Unequal-arm interferometer-based laser radar system and speed measurement method

Abstract

The invention belongs to the technical field of laser radars, and discloses a laser radar system based on an unequal-arm interferometer and a speed measurement method.The laser radar system comprises a laser, a light splitting module, a light amplification module, a transmitting light path, a receiving light path, a filtering module, the unequal-arm interferometer, two paths of detection modules and a main control module, and collecting the first to fourth electric signals for data processing, calculating a first phase according to the first electric signal and the second electric signal, calculating a second phase according to the third electric signal and the fourth electric signal, and finally obtaining the speed information of the target according to the difference between the first phase and the second phase. Compared with the prior art, the method has the advantages that the echo signals are subjected to delay self-interference by the aid of the unequal-arm interferometer, Doppler frequency shift information of the target can be obtained, and accordingly the speed of the target is obtained. According to the scheme, double-pulse signals do not need to be transmitted, coherent detection and Fourier analysis do not need to be carried out, or frequency sweeping is carried out on echo signals, and the complexity of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a laser radar system based on an unequal-arm interferometer and a speed measurement method. Background Art

[0002] Radar plays a vital role in military, civil aviation, autonomous driving, and other fields. LiDAR, which uses shorter-wavelength lasers as information carriers, offers high resolution and can be used for target detection, tracking, and identification, as well as distance measurement, velocity measurement, and imaging.

[0003] For ranging and speed measurement, the commonly used method currently involves frequency-shifting the local oscillator (LO) light and coherently detecting it with an echo signal that has been continuously frequency-modulated or randomly amplitude- or phase-modulated. The Doppler frequency is then measured through Fourier analysis to obtain target velocity information. Coherent lidar (LIDAR) has a natural filtering effect. Using the LO light and the real signal for coherent detection not only filters out irrelevant background noise but also provides a certain gain. However, at long distances, the decoherence effect of the echo signal is more pronounced, making coherent detection difficult. The increased influence of background noise in sunlight reduces the system's signal-to-noise ratio. Patented invention with authorization number CN118011415B proposes a two-pulse relative phase encoding method to address decoherence issues caused by atmospheric turbulence and other factors. However, this solution cannot measure target velocity. Furthermore, when the target is moving at high speeds, the Doppler shift causes the echo signal frequency to change, resulting in a change in the phase difference between the two pulses. This, in turn, increases bit errors in interferometric decoding, affecting ranging performance. Summary of the Invention

[0004] In view of the above defects in the prior art, the present invention proposes a laser radar system based on an unequal-arm interferometer, comprising: A laser, used to generate a laser pulse signal; A light splitting module, used for splitting the laser pulse signal into a first light pulse and a second light pulse; an optical amplification module, configured to amplify the first optical pulse to a predetermined power; An emitting optical path, used for expanding the amplified first light pulse and irradiating it to a target; A receiving optical path for receiving an echo signal reflected from a target; A filtering module is used to filter out background stray light noise in the echo signal; An unequal-arm interferometer comprises two input ports and two output ports, and is configured to allow a second optical pulse to be incident from one input port, undergo delayed self-interference, and generate a first interference result and a second interference result, respectively, which are emitted from the two output ports; and to allow an echo signal to be incident from the other input port, undergo delayed self-interference, and generate a third interference result and a fourth interference result, respectively, which are emitted from the two output ports; wherein the second optical pulse and the echo signal enter the unequal-arm interferometer in a time-division multiplexing manner; A first detection module and a second detection module, wherein the first detection module is used to detect the first interference result and the third interference result, and respectively generate a first electrical signal and a third electrical signal; the second detection module is used to detect the second interference result and the fourth interference result, and respectively generate a second electrical signal and a fourth electrical signal; The main control module is used to control the system timing and collect the first to fourth electrical signals for data processing, calculate the first phase based on the first and second electrical signals, and calculate the second phase based on the third and fourth electrical signals, and finally obtain the target speed information based on the difference between the first phase and the second phase.

[0005] Preferably, the phase difference between the long and short arms of the unequal-arm interferometer is adjustable and maintained at π / 2 through feedback control.

[0006] Preferably, the unequal-arm interferometer includes a first beam splitter BS1, a second beam splitter BS2, and a first phase shifter PS1. The two output ports of the first beam splitter BS1 are connected to the two input ports of the second beam splitter BS2 through optical fibers of unequal lengths, forming a long arm and a short arm of the unequal-arm interferometer; the first phase shifter PS1 is arranged on the long arm; The two input ports of the first beam splitter BS1 serve as the two input ports of the unequal-arm interferometer respectively; the two output ports of the second beam splitter BS2 serve as the two output ports of the unequal-arm interferometer respectively; The first phase shifter PS1 is a fiber stretcher.

[0007] Preferably, the unequal-arm interferometer is an unequal-arm interferometer chip, comprising a first multimode interference coupler MMI1, a second multimode interference coupler MMI2, a second phase shifter PS2 and a waveguide delay line DL. The two output ports of the first multimode interference coupler MMI1 are connected to the two input ports of the second multimode interference coupler MMI2 through waveguides. A waveguide delay line DL and a second phase shifter PS2 are provided on one section of the waveguide to form the long arm of the unequal-arm interferometer; the other section of the waveguide forms the short arm of the unequal-arm interferometer. The two input ports of the first multimode interference coupler MMI1 serve as the two input ports of the unequal-arm interferometer chip respectively; the two output ports of the second multimode interference coupler MMI2 serve as the two output ports of the unequal-arm interferometer chip respectively; The second phase shifter PS2 is a thermally tuned phase shifter.

[0008] Preferably, the time domain width of the laser pulse signal is 50 ns; and the delay difference between the long arm and the short arm of the unequal-arm interferometer is 5 ns.

[0009] Preferably, the first detection module and the second detection module are a first photodetector PD1 and a second photodetector PD2.

[0010] Preferably, the first detection module and the second detection module are a first single photon detector SPD1 and a second single photon detector SPD2.

[0011] Preferably, the transmitting optical path and the receiving optical path are respectively a transmitting telescope and a receiving telescope, and the filtering module is a narrowband filter.

[0012] Preferably, the light splitting module is a third beam splitter BS3.

[0013] The present invention also discloses a laser radar velocity measurement method based on an unequal-arm interferometer, comprising the following steps: S1: The main control module drives the laser to emit a laser pulse signal, which is split into a first light pulse and a second light pulse by the optical splitting module; S2: The first optical pulse is amplified to a predetermined power by the optical amplifier module, and then irradiated toward the target after beam expansion through the transmitting optical path, and the echo signal reflected from the target is received by the receiving optical path; S3: The second light pulse enters the unequal-arm interferometer for delayed self-interference, generating the first interference result and the second interference result, and enters the first detection module and the second detection module for detection respectively, obtaining the first electrical signal and the second electrical signal ; By adjusting the phase difference of the unequal-arm interferometer, the first electrical signal and the second electrical signal remain equal; S4: The echo signal and the second optical pulse enter the unequal-arm interferometer through time division multiplexing for delayed self-interference, and the generated third interference result and fourth interference result are respectively detected by the first detection module and the second detection module to obtain the third electrical signal and the fourth electrical signal ; S5: The main control module collects the first to fourth electrical signals for data processing, and calculates the first phase according to the first and second electrical signals. , and calculate the second phase according to the third electrical signal and the fourth electrical signal Finally, the target speed is obtained based on the difference between the first phase and the second phase .

[0014] Compared with the prior art, the present invention has the following beneficial effects: This paper proposes a laser radar system and velocity measurement method based on an unequal-arm interferometer. Using the unequal-arm interferometer, the system delays the echo signal and self-interferes it, generating a phase difference. Subtracting the phase difference between the long and short arms of the unequal-arm interferometer, derived from the interference of local pulses, yields the target's Doppler shift information, and thus its velocity. This solution eliminates the need for dual-pulse signal transmission, coherent detection, Fourier analysis, or frequency sweeping of the echo signal, reducing system complexity. By adjusting the arm length difference of the unequal-arm interferometer, the system can be applied to scenarios with varying target speeds, offering broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of a laser radar system based on an unequal-arm interferometer according to the present invention; Figure 2 Schematic diagram of embodiment 1 of the laser radar system based on unequal-arm interferometer of the present invention; Figure 3 This is a schematic diagram of a second embodiment of a laser radar system based on an unequal-arm interferometer according to the present invention. DETAILED DESCRIPTION

[0016] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0017] like Figure 1 As shown, a laser radar system based on an unequal-arm interferometer includes a laser, a light splitting module, an optical amplification module, a transmitting optical path, a receiving optical path, a filtering module, a first detection module, a second detection module, and a main control module. The laser is used to generate a laser pulse signal; The optical splitting module is used to split the laser pulse signal into a first optical pulse and a second optical pulse; The optical amplification module is used to amplify the first optical pulse to a predetermined power; The emission optical path is used to expand the amplified first light pulse and irradiate the target; The receiving optical path is used to receive the echo signal reflected from the target; The filtering module is used to filter out background stray light noise in the echo signal; The unequal-arm interferometer comprises two input ports and two output ports, and is configured to allow a second optical pulse to be incident from one input port, undergo delayed self-interference, and generate a first interference result and a second interference result respectively emitted from the two output ports; and to allow an echo signal to be incident from the other input port, undergo delayed self-interference, and generate a third interference result and a fourth interference result respectively emitted from the two output ports; wherein the second optical pulse and the echo signal enter the unequal-arm interferometer in a time-division multiplexing manner; The first detection module is used to detect the first interference result and the third interference result, and respectively generate a first electrical signal and a third electrical signal; the second detection module is used to detect the second interference result and the fourth interference result, and respectively generate a second electrical signal and a fourth electrical signal; The main control module is used to control the system timing, and collect the first electrical signal to the fourth electrical signal for data processing, calculate the first phase according to the first electrical signal and the second electrical signal, and calculate the second phase according to the third electrical signal and the fourth electrical signal, and finally obtain the speed information of the target according to the difference between the first phase and the second phase.

[0018] The specific working process is as follows: The main control module drives the laser to emit a laser pulse signal, which is split into the first light pulse and the second light pulse by the light splitting module; the second light pulse enters the unequal arm interferometer for delayed self-interference, generating the first interference result and the second interference result, which can be written as , in, is the phase difference between the light pulses entering the long and short arms of the unequal-arm interferometer, and A is the amplitude of the second light pulse entering the unequal-arm interferometer. It can be calculated for , Since the arm length difference of the unequal-arm interferometer is ΔL, the time delay between the light pulse components traveling along the long arm and the short arm is Δt=n*ΔL / c, where n is the refractive index of the light pulse in the unequal-arm interferometer medium and c is the speed of light in vacuum. The frequency of the second light pulse is , so we can get , The first light pulse is amplified to a predetermined power by the optical amplifier module, and then irradiated to the target after beam expansion through the transmitting optical path. After being reflected by the target, it enters the receiving optical path and becomes an echo signal. It then enters the unequal-arm interferometer through the filtering module for interference. The third interference result and the fourth interference result emitted from its two input ports can be written as , in, is the phase difference between the light pulses entering the long and short arms of the unequal-arm interferometer, and A is the amplitude of the echo signal entering the unequal-arm interferometer. It can be calculated for , Assume that the Doppler effect of the target motion causes the frequency of the echo signal to be becomes , that is, the generated Doppler frequency shift is , we can get , Depend on and The relationship can be obtained , Since the velocity v and Doppler shift The relationship is , in, is the wavelength of the laser pulse signal. Finally, the target speed can be calculated as , Therefore, the main control module can calculate the speed of the target by collecting the electrical signals of the first detection module and the second detection module and performing data processing according to the above relationship.

[0019] like Figure 2 As shown, Example 1: The phase difference between the long and short arms of the unequal-arm interferometer is adjustable and maintained near π / 2 through feedback control.

[0020] The unequal-arm interferometer includes a first beam splitter BS1, a second beam splitter BS2, and a first phase shifter PS1. The two output ports of BS1 are connected to the two input ports of BS2 through optical fibers of unequal lengths, forming the long arm and short arm of the unequal-arm interferometer; the PS1 is arranged on the long arm; The two input ports of BS1 serve as the two input ports of the unequal-arm interferometer respectively; the two output ports of BS2 serve as the two output ports of the unequal-arm interferometer respectively; PS1 is a fiber stretcher.

[0021] The first detection module and the second detection module are photodetectors PD1 and PD2.

[0022] The transmitting optical path and the receiving optical path are respectively a transmitting telescope and a receiving telescope, and the filtering module is a narrowband filter.

[0023] The light splitting module is a third beam splitter BS3.

[0024] The specific working process of embodiment 1 is as follows: The main control module drives the laser to emit a laser pulse signal, which is split into the first light pulse and the second light pulse by BS3; the second light pulse enters the unequal-arm interferometer composed of BS1, BS2 and PS1 for delayed self-interference, generating the first interference result and the second interference result, which can be written as , in, is the phase difference between the light pulses entering the long and short arms of the unequal-arm interferometer, and A is the amplitude of the second light pulse entering the unequal-arm interferometer. It can be calculated for , When PS1 is adjusted so that , you know at this time .

[0025] Since the arm length difference of the unequal-arm interferometer is ΔL, the time delay between the light pulse components traveling along the long arm and the short arm is Δt=n*ΔL / c, where n is the refractive index of the light pulse in the unequal-arm interferometer medium and c is the speed of light in vacuum. The frequency of the second light pulse is , so we can get , The first light pulse is amplified to a predetermined power by a fiber amplifier, and then irradiated to the target after beam expansion through a transmitting telescope. After being reflected by the target, it enters the receiving telescope and becomes an echo signal. It then passes through a narrowband filter and enters the unequal-arm interferometer for interference. The third and fourth interference results emitted from its two input ports can be written as , in, is the phase difference between the light pulses entering the long and short arms of the unequal-arm interferometer, and A is the amplitude of the echo signal entering the unequal-arm interferometer. It can be calculated for , Assume that the Doppler effect of the target motion causes the frequency of the echo signal to be becomes , that is, the generated Doppler frequency shift is , we can get , Depend on and The relationship can be obtained , Since the velocity v and Doppler shift The relationship is , in, is the wavelength of the laser pulse signal. Finally, the target speed can be calculated as , Therefore, the main control module can calculate the speed of the target by collecting the electrical signals of the first detection module and the second detection module and performing data processing according to the above relationship.

[0026] like Figure 3 As shown, Example 2: The phase difference between the long and short arms of the unequal-arm interferometer is adjustable and maintained near π / 2 through feedback control.

[0027] The unequal-arm interferometer is an unequal-arm interferometer chip, comprising a first multimode interference coupler MMI1, a second multimode interference coupler MMI2, a second phase shifter PS2 and a waveguide delay line DL. The two output ports of MMI1 are connected to the two input ports of MMI2 through waveguides. One section of the waveguide is provided with a waveguide delay line DL and a second phase shifter PS2, forming the long arm of the unequal-arm interferometer; the other section of the waveguide forms the short arm of the unequal-arm interferometer. The two input ports of MMI1 serve as the two input ports of the unequal-arm interferometer chip; the two output ports of MMI 2 serve as the two output ports of the unequal-arm interferometer chip; PS2 is a thermally tuned phase shifter.

[0028] The first detection module and the second detection module are single photon detectors SPD1 and SPD2.

[0029] The transmitting optical path and the receiving optical path are respectively a transmitting telescope and a receiving telescope, and the filtering module is a narrowband filter.

[0030] The light splitting module is a third beam splitter BS3.

[0031] The specific working process of Example 2 is as follows: The main control module drives the laser to emit a laser pulse signal, which is split into the first light pulse and the second light pulse by BS3; the second light pulse enters the unequal-arm interferometer chip for delayed self-interference, generating the first interference result and the second interference result. The counts obtained after entering SPD1 and SPD2 for detection can be written as , in, is the phase difference between the light pulses entering the long and short arms of the unequal-arm interferometer chip, and A is the amplitude of the second light pulse entering the unequal-arm interferometer chip. It can be calculated for , When adjusting PS2 so , you know at this time .

[0032] Since the arm length difference of the unequal-arm interferometer chip is ΔL, the delay between the light pulse components traveling along the long arm and the short arm is Δt=n*ΔL / c, where n is the refractive index of the light pulse in the unequal-arm interferometer chip medium and c is the speed of light in vacuum. The frequency of the second light pulse is , so we can get , The first light pulse is amplified to a predetermined power by the fiber amplifier, and then irradiated to the target after beam expansion through the transmitting telescope. After being reflected by the target, it enters the receiving telescope and becomes an echo signal. It then passes through a narrowband filter and enters the unequal-arm interferometer chip for interference. The third interference result and the fourth interference result emitted from its two input ports enter SPD1 and SPD2 for detection respectively. The counts of the two can be written as , in, is the phase difference between the long and short arms of the light pulse entering the unequal-arm interferometer chip, and A is the amplitude of the echo signal entering the unequal-arm interferometer chip. It can be calculated for , Assume that the Doppler effect of the target motion causes the frequency of the echo signal to be becomes , that is, the generated Doppler frequency shift is , we can get , Depend on and The relationship can be obtained , Since the velocity v and Doppler shift The relationship is , in, is the wavelength of the laser pulse signal. Finally, the target speed can be calculated as , Therefore, the main control module can calculate the speed of the target by collecting the electrical signals of the first detection module and the second detection module and performing data processing according to the above relationship.

[0033] Based on the various embodiments and principles of the present invention, the present invention proposes a laser radar system and speed measurement method based on an unequal-arm interferometer. The unequal-arm interferometer is used to delay the self-interference of the echo signal, thereby obtaining a phase difference. By subtracting the phase difference between the long and short arms of the unequal-arm interferometer obtained from the interference result of the local pulse, the Doppler shift information of the target can be obtained, thereby determining the target's speed. This solution does not require the transmission of dual-pulse signals, coherent detection and Fourier analysis, or frequency sweeping of the echo signal, thus reducing the complexity of the system. By setting the arm length difference of the unequal-arm interferometer, it can be applied to scenarios with different target speeds, and has broad application prospects.

Claims

1. A laser radar system based on an unequal-arm interferometer, characterized in that: include: A laser, used to generate a laser pulse signal; A light splitting module, used for splitting the laser pulse signal into a first light pulse and a second light pulse; an optical amplification module, configured to amplify the first optical pulse to a predetermined power; An emitting optical path, used for expanding the amplified first light pulse and irradiating it to a target; A receiving optical path for receiving an echo signal reflected from a target; A filtering module is used to filter out background stray light noise in the echo signal; An unequal-arm interferometer comprises two input ports and two output ports, and is configured to allow a second optical pulse to be incident from one input port, undergo delayed self-interference, and generate a first interference result and a second interference result, respectively, which are emitted from the two output ports; and to allow an echo signal to be incident from the other input port, undergo delayed self-interference, and generate a third interference result and a fourth interference result, respectively, which are emitted from the two output ports; wherein the second optical pulse and the echo signal enter the unequal-arm interferometer in a time-division multiplexing manner; A first detection module and a second detection module, wherein the first detection module is used to detect the first interference result and the third interference result, and respectively generate a first electrical signal and a third electrical signal; the second detection module is used to detect the second interference result and the fourth interference result, and respectively generate a second electrical signal and a fourth electrical signal; The main control module is used to control the system timing and collect the first to fourth electrical signals for data processing, calculate the first phase based on the first and second electrical signals, and calculate the second phase based on the third and fourth electrical signals, and finally obtain the target speed information based on the difference between the first phase and the second phase.

2. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The phase difference between the long and short arms of the unequal-arm interferometer is adjustable and maintained at π / 2 through feedback control.

3. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The unequal-arm interferometer includes a first beam splitter BS1, a second beam splitter BS2, and a first phase shifter PS1. The two output ports of the first beam splitter BS1 are connected to the two input ports of the second beam splitter BS2 through optical fibers of unequal lengths, forming the long arm and short arm of the unequal-arm interferometer; the first phase shifter PS1 is arranged on the long arm; The two input ports of the first beam splitter BS1 serve as the two input ports of the unequal-arm interferometer respectively; The two output ports of the second beam splitter BS2 serve as the two output ports of the unequal-arm interferometer respectively; The first phase shifter PS1 is a fiber stretcher.

4. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The unequal-arm interferometer is an unequal-arm interferometer chip, comprising a first multimode interference coupler MMI1, a second multimode interference coupler MMI2, a second phase shifter PS2 and a waveguide delay line DL. The two output ports of the first multimode interference coupler MMI1 are connected to the two input ports of the second multimode interference coupler MMI2 through waveguides. A waveguide delay line DL and a second phase shifter PS2 are provided on one section of the waveguide to form the long arm of the unequal-arm interferometer; the other section of the waveguide forms the short arm of the unequal-arm interferometer. The two input ports of the first multimode interference coupler MMI1 serve as the two input ports of the unequal-arm interferometer chip respectively; the two output ports of the second multimode interference coupler MMI2 serve as the two output ports of the unequal-arm interferometer chip respectively; The second phase shifter PS2 is a thermally tuned phase shifter.

5. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The time domain width of the laser pulse signal is 50ns; the delay difference between the long and short arms of the unequal-arm interferometer is 5ns.

6. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The first detection module and the second detection module are a first photodetector PD1 and a second photodetector PD2.

7. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The first detection module and the second detection module are a first single photon detector SPD1 and a second single photon detector SPD2.

8. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The transmitting optical path and the receiving optical path are respectively a transmitting telescope and a receiving telescope, and the filtering module is a narrowband filter.

9. The laser radar system based on the unequal-arm interferometer according to claim 1, characterized in that: The light splitting module is a third beam splitter BS3.

10. A laser radar velocity measurement method based on unequal-arm interferometer, characterized in that: A laser radar system according to any one of claims 1 to 9, comprising the following steps: S1: The main control module drives the laser to emit a laser pulse signal, which is split into a first light pulse and a second light pulse by the optical splitting module; S2: The first optical pulse is amplified to a predetermined power by the optical amplifier module, and then irradiated toward the target after beam expansion through the transmitting optical path, and the echo signal reflected from the target is received by the receiving optical path; S3: The second light pulse enters the unequal-arm interferometer for delayed self-interference, generating the first interference result and the second interference result, and enters the first detection module and the second detection module for detection respectively, obtaining the first electrical signal and the second electrical signal ; By adjusting the phase difference of the unequal-arm interferometer, the first electrical signal and the second electrical signal remain equal; S4: The echo signal and the second optical pulse enter the unequal-arm interferometer through time division multiplexing for delayed self-interference, and the generated third interference result and fourth interference result are respectively detected by the first detection module and the second detection module to obtain the third electrical signal and the fourth electrical signal ; S5: The main control module collects the first to fourth electrical signals for data processing, and calculates the first phase according to the first and second electrical signals. , and calculate the second phase according to the third electrical signal and the fourth electrical signal Finally, the target speed is obtained based on the difference between the first phase and the second phase .

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