A time-gated single-photon detection imaging method and system

Abstract

The application discloses a time-gated single-photon detection imaging method and system, and belongs to the technical field of photoelectric detection and imaging. The method comprises the following steps: emitting pulsed laser to a detection target and receiving echo photons, and recording photon flight time data; based on the photon flight time data, iteratively calculating the most possible position of the target by using a maximum a posteriori probability estimation method; dynamically adjusting the gate opening time of a single-photon detector according to the calculation result; repeatedly executing until the iteration termination condition is met; and finally, reconstructing a target image based on the optimized data. Through continuous correction between the algorithm and the measured data, the application realizes adaptive estimation of the position of a non-cooperative target, solves the problem that the traditional gated detection technology needs to rely on prior distance information of the target, effectively suppresses background noise, and improves the imaging quality and efficiency. The method is realized by a system comprising a laser light source module, an optical mechanical system module, a single-photon detector module, a photon coincidence counting module and a data processing module.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection and imaging technology, specifically relating to a single-photon detection imaging method and system based on adaptive time gating, which is particularly suitable for high-sensitivity, low-noise laser imaging of non-cooperative targets with unknown distance information. Background Technology

[0002] Single-photon detection technology, with its extremely high sensitivity, picosecond-level temporal resolution, and excellent spatial resolution, has shown great application potential in fields such as long-range target detection, ultrafast phenomenon observation, underwater imaging, and target recognition. This technology can effectively detect extremely weak light signals and can even respond to a single photon, enabling high-quality imaging of distant or low-reflectivity targets while reducing laser emission power.

[0003] However, its high sensitivity also makes it highly susceptible to interference from background noise photons, resulting in redundant point cloud data and degraded imaging quality. To suppress background noise, two main methods are currently employed: algorithmic filtering and gated detection. Algorithmic filtering methods use software to filter noise photons based on differences in statistical characteristics or spatial distribution between noise and signal photons after data acquisition. While this method has some effectiveness, its processing is typically time-consuming, computationally resource-intensive, and the universality and adaptability of the algorithm are often limited. In contrast, gated detection technology is a more direct hardware-level noise suppression solution. Its core idea is to control the single-photon detector, making it only briefly activated within the expected arrival time window of the target echo. This physically isolates background noise during most irrelevant times, reducing the acquisition of invalid data at the source and significantly improving imaging efficiency and quality.

[0004] However, existing gating detection technologies face a fundamental application bottleneck: their effectiveness heavily relies on precise prior knowledge of the target's distance. In practical applications, the gating window needs to be calculated based on the time difference (i.e., time of flight) between the laser emission time and the arrival time of the target echo. For cooperative targets or static targets with known distances, this information can be obtained through laser rangefinders, radar, or pre-calibration. However, when facing non-cooperative targets with unknown distances, the inability to pre-determine the echo arrival time makes it difficult for traditional gating detection technologies to set an effective gating window, thus failing to realize their advantages and severely limiting their application scenarios. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that existing gated single-photon detection technology is limited in performance when facing non-cooperative targets with unknown distance information because it is impossible to determine an effective gating window. The invention proposes a method and system that iteratively estimates the target position and adaptively adjusts the detection gating.

[0006] To achieve the above objectives, the technical solution provided by this invention is:

[0007] One approach provides a time-gated single-photon detection imaging method, comprising the following steps:

[0008] Step 1: Emit a pulsed laser towards the target and receive its echo photons;

[0009] Step 2: Obtain the main wave electrical signal representing the moment of laser emission, and convert the echo photons into echo electrical signals;

[0010] Step 3: Record the time difference between the main wave electrical signal and the echo electrical signal to generate photon time-of-flight data;

[0011] Step 4: Based on the photon time-of-flight data, the most probable location of the target is iteratively calculated using the maximum a posteriori probability estimation method;

[0012] Step 5: Update the gating opening time of the single-photon detector based on the calculated most probable target location;

[0013] Step 6: Repeat the above echo reception, time recording, position calculation and gating update steps until the preset iteration termination condition is met;

[0014] Step 7: Reconstruct the target image based on the data obtained in the final iteration.

[0015] Furthermore, in step 4, the maximum a posteriori probability estimation method uses real-time acquired photon time-of-flight data to construct a likelihood function and evaluates the target location with the highest probability of echo photon appearance in an iterative optimization manner.

[0016] Furthermore, step 4 specifically includes:

[0017] Generate a photon flight time statistical histogram based on photon flight time data;

[0018] Using the generated statistical histogram as the basis for the likelihood function, the target distance estimate that maximizes the posterior probability is calculated through an iterative optimization algorithm.

[0019] Furthermore, in step 6, the preset iteration termination condition is any one of the following:

[0020] - The number of iterations has reached a predetermined threshold;

[0021] - The change in the target position obtained from two consecutive iterations is less than the preset tolerance.

[0022] Furthermore, in step 1, when emitting pulsed laser, the orientation of the laser irradiation to the target area is changed according to a preset scanning path by controlling the fast-reflecting mirror in the optomechanical system module.

[0023] On the other hand, a time-gated single-photon detection imaging system is provided to implement the above-mentioned time-gated single-photon detection imaging method. This system includes:

[0024] Laser source module, used to generate pulsed laser;

[0025] A laser beam splitter is placed in the output optical path of the laser source module to split the pulsed laser into an illumination beam and a main wave reference beam.

[0026] The optomechanical system module is used to expand the illumination beam and emit it to the detection target, and to receive the echo photons scattered by the target;

[0027] The main wave detector module is used to receive the main wave reference beam and generate the main wave electrical signal;

[0028] A single-photon detector module is used to receive echo photons and generate echo electrical signals;

[0029] The photon coincidence counting module is electrically connected to the main wave detector module and the single photon detector module, and is used to generate photon time-of-flight data based on the main wave electrical signal and the echo electrical signal.

[0030] The data processing module is electrically connected to the single-photon detector module and the photon coincidence counting module, and is configured to: execute the maximum a posteriori probability estimation algorithm to iteratively calculate the most probable position of the target based on the photon time-of-flight data; generate control signals according to the calculation results to adjust the gating opening time of the single-photon detector module; and reconstruct the target image after the iteration is completed.

[0031] Furthermore, the optomechanical system module includes a fast reflector, which is electrically connected to the data processing module to change the laser emission orientation.

[0032] Furthermore, the single-photon detector module includes an InGaAs single-photon detector and a host computer system that controls its operating modes, including free-running mode and gated mode.

[0033] Furthermore, the photon coincidence counting module includes a time-to-digital converter for recording the arrival time of echo photons.

[0034] Furthermore, the laser source module is a pulsed laser that emits a pulse width of 1 ns, a frequency of 1 kHz, and a wavelength of 1064 nm.

[0035] The advantages of this invention are:

[0036] 1. The time-gated single-photon detection imaging method provided by this invention employs a machine learning approach based on maximum a posteriori probability estimation. It iteratively optimizes the target location information using measured real data while simultaneously updating the single-photon detector gating time. This allows the method to autonomously and gradually approach and lock onto the target's true location through an iterative cycle of "emission-acquisition-estimation-update" without requiring prior distance information. This process significantly reduces the generation of redundant background noise data at the source of data production, lowering the computational burden of subsequent data processing. This achieves a substantial improvement in the effectiveness of point cloud data and the speed and quality of image reconstruction while maintaining high detection sensitivity. Furthermore, the adaptive nature of this method makes it particularly suitable for high-quality imaging of non-cooperative targets at unknown distances, solving the fundamental problem that traditional gated detection methods cannot be applied in such scenarios.

[0037] 2. The time-gated single-photon detection imaging system provided by this invention integrates the maximum a posteriori likelihood estimation algorithm into the data processing module and forms a closed-loop control with the single-photon detector module. This enables adaptive estimation of the distance information of non-cooperative targets, thereby achieving dynamic and precise control of the detector gating time. This not only effectively isolates background noise photons in irrelevant time periods at the physical level, significantly reducing the risk of noise damage to the single-photon detector and the amount of invalid data collection, but also significantly improves the system's signal-to-noise ratio and imaging efficiency. Simultaneously, through the synergy of algorithm and hardware, this hardware system achieves autonomous detection and imaging of unknown targets, breaking through the dependence of traditional gated detection systems on prior distance information and greatly expanding the application scope of single-photon imaging technology in complex scenarios. Attached Figure Description

[0038] The above and / or other features and advantages of the present invention will become more readily understood from the following description with reference to the accompanying drawings, in which:

[0039] Figure 1 This is a diagram illustrating the composition of the time-gated single-photon detection imaging system of the present invention;

[0040] Figure 2 This is a flowchart of the time-gated single-photon detection imaging method of the present invention.

[0041] In the diagram: 1-Laser source module; 2-Laser beam splitter; 3-Optical-mechanical system module; 4-Main wave detector module; 5-Single photon detector module; 6-Photon coincidence counting module; 7-Data processing module. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments thereof. It should be noted that the following detailed description of the present invention is for illustrative purposes only and is not intended to limit the scope of the invention.

[0043] This invention addresses the problem that gated detection cannot solve the detection and imaging of non-cooperative targets. It provides a time-gated single-photon detection imaging method and a time-gated single-photon detection imaging system. The method uses the maximum a posteriori likelihood estimation method to evaluate the location with the highest probability of echo occurrence and sends the suspected target location to the single-photon detector. By activating the single-photon detector, the echo of the target is reacquired. After multiple iterations and optimizations, adaptive gating imaging of non-cooperative targets is finally achieved.

[0044] Reference Figure 1 The time-gated single-photon detection imaging system, which is an exemplary embodiment of the present invention, mainly includes a laser source module 1, a laser beam splitter 2, an optomechanical system module 3, a main wave detector module 4, a single-photon detector module 5, a photon coincidence counting module 6, and a data processing module 7.

[0045] The laser source module 1 uses a pulsed laser with an emission pulse width of 1ns, a repetition frequency of 1kHz, and a center wavelength of 1064nm to generate the laser pulses required for illumination.

[0046] The laser beam splitter 2 is a precision optical element located in the output optical path of the laser source module 1, with a splitting ratio of 99:1. It splits the incident pulsed laser into two beams: the beam with 99% energy is used as the illumination beam and transmitted to the optomechanical system module 3; the beam with 1% energy is used as the main wave reference beam and transmitted to the main wave detector module 4 to provide a time reference for laser emission.

[0047] The optomechanical system module 3 is the core of the optical path control, including a laser emitting system, an echo receiving system, and a fast reflector. The laser emitting system typically consists of a beam expander assembly, used to expand the received illumination beam into collimated light with a very small divergence angle before emitting it towards the target area. The echo receiving system typically consists of a receiving telescope and a coupling lens assembly, used to efficiently collect the weak echo photons scattered by the target and couple them into the optical fiber. The fast reflector is placed in the emitting optical path, and its rotation axis is connected to the data processing module 7 via a drive circuit. Controlled by commands from the data processing module 7, it can precisely and rapidly deflect, thereby changing the spatial orientation of the laser illumination spot and completing two-dimensional or three-dimensional scanning of the target.

[0048] The main wave detector module 4 uses a high-speed response diode avalanche detector to receive the main wave reference beam with 1% energy and convert it into a TTL level electrical signal with a precise time mark, namely the main wave electrical signal. This signal marks the emission time of the laser pulse and serves as the starting point for time-of-flight measurement.

[0049] The single-photon detector module 5 is the core detection unit of this system. In this embodiment, an InGaAs-based gated single-photon detector is used. This module also includes a host computer control system, a power supply module, and a thermoelectric cooling system. The host computer control system receives instructions from the data processing module 7 and dynamically sets the detector's operating mode (free-running mode or gated mode) and key parameters (such as gate opening delay and gate width). The power supply module provides a stable operating voltage for the entire detector, and the thermoelectric cooling system cools the detector chip to tens of degrees below zero to significantly suppress dark counting. The core function of this module is to convert the echo photon events introduced through the optical fiber into TTL level electrical pulse signals, i.e., echo electrical signals.

[0050] The photon coincidence counting module 6 integrates a high-precision time-to-digital converter (TDC), a large-capacity data memory, and a programmable logic controller (FPGA). Its two input channels are connected to the outputs of the main wave detector module 4 and the single-photon detector module 5, respectively, receiving the main wave electrical signal and the echo electrical signal in real time. The TDC unit uses the main wave electrical signal as the start signal and the subsequent arriving echo electrical signal as the stop signal to accurately measure the flight time of each echo photon, achieving a resolution on the picosecond level, and accurately timestamping each valid photon event. All timestamp data is quickly and temporarily stored in the internal memory and can be packaged and transmitted to the data processing module 7 according to a set format.

[0051] The data processing module 7 serves as the control and data processing center for the entire system. It can be implemented by a high-performance computer or industrial control computer with a built-in professional data processing card, running dedicated control and imaging software including a maximum a posteriori likelihood estimation algorithm. This module communicates with the photon coincidence counting module 6 via a data bus to receive photon time-of-flight data; simultaneously, it connects to the host computer system of the single-photon detector module 5 and the fast-reflecting mirror driver of the optomechanical system module 3 via a communication interface. Its main functions include: receiving and buffering photon time-of-flight data; executing the maximum a posteriori probability estimation algorithm based on this data to iteratively estimate the most probable position of the target; generating control commands based on the estimation results to dynamically adjust the gating opening time of the single-photon detector module 5, forming an adaptive closed-loop control; sending scanning commands to control the movement of the fast-reflecting mirror; and finally, reconstructing and displaying a 3D image of the target using the optimized point cloud data.

[0052] Reference Figure 2 Based on the above system, the time-gated single-photon detection imaging method of the present invention includes the following steps:

[0053] Step S1: System initialization and parameter preset. (Refer to...) Figure 1The modules are assembled and connected, and the power is turned on for system preheating. Initial operating parameters are set through the software interface of the data processing module 7, including: preset scanning path for the fast-reflecting mirror, initial setting of the single-photon detector module 5 to free-running mode or a wide-gated mode based on the estimated maximum detection distance, and preset iteration convergence thresholds. In this embodiment, the preset iteration termination condition is that the distance change is less than 0.5 meters, but this convergence threshold can be other values ​​as needed. In other embodiments, the preset iteration termination condition can be that the change in target position calculated in two consecutive iterations is less than a preset tolerance.

[0054] Step S2: Data Acquisition. The laser source module 1 is activated, and the data processing module 7 controls the fast-reflecting mirror to sequentially illuminate different locations within the target area along a preset path using a pulsed laser beam. The main wave detector module 4 and the single-photon detector module 5 operate synchronously, generating a main wave electrical signal and an echo electrical signal (possibly containing target echoes and background noise) for each laser-illuminated location. The photon coincidence counting module 6 records the flight time of all photons, forming an initial photon flight time dataset with a low signal-to-noise ratio, and generates a corresponding flight time statistical histogram.

[0055] Step S3: Target position iterative estimation. This step is completed within the data processing module 7. For each specific position on the scanning path, the data processing module 7 reads the initial photon time-of-flight data.

[0056] a) First, a statistical histogram of photon flight time is generated based on this data.

[0057] b) Next, using this statistical histogram as the basis for the likelihood function, the maximum a posteriori probability estimation algorithm is run. This algorithm calculates, through iterative optimization (such as gradient descent, expectation-maximization, etc.), a target distance estimate that maximizes the posterior probability, i.e., the most likely location of the target:

[0058]

[0059] In the formula, The target location is estimated using the maximum a posteriori probability. For timestamps, For probability, The time of one detection cycle.

[0060] c) The data processing module 7 converts this estimate into the corresponding flight time and sends this time value as a gated delay parameter specific to this location to the single-photon detector module 5.

[0061] Step S4: Gating Update and Closed-Loop Optimization. The single-photon detector module 5 enables fine-gating mode based on the updated gating delay parameters for each location. The system repeats steps S2 and S3, that is, during the scanning process, new echo data is acquired for each location using the updated gating parameters, and the target location is estimated again. This "acquisition-estimation-update" closed-loop process is repeated until the changes in all estimated target locations are less than a preset threshold after several consecutive iterations, at which point the algorithm is considered to have converged and the target location has been successfully locked.

[0062] Step S5: Target Scanning and Imaging. After locking the target distance, the data processing module 7 controls the fast reflector in the optomechanical system module 3 to move the laser beam illumination point again according to the preset scanning trajectory. Throughout the scanning process, the single-photon detector module 5 always operates in the optimized precision gating mode, collecting only echo photons from the target area. The photon coincidence counting module 6 records the photon time-of-flight data for each pixel (corresponding to the orientation of one fast reflector).

[0063] Step S6: Image Generation and Output. After scanning, the data processing module 7 performs subsequent processing on all point cloud data collected in step S5, including coordinate transformation and noise filtering. By calculating the flight time of each photon and its corresponding spatial azimuth angle, a high signal-to-noise ratio three-dimensional range image or intensity image of the target can be reconstructed and displayed.

[0064] This embodiment demonstrates that the time-gated single-photon detection imaging system and method provided by the present invention, by utilizing a single-photon detection probability model and a machine learning method based on maximum a posteriori probability estimation, continuously iterates and optimizes the target location information using real experimental data, while updating the single-photon detector activation time. Through a continuous correction between the algorithm model and measured data, it achieves the estimation of the location information of non-cooperative targets, thus completing single-photon-gated detection imaging of distant unknown targets. Furthermore, in this invention, the single-photon detector is only activated when the target's echo photon enters the detector, thus not only isolating the detector from strong background noise and redundant data, but also improving mapping speed and imaging quality.

[0065] Finally, it should be noted that the features mentioned and / or shown in the above description of exemplary embodiments of the present invention can be combined in the same or similar manner with one or more other embodiments, combined with or substituted for corresponding features in other embodiments. These combined or substituted technical solutions should also be considered to be included within the scope of protection of the present invention.

Claims

1. A time-gated single-photon detection imaging method, characterized in that, Includes the following steps: Step 1: Emit a pulsed laser towards the target and receive its echo photons; Step 2: Obtain the main wave electrical signal representing the moment of laser emission, and convert the echo photons into echo electrical signals; Step 3: Record the time difference between the main wave electrical signal and the echo electrical signal to generate photon time-of-flight data; Step 4: Based on the photon time-of-flight data, the most probable location of the target is iteratively calculated using the maximum a posteriori probability estimation method; Step 5: Update the gating opening time of the single-photon detector based on the calculated most probable target location; Step 6: Repeat the above echo reception, time recording, position calculation and gating update steps until the preset iteration termination condition is met; Step 7: Reconstruct the target image based on the data obtained in the final iteration.

2. The time-gated single-photon detection imaging method according to claim 1, characterized in that, In step 4, the maximum a posteriori probability estimation method uses real-time acquired photon time-of-flight data to construct a likelihood function and evaluates the target location with the highest probability of echo photon occurrence in an iterative optimization manner.

3. The time-gated single-photon detection imaging method according to claim 2, characterized in that, Step 4 specifically includes: A photon flight time statistical histogram is generated based on the aforementioned photon flight time data; Using the generated statistical histogram as the basis for the likelihood function, the target distance estimate that maximizes the posterior probability is calculated through an iterative optimization algorithm.

4. The time-gated single-photon detection imaging method according to claim 1 or 2, characterized in that, In step 6, the preset iteration termination condition is any one of the following: - The number of iterations has reached a predetermined threshold; - The change in the target position obtained from two consecutive iterations is less than the preset tolerance.

5. The time-gated single-photon detection imaging method according to claim 1 or 2, characterized in that, In step 1, when emitting pulsed laser, the orientation of the laser irradiation to the target area is changed according to the preset scanning path by controlling the fast-reflecting mirror in the optomechanical system module.

6. A time-gated single-photon detection imaging system, characterized in that, The system for implementing the time-gated single-photon detection imaging method according to any one of claims 1 to 5 comprises: Laser source module (1), used to generate pulsed laser; A laser beam splitter (2) is disposed on the output optical path of the laser source module (1) to split the pulsed laser into an illumination beam and a main wave reference beam. The optomechanical system module (3) is used to expand the illumination beam and emit it to the detection target, and to receive the echo photons scattered by the target; The main wave detector module (4) is used to receive the main wave reference beam and generate the main wave electrical signal; The single-photon detector module (5) is used to receive the echo photons and generate echo electrical signals; The photon coincidence counting module (6) is electrically connected to the main wave detector module (4) and the single photon detector module (5) and is used to generate photon time-of-flight data based on the main wave electrical signal and the echo electrical signal. The data processing module (7) is electrically connected to the single-photon detector module (5) and the photon coincidence counting module (6), and the data processing module (7) is configured to: execute the maximum a posteriori probability estimation algorithm to iteratively calculate the most probable position of the target based on the photon time-of-flight data; generate a control signal according to the calculation result to adjust the gating opening time of the single-photon detector module (5); and reconstruct the target image after the iteration is completed.

7. The time-gated single-photon detection imaging system according to claim 6, characterized in that: The optomechanical system module (3) includes a fast reflector, which is electrically connected to the data processing module (7) to change the laser emission orientation.

8. The time-gated single-photon detection imaging system according to claim 6 or 7, characterized in that: The single-photon detector module (5) includes an InGaAs single-photon detector and a host computer system that controls its operating mode, the operating mode including free operation mode and gated mode.

9. The time-gated single-photon detection imaging system according to claim 6 or 7, characterized in that: The photon coincidence counting module (6) includes a time-to-digital converter for recording the arrival time of echo photons.

10. The time-gated single-photon detection imaging system according to claim 6 or 7, characterized in that: The laser source module (1) is a pulsed laser that emits a pulse width of 1ns, a frequency of 1kHz, and a wavelength of 1064nm.

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