Frequency-modulated continuous wave lidar based on multi-core fiber and three-dimensional velocity and distance measurement method

Abstract

The application provides a frequency-modulated continuous wave laser radar based on a multi-core optical fiber and a three-dimensional velocity and distance measuring method, and belongs to the technical field of laser radars.The application comprises two narrow-linewidth single-frequency optical fiber lasers, an arbitrary waveform generator, a modulator, a 1*2 optical fiber beam splitter, two wavelength division multiplexers, an optical circulator, a multi-core optical fiber fan-in and fan-out device, a multi-core optical fiber, an optical collimator, a transmitting / receiving telescope, a target object, two optical fiber couplers, two bifurcated optical fibers, two photodetectors, a balanced photodetector, a data acquisition card and an upper computer, wherein the first fiber core is an axial fiber core and is also a common fiber core of two radial fiber core groups, is used for radial sensing, a radial balanced photodetector and an axial photodetector are used for outputting signals to the upper computer, and the upper computer calculates radial and axial velocities and distances according to the calculation requirements.The application realizes the synchronous velocity and distance measurement in three-dimensional directions and can perform synchronous three-dimensional velocity and distance measurement.

Description

Technical Field

[0001] This invention relates to the field of lidar technology, and in particular to a frequency-modulated continuous wave lidar based on multi-core optical fiber and a three-dimensional velocity and distance measurement method. Background Technology

[0002] LiDAR (Light Detection and Ranging) emits laser beams through a transmitting unit. Upon encountering an obstacle, the beam is reflected and captured by a receiving unit. The distance to the obstacle is determined by measuring the time of flight (TOF) of each laser beam. Compared to traditional microwave radar technology, LiDAR operates in the shorter wavelength optical frequency band. This allows for a smaller divergence angle and better directionality in the emitted beam. The shorter operating wavelength also significantly improves the range and angular resolution achievable during radar detection. LiDAR can obtain rich information such as target distance, velocity, and reflectivity. The acquired 3D point cloud data is typically used to generate high-resolution 3D maps or models, and it is widely used in surveying, topography, forestry, atmospheric physics, laser guidance, aerospace, deep space exploration, and autonomous driving.

[0003] Traditional lidar typically measures only a single target, making simultaneous ranging and velocity measurement impossible and resulting in blind spots. However, lidar applications often involve measuring multiple targets simultaneously, which traditional lidar methods struggle to meet.

[0004] Frequency-modulated continuous-wave lidar (FMCW LiDAR) is a type of radar with a constant transmit power but a continuously periodically changing optical carrier frequency (or phase). It measures the modulation frequency difference introduced by range delay and the Doppler frequency difference introduced by relative velocity between the echo signal and the transmitted signal through coherent detection, thereby demodulating the target's range and velocity. Compared to traditional time-of-flight lidar, FMCW LiDAR offers advantages such as high resolution, high measurement accuracy, compact design, and low power consumption. Benefiting from using continuous optical signals for measurement, FMCW LiDAR also possesses unique performance characteristics such as high sensitivity, rich information content, and easy processing and demodulation. It is highly competitive for high-resolution and high-accuracy detection requirements and has excellent potential for integration, miniaturization, and low power consumption.

[0005] Traditional frequency-modulated continuous wave (FMCW) lidar typically only measures the relative distance and velocity of moving objects, failing to simultaneously measure the three-dimensional velocity of moving targets. Currently reported FMCW three-dimensional measurement systems, such as ultra-wideband terahertz FMCW imaging systems and millimeter-wave FMCW MIMO radar systems, are primarily microwave-based radar systems. Their designs are complex, and their systems are expensive, lacking the high precision and high resolution advantages of lidar. Therefore, a significant technological gap remains to be filled in the development of three-dimensional laser velocity and ranging radar.

[0006] Multi-core optical fiber is a novel type of microstructured optical fiber, characterized by multiple cores within the same cladding. It possesses advantages in core arrangement and multi-core, multi-optical-channel structure, resulting in significantly greater compactness compared to traditional optical fibers and fiber bundles. Therefore, leveraging the microstructure and small size of multi-core optical fiber, combined with frequency-modulated continuous wave lidar (FMCW LiDAR) technology, can effectively address current challenges in radar technology, fill technological gaps, and enable three-dimensional velocity and distance measurement using frequency-modulated continuous wave lasers, achieving miniaturization and cost reduction of measurement equipment. Summary of the Invention

[0007] In view of this, the present invention provides a frequency-modulated continuous wave lidar based on multi-core optical fiber and a three-dimensional velocity and distance measurement method. By combining multi-core optical fiber with frequency-modulated continuous wave, the three-dimensional velocity and distance of a moving target can be measured synchronously, which has the advantage of low cost.

[0008] The technical solution adopted by the embodiments of the present invention to solve its technical problem is as follows:

[0009] A frequency-modulated continuous wave lidar based on multi-core optical fiber includes: a first narrow-linewidth single-frequency fiber laser (1), a second narrow-linewidth single-frequency fiber laser (2), an arbitrary waveform generator (3), a modulator (4), a 1×2 fiber beam splitter (5), a first wavelength division multiplexer (6), an optical circulator (7), a multi-core fiber fan-in / fan-out unit (8), a multi-core fiber (9), an optical collimator (10), a transmitting / receiving telescope (11), a target object (12), a second wavelength division multiplexer (13), a first fiber coupler (14), a first branched fiber (15), a second branched fiber (16), a first photodetector (17), a second photodetector (18), a second fiber coupler (19), a balanced detector (20), a data acquisition card (21), a host computer (22), a first filter (23-1), a second filter (23-2), a third filter (23-3), and a fourth filter (23-4).

[0010] The first narrow-linewidth single-frequency fiber laser (1) is used to emit continuous light with a wavelength of λ1. The arbitrary waveform generator (3) is used to generate a linear frequency modulated signal in the form of a triangular wave as the driving signal of the modulator (4). The optical signal input port of the modulator (4) is connected to the first narrow-linewidth single-frequency fiber laser (1), the microwave signal input port is connected to the arbitrary waveform generator (3), and the optical signal output port is connected to the input port of the 1×2 fiber beam splitter (5). The modulator (4) is used to output the modulated light with a wavelength of λ1 to the 1×2 fiber beam splitter (5). The 1×2 fiber beam splitter (5) is used to split the light into local oscillator light and probe light. The first output port of the 1×2 fiber beam splitter (5) is connected to the first input port of the second fiber coupler (19), and the second output port is connected to the first input port of the second fiber coupler (19). The first input port of the first wavelength division multiplexer (6) is connected; the second narrow linewidth single-frequency fiber laser (2) is used to generate continuous light with wavelength λ2, λ1≠λ2; the first ports of the second narrow linewidth single-frequency fiber laser (2), the first wavelength division multiplexer (6), and the optical circulator (7) are connected sequentially along the optical path; the first wavelength division multiplexer (6) is used to combine two wavelengths of light into a composite probe light and input it to the optical circulator (7); the second port of the optical circulator (7), the input and output ports (8-1) of the multi-core fiber fan-in fan-out device (8), the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and the transmitting and receiving telescope (11) are connected sequentially along the optical path, and the composite probe light is emitted from the transmitting and receiving telescope (11);

[0011] The echo signal reflected by the target object (12) passes sequentially through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out (8), and enters the optical circulator (7) from the second port. The third port of the optical circulator (7) is connected to the input port of the second wavelength division multiplexer (13). The second wavelength division multiplexer (13) is used to divide the echo signal transmitted by the optical circulator (7) into two wavelengths. The first output port of the second wavelength division multiplexer (13) is connected to the second input port of the second fiber coupler (19). The first wavelength division multiplexer (13) is used to output the first wavelength division multiplexer (14) with a wavelength of λ1. The second output port of the second wavelength division multiplexer (13) is connected to the input port of the first fiber coupler (14). The second wavelength division multiplexer (19) is used to combine the local oscillator light output by the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then split it into two paths to output to the balanced detector (20). The two output ports of the second fiber coupler (19) are connected to the two input ports of the balanced detector (20) respectively. The balanced detector (20) is used to beat the frequency to obtain the intermediate frequency signal corresponding to the axial velocity in the z direction.

[0012] The multi-core fiber (9) has 5 cores. The core located in the center is connected to port (8-1) of the multi-core fiber fan-in fan-out device (8). The other 4 cores are symmetrically and evenly distributed along the same circumference and are sequentially connected to ports (8-2), (8-3), (8-4), and (8-5) of the multi-core fiber fan-in fan-out device (8).

[0013] The first filter (23-1), the second filter (23-2), the third filter (23-3), and the fourth filter (23-4) are all used to filter out waves with wavelengths other than λ2 in the echo signal; the first output port of the first fiber coupler (14) is connected to the first input port of the first branch fiber (15), and the second input port of the first branch fiber (15) is connected sequentially along the optical path, as are the second input ports of the first filter (23-1) and the first branch fiber (15); the output end of the first branch fiber (15) is connected to the first photodetector (17). The first photodetector (17) is used to input three optical signals with wavelength λ2 in the x-axis direction; the second output port of the first fiber coupler (14) is connected to the first input port of the second branch fiber (16), the port (8-3), the third filter (23-3), and the second input port of the second branch fiber (16) are connected sequentially along the optical path, the port (8-5), the fourth filter (23-4), and the third input port of the second branch fiber (16) are connected sequentially along the optical path, and the output end of the second branch fiber (16) is connected to the second photodetector (18), which is used to input three optical signals with wavelength λ2 in the y-axis direction to the first photodetector (17);

[0014] The three input terminals of the data acquisition card (21) are respectively connected to the output terminals of the first photodetector (17), the second photodetector (18), and the balance detector (20); the output terminal of the data acquisition card (21) is connected to the host computer (22), which is used to receive the three sets of electrical signals acquired by the data acquisition card (21) and perform speed and distance measurement of the target object.

[0015] Preferably, the modulated light is a single-sideband modulated laser, composed of a positive first-order sideband or a negative first-order sideband.

[0016] Ideally, the distance R along the z-axis and the velocity v z The calculation formula is:

[0017]

[0018]

[0019] In the formula, T is the modulation period of the linear frequency modulated signal, B is the modulation bandwidth of the linear frequency modulated signal, c is the speed of light, and λ1 is the wavelength of the modulated light; the signal transmitted by the balanced detector (20) includes the electrical signal corresponding to the local oscillator light and the electrical signal corresponding to the first wavelet. The host computer is used to perform Fourier transform on the signal transmitted by the balanced detector (20) in the rising and falling frequency bands of the triangular wave to obtain two beat frequencies f. up and f duwn f up >f duwn ;

[0020] velocity v along the x-axis x and the velocity v in the y-axis direction y The calculation formula is:

[0021] v x =p x f x

[0022] v y =p y f y

[0023] In the formula, f x f is the output signal frequency of the first photodetector (17). y p is the output signal frequency of the second photodetector (18). x It is the distance between the cores in the x-direction of the multi-core optical fiber (9), p y It is the distance between the cores in the y-direction of the multi-core optical fiber (9);

[0024] Total radial velocity v xy The calculation formula is:

[0025]

[0026] Among them, v x Direction and v xy The angle between the directions is θ:

[0027]

[0028] Furthermore, this invention provides a three-dimensional velocity and ranging method for a frequency-modulated continuous wave lidar based on multi-core optical fiber, employing the aforementioned frequency-modulated continuous wave lidar based on multi-core optical fiber, and the steps include:

[0029] Step S1: After reliably connecting all components in the frequency-modulated continuous wave lidar based on multi-core optical fiber, start the machine. At this time, the first narrow linewidth single-frequency fiber laser generates continuous light with wavelength λ1, the second narrow linewidth single-frequency fiber laser (2) generates continuous light with wavelength λ2, λ1≠λ2, and the arbitrary waveform generator (3) generates a linear frequency-modulated signal in the form of a triangular wave as the driving signal of the modulator (4).

[0030] Step S2, the modulator (4) modulates the continuous light with wavelength λ1 according to the driving signal and generates modulated light with wavelength λ1 and outputs it to the 1×2 fiber beam splitter (5).

[0031] Step S3, the 1×2 fiber beam splitter (5) splits the modulated light into local oscillator light and probe light, which are then sent to the second fiber coupler (19) and the first wavelength division multiplexer (6), respectively.

[0032] Step S4, the first wavelength division multiplexer (6) combines the light of the two wavelengths into a composite probe light and inputs it into the optical circulator (7);

[0033] In step S5, the optical circulator (7) outputs the composite probe light to the multi-core fiber fan-in fan-out device (8). The composite probe light passes through the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and finally exits through the transmitting and receiving telescope (11) to illuminate the target object (12).

[0034] Step S6: The echo signal reflected by the target object (12) passes through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out device (8) in sequence, enters the optical circulator (7) from the second port of the optical circulator (7), and finally reaches the second wavelength division multiplexer (13).

[0035] Step S7, the second wavelength division multiplexer (13) divides the echo signal to obtain two wavelength signals. The first wavelength division multiplexer with wavelength λ1 is output to the second fiber coupler (19), and the second wavelength division multiplexer with wavelength λ2 is output to the first fiber coupler (14). The first fiber coupler (14) inputs the second wavelength division multiplexer to the first branch fiber (15) and the second branch fiber (16) respectively.

[0036] Step S8, the second fiber coupler (19) combines the local oscillator light output from the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then splits it into two paths to output to the balanced detector (20).

[0037] Step S9, the balance detector (20) performs beat frequency and obtains the intermediate frequency signal of the axial velocity in the z direction;

[0038] In step S10, the echo signals are output through ports (8-2) and (8-4) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the first filter (23-1) and the second filter (23-2), they become two echo signals with a wavelength of λ2 and enter the first branch fiber (15); the echo signals are output through ports (8-3) and (8-5) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the third filter (23-3) and the fourth filter (23-4), they become two echo signals with a wavelength of λ2 and enter the second branch fiber (16);

[0039] In step S11, the first branched fiber (15) inputs three signals with wavelength λ2 in the x-axis direction into the first photodetector (17); the second branched fiber (16) inputs three signals with wavelength λ2 in the y-axis direction into the second photodetector (18).

[0040] Step S12: The data acquisition card (21) acquires the output signal of the first photodetector (17), the output signal of the second photodetector (18), and the output signal of the balance detector (20), and outputs the three sets of acquired signals to the host computer (22).

[0041] In step S13, the host computer (22) receives the three sets of electrical signals collected by the data acquisition card (21) and performs speed and distance measurement of the target object.

[0042] As can be seen from the above technical solution, the frequency-modulated continuous wave lidar and three-dimensional velocity and distance measurement method based on multi-core optical fiber provided in this embodiment of the invention consists of two narrow-linewidth single-frequency fiber lasers, an arbitrary waveform generator, a modulator, a 1×2 fiber beam splitter, two wavelength division multiplexers, an optical circulator, a multi-core optical fiber fan-in / fan-out unit, a multi-core optical fiber, an optical collimator, a transmitting / receiving telescope, a target object, a filter, two fiber couplers, two branched optical fibers, two photodetectors, a balanced detector, a data acquisition card, and a host computer. Among them, fiber core 1 is both the axial fiber core and the common fiber core of two radial fiber core groups, used for radial sensing. The radial balanced detector and the axial photodetector are used to output signals to the host computer. The host computer performs radial and axial velocity and distance calculations according to the calculation requirements. This invention realizes synchronous velocity and distance calculation in three dimensions, and can perform synchronous three-dimensional velocity and distance measurement, with the advantage of low cost. Attached Figure Description

[0043] Figure 1 This invention relates to a frequency-modulated continuous wave lidar based on multi-core optical fiber.

[0044] Figure 2 This is a three-dimensional velocity diagram of a moving target.

[0045] Figure 3 This is a schematic diagram of the composition of the fiber core assembly at the end face of a multi-core optical fiber.

[0046] Figure 4 This is a schematic diagram of axial signal acquisition.

[0047] Figure 5 This is a schematic diagram of radial signal acquisition.

[0048] Figure 1 The following are the markings: (1) First narrow linewidth single-frequency fiber laser; (2) Second narrow linewidth single-frequency fiber laser; (3) Arbitrary waveform generator; (4) Modulator; (5) 1×2 fiber beam splitter; (6) First wavelength division multiplexer; (7) Optical circulator; (8) Multi-core fiber fan-in fan-out; (9) Multi-core fiber; (10) Optical collimator; (11) Transmitting / receiving telescope; (12) Target object; (13) Second wavelength division multiplexer; (14) First fiber coupler; (15) First branched fiber; (16) Second branched fiber; (17) Photodetector; (18) Photodetector; (19) Second fiber coupler; (20) Balance detector; (21) Data acquisition card; (22) Host computer; (23-1) First filter; (23-2) Second filter; (23-3) Third filter; (23-4) Fourth filter.

[0049] Figure 4 In this context, T represents the sweep frequency period, and f... D τ is the Doppler frequency shift; τ is the time delay between the reflected light and the reference light; f up with f down These are the beat frequencies obtained during the rising and falling segments of the sweep frequency, respectively.

[0050] Figure 5 In the figure, (a) is the time-domain waveform of the signal corresponding to the x-direction, (b) is the frequency-domain waveform of the signal corresponding to the x-direction, (c) is the time-domain waveform of the signal corresponding to the y-direction, and (d) is the time-domain waveform of the signal corresponding to the y-direction. Detailed Implementation

[0051] The technical solution and effects of the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] This invention introduces multi-core optical fiber and proposes a frequency-modulated continuous wave lidar and three-dimensional velocity and distance measurement method based on multi-core optical fiber. Multi-core optical fiber is a novel type of microstructured optical fiber with multiple cores in the same cladding. Its structural compactness is significantly superior to traditional optical fibers and fiber bundles. Furthermore, by utilizing its core arrangement characteristics and the advantages of multiple cores and multiple optical channels, combined with frequency-modulated continuous wave technology, the problem of synchronous measurement of three-dimensional velocity and distance of moving targets can be solved.

[0053] like Figure 1 As shown, the frequency-modulated continuous wave lidar based on multi-core optical fiber provided by the present invention includes: a first narrow linewidth single-frequency fiber laser (1), a second narrow linewidth single-frequency fiber laser (2), an arbitrary waveform generator (3), a modulator (4), a 1×2 fiber beam splitter (5), a first wavelength division multiplexer (6), an optical circulator (7), a multi-core optical fiber fan-in fan-out unit (8), a multi-core optical fiber (9), an optical collimator (10), a transmitting / receiving telescope (11), a target object (12), a second wavelength division multiplexer (13), a first optical fiber coupler (14), a first branched optical fiber (15), a second branched optical fiber (16), a first photodetector (17), a second photodetector (18), a second optical fiber coupler (19), a balanced detector (20), a data acquisition card (21), a host computer (22), a first filter (23-1), a second filter (23-2), a third filter (23-3), and a fourth filter (23-4);

[0054] The first narrow-linewidth single-frequency fiber laser (1) is used to emit continuous light with a wavelength of λ1. The arbitrary waveform generator (3) is used to generate a linear frequency modulated signal in the form of a triangular wave as the driving signal of the modulator (4). The modulator (4) performs linear frequency modulation on the narrow-linewidth single-frequency fiber laser (1) to achieve single-sideband modulation under carrier suppression and improve the signal-to-noise ratio. The optical signal input port of the modulator (4) is connected to the first narrow-linewidth single-frequency fiber laser (1), the microwave signal input port is connected to the arbitrary waveform generator (3), and the optical signal output port is connected to the input port of the 1×2 fiber beam splitter (5). The modulator (4) is used to output the modulated light with a wavelength of λ1 to the 1×2 fiber beam splitter (5). Here, the modulated light is a single-sideband modulated laser, which is composed of positive first-order sideband or negative first-order sideband.

[0055] The 1×2 fiber beam splitter (5) is used to split the light into local oscillator light and probe light. The first output port of the 1×2 fiber beam splitter (5) is connected to the first input port of the second fiber coupler (19), and the second output port is connected to the first input port of the first wavelength division multiplexer (6).

[0056] The second narrow linewidth single-frequency fiber laser (2) is used to generate continuous light with wavelength λ2, where λ1 ≠ λ2; the first ports of the second narrow linewidth single-frequency fiber laser (2), the first wavelength division multiplexer (6), and the optical circulator (7) are connected sequentially along the optical path; the first wavelength division multiplexer (6) is used to combine two wavelengths of light into a composite probe light and input it into the optical circulator (7); the second port of the optical circulator (7), the input and output ports (8-1) of the multi-core fiber fan-in fan-out device (8), the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and the transmitting and receiving telescope (11) are connected sequentially along the optical path, and the composite probe light is emitted from the transmitting and receiving telescope (11);

[0057] The echo signal reflected by the target object (12) passes sequentially through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out (8), and enters the optical circulator (7) from the second port of the optical circulator (7); the third port of the optical circulator (7) is connected to the input port of the second wavelength division multiplexer (13); the second wavelength division multiplexer (13) is used to divide the echo signal transmitted by the optical circulator (7) into two wavelengths, and the first output port of the second wavelength division multiplexer (13) is connected to the second input port of the second fiber coupler (19) to output the first wavelength division multiplexer with wavelength λ1. The output port is connected to the input port of the first fiber coupler (14) and is used to output the second wavelength division multiplexer (λ2). The second fiber coupler (19) is used to combine the local oscillator light output by the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then split it into two paths to output to the balanced detector (20). The two output ports of the second fiber coupler (19) are connected to the two input ports of the balanced detector (20) respectively. The probe light passes through the optical circulator (7) and then passes through the optical collimator (10) and the transmitting / receiving telescope (11) to be emitted onto the object. The probe light reflected by the target enters the circulator and then enters the balanced detector (20) with the local oscillator light for coherent mixing, thereby obtaining the intermediate frequency signal.

[0058] The frequency-modulated continuous wave lidar based on multi-core optical fiber of the present invention uses a transmitting / receiving telescope (11) to emit detection light and receive the light signal reflected by the moving object, so as to achieve the function of simultaneous transmission and reception of multiple fields of view. The target object (12) selects the rotating disk as the target.

[0059] refer to Figure 3 The multi-core fiber (9) has 5 cores, each core receiving reflected light signals. The corresponding multi-core fiber fan-in fan-out has five ports. The received reflected light signals pass through the ports of the multi-core fiber fan-in fan-out in sequence. Core 1, located in the center, is connected to port (8-1) of the multi-core fiber fan-in fan-out (8). Core 1 can be used for radial velocity measurement and axial velocity measurement. It is a common channel. The echo signal received by core 1 measures the corresponding axial velocity and distance. The other 4 cores are symmetrically and evenly distributed along the same circumference and are sequentially connected to ports (8-2), (8-3), (8-4), and (8-5) of the multi-core fiber fan-in fan-out (8). Cores 1, 2, and 4 form an array corresponding to the velocity related to the x-axis direction. Cores 1, 3, and 5 form an array corresponding to the velocity related to the y-axis direction.

[0060] The first filter (23-1), the second filter (23-2), the third filter (23-3), and the fourth filter (23-4) are all used to filter out waves with wavelengths other than λ2 in the echo signal; the output port (8-2) of the multi-core fiber fan-in fan-out unit (8) is connected to the input port of the filter (23-1), the output port (8-4) is connected to the input port of the filter (23-2), the output ports of the filters (23-1) and (23-2) are connected to the input port of the first branch fiber (15), and the first output port of the fiber coupler (14), the output port of the first filter (23-1), and the second filter (23-2) are all connected. The output port of the fiber is connected to the input port of the first branch fiber (15); the output port (8-3) of the multi-core fiber fan-in fan-out (8) is connected to the input port of the filter (23-3), the output port (8-5) is connected to the input port of the filter (23-4), the second output port of the fiber coupler (14), the output port of the third filter (23-3) and the output port of the fourth filter (23-4) are connected to the input port of the branch fiber (16), the output port of the first branch fiber (15) is connected to the input port of the photodetector (17), and the output port of the second branch fiber (16) is connected to the input port of the photodetector (18).

[0061] The first output port of the first fiber coupler (14) is connected to the first input port of the first branch fiber (15). The second input port of the first branch fiber (15), the first filter (23-1), and the first branch fiber (15) are connected sequentially along the optical path. The third input port of the first branch fiber (15), the second filter (23-2), and the first branch fiber (15) are connected sequentially along the optical path. The output end of the first branch fiber (15) is connected to the first photodetector (17) to input three optical signals with a wavelength of λ2 in the x-axis direction into the first photodetector (17). The second output port of the first fiber coupler (14) is connected to the first input port of the second branch fiber (16). The port (8-3), the third filter (23-3), and the second input port of the second branch fiber (16) are connected sequentially along the optical path. The port (8-5), the fourth filter (23-4), and the third input port of the second branch fiber (16) are connected sequentially along the optical path. The output end of the second branch fiber (16) is connected to the second photodetector (18) to input three optical signals with a wavelength of λ2 in the y-axis direction into the first photodetector (17).

[0062] The three input terminals of the data acquisition card (21) are respectively connected to the output terminals of the first photodetector (17), the second photodetector (18), and the balance detector (20); the output terminal of the data acquisition card (21) is connected to the host computer (22), which is used to receive the three sets of electrical signals acquired by the data acquisition card (21) and perform speed and distance measurement of the target object.

[0063] z-axis distance R and velocity v z The calculation formula is:

[0064]

[0065]

[0066] In the formula, T is the modulation period of the linear frequency modulated signal, B is the modulation bandwidth of the linear frequency modulated signal, c is the speed of light, and λ1 is the wavelength of the modulated light; the signal transmitted by the balanced detector (20) includes the electrical signal corresponding to the local oscillator light and the electrical signal corresponding to the first wavelet. The host computer is used to perform Fourier transforms on the signal transmitted by the balanced detector (20) in the rising and falling frequency bands of the triangular wave to obtain two beat frequencies f. up and f duwn like Figure 4 As shown, f up >f duwn ;

[0067] The laser emitted by the second narrow-linewidth single-frequency fiber laser 2 passes through the optical circulator 7, then through the optical collimator 10 and the transmitting / receiving telescope 11, and is emitted onto the object. The detected light reflected from the target is split into three paths. The first path returns to port 8-1 of the multi-core fiber fan-in / fan-out unit 8 and enters port 2 of the optical circulator 7. After passing through a wavelength division multiplexer, it is split into two paths by an optical coupler, entering the first branch fiber 15 corresponding to the x-direction and the second branch fiber 16 corresponding to the y-direction, respectively. The second path is transmitted to ports 8-2 and 8-4, where it merges with the first path entering the first branch fiber 15 and is received by the photodetector 17. The signal corresponding to the velocity in the x-axis direction is processed to calculate the velocity in the x-direction. The third path is transmitted to ports 8-3 and 8-5, where it merges with the first path entering the second branch fiber 16 and is received by the photodetector 18. The signal corresponding to the velocity in the y-axis direction is processed to calculate the velocity in the y-direction. (Reference) Figure 5 As shown, (a) is the time-domain waveform of the signal corresponding to the x-direction, (b) is the frequency-domain waveform of the signal corresponding to the x-direction, (c) is the time-domain waveform of the signal corresponding to the y-direction, and (d) is the time-domain waveform of the signal corresponding to the y-direction. From the above process, the velocities corresponding to the x-direction and y-direction can be obtained respectively; the x-axis velocity v... x and the velocity v in the y-axis direction yThe calculation formula is:

[0068] v x =p x f x (3)

[0069] v y =p y f y (4)

[0070] In the formula, f x f is the output signal frequency of the first photodetector (17). y p is the output signal frequency of the second photodetector (18). x It is the distance between the cores in the x-direction of the multi-core optical fiber (9), p y It is the distance between the cores in the y-direction of the multi-core optical fiber (9);

[0071] Total radial velocity v xy The calculation formula is:

[0072]

[0073] Among them, v x Direction and v xy The angle between the directions is θ:

[0074]

[0075] Furthermore, adopt Figure 1 The device shown performs speed and distance measurement, and the steps include:

[0076] Step S1: After reliably connecting all components in the frequency-modulated continuous wave lidar based on multi-core optical fiber, start the machine. At this time, the first narrow linewidth single-frequency fiber laser generates continuous light with wavelength λ1, the second narrow linewidth single-frequency fiber laser (2) generates continuous light with wavelength λ2, λ1≠λ2, and the arbitrary waveform generator (3) generates a linear frequency-modulated signal in the form of a triangular wave as the driving signal of the modulator (4).

[0077] Step S2, the modulator (4) modulates the continuous light with wavelength λ1 according to the driving signal and generates modulated light with wavelength λ1 and outputs it to the 1×2 fiber beam splitter (5).

[0078] Step S3, the 1×2 fiber beam splitter (5) splits the modulated light into local oscillator light and probe light, which are then fed into the second fiber coupler (19) and the first wavelength division multiplexer (6), respectively.

[0079] Step S4, the first wavelength division multiplexer (6) combines the light of the two wavelengths into a composite probe light and inputs it into the optical circulator (7);

[0080] In step S5, the optical circulator (7) outputs the composite probe light to the multi-core fiber fan-in fan-out device (8). The composite probe light passes through the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and finally exits through the transmitting and receiving telescope (11) to illuminate the target object (12).

[0081] Step S6: The echo signal reflected by the target object (12) passes through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out device (8) in sequence, enters the optical circulator (7) from the second port of the optical circulator (7), and finally reaches the second wavelength division multiplexer (13).

[0082] Step S7, the second wavelength division multiplexer (13) divides the echo signal to obtain two wavelength signals. The first wavelength division multiplexer with wavelength λ1 is output to the second fiber coupler (19), and the second wavelength division multiplexer with wavelength λ2 is output to the first fiber coupler (14). The first fiber coupler (14) inputs the second wavelength division multiplexer to the first branch fiber (15) and the second branch fiber (16) respectively.

[0083] Step S8: The second fiber coupler (19) combines the local oscillator light output from the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then splits it into two outputs to the balanced detector (20).

[0084] Step S9, the balance detector (20) performs beat frequency and obtains the intermediate frequency signal of the axial velocity in the z direction;

[0085] In step S10, the echo signals are output through ports (8-2) and (8-4) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the first filter (23-1) and the second filter (23-2), they become two echo signals with a wavelength of λ2 and enter the first branch fiber (15); the echo signals are output through ports (8-3) and (8-5) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the third filter (23-3) and the fourth filter (23-4), they become two echo signals with a wavelength of λ2 and enter the second branch fiber (16);

[0086] In step S11, the first branched fiber (15) inputs three signals with wavelength λ2 in the x-axis direction into the first photodetector (17); the second branched fiber (16) inputs three signals with wavelength λ2 in the y-axis direction into the second photodetector (18).

[0087] Step S12: The data acquisition card (21) acquires the output signal of the first photodetector (17), the output signal of the second photodetector (18), and the output signal of the balance detector (20), and outputs the three sets of acquired signals to the host computer (22).

[0088] In step S13, the host computer (22) receives the three sets of electrical signals collected by the data acquisition card (21) and performs speed and distance measurement on the target object. The specific calculation method is as described in formulas 1-6 above.

[0089] In this invention, two lasers emit lasers of different wavelengths. One laser is modulated with a triangular wave in a modulator. The modulated signal is used as a local oscillator and a probe light, and is transmitted along with the other laser. The signal is transmitted to the target object through a multi-core optical fiber. The reflected signal is transmitted in two paths. One path beats the local oscillator and is processed to obtain the axial velocity and distance of the object. The other path measures the radial velocity of the object. This invention overcomes the shortcomings of traditional frequency-modulated continuous wave lidar, which can only measure the relative distance and velocity of moving objects. By combining multi-core optical fiber with frequency-modulated continuous wave, the simultaneous measurement of the three-dimensional velocity and distance of a moving target is achieved.

[0090] The frequency-modulated continuous wave lidar based on multi-core optical fiber of the present invention has the advantage of low cost and has a better promotion advantage compared with the prior art.

[0091] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A frequency-modulated continuous wave lidar based on multi-core optical fiber, characterized in that, include: First narrow linewidth single-frequency fiber laser (1), second narrow linewidth single-frequency fiber laser (2), arbitrary waveform generator (3), modulator (4), 1×2 fiber beam splitter (5), first wavelength division multiplexer (6), optical circulator (7), multi-core fiber fan-in fan-out (8), multi-core fiber (9), optical collimator (10), transmitting / receiving telescope (11), target object (12), second wavelength division multiplexer (13), first fiber coupler (14), first branched fiber (15), second branched fiber (16), first photodetector (17), second photodetector (18), second fiber coupler (19), balanced detector (20), data acquisition card (21), host computer (22), first filter (23-1), second filter (23-2), third filter (23-3) and fourth filter (23-4); The first narrow-linewidth single-frequency fiber laser (1) is used to emit continuous light with a wavelength of λ1. The arbitrary waveform generator (3) is used to generate a linear frequency modulated signal in the form of a triangular wave as the driving signal of the modulator (4). The optical signal input port of the modulator (4) is connected to the first narrow-linewidth single-frequency fiber laser (1), the microwave signal input port is connected to the arbitrary waveform generator (3), and the optical signal output port is connected to the input port of the 1×2 fiber beam splitter (5). The modulator (4) is used to output the modulated light with a wavelength of λ1 to the 1×2 fiber beam splitter (5). The 1×2 fiber beam splitter (5) is used to split the light into local oscillator light and probe light. The first output port of the 1×2 fiber beam splitter (5) is connected to the first input port of the second fiber coupler (19), and the second output port is connected to the first input port of the first wavelength division multiplexer (6). The second narrow linewidth single-frequency fiber laser (2) is used to generate continuous light with wavelength λ2, where λ1 ≠ λ2; the first ports of the second narrow linewidth single-frequency fiber laser (2), the first wavelength division multiplexer (6), and the optical circulator (7) are connected sequentially along the optical path; the first wavelength division multiplexer (6) is used to combine two wavelengths of light into a composite probe light and input it to the optical circulator (7); the second port of the optical circulator (7), the input and output ports (8-1) of the multi-core fiber fan-in fan-out device (8), the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and the transmitting and receiving telescope (11) are connected sequentially along the optical path, and the composite probe light is emitted from the transmitting and receiving telescope (11); The echo signal reflected by the target object (12) passes sequentially through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out (8), and enters the optical circulator (7) from the second port; the third port of the optical circulator (7) is connected to the input port of the second wavelength division multiplexer (13); the second wavelength division multiplexer (13) is used to divide the echo signal transmitted by the optical circulator (7) into two wavelengths, and the first output port of the second wavelength division multiplexer (13) is connected to the second input port of the second fiber coupler (19). The second output port of the second wavelength division multiplexer (13) is connected to the input port of the first fiber coupler (14) and is used to output the second wavelength division multiplexer (14) with a wavelength of λ1. The second fiber coupler (19) is used to combine the local oscillator light output by the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then split it into two paths to output to the balanced detector (20). The two output ports of the second fiber coupler (19) are respectively connected to the two input ports of the balanced detector (20). The balanced detector (20) is used to beat the frequency to obtain the intermediate frequency signal corresponding to the axial velocity in the z direction. The multi-core fiber (9) has 5 cores. The core located in the center is connected to port (8-1) of the multi-core fiber fan-in fan-out device (8). The other 4 cores are symmetrically and evenly distributed along the same circumference and are sequentially connected to ports (8-2), (8-3), (8-4), and (8-5) of the multi-core fiber fan-in fan-out device (8). The first filter (23-1), the second filter (23-2), the third filter (23-3), and the fourth filter (23-4) are all used to filter out waves with wavelengths other than λ2 in the echo signal; the first output port of the first fiber coupler (14) is connected to the first input port of the first branch fiber (15), and the second input ports of the first filter (23-1) and the first branch fiber (15) are connected sequentially along the optical path, and the third input ports of the first filter (23-2) and the first branch fiber (15) are connected sequentially along the optical path; the output end of the first branch fiber (15) is connected to the first photodetector (17) to input the three optical signals with wavelengths of λ2 in the x-axis direction into the first photodetector (17); the second output port of the first fiber coupler (14) is connected to the second branch fiber (16) The first input port of the data acquisition card (21), the second input port of the port (8-3), the third filter (23-3), and the second input port of the second branch fiber (16) are connected sequentially along the optical path. The third input port of the port (8-5), the fourth filter (23-4), and the second branch fiber (16) are connected sequentially along the optical path. The output end of the second branch fiber (16) is connected to the second photodetector (18) to input three optical signals with wavelength λ2 in the y-axis direction into the first photodetector (17). The three input ends of the data acquisition card (21) are respectively connected to the output ends of the first photodetector (17), the second photodetector (18), and the balance detector (20). The output end of the data acquisition card (21) is connected to the host computer (22). The host computer (22) is used to receive the three sets of electrical signals acquired by the data acquisition card (21) and perform speed and distance measurement of the target object.

2. The frequency-modulated continuous wave lidar based on multi-core optical fiber as described in claim 1, characterized in that, The modulated light is a single-sideband modulated laser, composed of positive first-order sidebands or negative first-order sidebands.

3. The frequency-modulated continuous wave lidar based on multi-core optical fiber as described in claim 2, characterized in that: z-axis distance R and velocity v z The calculation formula is: In the formula, T is the modulation period of the linear frequency modulated signal, B is the modulation bandwidth of the linear frequency modulated signal, c is the speed of light, and λ1 is the wavelength of the modulated light; the signal transmitted by the balanced detector (20) includes the electrical signal corresponding to the local oscillator light and the electrical signal corresponding to the first wave division. The host computer is used to perform Fourier transform on the signal transmitted by the balanced detector (20) in the rising and falling frequency bands of the triangular wave to obtain two beat frequencies f. up and f duwn f up >f duwn ; velocity v along the x-axis x and the velocity v in the y-axis direction y The calculation formula is: v x =p x f x v y =p y f y In the formula, f x f is the output signal frequency of the first photodetector (17). y p is the output signal frequency of the second photodetector (18). x It is the distance between the cores in the x-direction of the multi-core optical fiber (9), p y It is the distance between the cores in the y-direction of the multi-core optical fiber (9); Total radial velocity v xy The calculation formula is: Among them, v x Direction and v xy The angle between the directions is θ:

4. A three-dimensional velocity and distance measurement method for a frequency-modulated continuous wave lidar based on multi-core optical fiber, characterized in that, The steps of using the frequency-modulated continuous wave lidar based on multi-core optical fiber as described in any one of claims 1-3 include: Step S1: After reliably connecting all components in the frequency-modulated continuous wave lidar based on multi-core optical fiber, start the machine. At this time, the first narrow linewidth single-frequency fiber laser generates continuous light with wavelength λ1, the second narrow linewidth single-frequency fiber laser (2) generates continuous light with wavelength λ2, λ1≠λ2, and the arbitrary waveform generator (3) generates a linear frequency-modulated signal in the form of a triangular wave as the driving signal of the modulator (4). Step S2, the modulator (4) modulates the continuous light with wavelength λ1 according to the driving signal and generates modulated light with wavelength λ1 and outputs it to the 1×2 fiber beam splitter (5). Step S3, the 1×2 fiber beam splitter (5) splits the modulated light into local oscillator light and probe light, which are then sent to the second fiber coupler (19) and the first wavelength division multiplexer (6), respectively. Step S4, the first wavelength division multiplexer (6) combines the light of the two wavelengths into a composite probe light and inputs it into the optical circulator (7); In step S5, the optical circulator (7) outputs the composite probe light to the multi-core fiber fan-in fan-out device (8). The composite probe light passes through the output port of the multi-core fiber fan-in fan-out device (8), the multi-core fiber (9), the optical collimator (10), and finally exits through the transmitting and receiving telescope (11) to illuminate the target object (12). Step S6: The echo signal reflected by the target object (12) passes through the input and output ports (8-1) of the transmitting and receiving telescope (11), the optical collimator (10), the multi-core fiber (9), and the multi-core fiber fan-in and fan-out device (8) in sequence, enters the optical circulator (7) from the second port of the optical circulator (7), and finally reaches the second wavelength division multiplexer (13). Step S7, the second wavelength division multiplexer (13) divides the echo signal to obtain two wavelength signals. The first wavelength division multiplexer with wavelength λ1 is output to the second fiber coupler (19), and the second wavelength division multiplexer with wavelength λ2 is output to the first fiber coupler (14). The first fiber coupler (14) inputs the second wavelength division multiplexer to the first branch fiber (15) and the second branch fiber (16) respectively. Step S8, the second fiber coupler (19) combines the local oscillator light output from the 1×2 fiber beam splitter (5) with the first wavelength division multiplexer (13) and then splits it into two paths to output to the balanced detector (20). Step S9, the balance detector (20) performs beat frequency and obtains the intermediate frequency signal of the axial velocity in the z direction; In step S10, the echo signals are output through ports (8-2) and (8-4) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the first filter (23-1) and the second filter (23-2), they become two echo signals with a wavelength of λ2 and enter the first branch fiber (15); the echo signals are output through ports (8-3) and (8-5) of the multi-core fiber fan-in fan-out unit (8), and after being filtered by the third filter (23-3) and the fourth filter (23-4), they become two echo signals with a wavelength of λ2 and enter the second branch fiber (16); In step S11, the first branched fiber (15) inputs three signals with wavelength λ2 in the x-axis direction into the first photodetector (17); the second branched fiber (16) inputs three signals with wavelength λ2 in the y-axis direction into the second photodetector (18). Step S12: The data acquisition card (21) acquires the output signal of the first photodetector (17), the output signal of the second photodetector (18), and the output signal of the balance detector (20), and outputs the three sets of acquired signals to the host computer (22). In step S13, the host computer (22) receives the three sets of electrical signals collected by the data acquisition card (21) and performs speed and distance measurement of the target object.

5. The three-dimensional velocity and distance measurement method of frequency-modulated continuous wave lidar based on multi-core optical fiber as described in claim 4, characterized in that: z-axis distance R and velocity v z The calculation formula is: In the formula, T is the modulation period of the linear frequency modulated signal, B is the modulation bandwidth of the linear frequency modulated signal, c is the speed of light, and λ1 is the wavelength of the modulated light; the signal transmitted by the balanced detector (20) includes the electrical signal corresponding to the local oscillator light and the electrical signal corresponding to the first wave division. The host computer is used to perform Fourier transform on the signal transmitted by the balanced detector (20) in the rising and falling frequency bands of the triangular wave to obtain two beat frequencies f. up and f duwn f up >f duwn ; velocity v along the x-axis x and the velocity v in the y-axis direction y The calculation formula is: v x =p x f x v y =p y f y In the formula, f x f is the output signal frequency of the first photodetector (17). y p is the output signal frequency of the second photodetector (18). x It is the distance between the cores in the x-direction of the multi-core optical fiber (9), p y It is the distance between the cores in the y-direction of the multi-core optical fiber (9); Total radial velocity v xy The calculation formula is: Among them, v x Direction and v xy The angle between the directions is θ:

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