Three-dimensional positioning laser radar and three-dimensional detection method thereof

Abstract

The application discloses a kind of three-dimensional positioning laser radar and its three-dimensional detection method, comprising: pulsed laser emits laser beam to target object, polarized beam splitter is respectively emitted to first lens and avalanche photodiode on laser beam, laser beam is shot to second lens after passing through first lens, is emitted to target object after passing through second lens, and avalanche photodiode is converted into electrical signal by received pulsed light signal, and electrical signal is transmitted to time correlation single photon counter;The light field signal of target object is collected by lens and sent to first beam splitter, and first, second beams are generated after being split by first beam splitter, and first second beams are split and handled by corresponding beam splitter, to obtain four-way beams;Four-way beams are transmitted by corresponding optical path respectively, and electrical signal is transmitted to four receiving ports of time correlation single photon counter;According to the four-way signal received, the three-dimensional space position prediction of target object is realized.

Description

Technical Field

[0001] This invention relates to the field of lidar three-dimensional detection technology, and in particular to a three-dimensional positioning lidar and its three-dimensional detection method. Background Technology

[0002] The statements in this section merely refer to the background art related to this invention and do not necessarily constitute prior art.

[0003] LiDAR is a relatively mature 3D detection technology with advantages such as high accuracy and long detection range. Therefore, LiDAR has been widely used in fields such as automatic navigation, environmental monitoring, and military security.

[0004] Currently available LiDAR systems can be broadly categorized into three types: mechanically rotating LiDAR, semi-solid-state LiDAR, and solid-state LiDAR. Mechanically rotating and semi-solid-state LiDAR systems contain internal scanning devices for imaging. However, scanning imaging inevitably results in a lower frame rate, which cannot meet the requirements of certain real-time detection scenarios. Furthermore, the scanning device limits the lifespan of the LiDAR system. Solid-state LiDAR systems capable of high frame rate imaging are those using flash imaging. The lateral resolution of flash imaging solid-state LiDAR systems is determined by the size of the detector array. Due to technological limitations, flash imaging solid-state LiDAR systems have small detector arrays and are expensive to manufacture.

[0005] In certain fields, such as 3D detection and localization of fast-moving targets, 3D imaging of the target is not required; only detection of the target is needed to obtain its 3D spatial position. Therefore, for scenarios and fields that do not require target imaging but demand real-time 3D detection of fast-moving targets, it is necessary to design and invent a solid-state lidar with high lateral spatial resolution and high frame rate. Summary of the Invention

[0006] To address the issues of low imaging frame rate and short lifespan in scanning lidar, as well as the limitation of lateral resolution in solid-state lidar by the size of the detector array, this invention provides a three-dimensional positioning lidar and its three-dimensional detection method; without imaging the target, it achieves three-dimensional detection of fast-moving targets with high lateral resolution and high frame rate.

[0007] In a first aspect, the present invention provides a three-dimensional positioning lidar;

[0008] A three-dimensional positioning lidar includes: a pulsed laser;

[0009] The pulsed laser emits a laser beam toward the target object. The laser beam is emitted through a half-wave plate to a polarization beam splitter, which then directs the laser beam onto a first lens and an avalanche photodiode. After passing through the first lens, the laser beam is directed to a second lens and then onto the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. Upon receiving the electrical signal, the time-correlated single-photon counter begins timing.

[0010] The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam.

[0011] The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter.

[0012] The time-correlated single-photon counter transmits the received signals to the computer, which then uses the four received signals to predict the three-dimensional spatial position of the target object.

[0013] Secondly, the present invention provides a three-dimensional detection method for a three-dimensional positioning lidar;

[0014] A three-dimensional detection method for a three-dimensional positioning lidar includes:

[0015] A pulsed laser emits a laser beam toward the target object. The laser beam passes through a half-wave plate and is then transmitted to a polarization beam splitter. The polarization beam splitter directs the laser beam onto a first lens and an avalanche photodiode. After passing through the first lens, the laser beam is directed to a second lens and then onto the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. Upon receiving the electrical signal, the time-correlated single-photon counter begins timing.

[0016] The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam.

[0017] The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence. After the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter. The time-correlated single-photon counter transmits the received signal to the computer, and the computer predicts the three-dimensional spatial position of the target object based on the received four signals.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] Compared to traditional scanning lidar, this invention uses four fixed masks to modulate the signal light. By utilizing only the number of photons detected by single-photon detectors in the four optical paths, the target's position distribution in lateral space can be calculated. This avoids the lidar system's dependence on scanning devices, provides higher resistance to mechanical vibration, and eliminates the lifespan limitation imposed by mechanical scanning devices. Furthermore, this invention can complete 3D target localization with a single data acquisition, solving the low frame rate problem of scanning lidar and enabling high-frame-rate 3D localization of fast-moving targets.

[0020] Compared to solid-state lidar using flash imaging, this invention overcomes the limitation that the system's lateral spatial resolution is determined by the size of the detector array, achieving high lateral spatial resolution three-dimensional detection using only four single-photon detectors. This invention utilizes a mask to modulate the light field and employs computational imaging to locate the target object in lateral space, ultimately achieving high lateral spatial resolution three-dimensional detection of the target object. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 This invention provides a schematic diagram of a novel three-dimensional positioning lidar system.

[0023] Figure 2 Provided by the present invention Figure 1 The transmittance distribution of the mask in the middle four-beam optical path from top to bottom;

[0024] Figure 3 This is a schematic diagram of the design of the special mask used in this invention;

[0025] Figure 4 This is a schematic diagram of the system calibration process provided by the present invention. Detailed Implementation

[0026] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0028] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0029] All data acquisition in this embodiment is carried out in accordance with laws and regulations and with user consent, and the data is used legally.

[0030] Example 1

[0031] This embodiment provides a three-dimensional positioning lidar;

[0032] like Figure 1 As shown, a three-dimensional positioning lidar includes: a pulsed laser;

[0033] The pulsed laser emits a laser beam toward the target object. The laser beam is emitted through a half-wave plate to a polarization beam splitter, which then directs the laser beam onto a first lens and an avalanche photodiode. After passing through the first lens, the laser beam is directed to a second lens and then onto the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. Upon receiving the electrical signal, the time-correlated single-photon counter begins timing.

[0034] The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam.

[0035] The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter.

[0036] The time-correlated single-photon counter transmits the received signals to the computer, which then uses the four received signals to predict the three-dimensional spatial position of the target object.

[0037] This invention combines mask modulation and time-correlated single-photon counting techniques to design a solid-state single-photon lidar system with high lateral resolution and high frame rate.

[0038] Furthermore, the pulsed laser serves as an active illumination source.

[0039] Furthermore, the polarization beam splitter, the first beam splitter, the second beam splitter, and the third beam splitter are used to disperse the laser beam.

[0040] Furthermore, the first, second, and third beamsplitters are implemented using 50:50 beamsplitters, which divide the received signal into four equal paths. These four beamsplitters use lenses, filters, multimode fibers, and single-photon detectors of the same specifications for photon collection, transmission, and detection.

[0041] Furthermore, the first lens and the second lens have different focal lengths, and the first lens and the second lens are used to adjust the divergence angle of the laser beam.

[0042] Furthermore, the polarization beam splitter is also used to send a portion of the pulsed laser energy to an avalanche photodiode, which is used to detect the pulsed light reflected by the polarization beam splitter and generate an electrical signal, thereby providing a synchronization signal for the laser pulse emission of the relevant single-photon counter.

[0043] Furthermore, the third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, each optical path comprising: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after detecting a photon, the single-photon detector in each optical path generates an electrical signal and transmits it to the four receiving ports of a time-correlated single-photon counter; wherein,

[0044] The third beam is transmitted through the first mask, the first filter, the third lens, and the first optical fiber to the first single-photon detector, and the signal generated therefrom is transmitted to the first stop channel of the time-correlated single-photon counter.

[0045] The fourth beam is transmitted through the second mask, the second filter, the fourth lens, and the second optical fiber to the second single-photon detector, and the signal generated therefrom is transmitted to the second stop channel of the time-correlated single-photon counter.

[0046] The fifth beam is transmitted through the third mask, the third filter, the fifth lens, and the third optical fiber to the third single-photon detector, and the signal generated therefrom is transmitted to the third stop channel of the time-correlated single-photon counter.

[0047] The sixth beam is transmitted through the fourth mask, the fourth filter, the sixth lens, and the fourth optical fiber to the fourth single-photon detector, and the signal generated is transmitted to the fourth stop channel of the time-correlated single-photon counter.

[0048] Furthermore, the first, second, third, and fourth masks are all used for the modulation of structured light. Figure 1 The four masks in the image are arranged from top to bottom: the top mask is the first mask, followed by the second mask, then the third mask, and the bottom mask is the fourth mask; the grayscale image of the first mask corresponds to... Figure 2 The first grayscale image; the grayscale image of the second mask corresponds to... Figure 2 The second grayscale image; the grayscale image of the third mask corresponds to... Figure 2 The third grayscale image; the grayscale image of the fourth mask corresponds to... Figure 2 The fourth grayscale image.

[0049] Furthermore, the fabrication processes of the first, second, third, and fourth masks are consistent, but the placement directions of the four masks differ. The grayscale values ​​of the first and second masks are symmetrically distributed relative to the vertical direction, while the grayscale values ​​of the third and fourth masks are symmetrically distributed relative to the horizontal direction.

[0050] Furthermore, the fabrication process of the first photomask includes:

[0051] First, design a grayscale image with a spatial resolution of 2304×2304. The grayscale value remains unchanged in the horizontal or vertical direction, and the grayscale value increases uniformly from the minimum value of 0 to the maximum value of 1 in the vertical or horizontal direction.

[0052] Then, using the Floyd-Steinberg error diffusion dithering method, the grayscale image is converted into a binary distribution modulated image with a transmittance of 0 or 1; 9×9 pixels are used as an equivalent pixel, and the spatial resolution of the mask is 256×256. The transmittance in the horizontal or vertical direction remains unchanged, while the transmittance in the vertical or horizontal direction decreases uniformly.

[0053] A chromium plating layer is coated on a quartz substrate, and a binary distribution modulation pattern is etched on the chromium plating layer.

[0054] Cut out the area covered by the binary distribution modulation pattern to obtain the mask.

[0055] Furthermore, the time-correlated single-photon counter receives the signal output by the single-photon detector, obtains the count of signal photons, and uses the time difference between the synchronization signal and the photon signal to obtain the flight time information of the signal photons.

[0056] Example 2

[0057] This embodiment provides a three-dimensional detection method using a three-dimensional positioning lidar;

[0058] A three-dimensional detection method for a three-dimensional positioning lidar includes:

[0059] A pulsed laser emits a laser beam toward the target object. The laser beam passes through a half-wave plate and is then transmitted to a polarization beam splitter. The polarization beam splitter directs the laser beam onto a first lens and an avalanche photodiode. After passing through the first lens, the laser beam is directed to a second lens and then onto the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. Upon receiving the electrical signal, the time-correlated single-photon counter begins timing.

[0060] The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam.

[0061] The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter.

[0062] The time-correlated single-photon counter transmits the received signals to the computer, which then uses the four received signals to predict the three-dimensional spatial position of the target object.

[0063] Furthermore, the method also includes:

[0064] Using the aforementioned three-dimensional positioning lidar, a laser beam is emitted toward a sample target object whose actual position in three-dimensional space is known, and the computer's predicted position in three-dimensional space of the sample target object is obtained, thereby obtaining a mapping table between the actual position in three-dimensional space of the sample target object and the predicted position in three-dimensional space of the sample target object.

[0065] Using the aforementioned three-dimensional positioning lidar, a laser beam is emitted toward the target object whose three-dimensional spatial location is unknown, and the computer obtains the predicted three-dimensional spatial location of the target object.

[0066] Based on the mapping table, the actual three-dimensional spatial position of the sample target object corresponding to the predicted three-dimensional spatial position of the target object to be tested is found in the table. The predicted three-dimensional spatial position of the target object to be tested is corrected according to the found actual three-dimensional spatial position of the sample target object, and the corrected three-dimensional spatial prediction position is obtained.

[0067] Furthermore, the time-correlated single-photon counter transmits the received signals to the computer, which then uses the received four signals to predict the three-dimensional spatial position of the target object, specifically including:

[0068] First, lateral spatial positioning is performed based on mask modulation: For a grayscale image, a two-dimensional Cartesian coordinate system is established based on the pixel coordinates, and then the grayscale image is represented by a two-dimensional density function F(x,y). A mask with uniformly varying transmittance is used to perform structured light modulation on the collected photons. Finally, the number S of signal photons detected by the single-photon detector through the mask is... i Represented as:

[0069]

[0070] Where F(x,y) is the two-dimensional density function of the detection region, and H i (x,y) is the modulation function of the mask, where x represents the horizontal coordinate of the pixel, y represents the vertical coordinate of the pixel, h is Planck's constant, λ is the wavelength of the active light source used, and i is the mode index.

[0071] The modulation process of the scene reflected light is realized by the first, second, third and fourth masks, and the corresponding mask modulation functions are represented by H1, H2, H3 and H4 respectively;

[0072]

[0073]

[0074]

[0075]

[0076] Moreover, since the four masks are identical masks placed symmetrically in pairs, the transmittance of the two symmetrically placed masks is superimposed to 1;

[0077] Therefore, the centroid coordinates (x, y) of the target object in the scene's horizontal space c yc ), represented as:

[0078]

[0079]

[0080] Where M represents the total light intensity of the scene, M x and M y S represents the light intensity value after integrating the scene with a special mask function. i The number of signal photons detected on optical path i;

[0081] The target spatial coordinates are then corrected using a mapping table to obtain the precise lateral spatial coordinates of the target object.

[0082] Then, after obtaining the centroid coordinates of the target object in the lateral space through signal photon counting and the lateral centroid algorithm, the depth position of the target object is determined based on the flight time of the selected signal photons.

[0083] A set of signal photons is selected within the integrated photon time distribution histogram by using a time window of a set size; the depth position z of the target object is calculated using the time centroid method based on the time labels of the selected signal photons and the photon count on each label.

[0084]

[0085] Where c is the speed of light, t i The time label for the time distribution histogram, t n -t m The selected time interval within the time distribution histogram, y i Let be the photon count value at the i-th time tag.

[0086] Finally, the corrected lateral spatial position and depth position are combined to complete the 3D detection of the target object with high lateral spatial resolution and high frame rate.

[0087] Furthermore, the step of selecting a set of signal photons within the integrated photon time distribution histogram by using a time window of a set size specifically includes:

[0088] For a target object without an environmental background, the time distribution histograms of the four beam paths are superimposed into an integrated time distribution histogram. A time window of a set size is selected, and the time region with the highest photon count is selected within the integrated time distribution histogram. The time region with the highest photon count is identified as the signal photon count. Then, the signal photons received by the four beam paths are extracted using the current time window to obtain the signal photon set.

[0089] Furthermore, the time distribution histograms of the four beam paths are provided, where the horizontal axis represents the flight time of the signal photon and the vertical axis represents the count of signal photons with the same flight time.

[0090] This invention primarily seeks solutions without acquiring target images within a scene. The lidar system designed in this invention centers on the principles of light field modulation and time-correlated single-photon counting, resulting in a solid-state lidar system capable of real-time 3D detection. First, based on the actual conditions of the mask, this invention establishes a modulation pattern model using a spatial error diffusion jitter method. Based on the principle of multi-beam optical path systems, a multi-path solid-state single-photon lidar system based on mask modulation is constructed. Subsequently, the lidar system is calibrated, a mapping table is established, and a system compensation algorithm is developed to improve the accuracy of the system in tracking the lateral spatial position of moving objects. Finally, the 3D spatial position of a rapidly moving target is obtained based on the count of signal photons and time-of-flight inversion.

[0091] Figure 2 This is a schematic diagram of the invented solid-state lidar system. The system first uses a pulsed laser as the active illumination source. The emitted pulsed laser light is polarized after passing through a half-wave plate and then incident on a polarization beam splitter. The vertically polarized light, containing a small portion of the pulse energy, is reflected by the polarization beam splitter onto the target surface of an avalanche photodiode. Its output electrical signal is then transmitted as a synchronization signal to the synchronization port of a time-correlated single-photon counter, at which point the time-correlated single-photon counter begins timing. The pulsed laser light, containing the majority of the energy, passes through the polarization beam splitter and is then diverged by a diverging unit composed of two lenses before illuminating the detection field of view. The signal light reflected by the target object is collected by a lens and split into four equal paths by three 50:50 beam splitters, each imaged onto a different mask. The different masks on the four beam paths modulate the image of the target object in two dimensions. The transmittance of the masks in the four beam paths, from top to bottom, is shown as follows: Figure 2 As shown, signal photons passing through different photomasks are detected by single-photon detectors in their respective quarter-segment optical paths after passing through lenses and filters. The output electrical signals are transmitted to the four channels of a time-correlated single-photon counter. After a set time period of acquisition, the time-correlated single-photon counter uploads the photon count and time information to a computer, which then performs calculations to obtain the three-dimensional positioning of the target object.

[0092] Figure 3 This describes the specific process of designing a photomask. The ideal modulation pattern for the photomask required in this invention is a grayscale pattern that gradually changes along a certain direction. However, due to limitations in processing technology, it is impossible to directly process grayscale patterns with different transmittances on the photomask glass. Therefore, the designed and processed photomask carries a binary image generated by a spatial dithering algorithm, as detailed below. Figure 3 As shown.

[0093] Figure 4 This is a schematic diagram of the system calibration process of the present invention. To avoid errors in the subsequent calculation of the centroid of the lateral space due to factors such as modulation pattern design, the present invention performs a calibration process on the system after its construction. The system calibration process is as follows: Figure 4 As shown:

[0094] First, a two-dimensional Cartesian coordinate system is established on the mask. The object is then moved uniformly to multiple positions along the direction of transmittance variation on the mask, thus imaging the object in regions of the mask with different transmittance. This yields the modulation effect corresponding to each position, and a mapping table between the actual position of the object and the predicted centroid coordinates is established.

[0095] For areas not measured, a linear difference algorithm is used to evaluate the mask modulation effect and obtain a complete mapping table. Furthermore, the calibration process only requires mask compensation mapping in one direction of the lateral space. In subsequent detection processes, the calculated positions in the x and y directions of the lateral space are combined with the mapping table to ultimately obtain the precise lateral spatial position.

[0096] Finally, based on the solid-state lidar system framework designed in this invention, the system's encoding, signal photon extraction, imaging frame rate, and lateral spatial resolution are explained in detail:

[0097] The encoding process is essentially a light field modulation process. First, this invention places four masks on four beam-splitting optical paths, and images the target object onto these masks. Utilizing the special transmittance structure of the masks, structured light modulation of the signal light can be achieved. Furthermore, the calculated lateral spatial position is revised using a mapping table obtained through system calibration. Through modulation using the masks of the four beam-splitting optical paths, the lidar system can achieve continuous, real-time encoding modulation of the target image, thereby enabling high frame rate 3D detection.

[0098] Signal photon extraction: The solid-state lidar system based on mask modulation designed in this invention receives not only signal photons from target objects in the scene, but also photons reflected back from background objects. Therefore, this invention is particularly suitable for work areas without environmental background (such as detecting and locating aerial drones). In such cases, the vast majority of photons received by the system are signal photons reflected back from target objects, and the flight time of the signal photons received by the four beam paths is concentrated. Therefore, for target objects without environmental background, the time distribution histograms of the four beam paths are superimposed into an integrated time distribution histogram. Based on the system parameters, a time window of a set size is selected, and the time region with the highest photon count within the integrated time distribution histogram is chosen. This time window is then identified as the time for signal photon counting. Subsequently, the signal photons received by the four beam paths are extracted using this window and further calculations are performed.

[0099] In many more operational scenarios, besides fast-moving target objects, the scene also includes background objects. In this case, the photons collected by the lidar system include reflected photons from both the target and background objects. Therefore, it is necessary to extract the signal photons from all received photons. For fixed application scenarios, the scene can be measured beforehand to obtain a time distribution histogram when there are no detected targets. At this time, the time distribution histogram only contains photons reflected back from background objects. Using this time distribution histogram as prior knowledge, when detecting moving targets, differential processing can be performed using this time distribution histogram to obtain the time distribution of signal photons when the target is present.

[0100] In addition, during real-time detection, the temporal distribution histogram of the previous frame and the temporal distribution histogram of the current detection can be differentially processed, and the difference between the signal photon distribution of the previous frame and the current detection can be obtained, which further provides conditions for extracting signal photons.

[0101] After obtaining the approximate location of the signal photon in the time distribution histogram using the two methods described above, the signal photon obtained by differentiating it from the background photon within the time window is extracted by selecting an appropriate time window. The three-dimensional spatial location of the target is then obtained using the following lateral spatial positioning algorithm and temporal centroid method.

[0102] The imaging frame rate is primarily determined by the time required for 3D detection of the target object. Traditional scanning lidar requires scanning imaging, with each detector completing the detection of multiple pixels before a single frame can be presented. This results in a linear increase in imaging time with the number of scanned pixels, significantly reducing the imaging frame rate. In contrast, this invention, similar to flash imaging solid-state lidar, only requires data acquisition from each detector once to complete the 3D localization of the target object, greatly reducing detection time and thus significantly improving the imaging frame rate.

[0103] Lateral spatial resolution: Unlike traditional flash imaging lidar, the lateral spatial resolution of this invention is not determined by the size of the detector array, but by the number of pixels in the mask within the system. After revising the obtained lateral spatial position of the target using a mapping table, the lateral spatial position is discretized according to the number of equivalent pixels in the mask, ultimately yielding a lateral spatial resolution of the same size as the equivalent pixel size of the mask. Therefore, the lidar system can further improve its lateral spatial resolution by increasing the number of pixels and reducing the size of the pixel units, thereby achieving real-time three-dimensional detection with higher lateral spatial resolution.

[0104] This invention introduces mask modulation technology into the lidar system, using a special mask to modulate signal photons, avoiding the dependence of scanning lidar on scanning devices, and breaking through the limitation that the imaging resolution of solid-state lidar is determined by the size of the detector array. It can perform high lateral spatial resolution and high frame rate three-dimensional rapid detection of moving targets with only four detectors.

[0105] Considering the impact of systematic errors, this invention calibrates a solid-state lidar system based on mask modulation, establishing a mapping relationship between the actual lateral spatial position of an object and the corresponding mask modulation effect, i.e., a mapping table. The obtained lateral spatial position is calibrated using this mapping table, thereby reducing the influence of systematic errors and obtaining accurate lateral spatial coordinates.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-dimensional positioning lidar, characterized in that, include: Pulsed laser; The pulsed laser emits a laser beam toward the target object. The laser beam is emitted to a polarization beam splitter through a half-wave plate. The polarization beam splitter emits the laser beam onto a first lens and an avalanche photodiode, respectively. After passing through the first lens, the laser beam is directed to a second lens and then emitted to the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. The time-correlated single-photon counter starts timing after receiving an electrical signal; The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam. The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter. The time-correlated single-photon counter transmits the received signals to the computer. Based on the four received signals, the computer predicts the three-dimensional spatial position of the target object, specifically including: The modulation process of the scene's reflected light is achieved using the first, second, third, and fourth masks, with the corresponding mask modulation functions being respectively... , , and express; Moreover, since the four masks are identical masks placed symmetrically in pairs, the transmittance of the two symmetrically placed masks is superimposed to 1; Therefore, the centroid coordinates of the target object in the horizontal space ( ), represented as: in, This represents the total light intensity value of the scene. and This represents the light intensity value after integrating the scene with a special mask function. for The number of signal photons detected on the optical path, The two-dimensional density function of the detection region; The obtained centroid coordinates are then corrected using a mapping table to finally obtain the precise lateral spatial coordinates of the target object.

2. The three-dimensional positioning lidar as described in claim 1, characterized in that, The polarization beam splitter, the first beam splitter, the second beam splitter, and the third beam splitter are used to disperse the laser beam. The polarization beam splitter is also used to send part of the pulsed laser energy to the avalanche photodiode. The avalanche photodiode is used to detect the pulsed light reflected by the polarization beam splitter and generate an electrical signal, which further provides a synchronization signal for the laser pulse emission of the relevant single-photon counter.

3. A three-dimensional positioning lidar as described in claim 1, characterized in that, The first, second, and third beam splitters are implemented using a 50:50 beam splitter, which divides the received signal into four equal paths.

4. A three-dimensional positioning lidar as described in claim 1, characterized in that, The first lens and the second lens have different focal lengths, and the first lens and the second lens are used to adjust the divergence angle of the laser beam.

5. A three-dimensional positioning lidar as described in claim 1, characterized in that, The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, each comprising: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence; after detecting a photon, the single-photon detector in each optical path generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter; wherein, the third beam is transmitted through the first mask, the first filter, the third lens, and the first optical fiber to the first single-photon detector, and the signal generated therefrom is transmitted to the first stop channel of the time-correlated single-photon counter; The fourth beam is transmitted through the second mask, the second filter, the fourth lens, and the second optical fiber to the second single-photon detector, and the signal generated therefrom is transmitted to the second stop channel of the time-correlated single-photon counter. The fifth beam is transmitted through the third mask, the third filter, the fifth lens, and the third optical fiber to the third single-photon detector, and the signal generated therefrom is transmitted to the third stop channel of the time-correlated single-photon counter. The sixth beam is transmitted through the fourth mask, the fourth filter, the sixth lens, and the fourth optical fiber to the fourth single-photon detector, and the signal generated is transmitted to the fourth stop channel of the time-correlated single-photon counter. The fabrication processes of the first, second, third, and fourth masks are consistent, but the placement directions of the four masks differ. The grayscale values ​​of the first and second masks are symmetrically distributed with respect to the vertical direction, while the grayscale values ​​of the third and fourth masks are symmetrically distributed with respect to the horizontal direction.

6. The three-dimensional detection method using a three-dimensional positioning lidar as described in claim 1, characterized in that, include: A pulsed laser emits a laser beam toward the target object. The laser beam is emitted through a half-wave plate to a polarization beam splitter. The polarization beam splitter emits the laser beam onto a first lens and an avalanche photodiode. After passing through the first lens, the laser beam is emitted into a second lens and then onto the target object. The avalanche photodiode converts the received pulsed light signal into an electrical signal and transmits the electrical signal to a time-correlated single-photon counter. The time-correlated single-photon counter starts timing after receiving an electrical signal; The light field signal of the target object is acquired by the lens and sent to the first beam splitter. After being split by the first beam splitter, a first beam and a second beam are generated. The first beam is input into the second beam splitter and is split by the second beam splitter to obtain a third beam and a fourth beam. The second beam is input into the third beam splitter and is split by the third beam splitter to obtain a fifth beam and a sixth beam. The third, fourth, fifth, and sixth beams are transmitted through their respective optical paths, which include: a mask, a filter, a lens, an optical fiber, and a single-photon detector connected in sequence. After the single-photon detector of each optical path detects a photon, it generates an electrical signal and transmits it to the four receiving ports of the time-correlated single-photon counter. The time-correlated single-photon counter transmits the received signal to the computer, and the computer predicts the three-dimensional spatial position of the target object based on the received four signals.

7. The three-dimensional detection method of a three-dimensional positioning lidar as described in claim 6, characterized in that, The method further includes: Using the aforementioned three-dimensional positioning lidar, a laser beam is emitted toward a sample target object whose actual position in three-dimensional space is known, and the computer's predicted position in three-dimensional space of the sample target object is obtained, thereby obtaining a mapping table between the actual position in three-dimensional space of the sample target object and the predicted position in three-dimensional space of the sample target object. Using the aforementioned three-dimensional positioning lidar, a laser beam is emitted toward the target object whose three-dimensional spatial location is unknown, and the computer obtains the predicted three-dimensional spatial location of the target object. Based on the mapping table, the actual three-dimensional spatial position corresponding to the predicted three-dimensional spatial position of the target object is found in the table. The predicted three-dimensional spatial position of the target object is then corrected based on the found actual three-dimensional spatial position to obtain the corrected predicted three-dimensional spatial position.

8. A three-dimensional detection method for a three-dimensional positioning lidar as described in claim 6, characterized in that, The time-correlated single-photon counter transmits the received signals to the computer. Based on the received four signals, the computer predicts the three-dimensional spatial position of the target object, specifically including: First, lateral spatial positioning is performed based on mask modulation: For a grayscale image, a two-dimensional Cartesian coordinate system is established based on the pixel coordinates, and then a two-dimensional density function is used. To represent the grayscale image, a mask with uniformly varying transmittance is used to perform structured light modulation on the collected photons. Finally, the number of signal photons detected by the single-photon detector through the mask is... Represented as: in, For the two-dimensional density function of the detection region, The modulation function of the mask. Represents the x-coordinate of a pixel. Represents the ordinate of a pixel. Let be Planck's constant. The wavelength of the active light source used. For pattern index; Then, after obtaining the centroid coordinates of the target object in the lateral space through signal photon counting and the lateral centroid algorithm, the depth position of the target object is determined based on the flight time of the selected signal photons. A set of signal photons is selected within the integrated photon time distribution histogram by using a time window of a set size; the depth position of the target object is calculated using the time centroid method based on the time labels of the selected signal photons and the photon count on each label. : in, At the speed of light, Time labels for the time distribution histogram. - It refers to the selected time interval within the time distribution histogram. For the first Photon count values ​​on each time stamp; Finally, the corrected lateral spatial position and depth position are combined to complete the 3D detection of the target object with high lateral spatial resolution and high frame rate.

9. A three-dimensional detection method for a three-dimensional positioning lidar as described in claim 8, characterized in that, The selection of a set of signal photons within the integrated photon time distribution histogram by using a time window of a set size specifically includes: For a target object without an environmental background, the time distribution histograms of the four beam paths are superimposed into an integrated time distribution histogram. A time window of a set size is selected, and the time region with the highest photon count is selected within the integrated time distribution histogram. The time region with the highest photon count is identified as the signal photon count. Then, the signal photons received by the four beam paths are extracted using the current time window to obtain the signal photon set.

10. A three-dimensional detection method for a three-dimensional positioning lidar as described in claim 9, characterized in that, The time distribution histograms of the four beam paths are shown, where the horizontal axis represents the flight time of the signal photon and the vertical axis represents the count of signal photons with the same flight time.

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