Infrared dual-band single-photon laser radar imaging system

Abstract

The invention discloses an infrared dual-band single-photon laser radar imaging system, and belongs to the field of laser radar detection. The system comprises an infrared dual-band light source, a beam splitter, a first delay line, a light splitting module, a transceiver module, a frequency up-conversion module, a photoelectric detector, a single-photon detector, a signal acquisition module and a signal processing module. The infrared dual-band light source generates near-infrared and intermediate-infrared pulse laser; near-infrared laser is used for near-infrared detection, frequency up-conversion pumping and initial signals after passing through a beam splitter, intermediate-infrared laser is used for intermediate-infrared detection, intermediate-infrared detection signal echoes are subjected to time domain gating and frequency up-conversion by near-infrared pumping signals and then injected into a single-photon detector together with near-infrared detection signal echoes through time division multiplexing, and the intermediate-infrared detection signal echoes and the near-infrared detection signal echoes are subjected to frequency up-conversion. And detection imaging is realized through signal acquisition and processing. According to the invention, the weak target detection imaging capability of the single-photon laser radar in environments of gas, strong background noise and the like can be improved, and the multi-band sensing capability of the radar on target characteristics is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser radar detection, and in particular relates to an infrared dual-band single-photon laser radar imaging system. Background Art

[0002] LiDAR can obtain information such as the distance, shape, and speed of a target by measuring the time and intensity of the echo of the emitted laser, achieving high-precision environmental perception and three-dimensional imaging. It has been widely used in the fields of autonomous driving, remote sensing and mapping. However, due to the low detection sensitivity of traditional LiDAR, it is difficult to achieve effective detection in scenarios such as long-distance, low signal-to-noise ratio, and weak target detection. Single-photon LiDAR effectively improves detection sensitivity and temporal resolution, and can achieve long-distance ranging and imaging through time-correlated single-photon counting technology.

[0003] However, the detection performance of existing single-band single-photon lidar is limited in some special environments such as smoke and gas. For example, when imaging some disaster sites, smoke, gas, dust, etc. will strongly absorb and scatter laser signals, affecting the imaging quality; when imaging at long distances in special environments, since CO2 has strong absorption peaks in the 2 μm and far-infrared bands, water molecules have strong absorption peaks in multiple bands, and many gases have absorption peaks in the near-infrared and mid-infrared bands, single-band single-photon lidar is difficult to achieve accurate ranging and imaging.

[0004] In addition, existing single-band single-photon laser radars can often only use information in a single spectral range for detection and imaging, which limits their comprehensive perception of target characteristics. Different materials have significant differences in reflection, scattering, absorption and other characteristics of light of different wavelengths. For example: in the military field, some camouflage materials can only have a good stealth effect on light of a specific wavelength; in industrial inspection, for some materials with complex surface characteristics, single-band laser radars are difficult to obtain comprehensive physical property information, affecting detection accuracy.

[0005] In terms of noise and interference, single-band single-photon lidar is more susceptible to noise and thus affects the imaging effect, especially when conducting long-distance detection, where weak echo signals are more easily drowned out by noise. For example, in the visible light band, there is extremely strong solar radiation, and the wavelength range of the earth's radiation to space is about 4 to 120 μm, with the strongest wavelength being about 9.7 μm. Therefore, single-band detection is very susceptible to background radiation noise. Summary of the invention

[0006] The purpose of the present invention is to provide an infrared dual-band single-photon lidar imaging system, which realizes the detection of mid-infrared and near-infrared detection signal echoes in a single-photon lidar imaging system through frequency up-conversion technology and time division multiplexing technology, realizes noise filtering through time domain gating of up-conversion pump signals, improves the scene adaptability of the detection system, reduces the influence of specific wavelength absorption and radiation noise on detection performance, and enhances the perception ability of target characteristics.

[0007] The purpose of the present invention is achieved through the following technical solutions: The invention discloses an infrared dual-band single-photon laser radar imaging system, comprising an infrared dual-band light source, a beam splitter, a first delay line, a light splitting module, a transceiver module, a frequency up-conversion module, a photoelectric detector, a single-photon detector, a signal acquisition module, and a signal processing module.

[0008] Among them, the infrared dual-band light source generates near-infrared and mid-infrared pulsed lasers; the near-infrared pulsed laser is divided into three by a beam splitter, the first beam is injected into the photodetector as the initial signal, the second beam is injected into the frequency up-conversion module as the frequency up-conversion pump signal, and the third beam is used as the near-infrared detection signal after passing through the first delay line; the mid-infrared pulsed laser is used as the mid-infrared detection signal; the mid-infrared detection signal and the near-infrared detection signal enter the transceiver module through the spectrometer module, and an echo signal is formed by scanning the target pixel by pixel, and the echo signal returns to the transceiver module and the spectrometer module; the mid-infrared detection signal echo is time-domain selected by the near-infrared pump signal and frequency-up-converted to form a first trigger signal, and the near-infrared detection signal echo is used as the second trigger signal, and is injected into the single-photon detector through time division multiplexing with the first trigger signal; the signal acquisition module is used to receive the initial signal and the trigger signal to form data information, and the data information is processed by the signal processing module to realize target detection and imaging.

[0009] The infrared dual-band light source is used to generate near-infrared band and mid-infrared band laser pulses.

[0010] The first delay line is used to delay the near-infrared laser pulse emitted by the infrared dual-band light source by ∆ T , thereby realizing dual-band time division multiplexing.

[0011] The spectroscopic module is used to transmit the near-infrared and mid-infrared laser pulses emitted by the dual-band light source to the transceiver module, and to split the echo signal received by the transceiver module, transmit the mid-infrared echo signal to the frequency up-conversion module, and transmit the near-infrared echo signal to the single-photon detector.

[0012] The transceiver module is used to irradiate the laser pulse onto the target and receive the generated echo signal, and the transceiver module is used to realize beam scanning and beam expansion.

[0013] The frequency up-conversion module is used to convert the mid-infrared echo signal to the near-infrared band, wherein the up-conversion pump signal is generated by the infrared dual-band light source, and the second delay line delays the up-conversion pump signal by ∆ τ When the up-conversion pump pulse signal and the mid-infrared detection signal echo coincide in the time domain, the mid-infrared detection signal echo and the up-conversion pump signal are frequency-converted to the near-infrared band via the nonlinear crystal, and then play a gated filtering role in the time domain, avoiding the background noise influence of the non-echo pulse duty time within the pulse period. The filter is used to filter out noise signals other than the required first trigger signal.

[0014] The single-photon detector operates in the near-infrared band and is used to detect the first trigger signal and the second trigger signal and output an electrical pulse trigger signal.

[0015] The signal acquisition module obtains a start signal from a photoelectric detector, obtains a trigger signal from a single-photon detector, and records time information.

[0016] The signal processing module is used to calculate the flight time and distance of near-infrared and mid-infrared photons, perform time demultiplexing and data fusion processing on the data information containing dual bands, and realize target imaging based on the imaging processing algorithm. Beneficial Effects

[0017] 1. The present invention discloses an infrared dual-band single-photon laser radar imaging system, which realizes near-infrared and mid-infrared dual-band detection in a single laser radar system based on a frequency up-conversion method, improves the radar's multi-band perception capability of target characteristics, and improves the weak target detection and imaging capability of the single-photon laser radar in special scenarios such as smoke, gas, and long-distance detection.

[0018] 2. The present invention discloses an infrared dual-band single-photon lidar imaging system, which detects and counts near-infrared detection echo signals and mid-infrared detection echo signals by a single-photon detector through a time multiplexing method, thereby reducing the cost required for infrared dual-band single-photon detection.

[0019] 3. The present invention discloses an infrared dual-band single-photon laser radar imaging system, which can filter out part of the noise by frequency up-converting the pump pulse time gating. In the nonlinear crystal, frequency up-conversion can only be achieved when the pump pulse and the detection pulse coincide in time domain. Therefore, the influence of the noise signal within the pulse period is greatly reduced, and the anti-noise interference capability of the single-photon laser radar is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the structure of a dual-band single-photon laser radar imaging system according to an embodiment of the present invention; Figure 2is a schematic diagram of the structure of a frequency up-conversion module according to an embodiment of the present invention; Figure 3 Schematic diagram of pulse timing of an embodiment of the present invention.

[0021] Among them: 1—infrared dual-band light source, 2—beam splitter, 3—photoelectric detector, 4—frequency up-conversion module, 5—first delay line, 6—spectroscopy module, 7—transceiver module, 8—single photon detector, 9—signal acquisition module, 10—signal processing module, 41—second delay line, 42—nonlinear crystal, 43—filter. DETAILED DESCRIPTION

[0022] In order to make the purpose, scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and drawings. In order to describe the present invention more clearly, many specific details of the embodiments are described below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] like Figure 1 As shown, the present embodiment discloses an infrared dual-band single-photon lidar imaging system, including an infrared dual-band light source 1, a beam splitter 2, a photodetector 3, a frequency up-conversion module 4, a first delay line 5, a spectroscopic module 6, a transceiver module 7, a single-photon detector 8, a signal acquisition module 9, and a signal processing module 10.

[0024] The infrared dual-band light source 1 includes but is not limited to one of an optical parametric oscillator, a plurality of pulse lasers in different bands, and the like.

[0025] The infrared dual-band light source 1 adopts an optical parametric oscillator. A pulsed laser with a central wavelength of 800 nm is injected into the optical parametric oscillator to generate a near-infrared pulsed laser with a central wavelength of 1056 nm and an average power of 2 W and an idler mid-infrared pulsed laser with a central wavelength of 3300 nm and an average power of 200 mW. The repetition frequency of the two pulsed lasers is the same, both of which are 1 MHz, the pulse period is 1 us, and the pulse width is about 1 ps.

[0026] The near-infrared laser pulse with a central wavelength of 1056 nm is divided into three. The first beam of near-infrared pulse laser with a power of 100 mW is injected into the photodetector 3 as the initial signal of the time-of-flight ranging method. The second beam of near-infrared pulse laser with a power of 1.5 W is injected into the frequency up-conversion module 4 as the pump signal for frequency up-conversion. The third beam of near-infrared pulse laser with a power of 400 mW is injected into the spectrometer module 6 as the near-infrared detection signal after passing through the first delay line 5.

[0027] The first delay line 5 is used to delay the near-infrared laser pulse emitted by the infrared dual-band light source 1. The time difference between the near-infrared detection signal and the mid-infrared detection signal after the delay is ∆ T = 500 ns, used to realize dual-band time division multiplexing, and then use a single single photon detector 8 to detect the dual-band detection signal echo, ∆ T It should be greater than the flight time of the photon to and from the target to avoid being unable to distinguish the initial signal pulse corresponding to the echo signal.

[0028] According to an embodiment of the present invention, the transceiver module 7 includes but is not limited to systems such as a galvanometer, a beam expander, and a telescope.

[0029] The transceiver module 7 is used to irradiate the laser pulse onto the target and receive the generated echo signal. The transceiver module 7 realizes beam scanning through the galvanometer and realizes laser beam expansion through the beam expander. The target in this embodiment is set as a polyethylene humanoid model target at a distance of 50 m. The scene is located outdoors, during the day, with a certain amount of solar radiation and earth radiation. In addition to air, there is an interfering medium such as smoke between the radar and the target.

[0030] The frequency up-conversion light source used by the frequency up-conversion module 4 includes but is not limited to the laser generated by the dual-band light source, or other specific wavelength lasers for the frequency up-conversion band. The nonlinear crystal 42 includes but is not limited to crystals, nonlinear waveguides, etc. The nonlinear frequency conversion process includes but is not limited to difference frequency, sum frequency and other methods.

[0031] like Figure 2 As shown, the frequency up-conversion module 4 is used to perform frequency conversion on the mid-infrared echo signal to the near-infrared band, wherein the up-conversion pump signal is a near-infrared laser pulse with a central wavelength of 1056 nm generated by the infrared dual-band light source 1, the nonlinear crystal 42 is a periodically poled lithium niobate (PPLN) crystal, and the second delay line 41 delays the up-conversion pump signal by ∆ τ ,∆ τ = 2*L / c, where L is the target distance, c is the speed of light, and the delay ∆ corresponding to the target echo at a distance of 50 m τ About 333 ns (e.g. Figure 3As shown), after fine adjustment of the second delay line 41, only when the up-conversion pump pulse in the PPLN crystal coincides with the mid-infrared detection signal echo pulse in the time domain, the mid-infrared detection signal echo of λ2=3300 nm and the up-conversion pump signal of λ1=1056 nm are frequency-differencing to the near-infrared band λ3 = 1 / (1 / λ1-1 / λ2) = 1553 nm. Since the frequency up-conversion pump signal is an ultrashort pulse signal with high peak power, a difference frequency signal can be generated only when the pulses coincide in time domain, thereby playing a role of gated selection filtering in the time domain, avoiding the background noise influence of the non-echo pulse duty time in the pulse period, and the filter 43 is used to filter out noise signals other than the difference frequency signal. The frequency up-conversion module 4 outputs a signal as the first trigger signal.

[0032] The single-photon detector 8 includes but is not limited to an avalanche photodiode (APD) detector, a superconducting nanowire single-photon detector (SNSPD), etc. The number of detectors includes but is not limited to a single one. In addition to the time-division multiplexing method described in the embodiment based on a single single-photon detector 8 for detection, multiple single-photon detectors can also be used to detect the mid-infrared detection signal echo and the near-infrared detection signal echo respectively, as well as other single-photon detector combinations.

[0033] The single-photon detector 8 adopts a near-infrared band APD detector, and the detection efficiency is more than 20% at 1550 nm and 1064 nm. The single-photon detector 8 is used to detect the first trigger signal and the second trigger signal, and output an electrical pulse trigger signal.

[0034] The signal acquisition module 9 obtains the start signal from the photodetector 3 and the trigger signal from the single photon detector 8, such as Figure 3 As shown, the time difference between the trigger signal and the start signal is ∆ τ The signal acquisition module 9 is a time-correlated single photon counting system, which collects and records the echo signal and noise signal of each frame of each pixel in the scanning process of the galvanometer to form data information.

[0035] The signal processing module 10 calculates the flight time and distance of near-infrared and mid-infrared photons, performs time demultiplexing on the data information containing the dual bands, obtains the mid-infrared detection signal echo information and the near-infrared detection signal echo information, respectively, processes the dual-band data separately and fuses them, realizes target imaging based on the imaging processing algorithm, compares and analyzes the mid-infrared detection imaging results and the near-infrared detection imaging results in the scenario of this embodiment, as well as the optimized imaging results after data fusion processing, to achieve performance improvement of single-band detection imaging.

[0036] This embodiment uses frequency up-conversion, time division multiplexing and time domain gating methods to enable the single-photon lidar system to simultaneously complete near-infrared and mid-infrared detection and imaging, and achieve a certain noise filtering effect, to compensate for the limited detection performance of single-band radar in special environments and limited target characteristic perception, and to enhance the detection and imaging capabilities of single-photon lidar in complex environments.

[0037] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An infrared dual-band single-photon laser radar imaging system, characterized in that: It comprises an infrared dual-band light source (1), a beam splitter (2), a photodetector (3), a frequency up-conversion module (4), a first delay line (5), a light splitting module (6), a transceiver module (7), a single photon detector (8), a signal acquisition module (9), and a signal processing module (10); The infrared dual-band light source (1) generates near-infrared and mid-infrared pulsed lasers; the near-infrared pulsed laser is split into three by a beam splitter (2); the first beam is injected into a photodetector (3) as an initial signal, the second beam is injected into a frequency up-conversion module (4) as a frequency up-conversion pump signal, and the third beam is injected into a near-infrared detection signal after passing through a first delay line (5); the mid-infrared pulsed laser is used as a mid-infrared detection signal; the mid-infrared detection signal and the near-infrared detection signal enter a transceiver module (7) through a light splitting module (6), and an echo signal is formed by scanning the target pixel by pixel, and the echo signal returns to the transceiver module (7) and the light splitting module (6); the mid-infrared detection signal echo is selected by the near-infrared pump signal in the time domain and frequency up-converted to form a first trigger signal, and the near-infrared detection signal echo is used as a second trigger signal and is injected into a single photon detector (8) through time division multiplexing with the first trigger signal; the signal acquisition module (9) is used to receive the initial signal and the trigger signal to form data information, and the data information is processed by the signal processing module (10) to realize target detection imaging.

2. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The infrared dual-band light source (1) is used to generate near-infrared band and mid-infrared band laser pulses.

3. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The first delay line (5) is used to delay the near-infrared laser pulse emitted by the infrared dual-band light source (1) by ∆ T , thereby realizing dual-band time division multiplexing.

4. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The light splitting module (6) is used to transmit the near-infrared and mid-infrared laser pulses emitted by the dual-band light source to the transceiver module (7), and to split the echo signal received by the transceiver module (7), transmit the mid-infrared echo signal to the frequency up-conversion module (4), and transmit the near-infrared echo signal to the single-photon detector (8).

5. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The transceiver module (7) is used to irradiate the laser pulse onto the target and receive the generated echo signal, and the transceiver module is used to realize beam scanning and beam expansion.

6. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The frequency up-conversion module (4) is used to perform frequency conversion on the mid-infrared echo signal to the near-infrared band, wherein the up-conversion pump signal is generated by the infrared dual-band light source (1), and the second delay line (41) delays the up-conversion pump signal by ∆ τ When the up-conversion pump pulse signal and the mid-infrared detection signal echo overlap in the time domain, the mid-infrared detection signal echo and the up-conversion pump signal are frequency-converted to the near-infrared band via the nonlinear crystal (42), thereby playing a gated filtering role in the time domain, thereby avoiding the influence of background noise of the non-echo pulse duty time within the pulse cycle, and the filter (43) can be used to filter out noise signals other than the required first trigger signal.

7. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The single-photon detector (8) operates in a near-infrared band and is used to detect the first trigger signal and the second trigger signal and output an electrical pulse trigger signal.

8. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The signal acquisition module (9) obtains a start signal from the photoelectric detector (3), obtains a trigger signal from the single-photon detector (8), and records time information.

9. The infrared dual-band single-photon laser radar imaging system according to claim 1, characterized in that: The signal processing module (10) is used to calculate the flight time of near-infrared and mid-infrared photons and corresponding distance information, perform time demultiplexing and data fusion processing on data information containing dual bands, and realize imaging of the target based on an imaging processing algorithm.

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