CN112526537A - Frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML - Google Patents

Frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML Download PDF

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Publication number
CN112526537A
CN112526537A CN202011380065.5A CN202011380065A CN112526537A CN 112526537 A CN112526537 A CN 112526537A CN 202011380065 A CN202011380065 A CN 202011380065A CN 112526537 A CN112526537 A CN 112526537A
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China
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laser
target
fiber coupler
fdml
sweep
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Inventor
徐迎彬
邵理阳
林伟浩
赵方
陈云
余飞宏
柳钰慧
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Southwest University of Science and Technology
Southern University of Science and Technology
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Southwest University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4911—Transmitters

Abstract

The invention relates to the technical field of laser radar ranging, in particular to a frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML. The system comprises: the three-dimensional turntable unit is used for acquiring direction information of the target to be detected; the scanning light source unit is used for emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected and locking the position of the target to be detected; the optical fiber interference unit is used for receiving the laser signal reflected by the target and obtaining an electric signal; and the signal acquisition and processing unit is used for obtaining the distance and the speed of the target to be detected based on the electric signals. The technical problems of low resolution and measurement precision and single measurement result of frequency modulation continuous wave laser distance measurement are solved.

Description

Frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML
Technical Field
The invention relates to the technical field of laser radar ranging, in particular to a frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML.
Background
The laser radar is a non-contact active optical ranging system, has the characteristics of high ranging precision, good real-time performance, high resolution, definite directivity and strong anti-interference capability, and can stably and reliably measure the information such as the distance, the size, the strength and the like of a target object in a space. In the fields of automobile unmanned driving, robot three-dimensional vision and the like, the laser radar can provide high-resolution point cloud data and a three-dimensional scene reconstruction function and cannot be interfered by external factors (such as day and night, temperature, environment, weather and the like).
Among various laser radars, the frequency modulation continuous wave laser radar has the characteristics of simple processing circuit, low power, compact structure, light weight, low power consumption and the like, can simultaneously measure two parameters of the speed and the distance of a target, plays an important role in the field of high-precision large-size space measurement, and has very wide development space and prospect.
Although there are many advantages to fm cw laser ranging, it has been limited by the modulation range and modulation linearity of the laser, which affects the resolution and accuracy of the laser measurement. In addition, the existing laser radar has a single test result, and cannot simultaneously measure the distance and the speed.
Disclosure of Invention
Technical problem to be solved
In view of the above disadvantages and shortcomings of the prior art, the present invention provides a system and a method for capturing frequency modulated continuous wave three-dimensional lidar based on FDML, which solves the technical problems of low resolution and measurement accuracy of frequency modulated continuous wave lidar and single measurement result.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
in a first aspect, an embodiment of the present invention provides an FDML-based frequency modulated continuous wave three-dimensional lidar capturing system, including:
the three-dimensional turntable unit is used for acquiring direction information of the target to be detected;
the scanning light source unit is used for emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected and locking the position of the target to be detected;
the optical fiber interference unit is used for receiving the laser signal reflected by the target and obtaining an electric signal;
and the signal acquisition and processing unit is used for obtaining the distance and the speed of the target to be detected based on the electric signals.
According to the frequency modulation continuous wave three-dimensional laser radar capturing system based on the FDML, firstly, the three-dimensional turntable unit is used for obtaining the direction information of the target to be detected, and then based on the FDML technology and a coherent detection mode, the scanning laser output with high scanning speed, wide scanning range, narrow instantaneous line width and high phase stability is achieved, the distance measurement precision of the laser radar is higher, the response time is faster, the stability is better, and the high-precision distance and speed measurement is achieved.
Optionally, the three-dimensional turntable unit comprises a horizontal hollow rotary platform and a vertical hollow rotary platform, wherein the rotation angle of the horizontal hollow rotary platform is 180 degrees, and the rotation angle of the vertical hollow rotary platform is 360 degrees;
the horizontal hollow rotary platform and the vertical hollow rotary platform are both connected with the signal acquisition and processing unit.
Optionally, a camera and a liquid lens are arranged 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;
the camera and the liquid lens are both connected with the signal acquisition and processing unit.
Optionally, the scanning light source unit selects an FDML laser as a light source of the frequency modulation continuous wave laser radar capturing 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 fiber and a first fiber coupler which are connected in sequence;
the drive circuit is used for emitting sweep-frequency laser, and the sweep-frequency laser sequentially passes through the filter, the first optical isolator, the semiconductor amplifier, the second optical isolator, the dispersion compensation fiber and the first fiber coupler;
the first optical fiber coupler is used for dividing the sweep laser into an A-path sweep laser and a B-path sweep laser, and the splitting ratio of the first optical fiber coupler is 20: 80;
wherein, the A path of sweep frequency laser is used as the output of the FDML laser and outputs 20 percent of sweep frequency laser energy; the B-path swept laser returns to the ring resonator of the FDML laser, and 80% of swept laser energy is output.
Optionally, the optical fiber interference unit includes a second optical fiber coupler, a third optical fiber coupler, a circulator, a transceiver, a target to be measured, a fourth optical fiber coupler, a first photodetector, a fifth optical fiber coupler, a sixth optical fiber coupler, and a second photodetector;
the second optical fiber coupler is connected with the third optical fiber coupler, the circulator, the transceiver and the target to be detected in sequence;
the fourth optical fiber coupler is connected with the first photoelectric detector in sequence;
the second optical fiber coupler is also sequentially connected with the sixth optical fiber coupler and the second photoelectric detector;
the second optical fiber coupler is used for dividing the A-path sweep laser into a C-path sweep laser and a D-path sweep laser, and the splitting ratio of the second optical fiber coupler is 50: 50;
wherein, the C-path sweep laser outputs 50% of sweep laser energy to the third optical fiber coupler; the D-path sweep laser outputs 50% of sweep laser energy to the fifth fiber coupler.
Optionally, the third fiber coupler is configured to divide the C-path swept laser into a C1-path swept laser and a C2-path swept laser, and a splitting ratio of the third fiber coupler is 50: 50;
the C1-path sweep laser enters the fourth fiber coupler through the delay fiber; the C2-path sweep laser is transmitted to a target to be detected sequentially through the circulator and the transceiver, the transceiver receives reflected laser reflected from the target to be detected, the reflected laser enters the fourth optical fiber coupler after passing through the circulator and generates difference frequency interference with the C1-path sweep laser to generate an emitted light signal;
the first photoelectric detector is used for converting the emergent light signal into a first electric signal through photoelectric conversion.
Optionally, the fifth fiber coupler is configured to divide the D-path swept laser into a D1-path swept laser and a D2-path swept laser, and a splitting ratio of the fifth fiber coupler is 50: 50;
the D1-path sweep laser enters the sixth fiber coupler through the delay fiber; d2 sweep laser enters a sixth fiber coupler through a single mode fiber, and generates difference frequency interference with D1 sweep laser to generate an echo signal;
the second photoelectric detector is used for converting the echo signal into a second electric signal through photoelectric conversion.
Optionally, the signal acquisition and processing unit includes an FPGA and a computer, the FPGA is configured 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 difference frequency signal main frequency, obtain the distance and the speed of the target to be detected according to the difference frequency signal main frequency and by combining parameter information of the FDML laser, and store the distance and the speed in the computer.
Optionally, six interfaces are arranged on the FPGA, which are a camera information interface for connecting with a camera, a ranging interface for connecting with an optical fiber interference unit, a liquid lens control interface for connecting with a liquid lens, a horizontal turntable control interface for connecting with a horizontal turntable, a vertical turntable control interface for connecting with a vertical turntable, and a communication interface for connecting with a computer.
In a second aspect, an embodiment of the present invention provides an FDML-based frequency modulated continuous wave three-dimensional lidar capturing method, where the method is based on any one of the above schemes, and includes the following steps:
s1, acquiring direction information of the target to be detected;
s2, emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected, and locking the position of the target to be detected;
s3, receiving the laser signal reflected by the target by adopting a coherent detection mode and obtaining an electric signal;
and S4, obtaining the distance and the speed of the target to be measured based on the electric signals.
The frequency modulation continuous wave three-dimensional laser radar capturing method based on the FDML provided by the embodiment of the invention obtains the direction information of the target to be detected, realizes sweep frequency laser output with high scanning speed, wide scanning range, narrow instantaneous line width and high phase stability based on the FDML technology and a coherent detection mode, can enable the distance measurement precision of the laser radar to be higher, response time to be faster and stability to be better, and realizes high-precision distance and speed measurement.
(III) advantageous effects
The invention has the beneficial effects that: the FDML-based frequency modulation continuous wave three-dimensional laser radar capturing system and method provided by the invention have the advantages that the FDML laser is adopted as the sweep frequency light source of the laser radar capturing system, the laser works in a quasi-stable state, the FDML technology overcomes the limitations of the existing sweep frequency light source in the aspects of output power, sweep frequency speed, spectral line width and the like, the sweep frequency laser output with high scanning speed, wide scanning range, narrow instantaneous line width and high phase stability is realized, the distance measurement precision of the laser radar is higher, the response time is faster, the stability is better, the three-dimensional capturing of a target to be measured is realized, the high-precision distance and speed measurement is carried out, meanwhile, the system is simple and compact in structure, the space is saved, and the anti-interference capability.
Drawings
FIG. 1 is a block diagram of a FDML-based frequency modulated continuous wave three-dimensional lidar capture system of the present invention;
FIG. 2 is a schematic structural diagram of a scanning light source unit according to the present invention;
FIG. 3 is a schematic structural diagram of an optical fiber interference unit according to the present invention;
FIG. 4 is a schematic structural diagram of a signal acquisition and processing unit according to the present invention;
FIG. 5 is a schematic diagram of a frequency modulated continuous wave three-dimensional lidar capture system of the present invention based on FDML;
FIG. 6 is a flow chart of a FDML-based frequency modulated continuous wave three-dimensional lidar capture method of the present invention.
[ description of reference ]
1: a drive circuit; 2: a filter; 3: a first optical isolator; 4: the semiconductor amplifier 5: a second optical isolator; 6: a dispersion compensating fiber; 7: a first fiber coupler; 8: a second fiber coupler; 9: a third fiber coupler; 10: a circulator; 11: a transceiver device; 12: a target to be measured; 13: a fourth fiber coupler; 14: a first photodetector; 15: a fifth fiber coupler; 16: a sixth fiber coupler; 17: a second photodetector; 18: an FPGA; 19: and (4) a computer.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
The FDML-based frequency modulation continuous wave three-dimensional laser radar capturing system and method provided by the embodiment of the invention combine an FDML mode-locking frequency-sweeping laser source with a frequency modulation continuous wave distance measuring method, and are used for realizing three-dimensional high-precision capturing of a target object and synchronous measurement of distance and speed. The system has the characteristics of capability of capturing a target object, simple structure, high measurement speed, high precision, strong anti-interference capability and the like.
In order 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. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Example 1
The embodiment provides a frequency modulation continuous wave three-dimensional laser radar capturing system based on the FDML technology, and as shown in FIG. 1, the system comprises a three-dimensional turntable unit, a scanning light source unit, an optical fiber interference unit and a signal acquisition and processing unit. The scanning light source unit is used for emitting laser to the direction of the target to be detected based on an FDML technology according to the direction information of the target to be detected, and locking the position of the target to be detected; the optical fiber interference unit is used for receiving laser signals reflected by the target and obtaining electric signals, and the signal acquisition and processing unit is used for obtaining the distance and the speed of the target to be measured based on the electric signals.
The three-dimensional turntable unit comprises a horizontal hollow rotating platform and a vertical hollow rotating platform, wherein the rotating angle of the horizontal hollow rotating platform is 180 degrees, and the rotating angle of the vertical hollow rotating platform is 360 degrees. The three-dimensional turntable unit is provided with a camera and a liquid lens, and the camera and the liquid lens rotate along with the horizontal hollow rotating platform and the vertical hollow rotating platform. The interfaces of the horizontal hollow rotary platform, the vertical hollow rotary platform, the camera and the liquid lens are all connected with the FPGA.
Further, it is assumed that the normal vector of the plane of the rectangular mirror when the turntable is in the reference attitude
Figure BDA0002808254830000061
Comprises the following steps:
Figure BDA0002808254830000062
in order to clearly describe the change relationship, the horizontal axis of the rotary table rotates around the self-rotation angle to form a pitch angle, the anticlockwise direction is positive, and the angle is set to be gamma; the rotation angle of the rotary table vertically around the self axis is a yaw angle, the anticlockwise is positive, and the angle is set as
Figure BDA0002808254830000063
Then any angle coordinate
Figure BDA0002808254830000064
Comprises the following steps:
Figure BDA0002808254830000065
suppose OL、OCRespectively is the intersection point of the laser optical axis of the scanning laser light source and the optical axis of the three-dimensional turntable unit camera on the plane of the rectangular reflector, GLG can be obtained based on space vector plane mirror reflection law for emitting guide light spot position of current scanning light sourceLSpace point location vector of
Figure BDA0002808254830000071
Comprises the following steps:
Figure BDA0002808254830000072
wherein L is an intersection OLTo the guide light spot GLThe distance of (c).
Assuming that there is a point M (x, y, z) on the mirror surface of the current rectangular mirror, the plane equation of the rectangular mirror with the current turntable in the reference pose is obtained as follows:
Figure BDA0002808254830000073
according to GLThe space point positioning vector can obtain the space point positioning vector of the target to be measured
Figure BDA0002808254830000074
Comprises the following steps:
Figure BDA0002808254830000075
wherein P is the target to be measured and L' is the intersection point OLDistance to the target to be measured, gamma
Figure BDA0002808254830000076
The pitch angle and the yaw angle of the rectangular reflector, L ', gamma' and
Figure BDA0002808254830000077
are all unknown quantities.
Suppose OC' is a reflection point of the camera lens with respect to the rectangular mirror in the current pose, GCThe equivalent camera optical axis vector can be obtained for the intersection point of the reflected camera optical axis and the target imaging surface
Figure BDA0002808254830000078
Comprises the following steps:
Figure BDA0002808254830000079
wherein D is the distance between the laser optical axis of the scanning laser light source and the optical axis of the three-dimensional turntable unit camera, and D is the guide light spot GLAnd the intersection point OLThe distance of (c).
Suppose the coordinate of the target to be measured is (x)p,yp) Intersection point GCHas the coordinates of (x)gc,ygc) Since the equivalent camera optical axis vector is obtained, the image coordinate of the image of the target to be measured in the reflector captured by the camera can be equivalent to the image coordinate of the image of the target to be measured in the symmetrical point of the camera lens relative to the current reflector, and the projection angle α of the target to be measured on the X axis relative to the equivalent camera optical axis can be obtainedHAnd a projection angle alpha on the Y axisv：
Figure BDA00028082548300000710
Figure BDA0002808254830000081
Where H is the horizontal resolution of the captured image, W is the vertical resolution of the captured image, α is the horizontal angle of view of the camera, and β is the vertical angle of view of the camera.
Due to the projection angle alphaHAnd alphavThe positive and negative of (2) are not definite, and the projection angle alpha is obtained according to the situation and needs to be discussedHAnd alphavBy the sine theoremSpace point location vector to target to be measured
Figure BDA0002808254830000082
Figure BDA0002808254830000083
Space point positioning vector based on target P to be measured
Figure BDA0002808254830000084
Obtaining the pitch angle gamma' and the yaw angle of the rotary table when the target to be detected is captured
Figure BDA0002808254830000085
Figure BDA0002808254830000086
Figure BDA0002808254830000087
In the formula, xOLPAs coordinates of spatial points of the object to be measured along the x-axis, yOLPAs coordinates of a spatial point of the object to be measured along the y-axis, zOLPIs the coordinate of the space point of the object to be measured along the z-axis.
Based on the pitch angle gamma' and yaw angle
Figure BDA0002808254830000088
The three-dimensional turntable unit can realize the control of rotating the guide light spot to the target to be measured.
The camera is used for capturing the position of the target to be detected, feeding the position of the target to be detected back to the FPGA, capturing a focusing light spot guiding laser at the position of the target to be detected by using the camera, adjusting the driving current value of the liquid lens by analyzing the size of the focusing light spot, and stopping changing the driving current when the size of the focusing light spot reaches the minimum value.
The liquid lens is used for focusing the position of the target to be measured, the liquid lens selects guide laser as visible light wavelength, and the measuring laser wavelength is 1550 nm. In the measuring process, the position of the target to be measured is found by using the guide laser, and after the target point is positioned by the guide laser, the distance between the target point and the target point is measured after the target point is accurately positioned. In the guiding stage, the laser is guided to position a target point, and the driving current value of the liquid lens is adjusted by using the camera to assist feedback so as to ensure that the guided laser reaches the optimal focusing state and the focusing light spot is minimum. And secondly, measuring laser focusing, and entering a measuring stage from a guiding stage. Through calculation, the driving current code value of the liquid lens when the guiding laser is optimally focused is converted into the driving current code value required by the measuring laser 1550nm to reach the optimal focusing state, and the converted current code is output to the liquid lens, so that the one-step rapid focusing of the ranging laser can be realized.
The scanning light source unit selects an FDML laser as a light source of the frequency-modulated continuous wave three-dimensional laser radar capturing system, and as shown in FIG. 2, 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 fiber 6 and a first fiber coupler 7 which are sequentially connected. The filter 2 is controlled to be opened and closed by the driving circuit 1, the typical working wavelength of the filter 2 is 1550nm, the tuning voltage range is-20-50V, and the free spectrum range is 50-60 nm. Specifically, the sweep laser is emitted under the control of the driving circuit 1, and passes through the filter 2, the first optical isolator 3, the semiconductor amplifier 4, the second optical isolator 5, the dispersion compensation fiber 6 and the first fiber coupler 7 in sequence, and is divided into a path a of sweep laser and a path B of sweep laser after passing through the first fiber coupler 7, and the splitting ratio of the first fiber coupler 7 is 20: 80, wherein the A-path swept laser is used as the output of the FDML laser to output 20% of swept laser energy; the B path of sweep laser returns to the annular resonant cavity of the FDML laser, and one path of sweep laser circulates to output 80% of sweep laser energy.
Further, the difference between the FDML laser and the conventional laser is that the dispersion compensation fiber 6 is used for dispersion management, and the period of the driving voltage of the narrow-band optical filter 2 is matched with the time of one cycle of the propagation of the swept-frequency laser in the ring resonator, that is, the former time and the latter time are equal or the latter time is an integral multiple of the former time. Therefore, a quasi-steady-state mode is generated, the period of the driving voltage of the filter 2 is equal to the time that the sweep-frequency laser propagates for one circle around the ring-shaped resonant cavity, so that when the sweep-frequency laser with a certain frequency or wavelength passes through the filter 2 and propagates for one circle in the ring-shaped resonant cavity and then returns to the filter 2 again, the cavity length of the filter 2 is just tuned to the condition that the sweep-frequency laser can pass through, so that the sweep-frequency laser in the previous loop period is coupled back to the gain medium, the establishment of the sweep-frequency laser does not need to depend on the spontaneous radiation of the gain medium any more, each longitudinal mode is accurately locked, and continuous.
As shown in fig. 3, the optical fiber interference unit includes a second optical fiber coupler 8, a third optical fiber coupler 9, a circulator 10, a transceiver 11, an object 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 a-path sweep laser is divided into a C-path sweep laser and a D-path sweep laser after passing through the second fiber coupler 8, and the splitting ratio of the second fiber coupler 8 is 50: and 50, wherein the C-path swept laser outputs 50% of swept laser energy to the third fiber coupler 9, and the D-path swept laser outputs 50% of swept laser energy to the fifth fiber coupler 15.
The C-path swept laser is divided into C1-path swept laser and C2-path swept laser after passing through the third fiber coupler 9, and the splitting ratio of the third fiber coupler 9 is 50: 50, wherein C1 way sweep laser enters the fourth fiber coupler 13 through the time delay fiber, C2 way sweep laser passes through the circulator 10 and the transceiver 11 in order to be emitted to the target 12 to be measured, the transceiver 11 receives the reflected laser reflected from the target 12 to be measured, the reflected laser enters the fourth fiber coupler 13 after passing through the circulator 10, and generates difference frequency interference with the C1 way sweep laser to generate an emergent light signal, the emergent light signal is received by the first photoelectric detector 14, and the first photoelectric detector 14 converts the emergent light signal into a first electric signal through photoelectric conversion.
The D-path swept laser is divided into D1-path swept laser and D2-path swept laser after passing through the fifth fiber coupler 15, and the splitting ratio of the fifth fiber coupler 15 is 50: 50, the D1-path swept laser enters the sixth optical fiber coupler 16 through the delay optical fiber, the D2-path swept laser enters the sixth optical fiber coupler 16 through the common single-mode optical fiber, and performs difference frequency interference with the D1-path swept laser to generate 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.
Furthermore, the C-path frequency-sweeping laser and the D-path frequency-sweeping laser form a double interference light path, two beams of laser are emitted by the same light source, wherein the C-path frequency-sweeping laser is used as a measurement interference light path, the D-path frequency-sweeping laser is a Mach-Zehnder interference light path and is used as an auxiliary interference light path, the delay optical fiber is used for increasing an optical path and performing equal-frequency resampling on an echo signal, the influence of modulation nonlinearity of the FDML laser can be effectively eliminated, and the noise reduction effect is achieved.
Measuring emergent light signal S of interference light path (C path sweep laser)TX(t) is:
Figure BDA0002808254830000111
wherein A is amplitude, j is an imaginary unit, f0Is the initial frequency of frequency modulation, T is the modulation time, T belongs to [0, T ∈m]，TmFor a period of modulation of the triangular wave, alpha0In order to be the slope of the frequency modulation,
Figure BDA0002808254830000112
and B is the working bandwidth of the scanning light source.
Echo signal S of auxiliary interference light path (D path sweep laser)RX(t) is:
Figure BDA0002808254830000113
wherein T 'is the transmission time of echo signal, and T' is the [ tau, T ∈ [ ]m+τ]Tau is the time required by the object to be measured to transmit the echo signal,
Figure BDA0002808254830000114
d is the distance of the target to be measured, and c is the speed of light.
Emergent light signal STX(t) and echo signal SRX(t) optical beat signal S generated by the meetLB(t) when the beat frequency is stable:
Figure BDA0002808254830000115
wherein T is the time difference generated by the optical beat signal, and T is the element [ tau, T ∈ [ ]m]。
If using fBThe stable frequency of the optical beat signal is represented by:
fB＝α0τ (4)。
as shown in fig. 4, the signal acquisition and processing unit includes an FPGA18 and a computer 19. The FPGA18 receives the first electrical signal of the first photodetector 14 and the second electrical signal of the second photodetector 17, processes the first electrical signal and the second electrical signal to obtain the distance and the speed of the target 12, and stores the distance and the speed of the target 12 in the computer 19. Six interfaces are arranged on the FPGA18, namely a camera information interface used for being connected with a camera, a ranging interface used for being connected with an optical fiber interference unit, a liquid lens control interface used for being connected with a liquid lens, a horizontal rotary table control interface used for being connected with a horizontal rotary table, a vertical rotary table control interface used for being connected with a vertical rotary table and a communication interface used for being connected with a computer 19. In addition, the FPGA18 is supplied with power through the driving circuit 1 in the scanning light source unit. The communication interface is connected with the USB interface and used for providing physical layer support for the network.
Further, the FPGA18 is configured to perform a difference between the first electrical signal and the second electrical signal to obtain a difference frequency signal main frequency, and obtain a distance R and a speed V of the target 12 to be measured according to the difference frequency signal main frequency and by combining parameter information of the FDML laser:
the distance D of the target 12 to be measured and the speed V of the target to be measured are respectively:
Figure BDA0002808254830000121
Figure BDA0002808254830000122
in the formula, λ is the wavelength of the measuring laser.
As shown in fig. 5, a schematic diagram of an FDML-based frequency modulated continuous wave three-dimensional lidar capture system provided in this embodiment includes the following steps:
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 to capture the target to be detected;
102. capturing the position of a target to be detected by a camera, feeding the position of the target to be detected back to the FPGA, and capturing a focusing light spot guiding laser at the position of the target to be detected by the camera;
103. focusing the liquid lens, and focusing the target to be measured by using guide laser and measurement laser in the measurement process to obtain the direction information of the target to be measured;
104. the FDML laser emits laser to the direction of the target to be detected according to the direction information of the target to be detected;
105. receiving a laser signal reflected by a target and obtaining an electric signal;
106. and obtaining the distance and the speed of the target to be measured based on the electric signals.
Example 2
The embodiment provides a frequency-modulated continuous wave three-dimensional laser radar capturing method based on FDML, and as shown in FIG. 6, the method is a flowchart. The method is based on the frequency modulation continuous wave three-dimensional laser radar capturing system based on the FDML provided by the embodiment 1, and comprises the following steps:
s1, rotating the three-dimensional turntable platform to acquire direction information of the target to be detected;
s2, emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected, and locking the position of the target to be detected;
s3, receiving the laser reflected by the target to be detected in a coherent detection mode and obtaining an electric signal;
and S4, obtaining the distance and the speed of the target to be measured based on the electric signals.
In summary, the system and the method for capturing frequency modulated continuous wave three-dimensional laser radar based on FDML provided by the invention combine the FDML mode-locked swept laser source with the frequency modulated continuous wave distance measurement method for the first time, and are used for realizing three-dimensional high-precision capturing of a target object and synchronous measurement of distance and speed. The invention is especially suitable for the distance and speed test of objects with close distance and high precision, can capture the target to be tested, has the characteristics of simple structure, high measuring speed, high precision, strong anti-interference capability and the like, is very favorable for commercialization, and has wide application prospect.
The camera is matched with the three-dimensional rotating platform, so that the primary capture of the target to be detected can be realized. The liquid lens is adopted for focusing, so that the focus is quickly and accurately locked on a target object, and the system precision is effectively improved. The FDML laser is adopted as the sweep frequency light source, so that the limitations of the existing sweep frequency light source in the aspects of output power, sweep frequency speed, spectral line width and the like can be overcome, the sweep frequency laser output with high scanning speed, wide scanning range, narrow instantaneous line width and high phase stability is realized, and the laser radar has the advantages of higher ranging precision, quicker response time and better stability. The light interference unit adopts signal difference frequency processing to reduce noise by interference. The method has low cost and good effect, and can reduce the data calculation amount, thereby improving the system operation speed.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium; either as communication within the two elements or as an interactive relationship of the two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, a first feature may be "on" or "under" a second feature, and the first and second features may be in direct contact, or the first and second features may be in indirect contact via an intermediate. Also, a first feature "on," "above," and "over" a second feature may be directly or obliquely above the second feature, or simply mean that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the second feature, or may simply mean that the first feature is at a lower level than the second feature.
In the description herein, the description of the terms "one embodiment," "some embodiments," "an embodiment," "an example," "a specific example" or "some examples" or the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and not restrictive, and that those skilled in the art may make changes, modifications, substitutions and alterations to the above embodiments without departing from the scope of the present invention.

Claims (10)

1. A frequency modulated continuous wave three dimensional lidar capture system based on FDML, comprising:
the three-dimensional turntable unit is used for acquiring direction information of the target to be detected;
the scanning light source unit is used for emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected and locking the position of the target to be detected;
the optical fiber interference unit is used for receiving the laser signal reflected by the target in a coherent detection mode and obtaining an electric signal;
and the signal acquisition and processing unit is used for obtaining the distance and the speed of the target to be detected based on the electric signals.
2. A FDML-based frequency modulated continuous wave three dimensional lidar capture system of claim 1, wherein the three dimensional turret unit comprises 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 °;
and the horizontal hollow rotary platform and the vertical hollow rotary platform are both connected with a signal acquisition and processing unit.
3. A FDML-based frequency modulated continuous wave three dimensional lidar capture system as claimed in claim 2 wherein said three dimensional turret unit has a camera and a liquid lens disposed thereon, said camera and liquid lens following rotational movement of said horizontal and vertical hollow rotating platforms;
the camera and the liquid lens are both connected with the signal acquisition and processing unit.
4. A FDML-based frequency modulated continuous wave three dimensional lidar capture system according to claim 3 wherein the scanning light source unit is a FDML laser as the light source of the frequency modulated continuous wave lidar capture system, the FDML laser comprising a driver circuit (1), a filter (2), a first optical isolator (3), a semiconductor amplifier (4), a second optical isolator (5), a dispersion compensating fiber (6), and a first fiber coupler (7) connected in sequence;
the drive circuit (1) is used for emitting sweep laser, and the sweep laser sequentially passes through the filter (2), the first optical isolator (3), the semiconductor amplifier (4), the second optical isolator (5), the dispersion compensation fiber (6) and the first fiber coupler (7);
the first optical fiber coupler (7) is used for dividing the sweep laser into an A-path sweep laser and a B-path sweep laser, and the splitting ratio of the first optical fiber coupler (7) is 20: 80;
wherein, the A path of sweep frequency laser is used as the output of the FDML laser and outputs 20 percent of sweep frequency laser energy; the B-path swept laser returns to the ring resonator of the FDML laser, and 80% of swept laser energy is output.
5. A FDML based frequency modulated continuous wave three dimensional lidar capture system according to claim wherein the fiber optic interference unit comprises a second fiber coupler (8), a third fiber coupler (9), a circulator (10), a transceiver device (11), an object to be measured (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);
the second optical fiber coupler (8) is sequentially connected with the third optical fiber coupler (9), the circulator (10), the transceiver (11) and the target to be measured (12);
the fourth optical fiber coupler (13) is connected with the first photoelectric detector (14) in sequence;
the second optical fiber coupler (8) is also sequentially connected with a sixth optical fiber coupler (16) and a second photoelectric detector (17);
the second optical fiber coupler (8) is used for dividing the A-path sweep laser into a C-path sweep laser and a D-path sweep laser, and the splitting ratio of the second optical fiber coupler (8) is 50: 50;
wherein, the C-path sweep laser outputs 50% of sweep laser energy to a third optical fiber coupler (9); the D-path sweep laser outputs 50% of sweep laser energy to a fifth fiber coupler (15).
6. A FDML based frequency modulated continuous wave three dimensional lidar capture system according to claim 5 wherein the third fiber coupler (9) is configured to split the C-path swept laser into C1-path swept laser and C2-path swept laser, the third fiber coupler (9) having a splitting ratio of 50: 50;
wherein, the C1-path sweep laser enters a fourth fiber coupler (13) through a time delay fiber; the C2 frequency sweeping laser is transmitted to a target to be measured (12) sequentially through the circulator (10) and the transceiver (11), the transceiver (11) receives reflected laser reflected from the target to be measured (12), the reflected laser enters the fourth optical fiber coupler (13) after passing through the circulator (10) and generates difference frequency interference with the C1 frequency sweeping laser to generate an incident light signal;
the first photoelectric detector (14) is used for converting the emergent light signal into a first electric signal through photoelectric conversion.
7. A FDML based frequency modulated continuous wave three dimensional lidar capture system according to claim 5 wherein the fifth fiber coupler (15) is configured to split the D-path swept laser into D1-path swept laser and D2-path swept laser, the fifth fiber coupler (15) having a splitting ratio of 50: 50;
the D1-path swept laser enters a sixth fiber coupler (16) through a time delay fiber; d2 sweep frequency laser enters a sixth optical fiber coupler (16) through a single mode fiber, and generates difference frequency interference with D1 sweep frequency laser to generate an echo signal;
the second photodetector (17) is used for converting the echo signal into a second electric signal through photoelectric conversion.
8. The FDML-based frequency modulated continuous wave three-dimensional lidar capture system of claim 7, wherein the signal acquisition and processing unit comprises an FPGA (18) and a computer (19), the FPGA (18) is configured to receive the first electrical signal and the second electrical signal, to perform a difference between the first electrical signal and the second electrical signal to obtain a difference frequency signal dominant frequency, to obtain a distance and a speed of the target (12) to be detected according to the difference frequency signal dominant frequency and by combining parameter information of the FDML laser, and to store the distance and the speed in the computer (19).
9. A FDML based three dimensional lidar capturing system according to claim 8 wherein six interfaces are provided on the FPGA (18), respectively a camera information interface for connection to a camera, a ranging interface for connection to a fiber optic interference unit, a liquid lens control interface for connection to a liquid lens, a horizontal turret control interface for connection to a horizontal turret, a vertical turret control interface for connection to a vertical turret and a communication interface for connection to a computer (19).
10. An FDML-based frequency modulated continuous wave three dimensional lidar capture method based on any of claims 1-9, comprising the steps of:
s1, acquiring direction information of the target to be detected;
s2, emitting laser to the direction of the target to be detected based on the FDML technology according to the direction information of the target to be detected, and locking the position of the target to be detected;
s3, receiving the laser signal reflected by the target by adopting a coherent detection mode and obtaining an electric signal;
and S4, obtaining the distance and the speed of the target to be measured based on the electric signals.
CN202011380065.5A 2020-11-30 2020-11-30 Frequency modulation continuous wave three-dimensional laser radar capturing system and method based on FDML Pending CN112526537A (en)

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