own point cloud images, which are then stitched together through IPC (based on the detection area of ​​each SPAD) to form a whole large-field-of-view point cloud stitching image.

[0081] In summary, the present invention provides a compact distributed field of view stitching lidar system for thousand-beam long-distance three-dimensional detection, which adopts N×N beam narrow linewidth and small divergence angle laser emission to cover a large range of scenes at a long distance, adopts a high off-axis three-reflection optical system and a tapered fiber array-fiber splitting system to achieve point-to-point precise reception of N×N light beams, combines ultra-narrow band filtering to achieve background light noise suppression during daytime, and achieves high signal-to-noise ratio and long-distance independent detection of sub-fields through multiple small array SPADs and point-to-point clear imaging optical modules. Finally, the sub-field imaging results of multiple detectors are stitched by computer according to position to achieve long-distance large-field three-dimensional imaging.

[0082] Compared with the prior art, the present invention has the following technical effects:

[0083] 1. Real-time thousand-beam large-field-of-view staring coverage and high-precision three-dimensional point cloud acquisition of high-speed moving targets are achieved. There is currently no relevant design system, which is an important breakthrough in the field of ultra-large-field-of-view long-distance single-photon detection.

[0084] 2. Based on small array SPAD, long-distance, large field of view and all-day long-distance detection can be achieved.

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

[0086] 4. Based on narrow linewidth light sources, ultra-narrowband filtering technology and tapered fiber array-fiber splitting design and optimization are carried out to solve the problem of single-photon sensitivity detection and effective background light noise suppression in large arrays and large fields of view under all-day conditions, and improve the signal-to-noise ratio.

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

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

[0089] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above-mentioned embodiments only express several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A compact distributed field of view splicing laser radar system with thousands of beams and long-distance three-dimensional detection all day long, characterized in that: The system includes: IPC, multi-channel tunable narrow linewidth nanosecond fiber laser, collimated beam splitting emission optical system, off-axis three-mirror receiving optical system, tapered array fiber-array beam splitting system, precise imaging lens group, ultra-narrowband filtering system, trigger and temperature control module, small array SPAD; wherein: The multi-channel tunable narrow-linewidth nanosecond fiber laser uses a semiconductor single-frequency fiber laser with a tunable wavelength within a certain range as a seed source. After three-stage pre-amplification (the output of each stage is equipped with optical isolators, filters, pump sources and other optical devices), it enters the EOPM for phase modulation, and then passes through a 50:50 optical splitter. The optical route is divided into two equal-power routes and enters the main amplification system. Among them, each output of the three-stage pre-amplification includes an optical isolator, filter, and pump source. The collimated beam splitting emission optical system collimates and expands the optical fiber beam and emits it in two-dimensional space; the collimated beam splitting emission optical system consists of an off-axis aspheric mirror and a DOE element. The off-axis aspheric mirror is used to collimate the optical fiber beam and compress the divergence angle of the emitted beam. The DOE is used to emit the collimated beam in two dimensions in space according to the principle of equal energy division. 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; The off-axis three-mirror receiving optical system consists of an aspheric off-axis primary mirror, a receiving aperture mirror, and an off-axis correcting mirror, which is used to correct the edge field of view aberration, and the edge field of view dispersion spot is smaller than the core diameter of the multimode optical fiber; The tapered fiber array-array beam splitting system is used to connect the off-axis three-mirror receiving optical system and the precise imaging lens group. The optical fiber used is a gradient refractive index multimode optical fiber with a core / cladding ratio of 50 / 125. One end is treated with tapering and acid etching to make the core / cladding ratio 30 / 45. The precise imaging mirror set is used to connect the small-array single-photon detector and the sub-array end of the tapered array fiber-array beam splitting system; The ultra-narrowband filtering system consists of IF and FPI connected in series in the optical path, and the central wavelength of IF and FPI is consistent with the output laser; The trigger and temperature control modules provide triggers for the laser and small array SPAD respectively, and control the central wavelength of the ultra-narrowband filter system so that the central wavelength of the ultra-narrowband filter system does not fluctuate due to external environmental fluctuations. The trigger and temperature control modules are controlled in real time by the IPC through the serial port; The small array SPAD is composed of J channels, each of which performs photon-level sensitivity detection on the corresponding sub-array fiber signal and outputs a three-dimensional point cloud of the spatial area corresponding to the sub-array fiber. The J-channel small array SPAD outputs the corresponding J-channel area point cloud data to the IPC; IPC stitches the measured point cloud data of each array SPAD according to the corresponding spatial area to complete the inversion output of the three-dimensional point cloud image of the total field of view.

2. According to claim 1, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection is characterized in that: For multi-channel tunable narrow-linewidth nanosecond fiber lasers: The working wavelength is 1550nm, which is used to synchronously transmit multiple laser pulses, and the optical fiber transmission path is K; The main amplification system is a two-stage amplification system, in which 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 another stage of the main amplification system. The other stage of the main amplifier uses large-mode-field erbium-ytterbium co-doped active fiber. Through appropriate coiling and packaging technology, the fiber mode and beam quality are controlled within the target level range. On the time scale, it has a narrow pulse emission with a pulse width of nanoseconds, which is less than or equal to 3 nanoseconds; the laser wavelength is tunable in frequency with a tuning accuracy of picometers; and the output line width is less than 50 picometers.

3. According to claim 2, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection is characterized in that: For collimated beam splitting emission optical systems: The off-axis aspheric mirror is used to collimate the fiber beam and compress the divergence angle of the outgoing beam to no more than 0.15 mrad; 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. The angle between the beams is φ / N-1, where φ is the detection field of view of the system. The collimated beam splitting emission optical system consists of K off-axis mirrors and DOEs. Each channel is connected to an output laser fiber separately. Each channel covers a field of view of K channels are spliced ​​together to cover N×N points and areas, and the angle between the optical axes of each channel is φ / N-1.

4. According to claim 3, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection is characterized in that: The off-axis three-mirror receiving optical system consists of an aspherical off-axis primary mirror, which is used to achieve large-field and high-efficiency optical reception of large-array fiber arrays under the requirements of fixed receiving optical aperture and long focal length. The divergence angle of a single beam of output light is 0.15mrad, and the field angle of a single beam of receiving light is 0.2mrad.

5. According to claim 4, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection is characterized in that: For the tapered array fiber-array splitting system, the receiving end is connected to the off-axis three-mirror receiving optical system. The non-tapered end is an N×N array. The output end splits the N×N array into J beam sub-arrays, where J = N×N / A, A is the number of facets of a single small array detector, and each sub-array is split by the tapered end. The sub-array optical fiber spacing is 50um.

6. According to claim 5, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection is characterized in that: For the precise imaging mirror group, a multi-lens design is adopted to correct the edge field of view aberration, and each fiber image is aligned with the surface element one by one; at the same time, the intermediate optical path adopts a collimation design to compress the total divergence angle of the sub-array fiber and load the ultra-narrow band filtering system. The precise imaging mirror group consists of J groups of optical systems with the same parameters.

7. According to claim 6, a compact distributed field of view splicing laser radar system for all-day thousand-beam long-distance three-dimensional detection, characterized in that: For ultra-narrowband filtering systems, the IF bandwidth is 350pm and the FPI bandwidth is 50pm.

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