Range-gated imaging system based on pulse phase shift

Abstract

The application discloses a distance gate imaging system based on pulse phase shift, comprising a digital control unit for generating M laser pulse signals and shutter control signals, M laser driver modules, M groups of laser diodes, a fiber combiner for combining the laser output by each group of laser diodes, and an imaging unit receiving the shutter control signals and comprising an image intensifier and a driving module thereof for gating imaging of a target under the control of the shutter control signals; wherein M is greater than or equal to 2, the repetition frequencies of the laser pulse signals are the same but the phases have a difference; each laser driver module is connected with a laser pulse signal output end of the digital control unit; each group of laser diodes is connected with a laser driver module, and each group of laser diodes outputs laser under the driving of the corresponding laser pulse signal.

Description

Technical Field

[0001] This invention relates to the field of imaging technology, and more specifically to a range-gated imaging system based on pulse phase shift. Background Technology

[0002] Range-gated cameras, as key devices enabling long-distance, interference-resistant imaging, precisely control the time difference between laser emission and shutter opening, allowing reflected laser light from the target distance to enter the image, filtering out ambient light and background light interference, and improving image contrast and clarity. They are widely used in security monitoring, remote sensing, industrial inspection, and military reconnaissance. Existing range-gated cameras mostly use single-channel or multi-channel synchronously driven lasers, achieving fixed-distance imaging by adjusting the fixed delay time between the laser illuminator and the shutter.

[0003] Although existing technologies can basically achieve range-gated imaging, many problems and shortcomings still exist in practical applications. First, the output power of fiber-optic laser illuminators is limited. When driving multiple laser diodes to beam into a single fiber, if the combined laser power is too high, exceeding the fiber's capacity, it can damage the fiber. Second, the imaging range is limited. Traditional technologies can only image targets at a specific distance at a time. If information about targets at multiple distances needs to be acquired, the time delay must be repeatedly adjusted, resulting in low imaging efficiency and difficulty in meeting the needs of dynamic multi-target detection. Third, the trade-off between efficiency and cost is prominent in all-range detection. Mechanical scanning all-range detection is slow and cannot adapt to fast-moving targets. Fourth, the imaging quality is uneven at different distances. Near-range targets are prone to exposure saturation due to excessive reflected light, while far-range targets result in blurred images due to weak reflected light. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a range-gated imaging system based on pulse phase shift, which solves the problems of limited output power of fiber laser illuminators, single imaging distance, prominent contradiction between detection efficiency and cost at all distances, and uneven imaging quality at different distances in the existing technology.

[0005] Technical Solution: The distance-gated imaging system based on pulse phase shift described in this invention includes: a digital control unit for generating M laser pulse signals and a shutter control signal; M laser driver modules; M groups of laser diodes; an optical fiber combiner for combining the lasers output from each group of laser diodes; and an imaging unit that receives the shutter control signal and includes an image intensifier and its driver module for gating and imaging the target under the control of the shutter control signal; wherein M≥2, the repetition frequency of each laser pulse signal is the same but there is a phase difference; each laser driver module is connected to a laser pulse signal output terminal of the digital control unit; each group of laser diodes is connected to a laser driver module, and each group of laser diodes outputs lasers under the drive of the corresponding laser pulse signal.

[0006] Furthermore, the digital control unit is set to a high-brightness imaging mode, in which the phase of each laser pulse signal differs by 360° / M, so that each group of laser diodes works in turn; the shutter control signal is a periodic pulse signal, and its repetition frequency is M times the repetition frequency of a single laser pulse signal.

[0007] Furthermore, the digital control unit is set to a multi-target imaging mode, in which the phase difference of each laser pulse signal corresponds to different imaging distances; the shutter control signal is a periodic pulse signal with the same repetition frequency as the laser pulse signal; by adjusting the phase between the shutter control signal and each laser pulse signal, simultaneous gating imaging of targets at multiple distances can be achieved.

[0008] Furthermore, the digital control unit is set to full-range imaging mode, wherein the output time interval of each laser pulse signal is controlled by a pseudo-random number sequence; the shutter control signal is a periodic pulse signal with a fixed repetition frequency; by randomizing the laser emission time, the echo signal received by the imaging unit when the shutter is open corresponds to the target within the full range.

[0009] Furthermore, the digital control unit is set to a brightness equalization mode based on the number of light sources. The digital control unit has a built-in distance-phase-laser diode number mapping table. It determines the laser pulse signal of the corresponding phase according to the target distance and controls the number of enabled laser diodes in the corresponding group to adapt to the light intensity requirements of different distances.

[0010] Furthermore, the digital control unit is set to a brightness equalization mode based on duty cycle adjustment. The digital control unit has a built-in distance-phase-duty cycle mapping table. It adjusts the duty cycle of the output enable signal of the corresponding laser pulse signal according to the target distance to control the light output energy per unit time and achieve brightness equalization of imaging at different distances.

[0011] Furthermore, the digital control unit is implemented using field-programmable gate arrays (FPGAs), ASICs, or MCUs.

[0012] The range-gated imaging method based on pulse phase shift described in this invention includes the following steps:

[0013] (1) Generate M laser pulse signals with phase differences and corresponding shutter control signals, where M≥2;

[0014] (2) Each laser pulse signal drives the corresponding laser diode group to output laser;

[0015] (3) Combine the laser beams from each group and then illuminate the target;

[0016] (4) Control the shutter opening timing of the imaging unit according to the shutter control signal, receive the laser echo reflected by the target and perform imaging.

[0017] Furthermore, it also includes: achieving the alternating operation of laser diodes by sequentially differentiating the phases of each group of laser pulse signals by 360° / M, thereby reducing the peak optical power borne by the optical fiber; achieving simultaneous imaging of targets at multiple distances by setting the phase difference of each laser pulse signal to correspond to different imaging distances and adjusting the phase of the shutter control signal and each pulse signal; achieving random gating imaging across the entire distance range by controlling the emission time of each laser pulse signal through a pseudo-random sequence; and dynamically adjusting the number of working laser diodes or the output duty cycle of the laser pulse signal according to the target distance to achieve uniform imaging brightness at different distances.

[0018] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: For fiber-optic laser illuminators, in high-brightness imaging mode, this invention enables the fiber to withstand higher average optical power without damage, effectively improving imaging brightness. In multi-target imaging mode, this invention can simultaneously screen targets at multiple distances without needing to sequentially screen targets at multiple distances by gradually adjusting the phase. In full-range imaging mode, compared with the traditional method of continuously opening the shutter signal to achieve full-range imaging, the shutter signal in this invention is a pulse signal, thus having stronger ambient light interference suppression capability. In brightness equalization mode based on light source number control, this invention does not require additional light intensity attenuation or enhancement devices. Through dynamic gradient configuration of the number of working laser diodes, it can achieve precise adaptation of imaging brightness at different distances, which helps to improve the image quality balance across the entire range, reduce overexposure and underexposure problems, and at the same time, when detecting close-range targets, it reduces the number of laser diodes used, which helps to extend the life of laser diodes and reduce the energy consumption of the range-selective imaging system. In brightness equalization mode based on duty cycle adjustment, this invention can improve the image quality balance across the entire range. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention;

[0020] Figure 2 This invention relates to the application of the pulse phase shift-based range gating imaging technology in multi-target imaging mode. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] like Figure 1As shown, this embodiment of the invention provides a distance-gated imaging system based on pulse phase shift, comprising: using a digital circuit as the core control unit to synchronously output M (M≥2) laser pulse signals with a certain phase difference (laser pulse signal 1 to laser pulse signal M), each laser pulse signal being connected to a laser driver module (laser driver module 1 to laser driver module M). Laser driver module i drives the i-th group of laser diodes, the i-th group of laser diodes containing Ni laser diodes, i=1,2,…,M, where each Ni does not necessarily have to be the same. Each group of laser diodes outputs laser light under the control and drive of the corresponding laser pulse signal, and all laser light is converged to a beam expander lens through an optical fiber combiner. The shutter control signal output by the digital circuit is sent to the imaging unit. The shutter control signal is then sent to the image intensifier driver module in the imaging unit, which provides imaging control signals to the image intensifier.

[0023] Based on the aforementioned pulse phase shift range gating technique, this invention proposes several range gating imaging modes.

[0024] High-brightness imaging mode: To address the need for increased output power, the modular digital circuitry uses a preset phase allocation algorithm to assign laser pulse signals with the same repetition frequency to each group of laser diodes, but with phase differences of 360° / M, ensuring that each group of laser diodes operates in turn. The shutter control signal is a periodic pulse signal with a repetition frequency M times that of the laser pulse signal. In this mode, the peak optical power that the optical fiber can withstand is reduced to 1 / M of that under conditions where all laser diodes are emitting light simultaneously. This allows the optical fiber to withstand higher average optical power without damage, effectively improving image brightness.

[0025] Multi-target imaging mode: In this modular mode, the digital circuitry controls the phase of the laser pulse signal to simultaneously perform gating imaging at multiple distances. Specifically, laser pulse signals 1 to M have the same repetition frequency, but their phases are not necessarily the same; the phase difference corresponds to the difference in imaging distance. The shutter control signal is a periodic pulse signal with the same repetition frequency as laser pulse signal 1. During imaging, the phase between the shutter control signal and laser pulse signal i is adjusted to control the imaging distance corresponding to laser pulse signal i, i=1,2,…,M, thereby simultaneously gating imaging targets at M distances without needing to sequentially gating targets at M distances by gradually adjusting the phase. It should be noted that by controlling the phase or output enable of each laser pulse signal, this module can also simultaneously gating imaging targets at only K distances, K… <M。

[0026] Full-range imaging mode: In this modular mode, the output time interval of the laser pulse signal i is controlled by a pseudo-random number sequence i, where i = 1, 2, ..., M. The shutter signal is a periodic pulse signal with a fixed repetition frequency. When multiple laser diodes emit lasers together, if the laser power exceeds the fiber's capacity, the output of some laser pulse signals is turned off, thereby controlling the power of the emitted laser. Due to the randomness of the laser emission time, the target object distance corresponding to the laser echo signal received by the imaging unit when the shutter signal is open is also random. Therefore, the entire range of laser illumination can potentially be imaged in the imaging unit, thus achieving full-range imaging. Compared with the traditional method of continuously opening the shutter signal to achieve full-range imaging, the shutter signal in this method is a pulse signal, thus having stronger ambient light interference suppression capability. In addition, the full-range imaging module can also be implemented in the following way: the laser pulse signals allocated to each group of laser diodes have the same repetition frequency, but differ in phase by 360° / M; the shutter signal is a random pulse signal, and its output time interval is controlled by a pseudo-random number sequence.

[0027] Brightness equalization mode based on light source quantity control: In this modular design, the digital circuit adapts the number of working laser diodes in each group to the light intensity requirements at different distances, achieving balanced brightness for imaging across all distances. Specifically, the digital circuit has a built-in "distance-phase-number of laser diodes" mapping table. It determines the phase of the corresponding laser pulse signal based on the target distance, and then presets the number of enabled laser diodes in each group. This ensures that overexposure due to excessive light intensity at close range is avoided, and that insufficient light intensity at long range does not cause blurring. During imaging, the digital circuit outputs each laser pulse signal and controls the enable of the laser diodes in each laser driver module: for close-range targets, only a small number of laser diodes are enabled to control the output light intensity and avoid exposure saturation; for long-range targets, more laser diodes are enabled to increase the laser output intensity and compensate for losses during laser transmission. This mode does not require additional light intensity attenuation or enhancement devices. By dynamically configuring the number of working laser diodes, it can achieve precise adaptation of imaging brightness at different distances, which helps to improve the uniformity of imaging quality across the entire range and reduce overexposure and underexposure problems. At the same time, when detecting close-range targets, it reduces the number of laser diodes used, which helps to extend the lifespan of the laser diodes and reduce the energy consumption of the range-gated imaging system.

[0028] Brightness equalization mode based on duty cycle adjustment: In this modular mode, the digital circuit adjusts the phase of the laser pulse signal while simultaneously adjusting the output ratio of the laser pulse signal to achieve brightness equalization across the entire range. The output ratio of the laser pulse signal is achieved by controlling the duty cycle of the laser pulse signal's output enable signal. The digital circuit has a built-in "distance-phase-duty cycle" mapping table. When adjusting the pulse phase to match the target distance, the corresponding duty cycle parameter in the mapping table is called simultaneously: for close-range targets, the duty cycle of the laser pulse signal's output enable signal is reduced to decrease the emitted light energy per unit time, avoiding image exposure saturation; for distant targets, the duty cycle of the laser pulse signal's output enable signal is increased to increase the emitted light energy per unit time, enhancing the intensity of the reflected light signal, thereby improving the image quality equalization across the entire range.

[0029] Specific implementation examples: such as Figure 2 As shown, this embodiment demonstrates the application of the pulse phase-shift-based range gating imaging technology proposed in this invention in multi-target imaging mode. The digital circuitry is implemented using an FPGA of model XCKU060-2FFVA1156I. A laser diode LD is also included. 1_1 LD 1_2 LD 2_1 LD 2_2 A 50W peak power, 850nm pulsed laser diode is used. The image intensifier employs a second-generation ultra-low-light image intensifier. Laser driver module 1 drives the LD. 1_1 LD 1_2 Laser driver module 2 drives LD 2_1 LD 2_2 In actual testing, laser pulse signal 1, laser pulse signal 2, and shutter control signal were all 100kHz pulse signals with a pulse width of 5ns. The phase difference between laser pulse signal 1 and shutter control signal was 3.6°, and the phase difference between laser pulse signal 2 and shutter control signal was 7.2°. During imaging, the target objects at 15 meters and 30 meters could be observed simultaneously on the fluorescent screen of the image intensifier.

Claims

1. A range-gated imaging system based on pulse phase shift, characterized in that, include: The digital control unit generates M laser pulse signals and shutter control signals, M laser driver modules, M groups of laser diodes, and an optical fiber combiner to combine the lasers output from each group of laser diodes. The imaging unit receives the shutter control signals and includes an image intensifier and its driver module for gating and imaging the target under the control of the shutter control signals. M ≥ 2, and the laser pulse signals have the same repetition frequency but different phases. Each laser driver module is connected to one laser pulse signal output terminal of the digital control unit. Each group of laser diodes is connected to one laser driver module, and each group of laser diodes outputs lasers under the drive of its corresponding laser pulse signal. The digital control unit is set to a high-brightness imaging mode, where the phases of each laser pulse signal differ sequentially by 360° / M, ensuring that each group... The laser diodes operate alternately; the shutter control signal is a periodic pulse signal with a repetition frequency M times that of a single laser pulse signal; the digital control unit is set to multi-target imaging mode, where the phase difference of each laser pulse signal corresponds to different imaging distances; the shutter control signal is a periodic pulse signal with the same repetition frequency as the laser pulse signal; by adjusting the phase between the shutter control signal and each laser pulse signal, simultaneous gating imaging of targets at multiple distances is achieved; the digital control unit is set to full-range imaging mode, where the output time interval of each laser pulse signal is controlled by a pseudo-random number sequence; the shutter control signal is a periodic pulse signal with a fixed repetition frequency; by randomizing the laser emission time, the echo signal received by the imaging unit when the shutter is open corresponds to targets within the entire range.

2. The range-gated imaging system based on pulse phase shift according to claim 1, characterized in that, The digital control unit is set to a brightness equalization mode based on the number of light sources. The digital control unit has a built-in distance-phase-laser diode number mapping table. It determines the laser pulse signal of the corresponding phase according to the target distance and controls the number of enabled laser diodes in the corresponding group to adapt to the light intensity requirements of different distances.

3. The range-gated imaging system based on pulse phase shift according to claim 1, characterized in that, The digital control unit is set to a brightness equalization mode based on duty cycle adjustment. The digital control unit has a built-in distance-phase-duty cycle mapping table. It adjusts the duty cycle of the output enable signal of the corresponding laser pulse signal according to the target distance to control the light output energy per unit time and achieve equalization of imaging brightness at different distances.

4. The range-gated imaging system based on pulse phase shift according to claim 1, characterized in that, Digital control units are implemented using field-programmable gate arrays (FPGAs), ASICs, or MCUs.

5. A range-gated imaging method based on pulse phase shift, characterized in that, The system described in any one of claims 1-4 is implemented by comprising the following steps: (1) Generate M laser pulse signals with phase differences and corresponding shutter control signals, where M≥2; (2) Each laser pulse signal drives the corresponding laser diode group to output laser; (3) Combine the laser beams from each group and then illuminate the target; (4) Control the shutter opening timing of the imaging unit according to the shutter control signal, receive the laser echo reflected by the target and perform imaging.

6. The range-gated imaging method based on pulse phase shift according to claim 5, characterized in that, Also includes: By making the phase of each group of laser pulse signals differ by 360° / m, the laser diodes can work in turn, reducing the peak optical power that the optical fiber can withstand. By setting the phase difference of each laser pulse signal to correspond to different imaging distances and adjusting the phase of the shutter control signal and each pulse signal, simultaneous imaging of targets at multiple distances can be achieved; by controlling the emission time of each laser pulse signal through a pseudo-random sequence, random gating imaging across the entire range can be achieved; and by dynamically adjusting the number of working laser diodes or the output duty cycle of the laser pulse signal according to the target distance, balanced imaging brightness at different distances can be achieved.

Images