Frequency Modulated Continuous Wave 3D Lidar Capture System and Method Based on FDML

Abstract

The present invention relates to the field of laser radar ranging technology, and in particular to a frequency modulated continuous wave three-dimensional laser radar capture system and method based on FDML. The system includes: a three-dimensional turntable unit, used to obtain the direction information of the target to be measured; a scanning light source unit, used to emit laser in the direction of the target to be measured based on the FDML technology according to the direction information of the target to be measured, and lock the position of the target to be measured; a fiber optic interference unit, used to receive the laser signal reflected by the target and obtain an electrical signal; a signal acquisition and processing unit, used to obtain the distance and speed of the target to be measured based on the electrical signal. The system solves the technical problems of low resolution and measurement accuracy of frequency modulated continuous wave laser ranging and single measurement results.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar ranging, and in particular to a frequency modulated continuous wave three-dimensional laser radar capture system and method based on FDML. Background Art

[0002] LiDAR is a non-contact, active optical ranging system characterized by high ranging accuracy, excellent real-time performance, high resolution, clear directionality, and strong anti-interference capabilities. It can stably and reliably measure information such as the distance, size, and intensity of target objects in space. In areas such as autonomous driving and robotic 3D vision, LiDAR can provide high-resolution point cloud data and 3D scene reconstruction, unaffected by external factors (such as day and night, temperature, environment, and weather).

[0003] Among the many types of lidar, frequency-modulated continuous-wave lidar has the characteristics of simple processing circuit, low power, compact structure, light weight and low power consumption. It can simultaneously measure the speed and distance of the target. It occupies an important position in the field of high-precision large-scale space measurement, and has broad development space and prospects.

[0004] While frequency-modulated continuous-wave laser ranging offers numerous advantages, it has historically been limited by the laser's modulation range and linearity, which has hampered the resolution and accuracy of laser measurements. Furthermore, existing lidar test results are limited, and it cannot simultaneously measure distance and velocity. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a frequency modulated continuous wave three-dimensional lidar capture system and method based on FDML, which solves the technical problems of low resolution and measurement accuracy of frequency modulated continuous wave laser ranging and single measurement results.

[0007] (2) Technical solution

[0008] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] In a first aspect, an embodiment of the present invention provides a frequency modulated continuous wave three-dimensional laser radar acquisition system based on FDML, comprising:

[0010] A three-dimensional turntable unit is used to obtain the direction information of the target to be measured;

[0011] The scanning light source unit is used to emit laser light in the direction of the target to be measured based on the FDML technology according to the direction information of the target to be measured, and lock the position of the target to be measured;

[0012] A fiber optic interferometer unit is used to receive the laser signal reflected by the target and obtain an electrical signal;

[0013] The signal acquisition and processing unit is used to obtain the distance and speed of the target to be measured based on the electrical signal.

[0014] The FDML-based frequency modulated continuous wave three-dimensional lidar acquisition system proposed in an embodiment of the present invention first uses a three-dimensional turntable unit to obtain directional information of the target to be measured. Then, based on FDML technology and coherent detection, it achieves a swept laser output with high scanning speed, wide scanning range, narrow instantaneous linewidth and high phase stability. This can make the lidar's ranging accuracy higher, the response time faster, and the stability better, realizing high-precision distance and speed measurement.

[0015] Optionally, the three-dimensional turntable unit includes a horizontal hollow rotating platform and a vertical hollow rotating platform, wherein the rotation angle of the horizontal hollow rotating platform is 180° and the rotation angle of the vertical hollow rotating platform is 360°;

[0016] The horizontal hollow rotating platform and the vertical hollow rotating platform are both connected to the signal acquisition and processing unit.

[0017] Optionally, a camera and a liquid lens are provided on the three-dimensional turntable unit, and the camera and the liquid lens rotate along with the horizontal hollow rotating platform and the vertical hollow rotating platform;

[0018] The camera and the liquid lens are both connected to a signal acquisition and processing unit.

[0019] Optionally, the scanning light source unit selects an FDML laser as the light source of the frequency modulated continuous wave laser radar acquisition system, and the FDML laser includes a driving circuit, a filter, a first optical isolator, a semiconductor amplifier, a second optical isolator, a dispersion compensation optical fiber and a first optical fiber coupler connected in sequence;

[0020] The driving circuit is used to emit a frequency-sweeping laser, which sequentially passes through a filter, a first optical isolator, a semiconductor amplifier, a second optical isolator, a dispersion-compensating optical fiber, and a first optical fiber coupler;

[0021] The first fiber coupler is used to split the frequency-sweeping laser into a channel A frequency-sweeping laser and a channel B frequency-sweeping laser. The splitting ratio of the first fiber coupler is 20:80.

[0022] Among them, the A-path swept laser serves as the output of the FDML laser and outputs 20% of the swept laser energy; the B-path swept laser returns to the ring resonator of the FDML laser and outputs 80% of the swept laser energy.

[0023] Optionally, the fiber interferometer unit includes a second fiber coupler, a third fiber coupler, a circulator, a transceiver, a target to be measured, a fourth fiber coupler, a first photodetector, a fifth fiber coupler, a sixth fiber coupler, and a second photodetector;

[0024] The second optical fiber coupler is connected to the third optical fiber coupler, the circulator, the transceiver device, and the target to be measured in sequence;

[0025] The fourth optical fiber coupler and the first photodetector are connected in sequence;

[0026] The second optical fiber coupler is also connected to the sixth optical fiber coupler and the second photodetector in sequence;

[0027] The second fiber coupler is used to split the A-channel sweep laser into the C-channel sweep laser and the D-channel sweep laser, and the splitting ratio of the second fiber coupler is 50:50;

[0028] The C-channel sweep laser outputs 50% of the sweep laser energy to the third optical fiber coupler; the D-channel sweep laser outputs 50% of the sweep laser energy to the fifth optical fiber coupler.

[0029] Optionally, the third optical fiber coupler is used to split the C-channel swept laser into the C1-channel swept laser and the C2-channel swept laser, and the splitting ratio of the third optical fiber coupler is 50:50;

[0030] The C1-channel swept-frequency laser enters the fourth fiber coupler through the time-delayed optical fiber; the C2-channel swept-frequency laser is sequentially transmitted through the circulator and the transceiver to the target to be measured. The transceiver receives the reflected laser light reflected from the target to be measured. The reflected laser light passes through the circulator and enters the fourth fiber coupler, where it undergoes difference frequency interference with the C1-channel swept-frequency laser light to generate an outgoing light signal.

[0031] The first photodetector is used to convert the outgoing light signal into a first electrical signal through photoelectric conversion.

[0032] Optionally, the fifth optical fiber coupler is used to split the D-channel swept laser into the D1-channel swept laser and the D2-channel swept laser, and the splitting ratio of the fifth optical fiber coupler is 50:50;

[0033] Among them, the D1 channel swept frequency laser enters the sixth fiber coupler through the delay fiber; the D2 channel swept frequency laser enters the sixth fiber coupler through the single-mode fiber, and generates difference frequency interference with the D1 channel swept frequency laser to generate an echo signal;

[0034] The second photodetector is used to convert the echo signal into a second electrical signal through photoelectric conversion.

[0035] Optionally, the signal acquisition and processing unit includes an FPGA and a computer, the FPGA is used to receive the first electrical signal and the second electrical signal, perform a difference between the first electrical signal and the second electrical signal to obtain a main frequency of a difference frequency signal, obtain the distance and speed of the target to be measured according to the main frequency of the difference frequency signal and in combination with parameter information of the FDML laser, and store the distance and speed in the computer.

[0036] Optionally, six interfaces are provided on the FPGA, namely, a camera information interface for connecting to a camera, a ranging interface for connecting to a fiber optic interference unit, a liquid lens control interface for connecting to a liquid lens, a horizontal turntable control interface for connecting to a horizontal turntable, a vertical turntable control interface for connecting to a vertical turntable, and a communication interface for connecting to a computer.

[0037] In a second aspect, an embodiment of the present invention provides a frequency modulated continuous wave 3D laser radar acquisition method based on FDML. The method is based on the frequency modulated continuous wave 3D laser radar acquisition system based on FDML described in any of the above solutions, and includes the following steps:

[0038] S1. Obtain the direction information of the target to be measured;

[0039] S2. Based on the direction information of the target to be measured, a laser is emitted in the direction of the target to be measured based on the FDML technology to lock the position of the target to be measured;

[0040] S3, using a coherent detection method to receive the laser signal reflected by the target and obtain an electrical signal;

[0041] S4. Obtain the distance and speed of the target to be measured based on the electrical signal.

[0042] The FDML-based frequency modulated continuous wave three-dimensional lidar acquisition method proposed in the embodiment of the present invention obtains the direction information of the target to be measured. Based on the FDML technology and coherent detection method, it realizes a swept laser output with high scanning speed, wide scanning range, narrow instantaneous linewidth and high phase stability. It can make the lidar's ranging accuracy higher, the response time faster, and the stability better, and realize high-precision distance and speed measurement.

[0043] (3) Beneficial effects

[0044] The beneficial effects of the present invention are as follows: the FDML-based frequency modulated continuous wave three-dimensional laser radar capture system and method of the present invention adopts an FDML laser as a swept-frequency light source of the laser radar capture system, and the laser operates in a quasi-stable state. The FDML technology overcomes the limitations of existing swept-frequency light sources in terms of output power, sweeping speed, and spectral linewidth, and realizes a swept-frequency laser output with high scanning speed, wide scanning range, narrow instantaneous linewidth, and high phase stability. It can make the laser radar's ranging accuracy higher, the response time faster, and the stability better, realize three-dimensional capture of the target to be measured, and perform high-precision distance and speed measurement. At the same time, the system structure is simple and compact, saves space, and has strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a structural block diagram of the FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system of the present invention;

[0046] Figure 2 Schematic diagram of the structure of the scanning light source unit in the present invention;

[0047] Figure 3 Schematic diagram of the structure of the optical fiber interference unit in the present invention;

[0048] Figure 4 Schematic diagram of the structure of the signal acquisition and processing unit in the present invention;

[0049] Figure 5 This is a schematic diagram of the FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system of the present invention;

[0050] Figure 6 This is a flow chart of the FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition method of the present invention.

[0051] [Description of Reference Numerals]

[0052] 1: driving circuit; 2: filter; 3: first optical isolator; 4: semiconductor amplifier; 5: second optical isolator; 6: dispersion-compensating fiber; 7: first fiber coupler; 8: second fiber coupler; 9: third fiber coupler; 10: circulator; 11: transceiver; 12: target to be measured; 13: fourth fiber coupler; 14: first photodetector; 15: fifth fiber coupler; 16: sixth fiber coupler; 17: second photodetector; 18: FPGA; 19: computer. DETAILED DESCRIPTION

[0053] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0054] The FDML-based frequency modulated continuous wave (FMCW) 3D lidar acquisition system and method proposed in this invention combines an FDML mode-locked swept laser source with FMCW ranging to achieve high-precision 3D target capture and simultaneous distance and velocity measurement. This system features target capture, simple structure, fast measurement speed, high accuracy, and strong anti-interference capabilities.

[0055] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Instead, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0056] Example 1

[0057] This embodiment provides a frequency modulated continuous wave three-dimensional laser radar acquisition system based on FDML technology, such as Figure 1 As shown, the system includes a 3D turntable unit, a scanning light source unit, a fiber optic interferometer unit, and a signal acquisition and processing unit. The 3D turntable unit is used to obtain the direction information of the target to be measured. The scanning light source unit is used to emit laser light in the direction of the target to be measured based on the FDML technology, thereby locking the position of the target to be measured. The fiber optic interferometer unit is used to receive the laser signal reflected by the target and generate an electrical signal. The signal acquisition and processing unit is used to obtain the distance and speed of the target to be measured based on the electrical signal.

[0058] The 3D turntable unit consists of a horizontal hollow rotating platform and a vertical hollow rotating platform. The horizontal platform rotates 180°, while the vertical platform rotates 360°. A camera and a liquid lens are mounted on the 3D turntable unit, rotating in tandem with the horizontal and vertical platforms. The interfaces of these platforms, the camera, and the liquid lens are all connected to the FPGA.

[0059] Furthermore, assuming that the plane normal vector of the rectangular reflector is in the reference position, for:

[0060]

[0061] To clearly describe the change relationship, the angle of rotation of the turntable horizontal axis around itself is the pitch angle, which is positive in counterclockwise direction and is set to γ; the angle of rotation of the turntable vertically around its own axis is the yaw angle, which is positive in counterclockwise direction and is set to Then any angle coordinate for:

[0062]

[0063] Assumption O L , O C are the intersection points of the laser optical axis of the scanning laser light source and the optical axis of the 3D turntable unit camera on the plane of the rectangular reflector, G L is the position of the guiding light spot emitted by the current scanning light source. Based on the space vector plane mirror reflection law, G L The spatial point positioning vector for:

[0064]

[0065] Where L is the intersection point O L To the guiding light point G L distance.

[0066] Assuming that there is a point M(x, y, z) on the mirror surface of the current rectangular reflector, the plane equation of the rectangular reflector when the turntable is in the reference position is:

[0067]

[0068] According to G L The spatial point positioning vector of the target to be measured can be obtained by for:

[0069]

[0070] Where P is the target to be measured, L' is the intersection point O L The distance to the target, γ', are the pitch angle and yaw angle of the rectangular reflector when the target is captured, L', γ' and All are unknown quantities.

[0071] Assumption O C ' is the reflection point of the camera lens about the rectangular reflector in the current position, G C is the intersection of the camera optical axis and the target imaging surface after being reflected by the reflector, and the equivalent camera optical axis vector can be obtained for:

[0072]

[0073] Where d is the distance between the optical axis of the scanning laser light source and the optical axis of the 3D turntable unit camera, and D is the guide light point G. L The exit point and the intersection point O L distance.

[0074] Assume that the coordinates of the target to be measured are (x p ,yp ), intersection point G C The coordinates of (x gc ,y gc ), since the equivalent camera optical axis vector has been obtained above, the image coordinates of the image of the target to be measured taken by the camera in the reflector can be equivalent to the image coordinates of the image of the target to be measured at the symmetrical point of the camera lens with respect to the current reflector, and the projection angle α of the target to be measured relative to the equivalent camera optical axis on the X axis can be obtained. H and the projection angle α on the Y axis v :

[0075]

[0076]

[0077] Where H is the horizontal resolution of the captured image, W is the vertical resolution of the captured image, α is the horizontal viewing angle of the camera, and β is the vertical viewing angle of the camera.

[0078] Since the projection angle α H and α v The positive or negative value of is uncertain, and needs to be discussed in different cases to obtain the projection angle α H and α v The sine of the target is obtained by the sine theorem.

[0079]

[0080] Based on the spatial point positioning vector of the target P to be measured Get the pitch angle γ' and yaw angle of the turntable when capturing the target to be measured

[0081]

[0082]

[0083] Where x OLP is the coordinate of the spatial point of the target to be measured along the x-axis, y OLP is the coordinate of the spatial point of the target to be measured along the y-axis, z OLP is the coordinate of the spatial point of the target to be measured along the z-axis.

[0084] Based on the above pitch angle γ' and yaw angle The three-dimensional turntable unit can realize the control of rotating the guide light spot to the target to be measured.

[0085] The camera is used to capture the position of the target to be measured and feed it back to the FPGA. At the same time, the camera is used to capture the focused spot of the guide laser at the position of the target to be measured. The driving current value of the liquid lens is adjusted by analyzing the size of the focused spot. When the focused spot size reaches the minimum value, the driving current stops changing.

[0086] The liquid lens is used to focus on the position of the target to be measured. The liquid lens uses a guide laser with a visible light wavelength and a measuring laser with a wavelength of 1550nm. During the measurement process, the guide laser is first used to find the position of the target to be measured. After the guide laser locates the target point, the distance to the target point is measured after the target point is accurately located. That is, in the guidance stage, the guide laser locates the target point, and the camera-assisted feedback is used to adjust the driving current value of the liquid lens to ensure that the guide laser reaches the optimal focusing state and the focused spot is minimized. The second step is to measure the focus of the laser, and then enter the measurement stage from the guidance stage. Through calculation, the driving current coding value of the liquid lens when the guide laser is optimally focused is converted into the driving current coding value required for the measuring laser 1550nm to achieve the optimal focusing state. The converted current coding is output to the liquid lens, which can achieve one-step rapid focusing of the ranging laser.

[0087] The scanning light source unit uses FDML laser as the light source of the frequency modulated continuous wave three-dimensional laser radar capture system, such as Figure 2 As shown, the FDML laser includes a sequentially connected drive circuit 1, filter 2, first optical isolator 3, semiconductor amplifier 4, second optical isolator 5, dispersion-compensating fiber 6, and first fiber coupler 7. Filter 2 is controlled on and off by the drive circuit 1. Its typical operating wavelength is 1550 nm, its tuning voltage range is -20 to 50 V, and its free spectrum range is 50 to 60 nm. Specifically, a swept laser beam, emitted under the control of the drive circuit 1, passes sequentially through the filter 2, first optical isolator 3, semiconductor amplifier 4, second optical isolator 5, dispersion-compensating fiber 6, and first fiber coupler 7. After passing through the first fiber coupler 7, it is split into swept laser beam A and swept laser beam B. The splitting ratio of the first fiber coupler 7 is 20:80. Sweep laser beam A serves as the output of the FDML laser, delivering 20% ​​of the swept laser energy. Sweep laser beam B returns to the ring resonator of the FDML laser, circulates throughout the process, and delivers 80% of the swept laser energy.

[0088] Furthermore, the FDML laser differs from conventional lasers in that it employs dispersion-compensating fiber 6 for dispersion management, and the period of the driving voltage of the narrowband optical filter 2 matches the time it takes for the swept laser to propagate one cycle within the ring resonator, meaning the two times are equal or the latter is an integer multiple of the former. This creates a quasi-steady-state mode, where the period of the driving voltage of filter 2 is equal to the time it takes for the swept laser to propagate one cycle around the ring resonator. This allows the swept laser of a certain frequency or wavelength to propagate through filter 2 once within the ring resonator and then return to filter 2, where the cavity length of filter 2 is precisely tuned to allow the swept laser to pass through. This allows the swept laser from the previous loop cycle to couple back into the gain medium, eliminating the need for the establishment of the swept laser to rely solely on the spontaneous emission of the gain medium. This allows each longitudinal mode to be precisely locked, achieving continuous swept laser output.

[0089] like Figure 3 As shown, the fiber interferometer unit includes a second fiber coupler 8, a third fiber coupler 9, a circulator 10, a transceiver 11, a target 12, a fourth fiber coupler 13, a first photodetector 14, a fifth fiber coupler 15, a sixth fiber coupler 16, and a second photodetector 17. After passing through the second fiber coupler 8, the A-path swept laser is split into the C-path swept laser and the D-path swept laser. The second fiber coupler 8 has a 50:50 splitting ratio, wherein the C-path swept laser outputs 50% of the swept laser energy and is output to the third fiber coupler 9, and the D-path swept laser outputs 50% of the swept laser energy and is output to the fifth fiber coupler 15.

[0090] After passing through the third fiber coupler 9, the C-channel swept-frequency laser is split into the C1-channel swept-frequency laser and the C2-channel swept-frequency laser. The splitting ratio of the third fiber coupler 9 is 50:50. The C1-channel swept-frequency laser enters the fourth fiber coupler 13 through the delay fiber, and the C2-channel swept-frequency laser is sequentially transmitted through the circulator 10 and the transceiver 11 to the target to be measured 12. The transceiver 11 receives the reflected laser reflected from the target to be measured 12. The reflected laser passes through the circulator 10 and enters the fourth fiber coupler 13, where it undergoes difference frequency interference with the C1-channel swept-frequency laser to generate an outgoing light signal. The outgoing light signal is received by the first photodetector 14, and the first photodetector 14 converts the outgoing light signal into a first electrical signal through photoelectric conversion.

[0091] After passing through the fifth fiber coupler 15, the D-channel swept-frequency laser is split into the D1-channel swept-frequency laser and the D2-channel swept-frequency laser. The splitting ratio of the fifth fiber coupler 15 is 50:50. The D1-channel swept-frequency laser enters the sixth fiber coupler 16 through the delay fiber, and the D2-channel swept-frequency laser enters the sixth fiber coupler 16 through the ordinary single-mode fiber. It undergoes difference frequency interference with the D1-channel swept-frequency laser, generating an echo signal. The echo signal is received by the second photodetector 17, and the second photodetector 17 converts the echo signal into a second electrical signal through photoelectric conversion.

[0092] Furthermore, the C-path swept laser and the D-path swept laser form a dual interference optical path. The two laser beams are emitted by the same light source, of which the C-path swept laser serves as the measurement interference optical path, and the D-path swept laser is a Mach-Zehnder interference optical path, serving as an auxiliary interference optical path. The delay optical fiber is used to increase the optical path and perform equal-frequency resampling on the echo signal, which can effectively eliminate the influence of the FDML laser modulation nonlinearity and play a role in noise reduction.

[0093] Measure the outgoing light signal S of the interference optical path (C-path sweep laser) TX (t) is:

[0094]

[0095] Where A is the amplitude, j is the imaginary unit, f0 is the initial frequency of FM, t is the modulation time, t∈[0,T m ], T m is the triangle wave modulation period, α0 is the frequency modulation slope, B is the operating bandwidth of the scanning light source.

[0096] The echo signal S of the auxiliary interference optical path (D-path sweep laser) RX (t) is:

[0097]

[0098] Where t' is the echo signal transmission time, t'∈[τ,T m +τ], τ is the time required for the object to be measured to transmit the echo signal, D is the distance to the target, and c is the speed of light.

[0099] Outgoing light signal S TX (t) and the echo signal S RX (t) The optical beat signal S generated by the encounter LB (t) When the beat frequency is stable:

[0100]

[0101] Where t" is the time difference generated by the optical beat signal, t"∈[τ,Tm ].

[0102] If you use f B represents the stable frequency of the optical beat signal, then:

[0103] f B =α0τ (4).

[0104] like Figure 4 As shown, the signal acquisition and processing unit includes an FPGA 18 and a computer 19. The FPGA 18 receives the first electrical signal from the first photodetector 14 and the second electrical signal from the second photodetector 17, processes the first electrical signal and the second electrical signal to obtain the distance and speed of the target 12 to be measured, and stores the distance and speed of the target 12 to be measured in the computer 19. The FPGA 18 is provided with six interfaces, namely, a camera information interface for connecting to a camera, a distance measurement interface for connecting to a fiber optic interferometer unit, a liquid lens control interface for connecting to a liquid lens, a horizontal turntable control interface for connecting to a horizontal turntable, a vertical turntable control interface for connecting to a vertical turntable, and a communication interface for connecting to the computer 19. In addition, the FPGA 18 is powered by the driving circuit 1 in the scanning light source unit. The communication interface is connected to the USB interface to provide physical layer support for the network.

[0105] Furthermore, the FPGA 18 is used to perform a difference operation on the first electrical signal and the second electrical signal to obtain a main frequency of a difference frequency signal. Based on the main frequency of the difference frequency signal and in combination with the parameter information of the FDML laser, the distance R and the speed V of the target 12 to be measured are obtained:

[0106] The distance D of the target 12 to be measured and the speed V of the target to be measured are respectively:

[0107]

[0108]

[0109] Where λ is the measurement laser wavelength.

[0110] like Figure 5 FIG. 1 is a schematic diagram of a FDML-based 3D laser radar capture system, which includes the following steps:

[0111] 101. The three-dimensional turntable platform rotates, and the rotation angle is controlled through the horizontal turntable control interface and the vertical turntable control interface to start capturing the target to be measured;

[0112] 102. The camera captures the position of the target to be measured and feeds the position of the target to be measured back to the FPGA. At the same time, the camera is used to capture the focused spot of the guide laser at the position of the target to be measured;

[0113] 103. Liquid lens focusing: During the measurement process, the guide laser and the measuring laser are used to focus on the target to obtain the direction information of the target;

[0114] 104. The FDML laser emits laser light in the direction of the target according to the direction information of the target;

[0115] 105. Receive the laser signal reflected by the target and obtain an electrical signal;

[0116] 106. Obtain the distance and speed of the target to be measured based on the electrical signal.

[0117] Example 2

[0118] This embodiment provides a frequency modulated continuous wave three-dimensional laser radar acquisition method based on FDML, such as Figure 6 The method is based on the FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system provided in Example 1, and includes the following steps:

[0119] S1, the three-dimensional turntable platform rotates to obtain the direction information of the target to be measured;

[0120] S2. Based on the direction information of the target to be measured, a laser is emitted in the direction of the target to be measured based on the FDML technology to lock the position of the target to be measured;

[0121] S3, using a coherent detection method to receive the laser reflected by the target to be measured and obtain an electrical signal;

[0122] S4. Obtain the distance and speed of the target to be measured based on the electrical signal.

[0123] In summary, the FDML-based frequency modulated continuous wave (FMCW) 3D lidar acquisition system and method provided by the present invention combines an FDML mode-locked swept laser source with FMCW ranging for the first time, enabling high-precision 3D capture of target objects and simultaneous distance and velocity measurement. This system is particularly suitable for close-range, high-precision distance and velocity testing of objects, enabling the acquisition of targets. Its simple structure, fast measurement speed, high accuracy, and strong anti-interference capabilities make it highly commercially viable and offer broad application prospects.

[0124] By combining a camera with a three-dimensional rotating platform, a preliminary capture of the target to be measured can be achieved. Liquid lens focusing is used to quickly and accurately lock the focus on the target object, thereby effectively improving the accuracy of the system. The use of an FDML laser as a swept-frequency light source can overcome the limitations of existing swept-frequency light sources in terms of output power, sweep speed, and spectral linewidth, and achieve a swept-frequency laser output with high scanning speed, wide scanning range, narrow instantaneous linewidth, and high phase stability. This can make the laser radar's ranging accuracy higher, the response time faster, and the stability better. The light interference unit uses signal difference frequency processing and interference noise reduction. This method is low-cost and effective, and can reduce the amount of data calculation, thereby improving the system's operating speed.

[0125] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0126] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0127] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0128] In the description of this specification, the terms "one embodiment", "some embodiments", "embodiments", "examples", "specific examples" or "some examples" refer to the specific features, structures, materials or characteristics described in conjunction with the embodiment or example and included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0129] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A frequency modulated continuous wave three-dimensional laser radar acquisition system based on FDML, characterized in that: include: A three-dimensional turntable unit, used to obtain the direction information of the target to be measured; The scanning light source unit is used to emit laser in the direction of the target to be measured based on the FDML technology according to the direction information of the target to be measured, and lock the position of the target to be measured; The optical fiber interference unit is used to receive the laser signal reflected by the target by coherent detection and obtain an electrical signal; A signal acquisition and processing unit, used to obtain the distance and speed of the target to be measured based on the electrical signal; The scanning light source unit uses an FDML laser as the light source of the frequency modulated continuous wave laser radar capture system, and the FDML laser comprises a driving circuit (1), a filter (2), a first optical isolator (3), a semiconductor amplifier (4), a second optical isolator (5), a dispersion compensation optical fiber (6) and a first optical fiber coupler (7) which are connected in sequence; The driving circuit (1) is used to emit a frequency-sweeping laser, which sequentially passes through a filter (2), a first optical isolator (3), a semiconductor amplifier (4), a second optical isolator (5), a dispersion-compensating optical fiber (6), and a first optical fiber coupler (7); The first optical fiber coupler (7) is used to split the frequency-sweeping laser into a frequency-sweeping laser on a path A and a frequency-sweeping laser on a path B, and the splitting ratio of the first optical fiber coupler (7) is 20:80; Among them, the A-path swept laser is used as the output of the FDML laser, outputting 20% ​​of the swept laser energy; the B-path swept laser returns to the ring resonator of the FDML laser, outputting 80% of the swept laser energy; The optical fiber interference unit comprises a second optical fiber coupler (8), a third optical fiber coupler (9), a circulator (10), a transceiver device (11), a target to be measured (12), a fourth optical fiber coupler (13), a first photodetector (14), a fifth optical fiber coupler (15), a sixth optical fiber coupler (16) and a second photodetector (17); The second optical fiber coupler (8) is connected in sequence to the third optical fiber coupler (9), the circulator (10), the transceiver device (11), and the target to be measured (12); The fourth optical fiber coupler (13) and the first photodetector (14) are connected in sequence; The second optical fiber coupler (8) is also connected to the sixth optical fiber coupler (16) and the second photoelectric detector (17) in sequence; The second optical fiber coupler (8) is used to split the A-channel frequency-sweeping laser into the C-channel frequency-sweeping laser and the D-channel frequency-sweeping laser, and the splitting ratio of the second optical fiber coupler (8) is 50:50; The C-path sweep laser outputs 50% of the sweep laser energy and is output to the third optical fiber coupler (9); the D-path sweep laser outputs 50% of the sweep laser energy and is output to the fifth optical fiber coupler (15).

2. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system according to claim 1, characterized in that: The three-dimensional turntable unit includes a horizontal hollow rotating platform and a vertical hollow rotating platform, wherein the rotation angle of the horizontal hollow rotating platform is 180°, and the rotation angle of the vertical hollow rotating platform is 360°; The horizontal hollow rotating platform and the vertical hollow rotating platform are both connected to the signal acquisition and processing unit.

3. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system as claimed in claim 2, characterized in that: The three-dimensional turntable unit is provided with a camera and a liquid lens, and the camera and the liquid lens rotate following the horizontal hollow rotating platform and the vertical hollow rotating platform; The camera and the liquid lens are both connected to a signal acquisition and processing unit.

4. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system according to claim 1, characterized in that: The third optical fiber coupler (9) is used to split the C-channel swept laser into the C1-channel swept laser and the C2-channel swept laser, and the splitting ratio of the third optical fiber coupler (9) is 50:50; The C1-channel swept-frequency laser enters the fourth optical fiber coupler (13) through the time-delay optical fiber; the C2-channel swept-frequency laser is sequentially transmitted through the circulator (10) and the transceiver device (11) to the target to be measured (12); the transceiver device (11) receives the reflected laser reflected from the target to be measured (12); the reflected laser passes through the circulator (10) and enters the fourth optical fiber coupler (13), and generates difference frequency interference with the C1-channel swept-frequency laser to generate an output optical signal; The first photodetector (14) is used to convert the output light signal into a first electrical signal through photoelectric conversion.

5. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system according to claim 1, characterized in that: The fifth optical fiber coupler (15) is used to split the D-channel swept-frequency laser into the D1-channel swept-frequency laser and the D2-channel swept-frequency laser, and the splitting ratio of the fifth optical fiber coupler (15) is 50:50; The D1-channel swept-frequency laser enters the sixth optical fiber coupler (16) through the time-delay optical fiber; the D2-channel swept-frequency laser enters the sixth optical fiber coupler (16) through the single-mode optical fiber, and generates difference frequency interference with the D1-channel swept-frequency laser to generate an echo signal; The second photodetector (17) is used for converting the echo signal into a second electrical signal through photoelectric conversion.

6. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system as claimed in claim 5, characterized in that: The signal acquisition and processing unit comprises an FPGA (18) and a computer (19), wherein the FPGA (18) is used to receive a first electrical signal and a second electrical signal, perform a difference operation on the first electrical signal and the second electrical signal to obtain a main frequency of a difference frequency signal, obtain a distance and a speed of a target to be measured (12) based on the main frequency of the difference frequency signal and in combination with parameter information of an FDML laser, and store the distance and the speed in the computer (19).

7. The FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system according to claim 6, characterized in that: The FPGA (18) is provided with six interfaces, namely, a camera information interface for connecting to a camera, a distance measurement interface for connecting to a fiber optic interference unit, a liquid lens control interface for connecting to a liquid lens, a horizontal turntable control interface for connecting to a horizontal turntable, a vertical turntable control interface for connecting to a vertical turntable, and a communication interface for connecting to a computer (19).

8. A frequency modulated continuous wave three-dimensional laser radar acquisition method based on FDML, characterized in that: The method is based on the FDML-based frequency modulated continuous wave three-dimensional laser radar acquisition system described in any one of claims 1 to 7, and comprises the following steps: S1. Obtaining the direction information of the target to be measured; S2, according to the direction information of the target to be measured, based on the FDML technology, emit laser in the direction of the target to be measured, and lock the position of the target to be measured; S3, receiving the laser signal reflected by the target by coherent detection and obtaining an electrical signal; S4. Obtain the distance and speed of the target to be measured based on the electrical signal.

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