An infrared dual-band single-photon lidar imaging system

Abstract

An infrared dual-band single-photon lidar imaging system belongs to the field of lidar detection. The present invention includes an infrared dual-band light source, a beam splitter, a first delay line, a beam splitting module, a transceiver module, a frequency up-conversion module, a photodetector, a single-photon detector, a signal acquisition module, and a signal processing module. The infrared dual-band light source generates near-infrared and mid-infrared pulsed lasers; after the near-infrared laser passes through the beam splitter, it is respectively used for near-infrared detection, frequency up-conversion pumping, and initial signals, and the mid-infrared laser is used for mid-infrared detection. The echo of the mid-infrared detection signal is time-domain gated by the near-infrared pumping signal and frequency up-converted, and then, together with the echo of the near-infrared detection signal, is injected into the single-photon detector through time-division multiplexing, and detection imaging is achieved through signal acquisition and processing. The present invention can improve the weak target detection imaging ability of the single-photon lidar in environments such as gases and strong background noise, and enhance the multi-band sensing ability of the lidar for target characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of lidar detection, and particularly relates to an infrared dual-band single-photon lidar 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 information of the echo of the emitted laser, and achieve high-precision environmental perception and three-dimensional imaging. Currently, it has been widely used in fields such as autonomous driving and remote sensing 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 the detection sensitivity and time 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, due to the presence of smoke, gas, dust, etc., which will strongly absorb and scatter laser signals, affecting the imaging quality; when performing long-distance imaging in special environments, due to the strong absorption peaks of CO2 in the 2 μm and far-infrared bands, water molecules have strong absorption peaks in multiple bands, and various gases have absorption peaks in the near-infrared and mid-infrared bands, it is difficult for single-band single-photon lidar to achieve accurate ranging and imaging.

[0004] In addition, existing single-band single-photon lidar often can only detect and image using information in a single spectral range, which limits its comprehensive perception of target characteristics. Different substances have significant differences in the reflection, scattering, absorption, etc. of light with different wavelengths. For example: in the military field, some camouflage materials only have good stealth effects on light in specific bands; in industrial inspection, for some materials with complex surface characteristics, single-band lidar is difficult to obtain comprehensive physical characteristic information, affecting the detection accuracy.

[0005] In terms of noise and interference, single-band single-photon lidar is more susceptible to noise, which affects the imaging effect. Especially when performing long-distance detection, weak echo signals are more likely to be submerged by noise. For example, in the visible light band, there is extremely strong solar radiation, and the earth radiates into space in a wavelength range of about 4 - 120 μm, with the strongest wavelength of about 9.7 μm. Therefore, single-band detection is extremely susceptible to background radiation noise. Summary of the Invention

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

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] An infrared dual-band single-photon lidar imaging system disclosed by the present invention includes an infrared dual-band light source, a beam splitter, a first delay line, a beam splitting module, a transceiver module, a frequency up-conversion module, a photodetector, a single-photon detector, a signal acquisition module, and a signal processing module.

[0009] Among them, the infrared dual-band light source generates near-infrared and mid-infrared pulsed lasers; the near-infrared pulsed laser is split into three beams by the 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 beam splitting module, and echo signals are formed by scanning each pixel of the target. The echo signals return to the transceiver module and the beam splitting module; the echo of the mid-infrared detection signal is time-domain gated by the near-infrared pump signal and frequency up-converted to form a first trigger signal, and the echo of the near-infrared detection signal is used as the second trigger signal. The first trigger signal and the second trigger signal are injected into the single-photon detector through time-division multiplexing; 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 the detection and imaging of the target.

[0010] The infrared dual-band light source is used to generate laser pulses in the near-infrared band and the mid-infrared band.

[0011] 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.

[0012] The beam splitting 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 split the echo signals 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.

[0013] The transceiver module is used to irradiate the laser pulse on the target and receive the generated echo signal, and the transceiver module is used to realize beam scanning and beam expansion.

[0014] The described frequency up-conversion module is used to convert the mid-infrared echo signal to the near-infrared band. 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 coincides with the mid-infrared detection signal echo 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 a nonlinear crystal, thereby playing a gating and filtering role in the time domain and avoiding the influence of background noise in the non-echo pulse duty cycle within the pulse period. The filter is used to filter out noise signals other than the required first trigger signal.

[0015] The described 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.

[0016] The described signal acquisition module obtains the start signal from the photodetector, obtains the trigger signal from the single-photon detector, and records the time information.

[0017] The described signal processing module is used to calculate information such as the flight time and distance of near-infrared and mid-infrared photons. It performs time demultiplexing and data fusion processing on the data information containing dual bands, and realizes target imaging based on the imaging processing algorithm. Advantageous Effects

[0018] 1. An infrared dual-band single-photon lidar imaging system disclosed by the present invention realizes near-infrared and mid-infrared dual-band detection within a single lidar system based on the frequency up-conversion method, improving the multi-band perception ability of the lidar for target characteristics and the weak target detection and imaging ability of the single-photon lidar in special scenarios such as the presence of smoke, gas, and long-distance detection.

[0019] 2. An infrared dual-band single-photon lidar imaging system disclosed by the present invention uses the time multiplexing method to detect and count the near-infrared detection echo signal and the mid-infrared detection echo signal with a single-photon detector, reducing the cost required for infrared dual-band single-photon detection.

[0020] 3. An infrared dual-band single-photon lidar imaging system disclosed by the present invention can filter out some noise through the time gating of the frequency up-conversion pump pulse. In the nonlinear crystal, frequency up-conversion can only be achieved when the pump pulse coincides with the detection pulse in the time domain. Therefore, the influence of noise signals within the pulse period is greatly reduced, and the anti-noise interference ability of the single-photon lidar is improved. Brief Description of the Drawings

[0021] Figure 1 is a schematic structural diagram of the dual-band single-photon lidar imaging system according to the embodiment of the present invention;

[0022] Figure 2 It is a schematic structural diagram of the frequency up-conversion module according to an embodiment of the present invention;

[0023] Figure 3 It is a schematic diagram of the pulse timing according to an embodiment of the present invention.

[0024] Wherein: 1 - infrared dual-band light source, 2 - beam splitter, 3 - photodetector, 4 - frequency up-conversion module, 5 - first delay line, 6 - beam splitting 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. Specific embodiments

[0025] In order to make the purpose, solution and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. For a clearer description of the present invention, 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.

[0026] As Figure 1 shown, an infrared dual-band single-photon lidar imaging system disclosed in this embodiment includes 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 beam splitting module 6, a transceiver module 7, a single-photon detector 8, a signal acquisition module 9, and a signal processing module 10.

[0027] The infrared dual-band light source 1 includes, but is not limited to, one of an optical parametric oscillator, multiple pulsed lasers of different bands, etc.

[0028] The infrared dual-band light source 1 uses 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 frequencies of the two pulsed lasers are the same, both 1 MHz, the pulse periods are both 1 us, and the pulse widths are about 1 ps.

[0029] The near-infrared laser pulse with a central wavelength of 1056 nm is split into three parts. The first near-infrared pulsed laser with a power of 100 mW is injected into the photodetector 3 as the initial signal for time-of-flight ranging. The second near-infrared pulsed 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 near-infrared pulsed laser with a power of 400 mW is used as the near-infrared detection signal and injected into the beam splitting module 6 after passing through the first delay line 5.

[0030] The first delay line 5 is used to delay the near-infrared laser pulses emitted by the infrared dual-band light source 1. The time difference between the delayed near-infrared detection signal and the mid-infrared detection signal is ∆ T = 500 ns, which is used to achieve dual-band time-division multiplexing. Then, a single single-photon detector 8 is used to detect the echo of the dual-band detection signal. ∆ T should be greater than the flight time of photons traveling to and from the target to avoid being unable to distinguish the initial signal pulse corresponding to the echo signal.

[0031] According to the embodiments of the present invention, the transceiver module 7 includes, but is not limited to, systems such as galvanometric mirrors, beam expanders, and telescopes.

[0032] The transceiver module 7 is used to irradiate laser pulses onto the target and receive the generated echo signal. The transceiver module 7 realizes beam scanning through a galvanometric mirror and laser beam expansion through a beam expander. In this embodiment, the target is set as a polyethylene material humanoid model target at a distance of 50 m. The scene is located outdoors during the day, with certain solar radiation and terrestrial radiation, and there are interference media such as smoke between the radar and the target in addition to air.

[0033] The frequency up-conversion light source adopted 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 frequency up-conversion bands. 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, methods such as difference frequency and sum frequency.

[0034] As Figure 2 shown, the frequency up-conversion module 4 is used to convert the mid-infrared echo signal to the near-infrared band. The up-conversion pump signal is the near-infrared laser pulse with a central wavelength of 1056 nm generated by the infrared dual-band light source 1. The nonlinear crystal 42 uses a periodically poled lithium niobate (PPLN) crystal. The second delay line 41 delays the up-conversion pump signal by ∆ τ , ∆ τ = 2*L / c, where L is the target distance and c is the speed of light. The delay ∆ τ corresponding to the echo of a target at a distance of 50 m is approximately 333 ns (as Figure 3(as shown), after finely adjusting the second delay line 41, only when the up-conversion pump pulse and the mid-infrared detection signal echo pulse coincide in the time domain on the PPLN crystal, the mid-infrared detection signal echo with λ2 = 3300 nm and the up-conversion pump signal with λ1 = 1056 nm are difference-frequency converted 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 a high peak power, a difference-frequency signal can be generated only when the pulses coincide in the time domain, thereby playing a gating and filtering role in the time domain and avoiding the influence of background noise in the duty cycle of non-echo pulses within the pulse period. The filter 43 is used to filter out noise signals other than the difference-frequency signal, and the output signal of the frequency up-conversion module 4 serves as the first trigger signal.

[0035] 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 detecting based on a single single-photon detector 8 using the time-division multiplexing method as described in the embodiment, 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 combinations of single-photon detectors.

[0036] The single-photon detector 8 uses a near-infrared band APD detector, and the detection efficiency reaches more than 20% at both 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.

[0037] The signal acquisition module 9 obtains the start signal from the photodetector 3 and the trigger signal from the single-photon detector 8. As Figure 3 shown, the time difference between the trigger signal and the start signal is ∆ τ , and 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 during the galvanometer scanning process to form data information.

[0038] The signal processing module 10 calculates information such as the flight time and distance of near-infrared and mid-infrared photons, performs time demultiplexing on the data information containing dual bands, respectively obtains the mid-infrared detection signal echo information and the near-infrared detection signal echo information, separately processes and fuses the dual-band data, and realizes target imaging based on the imaging processing algorithm. By comparing and analyzing 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, the performance improvement of single-band detection imaging is achieved.

[0039] In this embodiment, by using the methods of frequency up-conversion, time-division multiplexing, and time-domain gating, the single-photon lidar system can simultaneously complete near-infrared and mid-infrared detection imaging, and achieve a certain noise filtering effect, making up for the limited detection performance of single-band radars in special environments and the limited perception of target characteristics, and improving the detection imaging ability of single-photon lidar in complex environments.

[0040] The above specific description further details the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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.

Images