Photonic high-efficiency scanning methods and ranging methods

Abstract

This invention provides a highly efficient photon scanning method and ranging technique, primarily combining rotational scanning and push-broom techniques, and employing a multi-beam emission method. When the aircraft is moving in a straight line, rotational scanning and push-brooming can be simultaneously achieved simply by rotating the light source. A single-photon array detector is used to collect the echo photons reflected from the detected surface by the probe laser. This invention significantly advances the rapid measurement of depth features of large-area targets. Rotational scanning makes the sampled target points denser and improves the spatial resolution of the detection; push-brooming allows the system to measure more target points in the scanning direction, increasing the detection area. This invention has good development potential in fields such as terrain mapping and single-photon 3D imaging.

Description

Technical Field

[0001] This invention relates to the field of photon detection technology, specifically providing a photon efficient scanning method and ranging method based on a combination of multiple scanning methods. Background Technology

[0002] Single-photon detection is an active detection technology that obtains target information by processing laser echoes. The energy of the laser echo is closely related to the receiving aperture and pulse power. To maximize the use of limited laser echo energy and reduce dependence on hardware such as large-aperture telescopes and high-power lasers, single-photon detection technology has received increasing attention. Single-photon detectors have extremely high sensitivity, capable of detecting very weak photon signals, significantly improving detection performance and showing great application potential in fields such as distance measurement. Combined with time-correlated single-photon counting (TCSPC) technology, the target distance can be calculated based on the temporal distribution of echo photons even under conditions of weak laser echo energy, and extensive scientific research has been conducted in this area both domestically and internationally.

[0003] A team led by He Qiaoying at the University of Chinese Academy of Sciences developed a system based on an MPPC array and conducted experimental detection on a target 37m away. They successfully detected the target with an average of approximately 1.98 photons per pixel, achieving a ranging accuracy of 0.268m in the target area. A team led by Buller at Heriot-Watt University built a single-photon detection lidar system and successfully performed depth measurements on a clock tower 800m away, a cable tower 6.8km away, and terrain features 10.5km away using a point-by-point scanning method. However, to date, most single-photon ranging laser systems only measure information from one location point at a time, failing to quickly acquire large amounts of point cloud data. Even some systems that have implemented pushbroom ranging still suffer from problems such as a single pushbroom method, limited information points acquired, and complex pushbroom path control. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a photonic high-efficiency scanning method and ranging method based on a combination of multiple scanning techniques. It primarily combines rotational scanning with push-broom scanning and employs a multi-beam emission mechanism. When the aircraft is moving in a straight line, rotational scanning and push-broom scanning can be achieved simultaneously simply by rotating the light source. Rotational scanning results in denser sampling points and improves the spatial resolution of the detection; push-broom scanning allows the system to measure more target points in the scanning direction, increasing the detection area. This method has good development potential in fields such as terrain mapping and single-photon 3D imaging.

[0005] The photonic high-efficiency scanning method provided by this invention performs push-broom and rotation scanning simultaneously, as detailed below:

[0006] The laser source emits at least two probe lasers, and each probe laser illuminates a different target point on the scanning target. When the laser source performs linear push-broom, the probe laser rotates at a constant speed around the center, and a single-photon array detector is used to collect the echo photons reflected by the probe laser from the probed surface.

[0007] Preferably, efficient scanning is performed by using a laser source carried by an aircraft.

[0008] Preferably, the connection between the aircraft and the laser source is a rotating connection, and the laser source rotates at a constant speed during efficient scanning.

[0009] Preferably, the single-photon array detector contains 1024 pixels, each of which integrates a timer, and the timer uses a time-correlated single-photon counting mode.

[0010] A photon-based high-efficiency scanning ranging method, the specific steps of which are as follows:

[0011] S1. The aircraft carries a laser source and performs a push-scan operation using a photon-efficient scanning method to obtain a depth map of the scanned target;

[0012] S2. Establish a statistical model for single-photon detection and obtain the probability density equation for photon arrival time as follows:

[0013] ;

[0014] in, This represents the coordinates of a pixel on the depth map. This indicates the pulse period of the probe laser. This represents the target distance at a given pixel. express t Photon flux over time This represents the quantum efficiency of a single-photon array detector. This represents the reflectance of the scanned target corresponding to a specific pixel. This represents the number of noise photons within one pulse cycle. c Represents the speed of light. L This represents the total number of signal photons generated in one pulse cycle;

[0015] S3. Based on the probability density of photon arrival time, the maximum likelihood function for the depth of the scanned target is obtained as follows:

[0016] ;

[0017] in, This represents the photon arrival time dataset, where S represents the pixel number. This represents the photon count.

[0018] Preferably, the laser source is a compound eye structure, that is, multiple light outlets and a laser are uniformly integrated on a hemispherical shell to split a single laser beam into multiple probe laser beams and ensure that each probe laser beam illuminates a different target point on the scanned target.

[0019] Preferably, the derivation of the probability density equation for photon arrival time is as follows:

[0020] The photon count rate collected by the single-photon array detector is calculated as follows:

[0021] ;

[0022] in, Represents background photon flux. The dark count rate represents the single-photon array detector;

[0023] One pulse cycle The number of noisy photons within is:

[0024] ;

[0025] The total number of signal photons generated in one pulse cycle is:

[0026] ;

[0027] The number of photons received by the single-photon array detector within one pulse cycle follows a Poisson distribution as follows:

[0028] ;

[0029] in, k This represents the number of photons detected within one pulse cycle.

[0030] The probability of no photon being detected within one pulse cycle is calculated as follows:

[0031] ;

[0032] N The actual photon count detected by each laser pulse It follows a binomial distribution, that is:

[0033] ;

[0034] Then the arrival time of the first photon W The probability distribution function is as follows:

[0035] ;

[0036] in, , ;

[0037] The probability density equation for the photon arrival time can be obtained from the above equation.

[0038] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0039] This invention has made significant progress in rapidly measuring the depth features of large-area targets. By splitting the laser beam to detect multiple target points, the detection area is effectively expanded. The push-broom method is used to illuminate other positions of the target with the detection laser beam group, realizing a large-area push-broom function. During the push-broom process, the detection laser beam group is rotated rapidly, and the distances of more and denser target scanning points can be measured in the same amount of time. While improving detection efficiency, it also improves the spatial resolution of the detection, making the depth features of the target in space more obvious. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure for high-efficiency photon scanning provided in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of a photonic high-efficiency scanning method provided according to an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram of a single-photon array detector acquiring signals according to an embodiment of the present invention;

[0043] Figure 4 This is a bar chart of target point distances provided according to an embodiment of the present invention;

[0044] Figure 5 This is a bar chart of ranging performance indicators provided according to an embodiment of the present invention.

[0045] The reference numerals in the figures include:

[0046] 1. Aircraft; 2. Laser source; 3. Detection laser. Detailed Implementation

[0047] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0049] Figure 1The structure for high-efficiency photonic scanning according to an embodiment of the present invention is shown.

[0050] like Figure 1 As shown, this embodiment of the invention utilizes a photon-based high-efficiency scanning method and ranging technique to scan and measure the distance to ground targets. The specific details are as follows:

[0051] S1. The photonic high-efficiency scanning method combines push-broom and rotational scanning. A laser source 2, carried by a spacecraft 1, performs efficient scanning. The laser source 2 is horizontally positioned at the bottom of the spacecraft 1 and fixed to it via a rotating shaft. Its rotation is controlled by a motor. During the linear push-broom motion of the spacecraft 1, the laser source 2 also rotates, achieving rotational scanning. The laser source 2 has a compound-eye structure, with multiple light-emitting ports and a laser uniformly integrated on a hemispherical shell. The single laser beam emitted by the laser is split into multiple probe lasers 3, each with a wavelength of 637.5 nm. This ensures that each probe laser 3 illuminates a different target point on the scanned target. This compound-eye structure effectively guarantees the output stability and homogeneity of the probe lasers 3. Alternatively, the laser source 2 can also be designed using multi-fiber integration, splitting the single laser beam emitted by the laser into multiple probe lasers 3 via multiple optical fibers.

[0052] The aircraft 1 is also equipped with a single-photon array detector, which is used to collect the echo photons reflected by the detection laser 3 by the target detection surface. The single-photon array detector contains 1024 pixels, and each pixel is integrated with a timer with an accuracy of 55ps. The timer adopts a time-correlated single-photon counting mode.

[0053] In addition, each probe laser 3 will have a squint error during the rotation scanning process, and the squint errors of different probe lasers 3 are different. In order to improve the ranging accuracy, it is first necessary to analyze and calculate the squint error of one of the probe lasers 3, and then correct the remaining probe lasers 3 one by one according to the spatial relationship of each probe laser 3.

[0054] Figure 2 This illustrates a photonic high-efficiency scanning method provided according to an embodiment of the present invention.

[0055] The scanning method for high-efficiency scanning ranging using the above-mentioned photon high-efficiency scanning method is as follows: Figure 2 The scanning path of each probe laser 3 is a spiral upward curve.

[0056] S2. Based on the depth map obtained by efficient scanning, a single-photon detection statistical model is established, and the probability density equation for photon arrival time is derived. The specific process is as follows:

[0057] The photon count rate collected by the single-photon array detector is calculated as follows:

[0058] ;

[0059] in, This represents the coordinates of a pixel on the depth map. This represents the target distance at a given pixel. express t Photon flux over time This represents the quantum efficiency of a single-photon array detector. This represents the reflectance of the scanned target corresponding to a specific pixel. Represents background photon flux. The dark count rate represents the single-photon array detector. c It represents the speed of light.

[0060] Based on the parameters of laser source 1, the pulse period of the detection laser 3 can be obtained as follows: One pulse cycle The number of noisy photons within is:

[0061] ;

[0062] The total number of signal photons generated in one pulse cycle is:

[0063] ;

[0064] Set the photon count to The number of photons received by the single-photon array detector within one pulse cycle follows a Poisson distribution as follows:

[0065] ;

[0066] in, k This represents the number of photons detected within one pulse cycle.

[0067] The probability of no photon being detected within one pulse cycle is calculated as follows:

[0068] ;

[0069] Because single-photon array detectors have a dead time, single-photon array detectors in At most, only one photon can be detected inside. N The actual photon count detected by each laser pulse It follows a binomial distribution, that is:

[0070] ;

[0071] Then the arrival time of the first photon W The probability distribution function is as follows:

[0072] ;

[0073] in, , ;

[0074] The probability density equation for the photon arrival time can be obtained from the above equation as follows:

[0075] .

[0076] S3. Based on the probability density equation of photon arrival time, the maximum likelihood function of the depth of the scanned target can be obtained, which is the distance between laser source 1 and the target point. The calculation formula is as follows:

[0077] ;

[0078] in, This represents the photon arrival time dataset, where S represents the pixel number.

[0079] Furthermore, when the target reflectivity is unavailable, the maximum likelihood function value of the depth of the scanned target can be simplified by using a log-matched filter estimate. Substitution, that is:

[0080] .

[0081] It should be noted that few-photon ranging is derived from a probability model, and the ranging result can be obtained by substituting the laser pulse number parameter. Traditional few-photon ranging fits a curve based on the distribution of photons over time, and the peak of the curve is the ranging result. However, this invention uses three-dimensional imaging to obtain the maximum likelihood function of the depth of the scanned target based on the probability density of photon arrival time, which is the ranging result. The method of this invention provides more accurate ranging results and simplifies the calculation.

[0082] Figure 3 The diagram illustrates a signal acquired by a single-photon array detector according to an embodiment of the present invention.

[0083] like Figure 3 As shown, to verify the effectiveness and high precision of the present invention, a verification simulation experiment was conducted using a photon high-efficiency scanning method and a ranging method. During the experiment, three probe lasers 3 were used, a total of 6 sets of data were collected, and the distances of 18 target points were measured.

[0084] Figure 4 A bar chart showing the distance to target points provided according to an embodiment of the present invention is shown.

[0085] like Figure 4As shown, time-correlated single-photon counting technology was used to measure the distances to 18 target points obtained from the scan, based on the statistical data of photon arrival times. The ranging results are as follows. Figure 4 .

[0086] Figure 5 A bar chart showing the ranging performance indicators provided according to an embodiment of the present invention is shown.

[0087] like Figure 5 As shown, in order to better understand the effectiveness and universality of the ranging results, the performance index of ranging of the center pixel of the target point on the single-photon array detector was investigated. Data was collected 50 times at each target point, and the standard deviation of the measured distance was used as the ranging accuracy; the root mean square error (RMSE) corresponding to the measured distance was used as the ranging accuracy.

[0088] Plot based on experimental data Figure 5 The bar chart shown represents the ranging performance indicators, where... Figure 5 (a) reflects the ranging accuracy. Figure 5 (b) reflects the accuracy of distance measurement.

[0089] Based on experimental results, the ranging accuracy of scanning and ranging using the photon high-efficiency scanning method and ranging method is better than 1.48 cm and the precision is better than 115.53 ps. Compared with existing scanning methods and ranging methods, the present invention has higher ranging accuracy and precision.

[0090] In addition, to further improve ranging accuracy, during the time-correlated single-photon counting process, the reflectivity of the target point can be calculated first, noise can be removed based on the spatial correlation of the reflectivity, and then the reflectivity can be substituted into the formula for solution.

[0091] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0092] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A photon-based high-efficiency scanning ranging method, characterized in that, The specific steps are as follows: S1. The aircraft carries a laser source and performs push-broom scanning in a photonic high-efficiency scanning mode to obtain a depth map of the scanned target. The photonic high-efficiency scanning mode is as follows: push-broom and rotation scanning are performed simultaneously. The laser source emits at least two probe lasers, and each probe laser illuminates a different target point on the scanned target. When the laser source performs linear push-broom, the probe laser rotates around the center at a uniform speed, and a single-photon array detector is used to collect the echo photons reflected by the probe laser from the probed surface. S2. Establish a statistical model for single-photon detection and obtain the probability density equation for photon arrival time as follows: ； in, This represents the coordinates of a pixel on the depth map. This indicates the pulse period of the probe laser. This represents the target distance at a given pixel. express t Photon flux over time This represents the quantum efficiency of a single-photon array detector. This represents the reflectance of the scanned target corresponding to a specific pixel. This represents the number of noise photons within one pulse cycle. c Represents the speed of light. L This represents the total number of signal photons generated in one pulse cycle; S3. Based on the probability density of photon arrival time, the maximum likelihood function for the depth of the scanned target is obtained as follows: ； in, This represents the photon arrival time dataset, where S represents the pixel number. This represents the photon count.

2. The photon-based high-efficiency scanning ranging method as described in claim 1, characterized in that, The laser source has a compound eye structure, which means that multiple light outlets and a laser are uniformly integrated on a hemispherical shell. This structure is used to split a single laser beam into multiple probe laser beams and ensure that each probe laser beam illuminates a different target point on the scanned target.

3. The photon-based high-efficiency scanning ranging method as described in claim 1, characterized in that, The derivation of the probability density equation for photon arrival time is as follows: The photon count rate collected by the single-photon array detector is calculated as follows: ； in, Represents background photon flux. The dark count rate represents the single-photon array detector. One pulse cycle The number of noisy photons within is: ； The total number of signal photons generated in one pulse cycle is: ； The number of photons received by the single-photon array detector within one pulse period follows a Poisson distribution as follows: ； in, k This represents the number of photons detected within one pulse cycle. The probability of no photon being detected within one pulse cycle is calculated as follows: ； N The actual photon count detected by each laser pulse It follows a binomial distribution, that is: ； Then the arrival time of the first photon W The probability distribution function is as follows: ； in, , ; The probability density equation for the arrival time of the photon can be obtained from the above equation.

4. The photon-based high-efficiency scanning ranging method as described in claim 1, characterized in that, Squinting error correction is performed on each probe laser beam during the rotational scanning process.

5. The photonic high-efficiency scanning method as described in claim 1, characterized in that, The laser source is carried by an aircraft for efficient scanning.

6. The photonic high-efficiency scanning method as described in claim 5, characterized in that, The connection between the aircraft and the laser source is a rotating connection. During high-efficiency scanning, the laser source rotates at a constant speed.

7. The photonic high-efficiency scanning method as described in claim 1, characterized in that, The single-photon array detector contains 1024 pixels, each of which is integrated with a timer. The timer uses a time-correlated single-photon counting mode.

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