Dual-band synchronous single-photon lidar system driven by single light source and ranging method

Abstract

The application discloses a single-light-source-driven dual-waveband synchronous single-photon laser radar system and a ranging method, and belongs to the fields of laser radar, nonlinear frequency conversion and single-photon detection. A short-wavelength main pulse is split to form short-wavelength detection light and short-wavelength pumping light; the short-wavelength pumping light drives a parametric down-conversion module to synchronously generate mid-infrared detection light and accompanying pumping light, and the accompanying pumping light is used for up-conversion at a receiving end after being subjected to adjustable delay. The short-wavelength echo is directly subjected to single-photon detection, and the mid-infrared echo is subjected to single-photon detection after being subjected to sum-frequency up-conversion into short-wavelength up-converted echo. Two channels take a unified synchronous signal as a common time reference, and dual-waveband distance information is obtained through distance gate control, fixed delay calibration and time-of-flight calculation and is subjected to information fusion. The application reduces the number of independent light sources and clocks, and is suitable for dual-waveband detection in a complex background.

Description

Technical Field

[0001] This invention belongs to the fields of lidar detection, nonlinear frequency conversion and single-photon detection technology, and particularly relates to a single-source-driven dual-band synchronous single-photon lidar system and ranging method. Background Technology

[0002] Single-photon lidar utilizes single-photon detectors and time-correlated single-photon counting technology to obtain the target echo flight time, enabling highly sensitive ranging and detection under long-range, low-light, and weak echo conditions. Short-wavelength pulsed laser sources can be near-infrared or visible light pulsed laser sources, featuring mature devices, stable output, and high engineering availability.

[0003] The mid-infrared band has advantages in atmospheric window detection, smoke and dust penetration, material identification, and molecular feature absorption sensing. However, directly obtaining high-performance mid-infrared pulsed lasers and directly performing mid-infrared single-photon detection usually increases system complexity. Therefore, the above-mentioned technical problems are urgent to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a single-source-driven dual-band synchronous single-photon lidar system and ranging method. A single short-wavelength master pulse laser source serves as the system's sole external active laser source and unified synchronization signal source. After beam splitting, one path forms a short-wavelength probe beam, while the other path acts as a short-wavelength pump entering the parametric down-conversion module. The short-wavelength master pulse generates a mid-infrared probe beam through parametric down-conversion, and the mid-infrared echo is converted to the short-wavelength band for detection via up-conversion at the receiving end. This approach combines mid-infrared detection capability with the mature advantages of short-wavelength single-photon detectors.

[0005] The first aspect discloses a single-source-driven dual-band synchronous single-photon lidar system, the system comprising:

[0006] The system includes a short-wavelength pulsed laser source, a beam splitting module, a short-wavelength transmitting branch, a parametric down-conversion module, a beam combining / coaxial transmitting module, a receiving optical module, a beam splitting / wavelength splitting unit, a short-wavelength single-photon detection channel, a mid-infrared echo up-conversion module, a first single-photon detector, a second single-photon detector, and a TCSPC / time stamping and joint processing module.

[0007] The short-wavelength pulsed laser source is used to output a short-wavelength main pulse and provides a unified synchronization signal to the TCSPC / time stamping and joint processing module through an electrical synchronization output terminal or an optical sampling detection terminal; the beam splitting module is used to split the short-wavelength main pulse into a short-wavelength probe light and a short-wavelength pump light; the short-wavelength emission branch is used to transmit the short-wavelength probe light to the beam combining / coaxial emission module; the parametric down-conversion module is used to generate a mid-infrared probe light and an accompanying pump light, and the accompanying pump light is used as an up-conversion pump light after an adjustable delay; the short-wavelength probe light and the mid-infrared probe light are combined or nearly coaxially emitted, and the target echo is separated into a short-wavelength echo and a mid-infrared echo; the short-wavelength echo is directly used for single-photon detection, and the mid-infrared echo and the up-conversion pump light are combined and converted into a short-wavelength up-conversion echo within a preset time window for single-photon detection; the TCSPC / time stamping and joint processing module performs time stamping, fixed delay calibration, distance calculation, and dual-band information fusion.

[0008] The second aspect discloses a single-source-driven dual-band synchronous single-photon lidar ranging method, applicable to a single-source-driven dual-band synchronous single-photon lidar system of the first aspect or any embodiment of the first aspect, the method comprising:

[0009] A short-wavelength pulsed laser source outputs a short-wavelength main pulse and obtains a unified synchronization signal corresponding to the short-wavelength main pulse;

[0010] The short-wavelength main pulse is split into a short-wavelength probe beam and a short-wavelength pump beam;

[0011] The short-wavelength pump light drives the parametric down-conversion module to generate mid-infrared detection light, and simultaneously generates accompanying pump light;

[0012] The short-wavelength detection light and the mid-infrared detection light are combined or nearly coaxially emitted to the target area;

[0013] Receives target echoes and separates them into short-wavelength echoes and mid-infrared echoes;

[0014] The short-wavelength echo is subjected to single-photon detection and a short-wavelength channel trigger signal is output.

[0015] Set or scan the adjustable delay of the accompanying pump light so that it coincides with the mid-infrared echo as the upconversion pump light within a preset time window, perform upconversion detection, and output the mid-infrared echo upconversion detection channel trigger signal.

[0016] Time stamping is performed based on the unified synchronization signal and the two-channel trigger signal. The fixed internal delay of the two channels obtained by known distance calibration is compensated respectively. The distance between the two bands is calculated according to the flight time, and the dual-band distance or photon count information of the same target is correlated and fused.

[0017] As can be seen from the above technical solutions, the present invention has the following beneficial effects:

[0018] This invention uses a single short-wavelength master pulse laser source as the sole main light source and unified synchronization signal source, reducing the complexity of multi-source synchronization and multi-clock calibration. Secondly, this invention generates mid-infrared detection light through parametric down-conversion and converts the mid-infrared echo to the short-wavelength band for detection through up-conversion at the receiving end, which is beneficial for using mature short-wavelength single-photon detectors to achieve mid-infrared echo detection. Furthermore, the mid-infrared detection light and accompanying pump light of this invention are derived from the same master pulse and have a fixed or calibrable delay relationship, which is beneficial for dual-band time alignment and information fusion. This invention can simultaneously acquire short-wavelength and mid-infrared dual-band echo information, which is beneficial for target detection and ranging in complex backgrounds, smoke and dust, weak targets, and material difference scenarios. Attached Figure Description

[0019] Figure 1 This invention provides a schematic diagram of a single-source-driven dual-band synchronous single-photon lidar system architecture.

[0020] Figure 2 The present invention provides an overall flowchart of a single-source-driven dual-band synchronous single-photon lidar ranging method.

[0021] The system includes: 1. Short-wavelength pulsed laser source; 2. Beam splitting module; 3. Short-wavelength transmission branch; 4. Parametric down-conversion module; 5. Beam combining / coaxial transmission module; 6. Target area; 7. Receiving optical module; 8. Beam splitting / wavelength splitting unit; 9. Short-wavelength single-photon detection channel; 10. Mid-infrared echo up-conversion module; 11. First single-photon detector; 12. Second single-photon detector; and 13. TCSPC / time stamping and joint processing module. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] In one embodiment, the present invention discloses a single-source-driven dual-band synchronous single-photon lidar system, such as... Figure 1 As shown, it specifically includes:

[0024] 1. Short-wavelength pulsed laser source; 2. Beam splitting module; 3. Short-wavelength emission branch; 4. Parametric down-conversion module; 5. Beam combining / coaxial emission module; 6. Receiving optical module; 7. Beam splitting / wavelength splitting unit; 8. Short-wavelength single-photon detection channel; 9. Mid-infrared echo up-conversion module; 10. First single-photon detector; 11. Second single-photon detector; 12. TCSPC (Time-Correlated Single Photon Counting) / time stamping and joint processing module; 13.

[0025] Specifically, the short-wavelength pulsed laser source 1 outputs a short-wavelength main pulse, and provides a unified synchronization signal to the TCSPC / time stamping and joint processing module 13 through the laser's electrical synchronization output terminal or through an electrical trigger signal generated by sampling the main pulse by an optical sampling detector. The short-wavelength pulsed laser source 1 can be a near-infrared pulsed laser source or a visible light pulsed laser source. Optionally, the center wavelength of the short-wavelength pulsed laser source is located in the range of 400 nm to 1.6 μm, and the mid-infrared detection light is located in the 2 μm to 12 μm band.

[0026] Beam splitting module 2 divides the main pulse into at least two paths. One path serves as a short-wavelength probe light entering the short-wavelength emission branch 3, while the other path serves as a short-wavelength pump light entering the parametric down-conversion module 4. Parametric down-conversion module 4 generates mid-infrared probe light and simultaneously generates accompanying short-wavelength pump light (hereinafter referred to as accompanying pump light); the accompanying pump light is used as up-conversion pump light at the receiving end.

[0027] Parametric down-conversion module 4, driven by the same short-wavelength master pulse in the nonlinear medium, generates mid-infrared probe light and simultaneously generates accompanying pump light. Since both the mid-infrared probe light and the accompanying pump light are derived from the same short-wavelength master pulse, they have a defined time synchronization relationship with the master pulse. The short-wavelength probe light and the mid-infrared probe light are emitted to the target area via beam combining or near-coaxial transmission. The accompanying pump light is then multiplexed for the mid-infrared echo up-conversion process at the receiving end, ensuring that the mid-infrared probe light generation process at the transmitting end and the mid-infrared echo up-conversion process at the receiving end share the same master pulse time reference. This reduces the synchronization error and system complexity introduced by independent up-conversion pump light sources.

[0028] The short-wavelength emission branch 3 outputs short-wavelength detection light, and the parametric down-conversion module 4 outputs mid-infrared detection light. Both enter the beam combining / coaxial emission module 5.

[0029] In one embodiment, the parametric down-conversion module 4 uses short-wavelength pump light as the pump input and synchronously generates the mid-infrared detection light and the accompanying pump light through a second-order nonlinear parametric down-conversion process.

[0030] The second-order nonlinear medium of the parametric down-conversion module can be a birefringent phase-matched crystal, a periodically polarized crystal, or a periodically polarized nonlinear waveguide. The second-order nonlinear parametric down-conversion process includes:

[0031] Short-wavelength pump light is focused or coupled into a second-order nonlinear medium, where energy conservation is maintained. And under phase-matched or quasi-phase-matched conditions, second-order nonlinear polarization generates mid-infrared probe light and accompanying pump light with frequencies lower than the pump light frequency, wherein, , and These are the angular frequencies of the short-wavelength pump light, the mid-infrared detector light, and the accompanying pump light, respectively. That is, the angular frequency of the short-wavelength pump light is equal to the sum of the angular frequencies of the mid-infrared detector light and the accompanying pump light.

[0032] In addition, the mid-infrared detection light and the accompanying pump light are separated by a dichroic mirror or a wavelength division multiplexing element and then coupled to the mid-infrared emission light path and the mid-infrared echo up-conversion module 10, respectively.

[0033] Let the angular frequencies of the short-wavelength main pulse, the accompanying pump light, the mid-infrared probe light, and the short-wavelength upconversion echo be respectively... , , and Then the parametric downtransformation satisfies:

[0034] ;

[0035] Sum-frequency upconversion satisfies:

[0036] ;

[0037] From this we can obtain The corresponding wavelength satisfies:

[0038] ;

[0039] ;

[0040] By selecting the accompanying pump light wavelength based on the predetermined mid-infrared detection wavelength and short-wavelength main pulse wavelength, and ensuring that each wavelength falls within the phase-matched or quasi-phase-matched receiving bandwidth of the nonlinear medium, the frequency matching relationship is satisfied. , , and These represent the vacuum wavelengths of the short-wavelength main pulse, the accompanying pump light, the mid-infrared detector light, and the short-wavelength upconversion echo, respectively. =0.532μm, Taking 0.627μm as an example, from get The wavelength is approximately 3.511 μm; the receiving end uses up-conversion pump light of approximately 0.627 μm and mid-infrared echo of approximately 3.511 μm for frequency summation to obtain... It is approximately 0.532 μm. The above relationship represents the conservation of frequency or the reciprocal of wavelength, and does not mean that the wavelength values ​​are directly added together.

[0041] The beam combining / coaxial emission module 5 combines or nearly coaxially emits short-wavelength detection light and mid-infrared detection light to the target area 6.

[0042] In specific implementation, the beam combining / coaxial emission module 5 includes one or more of the following: a dichroic beam combiner, a broadband reflective beam combiner, a lens group, a beam expander and collimator assembly, and a pointing adjustment assembly. Preferably, when using beam combining, the dichroic beam combiner transmits to one wavelength band and reflects to the other. By adjusting the direction and spot position of the two incident lights, the central optical axes of the short-wavelength detection light and the mid-infrared detection light are aligned and combined to form a dual-band beam combining light from the same exit aperture. When using near-coaxial mode, the two detection lights are emitted from adjacent exit apertures, and their central optical axes are parallel to each other or intersect at a predetermined working distance, so that the illumination spots of the two wavelength bands overlap within the target area 6. The beam combining / coaxial emission module 5 is used to ensure that the two wavelength bands detect the same target field of view and reduce the spatial registration error of the subsequent dual-band detection field of view.

[0043] The target region 6 returns a dual-band target echo, which is collected by the receiving optical module 7 and then enters the beam splitter / wavelength splitter unit 8. The beam splitter / wavelength splitter unit 8 separates the dual-band target echo into a short-wavelength echo and a mid-infrared echo. The receiving optical module 7 can be a common-aperture receiving telescope.

[0044] The short-wavelength echo enters the short-wavelength single-photon detection channel 9, and is then detected by the second single-photon detector 12. The second single-photon detector 12 outputs a short-wavelength channel trigger signal to the TCSPC / time stamping and joint processing module 13. The mid-infrared echo enters the mid-infrared echo up-conversion module 10, along with the pump light. After the two coincide in the time and space in the nonlinear up-conversion unit, the mid-infrared echo is up-converted into a short-wavelength up-converted echo.

[0045] In one embodiment, the mid-infrared echo upconversion module 10 includes a pump delay adjustment unit, a nonlinear upconversion unit, a filtering unit, and an optical path coupling unit.

[0046] The pump delay adjustment unit includes an adjustable optical delay line, a mirror group, an optical fiber delay line, or a combination thereof, used to adjust the optical path of the accompanying pump light and compensate for its arrival time difference with the mid-infrared echo; the optical path coupling unit includes a dichroic mirror, a beam combiner, a lens, a mirror, an optical fiber coupler, a waveguide coupler, or a combination thereof, used to achieve spatial and angular overlap between the accompanying pump light and the mid-infrared echo within the nonlinear upconversion unit and satisfy a preset polarization configuration; the nonlinear upconversion unit includes a second-order nonlinear crystal or a periodically polarized nonlinear waveguide, used to convert the mid-infrared echo into a short-wavelength upconverted echo through sum-frequency upconversion; the filtering unit includes a short-pass filter, a band-pass filter, a dichroic mirror, a grating, or a combination thereof, used to suppress residual accompanying pump light, mid-infrared echo, and background light and transmit the short-wavelength upconverted echo.

[0047] To control the upconversion distance gate, a fixed internal delay is assumed between the generation location of the accompanying pump light and the nonlinear upconversion unit. The delay introduced by the adjustable delay unit is The fixed internal delay of the mid-infrared detection light generation, emission, and reception optical path is... The group velocity of mid-infrared light in the propagation medium is The effective time overlap window is When the mid-infrared echo corresponding to the distance R between the pump light and the target satisfies the following equation, effective temporal overlap can be achieved within the nonlinear upconversion unit:

[0048] ;

[0049] in, It is determined by the mid-infrared echo pulse width, the upconversion pump pulse width, the group velocity mismatch in the nonlinear medium, and the detection and timing jitter.

[0050] When the target distance is known or has a rough prior, the above relationship is set. When the target distance is unknown, the preset delay step size applies. Scan multiple delay levels and record the mid-infrared echo upconversion photon counts for each delay level. The q-th delay level... It can be represented as:

[0051] ;

[0052] in, This indicates the minimum delay, and the corresponding upward conversion distance from the door center. for:

[0053] ;

[0054] Distance from the full width of the door Approximately:

[0055] ;

[0056] In this context, sum-frequency upconversion refers to the mixing of the mid-infrared echo and the accompanying pump light in a second-order nonlinear medium, producing a short-wavelength upconverted echo with an angular frequency equal to the sum of the two angular frequencies. ,in, , and These are the angular frequencies of the short-wavelength upconversion echo, the mid-infrared echo, and the accompanying pump light, respectively. The mid-infrared echo and the accompanying pump light achieve temporal and spatial coincidence in the second-order nonlinear medium and satisfy the phase-matching or quasi-phase-matching conditions.

[0057] In one embodiment, the phase matching condition is satisfied in the following manner:

[0058] The refractive index at various wavelengths and temperatures was obtained based on the Sellmeier equation for the selected nonlinear medium. Calculate the magnitude of the wave vector of each participating light wave, where, Represents the wave vector. Indicates refractive index, This represents the wavelength of the light wave. In a collinear natural phase-matched configuration, adjusting the crystal cutting angle or incident angle, crystal temperature, and the polarization configuration of each light wave adjusts the phase mismatch during parametric down-conversion. Approaching zero, where, This indicates the phase mismatch. The wave vector representing the short-wavelength main pulse. This represents the wave vector accompanying the pump light. This represents the wave vector of the mid-infrared detection light.

[0059] In the quasi-phase-matched mode, the nonlinear medium is periodically polarized, and the polarization period is selected. Quasi-phase matching order And the direction of the reciprocal lattice vector, so that the effective phase mismatch is close to zero, the effective phase mismatch The specific formula is as follows:

[0060] ;

[0061] Among them, reciprocal lattice vector The specific formula is as follows:

[0062] ;

[0063] For the receiver and up-conversion, the phase mismatch amount Approaching zero; in quasi-phase matching, this makes the effective phase mismatch amount close to zero. Approaching zero. Among them, , and These are the wave vectors of the short-wavelength upconversion echo, the upconversion pump light, and the mid-infrared echo, respectively. Let L be the reciprocal lattice vector, and L be the effective operating length of the nonlinear medium. This represents the phase mismatch in the corresponding down-conversion or up-conversion process. According to the formula sinc(x) = sin(x) / x, in actual adjustment, the crystal angle or temperature is adjusted, or a nonlinear medium with different polarization periods is selected, to make sinc²(ΔkL / 2) or the converted optical power reach a preset threshold. Taking a 532nm short-wavelength pump, a 627nm accompanying pump, and approximately 3.511μm mid-infrared probe light as an example, parametric down-conversion satisfies the conservation of the three wavelengths; at the receiving end, the approximately 627nm up-conversion pump light and the approximately 3.511μm mid-infrared echo are summed to obtain the approximately 532nm short-wavelength up-conversion echo.

[0064] In practice, the materials, effective working length, cut angle or polarization period, operating temperature, and polarization configuration of the downconversion and upconversion media are determined based on the transparency range of the selected wavelength combination, the Sellmeier equation, and the phase matching condition. The pulse width, repetition frequency, single pulse energy, and beam waist of the main pulse, as well as the filter bandwidth, detector efficiency, and time jitter, are selected based on the predetermined working distance, range resolution, and target echo intensity, and the system is calibrated using a target at a known distance.

[0065] The short-wavelength upconversion echo enters the first single-photon detector 11, and the first single-photon detector 11 outputs a trigger signal to the TCSPC / time stamping and joint processing module 13. The first single-photon detector 11 and the second single-photon detector 12 are preferably Si-SPADs, but can also be other single-photon detectors suitable for the corresponding wavelength band.

[0066] Let the time bin width of TCSPC be... The combined time jitter of the detector and electronic links is The corresponding distance sampling interval for:

[0067] ;

[0068] in, It represents the speed of light.

[0069] The degree of distance uncertainty caused by timing jitter for:

[0070] ;

[0071] in, and It should match the predetermined distance resolution and effective time window.

[0072] The TCSPC / time stamping and joint processing module 13 receives a unified synchronization signal, a short-wavelength channel trigger signal, and a mid-infrared echo up-conversion detection channel trigger signal. It establishes arrival time histograms for both photon events and performs background subtraction, arrival time estimation, fixed delay compensation, distance calculation, and dual-band information correlation. The arrival time can be estimated using at least one method selected from echo peak maximum count position, peak centroid, template correlation matching, or parameter fitting.

[0073] Among them, adjustable pump delay Used to change the upconversion time window and distance gate position; short-wavelength channel has fixed internal delay. Fixed internal delay of mid-infrared echo upconversion detection channel It is the calibration quantity obtained by passing a target at a known distance, after the optical path and electronic links have been determined and remain unchanged. and This includes the fixed optical path length, group delay, nonlinear conversion fixed delay, detector response delay, and electronic delay for the corresponding channel, but excludes the delay that varies with the range gate. .

[0074] Let the start time corresponding to the unified synchronization signal be . The estimated echo arrival times for the short-wavelength channel and the mid-infrared echo upconversion detection channel are respectively... and The group velocities of the two bands in the propagation medium are respectively and Then the short wavelength distance Mid-infrared distance When air propagation is possible and fine refractive index correction is not required, the c approximation can be used. and When dispersion needs to be considered, the group velocities corresponding to the two bands should be used respectively.

[0075] Use the known distance The common calibration target at each location was used to measure the calibration start time. and two-channel calibration arrival time The fixed internal delay is obtained using the following formula. :

[0076] ;

[0077] Where i∈{S,U}. If the repetition frequency of the short-wavelength pulsed laser source is... The repetition period is Without pulse numbering, coding, or other periodic discrimination measures, there is no ambiguity in the distance. When the distance to be measured exceeds When a delayed scan spans multiple repetition cycles, the main pulse number, delay level, and photon event are recorded together to avoid cycle aliasing.

[0078] Furthermore, the parametric down-conversion module 4 of this invention does not require a separate output of a synchronization signal to the TCSPC / time stamping and joint processing module 13; the delays of the mid-infrared detection light and the accompanying pump light relative to the main pulse are fixed or calibrable. In this invention, the mid-infrared detection light and the accompanying pump light are derived from the same main pulse and have a fixed or calibrable delay relationship, which is beneficial for dual-band time alignment and information fusion. Additionally, this invention can simultaneously acquire short-wavelength and mid-infrared dual-band echo information, which is beneficial for target detection and ranging in complex backgrounds, smoke and dust, weak targets, and material difference scenarios.

[0079] In one embodiment, the present invention discloses a single-source-driven dual-band synchronous single-photon lidar ranging method, such as... Figure 2 As shown, it specifically includes:

[0080] S1. The short-wavelength pulsed laser source outputs a short-wavelength main pulse and obtains a unified synchronization signal corresponding to the short-wavelength main pulse;

[0081] S2. Split the short-wavelength main pulse into a short-wavelength probe light and a short-wavelength pump light;

[0082] S3. The short-wavelength pump light drives the parametric down-conversion module to generate mid-infrared detection light, and simultaneously generates accompanying pump light;

[0083] S4. Combine the short-wavelength detection light with the mid-infrared detection light or emit them nearly coaxially to the target area;

[0084] S5. Receive the target echo and separate it into short-wavelength echo and mid-infrared echo;

[0085] S6. Perform single-photon detection on the short-wavelength echo and output a short-wavelength channel trigger signal;

[0086] S7. Set or scan the adjustable delay of the accompanying pump light so that it coincides with the mid-infrared echo as the upconversion pump light within a preset time window, perform upconversion detection, and output the mid-infrared echo upconversion detection channel trigger signal.

[0087] S8. Time stamping is performed based on the unified synchronization signal and the two-channel trigger signal. The fixed internal delay of the two channels obtained by the known distance calibration is used for compensation. The distance between the two bands is calculated according to the flight time. The dual-band distance or photon count information of the same target is correlated and fused.

[0088] Specifically, the short-wavelength main pulse is split into a short-wavelength detection branch and a short-wavelength pump branch; the two branches share a unified synchronization signal and have a definite or calibrable time relationship. Steps S6 and S7 can be acquired in parallel within the same transmission cycle, or acquired in a time-division manner according to a predetermined time sequence; the term "dual-band synchronization" refers to the two channels using a unified synchronization signal as a common time reference.

[0089] Since the technical principles of the method embodiments and the system embodiments are basically the same, please refer to the corresponding description of the above system embodiments for details of the relevant technical features and implementation effects.

[0090] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in a different order than that shown in the embodiments and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0091] It should be understood that the above description of the preferred embodiments is quite detailed and should not be construed as a limitation on the scope of protection of the present invention. Those skilled in the art can make substitutions or modifications under the guidance of the present invention without departing from the scope of protection of the claims of the present invention, and all such substitutions or modifications fall within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the appended claims.

Claims

1. A single-source-driven dual-band synchronous single-photon lidar system, characterized in that, The system includes: The system includes a short-wavelength pulsed laser source (1), a beam splitting module (2), a short-wavelength transmission branch (3), a parametric down-conversion module (4), a beam combining / coaxial transmission module (5), a receiving optical module (7), a beam splitting / wavelength splitting unit (8), a short-wavelength single-photon detection channel (9), a mid-infrared echo up-conversion module (10), a first single-photon detector (11), a second single-photon detector (12), and a TCSPC / time stamping and joint processing module (13). The short-wavelength pulsed laser source (1) is used to output a short-wavelength main pulse and provide a unified synchronization signal to the TCSPC / time stamping and joint processing module (13) through an electrical synchronization output terminal or an optical sampling and detection terminal; the beam splitting module (2) is used to split the short-wavelength main pulse into a short-wavelength probe light and a short-wavelength pump light; the short-wavelength emission branch (3) is used to transmit the short-wavelength probe light to the beam combining / coaxial emission module (5); the parametric down-conversion module (4) is used to use the short-wavelength pump light as the pump input and generate a mid-infrared probe light and a companion pump light, the companion pump light being adjusted and then used as an up-conversion pump light input to the mid-infrared echo up-conversion module (10); the short-wavelength probe light and the mid-infrared probe light... The photometric beam is combined or nearly coaxially emitted by the beam combining / coaxial emission module (5); the target echo is received by the receiving optical module (7) and separated into short-wavelength echo and mid-infrared echo by the beam splitting / wavelength splitting unit (8); the short-wavelength echo is detected by the short-wavelength single-photon detection channel (9) and the second single-photon detector (12); the mid-infrared echo and the upconversion pump light overlap and are converted into short-wavelength upconversion echo within a preset time window, and are detected by the first single-photon detector (11); the TCSPC / time stamping and joint processing module (13) is used to perform time stamping, fixed delay calibration, distance calculation and dual-band information fusion based on the unified synchronization signal and the trigger signal output by the two detectors.

2. The single-source-driven dual-band synchronous single-photon lidar system according to claim 1, characterized in that, The mid-infrared detection light and the accompanying pump light are derived from the same short-wavelength main pulse and have a definite or calibrable time relationship with the unified synchronization signal; the accompanying pump light is adjusted to form an upconversion distance gate to select mid-infrared echoes within a preset target distance or a preset distance range.

3. The single-source-driven dual-band synchronous single-photon lidar system according to claim 1, characterized in that, The parametric down-conversion module (4) is used to generate mid-infrared probe light and accompanying pump light by using short-wavelength pump light as pump input, including: The parametric downconversion module (4) uses short-wavelength pump light as pump input and generates the mid-infrared detection light and the accompanying pump light synchronously through a second-order nonlinear parametric downconversion process.

4. A single-source-driven dual-band synchronous single-photon lidar system according to claim 3, characterized in that, The parametric down-conversion module (4) uses short-wavelength pump light as the pump input and synchronously generates the mid-infrared detector light and the accompanying pump light through a second-order nonlinear parametric down-conversion process, including: The short-wavelength pump light is focused or coupled into a second-order nonlinear medium via waveguide; Under the conditions of energy conservation and phase matching, a mid-infrared probe light and an accompanying pump light with a frequency lower than that of the short-wavelength pump light are generated by second-order nonlinear medium polarization. The energy conservation relationship is that the angular frequency of the short-wavelength pump light is equal to the sum of the angular frequencies of the mid-infrared probe light and the accompanying pump light.

5. A single-source-driven dual-band synchronous single-photon lidar system according to claim 4, characterized in that, The second-order nonlinear medium is a birefringent phase-matching crystal, a periodically polarized crystal, or a periodically polarized nonlinear waveguide that satisfies the phase-matching condition. The phase-matching condition is achieved by adjusting the crystal cutting angle, crystal temperature, and polarization configuration of each light wave to make the phase mismatch of the parametric down-conversion close to zero.

6. A single-source-driven dual-band synchronous single-photon lidar system according to claim 1, characterized in that, The mid-infrared echo upconversion module (10) includes a pump delay adjustment unit, an optical path coupling unit, a nonlinear upconversion unit, and a filtering unit; The pump delay adjustment unit is used to adjust the optical path of the accompanying pump light so that it coincides with the mid-infrared echo within a preset time window; the optical path coupling unit is used to make the accompanying pump light and the mid-infrared echo spatially and angularly coincide within the nonlinear upconversion unit; the nonlinear upconversion unit is used to convert the mid-infrared echo into a short-wavelength upconversion echo through mixing processing; the filtering unit is used to suppress residual accompanying pump light, mid-infrared echo and background light and transmit the short-wavelength upconversion echo.

7. A single-source-driven dual-band synchronous single-photon lidar system according to claim 6, characterized in that, The nonlinear upconversion unit is used to convert the mid-infrared echo into a short-wavelength upconversion echo through mixing processing, including: The mid-infrared echo and the accompanying pump light are mixed in a second-order nonlinear medium to generate a short-wavelength upconversion echo with an angular frequency equal to the sum of the angular frequencies of the mid-infrared echo and the accompanying pump light.

8. A single-source-driven dual-band synchronous single-photon lidar system according to claim 1, characterized in that, The TCSPC / time stamping and joint processing module (13) is also used to calibrate and compensate the fixed internal delays of the short-wavelength single-photon detection channel and the mid-infrared echo upconversion detection channel respectively; the fixed internal delays do not include the adjustable pump delay used to select the distance window.

9. A single-source-driven dual-band synchronous single-photon lidar system according to claim 1, characterized in that, The beam combining / coaxial emission module (5) includes a dichroic beam combiner, which is used to adjust the direction and spot position of the two incident lights so that the central optical axis of the short-wavelength detection light and the mid-infrared detection light are aligned and combined into a dual-band beam combining light from the same emission aperture.

10. A single-source-driven dual-band synchronous single-photon lidar ranging method, applied to the single-source-driven dual-band synchronous single-photon lidar system according to any one of claims 1-9, characterized in that, The method includes: A short-wavelength pulsed laser source outputs a short-wavelength main pulse and obtains a unified synchronization signal corresponding to the short-wavelength main pulse; The short-wavelength main pulse is split into a short-wavelength probe beam and a short-wavelength pump beam; The short-wavelength pump light drives the parametric down-conversion module to generate mid-infrared detection light, and simultaneously generates accompanying pump light; The short-wavelength detection light and the mid-infrared detection light are combined or nearly coaxially emitted to the target area (6). Receives target echoes and separates them into short-wavelength echoes and mid-infrared echoes; The short-wavelength echo is subjected to single-photon detection and a short-wavelength channel trigger signal is output. Set or scan the adjustable delay of the accompanying pump light so that it coincides with the mid-infrared echo as the upconversion pump light within a preset time window, perform upconversion detection, and output the mid-infrared echo upconversion detection channel trigger signal. Time stamping is performed based on the unified synchronization signal, the short-wavelength channel trigger signal, and the mid-infrared echo upconversion detection channel trigger signal. The fixed internal delay of the two channels, obtained by known distance calibration, is compensated respectively. The short-wavelength distance and mid-infrared distance are calculated based on the flight time, and the dual-band distance or photon count information of the same target is correlated and fused.

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