CN115616594A - Speed and distance measuring device and method for frequency-modulated continuous wave laser radar - Google Patents
Speed and distance measuring device and method for frequency-modulated continuous wave laser radar Download PDFInfo
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- CN115616594A CN115616594A CN202211026114.4A CN202211026114A CN115616594A CN 115616594 A CN115616594 A CN 115616594A CN 202211026114 A CN202211026114 A CN 202211026114A CN 115616594 A CN115616594 A CN 115616594A
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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
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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
- 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
- G01S7/481—Constructional features, e.g. arrangements of optical elements
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Abstract
The invention discloses a speed and distance measuring device and method for a frequency modulation continuous wave laser radar, wherein the speed and distance measuring device comprises: a single-frequency seed laser; the modulation frequency sweep module is positioned in the emergent direction of the single-frequency seed laser; the laser beam splitter is used for dividing the sweep frequency laser into two beams; the acousto-optic frequency shift module is used for carrying out frequency shift on the first beam of sweep frequency laser and then irradiating a target, or carrying out frequency shift on the second beam of sweep frequency laser; the laser beam combiner is used for combining the second swept laser beam and the echo laser reflected by the target; and the data acquisition and analysis module is used for acquiring the laser of the set beam to output the speed and/or distance of the target. The laser is modulated into the triangular wave type sweep laser by the modulation sweep module, and then the first beam of sweep laser or the second beam of sweep laser is subjected to frequency shift by the acousto-optic frequency shift module, so that the problem of frequency aliasing caused by the fact that the Doppler frequency shift of a speed measurement target is larger than the target distance is solved, and the accuracy of speed measurement and distance measurement is higher.
Description
Technical Field
The invention relates to the technical field of radar speed and distance measurement, in particular to a speed and distance measuring device and method for a frequency modulation continuous wave laser radar.
Background
With the advent of the era of autonomous driving, a laser radar having a long distance and high accuracy has become a research hotspot at present. Frequency Modulated Continuous Wave (FMCW) and Time Of Flight (TOF) are two mainstream techniques in the laser radar at present, wherein the FMCW technique is widely considered as a final scheme Of the vehicle-mounted laser radar due to its high ranging resolution and real-Time speed measurement function.
The main working principle of the FMCW technique is: generating a sweep frequency light source by adopting an external modulation or internal modulation mode, wherein instantaneous laser has a narrower line width, and the sweep frequency mode is triangular wave; and performing power amplification on the weak swept laser through a laser power amplifier, and then splitting the swept laser into beams, wherein one beam is used as local oscillation laser, and the other beam is used as detection laser. The detection laser is incident into the air after passing through the circulator and the beam expander and irradiates on a target, a laser echo signal reflected by the target enters a beam combiner after passing through the beam expander and the circulator and is subjected to optical frequency mixing with local oscillator laser, finally, a beat frequency signal is detected through the photoelectric balance detector, and distance and speed information of the target is extracted. The static target only introduces a frequency shift related to the distance delay into the beat signal, and the moving target superimposes the Doppler shift on the beat signal, which shows that two frequencies are generated when the triangular wave is swept up and down. The two frequencies are obtained by adding and subtracting the Doppler frequency shift on the basis of the distance delay frequency shift, so that when the Doppler frequency shift is greater than the distance delay frequency shift, a frequency aliasing phenomenon occurs, and misjudgment of the speed and the distance is caused.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a speed and distance measuring device and method for frequency modulated continuous wave lidar, aiming at solving the problem of inaccurate speed and distance measurement caused by frequency aliasing of doppler frequency shift in the prior art.
The technical scheme adopted by the invention for solving the technical problem is as follows:
the utility model provides a frequency modulation continuous wave laser radar speed measuring range unit, wherein includes:
a single frequency seed laser;
the modulation frequency sweep module is positioned in the emergent direction of the single-frequency seed laser;
the laser beam splitter is positioned in the emergent direction of the modulation frequency sweeping module and is used for splitting the frequency sweeping laser into two beams;
the acousto-optic frequency shift module is positioned in the emergent direction of the first beam of sweep laser and is used for carrying out frequency shift on the first beam of sweep laser and then irradiating a target, or is positioned in the emergent direction of the second beam of sweep laser and is used for carrying out frequency shift on the second beam of sweep laser;
the laser beam combiner is used for combining the second beam of sweep frequency laser and the echo laser reflected by the target;
the data acquisition and analysis module is used for acquiring the laser of the set beam to output the speed and/or distance of the target;
the modulation frequency sweep module modulates and sweeps laser emitted by the single-frequency seed laser into triangular-wave type swept laser;
the target is in a moving state relative to the single frequency seed laser.
Frequency modulation continuous wave laser radar speed measuring range unit, wherein, modulation frequency sweep module includes:
the carrier suppression type single-side band modulator is positioned in the emergent direction of the single-frequency seed laser;
and the sweep frequency source is connected with the carrier suppression type single-sideband modulator.
The frequency modulation continuous wave laser radar speed and distance measuring device is characterized in that the carrier suppression type single side band modulator is one of a lithium niobate modulator or a silicon optical modulator;
the sweep frequency source is one of a DDS, a DAC or a phase-locked feedback type voltage-controlled oscillator, and the sweep frequency bandwidth of the sweep frequency source is greater than or equal to 500MHz.
Frequency modulation continuous wave laser radar speed measuring range unit, wherein, the reputation frequency shift module includes:
the acousto-optic modulator is positioned in the emergent direction of the first beam of sweep frequency laser of the laser beam splitter or in the emergent direction of the second beam of sweep frequency laser;
and the driving source is connected with the acousto-optic modulator.
The frequency modulation continuous wave laser radar speed and distance measuring device is characterized in that the acousto-optic modulator is one of an optical fiber coupling or a free space modulator, and the acousto-optic modulator is used for detecting the frequency shift of light;
the output frequency of the driving source is a radio frequency signal of 30MHz to 500MHz.
The frequency modulation continuous wave laser radar speed and distance measuring device is characterized in that the single-frequency seed laser is a 1.5 mu m or 1.3 mu m laser with the line width less than or equal to 500 kHz;
the single-frequency seed laser is one of a semiconductor laser, a fiber laser or a solid gain medium laser;
the laser beam splitter is one of an optical fiber coupler, a lens plated with a light splitting film and a spatial polarization beam splitter, and the power ratio of the first beam of sweep laser to the second beam of sweep laser is more than 8;
the laser beam combiner is one of an optical fiber or a free space beam combiner.
The frequency modulation continuous wave laser radar speed and distance measuring device is characterized in that a laser power amplifier is arranged between the modulation frequency sweep module and the laser beam splitter and used for amplifying the power of sweep laser;
and a laser circulator and a laser beam expander are arranged between the acousto-optic frequency shift module and the target, the laser circulator is used for separating the first beam of sweep laser and the echo laser reflected by the target, and the laser beam expander is used for compressing the divergence angle of the first beam of sweep laser and irradiating the first beam of sweep laser onto the target.
The laser power amplifier is one of EDFAEYDFA and semiconductor laser amplifier;
the laser circulator is one of an optical fiber circulator or a space laser circulator;
the laser beam expander is one of a transmission type beam expander or a reflection type beam expander.
Frequency modulation continuous wave laser radar speed measuring range unit, wherein, data acquisition analysis module includes:
the photoelectric balance detector is used for converting the combined laser into an electric signal;
the data acquisition module is used for acquiring the electric signals;
and the data processing module is used for processing the acquired electric signals so as to output the speed and/or the distance of the target.
The frequency modulation continuous wave laser radar speed and distance measuring device is characterized in that the photoelectric balance detector is one of a PIN balance detector and an APD balance detector;
the data acquisition module is an ADC (analog-to-digital converter);
the data processing module is an FPGA module or a DSP module.
A speed and distance measuring method of a frequency modulation continuous wave laser radar comprises the following steps:
the method comprises the following steps of modulating laser emitted by a single-frequency seed laser, carrying out frequency sweep treatment, and splitting into a first beam of frequency sweep laser and a second beam of frequency sweep laser; the first beam of sweep-frequency laser and the second beam of sweep-frequency laser are both triangular wave type sweep-frequency lasers;
carrying out frequency shift on the first beam of sweep frequency laser and then irradiating a target; wherein the target is in a moving state relative to the single frequency seed laser;
combining the second beam of sweep frequency laser and echo laser reflected by the target;
and obtaining the speed and/or distance of the target according to the combined laser.
The speed and distance measuring method of the frequency modulation continuous wave laser radar comprises the following steps of:
acquiring a beat frequency signal of a triangular wave period by adopting the laser of the beam set, and determining the slope of the sweep frequency triangular wave and/or the frequency of the laser of the beam combination;
performing FFT calculation on the beat frequency signal of one triangular wave period to obtain a processed beat frequency signal;
denoising the processed beat frequency signal, and determining two peak values of the processed beat frequency signal;
calculating the distance of the target according to the two peak values and the slope of the sweep-frequency triangular wave; and/or calculating the speed of the target according to the two peaks and the frequency of the combined laser.
The speed and distance measuring method of the frequency modulation continuous wave laser radar comprises the following steps:
where D represents the distance of the target, f 1 Frequency component representing sweep frequency of beat signal of combined laser on triangular wave, f 2 The frequency component of the sweep frequency of the beat frequency signal of the laser of the combined beam under the triangular wave is shown, alpha represents the slope of the sweep frequency triangular wave of the laser of the combined beam, and c represents the light speed;
the speed of the target is:
where upsilon denotes the velocity of the target, λ denotes the frequency of the combined laser light, f AOM Representing the frequency shift, f, of the first beam of swept laser doppler Indicating the doppler shift caused by velocity.
Has the advantages that: according to the invention, the modulation frequency sweep module is adopted to modulate the laser into the triangular wave type frequency sweep laser, and then the acousto-optic frequency shift module is used for shifting the frequency of the first beam of frequency sweep laser or the second beam of frequency sweep laser, so that the problem of frequency aliasing caused by the fact that the Doppler frequency shift of a speed measurement target is greater than the target distance can be avoided, and the accuracy of speed measurement and distance measurement is higher.
Drawings
FIG. 1 is a schematic diagram of a speed and distance measuring device of frequency modulated continuous wave lidar in the invention.
FIG. 2 is a schematic diagram of time, laser frequency, and beat frequency signals in the present invention.
FIG. 3 is a flow chart of the method for measuring speed and distance of frequency modulated continuous wave lidar in the invention.
Description of the reference numerals:
101. a single frequency seed laser; 102. a carrier-suppressed single sideband modulator; 103. sweeping the frequency source; 104. a laser power amplifier; 105. a laser beam splitter; 106. an acousto-optic modulator; 107. a drive source; 108. a laser circulator; 1. a first port; 2. a second port; 3. a third port; 109. a laser beam expander; 110. a laser beam combiner; 111. a photoelectric balance detector; 112. a data acquisition module; 113. and a data processing module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Referring to fig. 1-3, the present invention provides embodiments of a frequency modulated continuous wave lidar speed and distance measuring device.
The speed and distance measuring device of the frequency modulation continuous wave laser radar is applied to a vehicle-mounted laser radar, the speed and distance measuring device of the frequency modulation continuous wave laser radar is arranged on a vehicle, the speed and distance of a target around the vehicle are measured by the speed and distance measuring device of the frequency modulation continuous wave laser radar, the target can be a moving target or a static target, the vehicle can be a stopped vehicle or a running vehicle, of course, the vehicle and the target can move relatively (at least one of the vehicle and the target is in a moving state, and the speeds of the two are different), namely, the target is in a moving state relative to the speed and distance measuring device of the frequency modulation continuous wave laser radar,
as shown in fig. 1-2, the present invention provides a frequency modulated continuous wave lidar speed and distance measuring device, which comprises:
a single frequency seed laser 101;
the modulation frequency sweep module is positioned in the emergent direction of the single-frequency seed laser 101;
the laser beam splitter 105 is positioned in the emitting direction of the modulation frequency sweeping module and is used for splitting the frequency sweeping laser into two beams;
the acousto-optic frequency shift module is positioned in the emergent direction of the first beam of sweep laser and is used for carrying out frequency shift on the first beam of sweep laser and then irradiating a target, or is positioned in the emergent direction of the second beam of sweep laser and is used for carrying out frequency shift on the second beam of sweep laser;
a laser beam combiner 110, configured to combine the second swept laser beam and the echo laser beam reflected by the target;
the data acquisition and analysis module is used for acquiring the laser of the set beam to output the speed and/or distance of the target;
the modulation frequency sweep module modulates and sweeps laser emitted by the single-frequency seed laser 101 into triangular-wave type swept laser;
the target is in a moving state relative to the single frequency seed laser 101.
Specifically, the laser is modulated into the triangular wave type sweep laser by the modulation sweep module, and then the first beam of sweep laser or the second beam of sweep laser is subjected to frequency shift by the acousto-optic frequency shift module, so that the problem of frequency aliasing caused by the fact that the Doppler frequency shift of a speed measurement target is larger than the target distance is solved, and the accuracy of speed measurement and distance measurement is higher.
The modulation frequency sweep module modulates the laser into triangular wave type frequency sweep laser, the slope of the triangular wave type frequency sweep laser is alpha, and the acousto-optic frequency shift module shifts the frequency f when the first beam of frequency sweep laser or the second beam of frequency sweep laser is shifted AOM Can be set as required. The relationship between the time of the second beam of sweep-frequency laser and the echo laser reflected by the target and the laser frequency is shown in fig. 2, the relationship between the time of the second beam of sweep-frequency laser and the echo laser reflected by the target and the beat frequency signal is shown in fig. 2, and the beat frequency signal is acquired by the data acquisition and analysis module. Can obtainThe following relationships:
f 1 ＝f AOM +α*τ+f doppler
f 2 ＝f AOM -α*τ+f doppler
wherein f is 1 Frequency component representing sweep frequency of beat signal of combined laser on triangular wave, f 2 Frequency components of a beat signal of the combined laser light swept under a triangular wave, α represents a slope of the triangular wave of the sweep of the combined laser light, c represents a speed of light, τ represents a time delay due to a distance, f doppler Indicating the doppler shift caused by velocity. From this it can be calculated:
the distance D of the target can be further calculated as:
the velocity of the target, v, is:
where λ represents the frequency of the combined laser light.
It will be understood that f AOM When the size of (b) is appropriate, so that f 1 And f 2 Frequencies less than 0 do not occur, thereby avoiding the occurrence of frequency aliasing. The speed and distance measuring device for the frequency modulation continuous wave laser radar of the embodiment of the invention avoids the problem of frequency aliasing caused by overlarge Doppler frequency shift. Compared with the prior method which adopts a complex algorithm and a receiving structure, the method has the characteristics of simplicity and practicability, and is beneficial to the FMCW technology on-vehicle excitationApplication in optical radar.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1 to fig. 2, the modulation frequency sweep module includes: a carrier-suppressed single-sideband modulator 102 located in the emission direction of the single-frequency seed laser 101;
and a sweep frequency source 103 connected with the carrier suppression type single sideband modulator 102.
Specifically, triangular wave type frequency sweeping of laser frequency is realized after passing through a carrier wave suppression type single side band modulator 102 and a frequency sweeping source 103 module of the seed laser.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the single-frequency seed laser 101 is a 1.5 μm laser with a line width of less than or equal to 200 kHz.
Specifically, the single-frequency seed laser 101 is a 1.5 μm narrow linewidth laser, the linewidth of which is less than 200kHz, and the output power of which is greater than 10dBm.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the single-frequency seed laser 101 is one of a semiconductor laser, a fiber laser, or a solid gain medium laser.
In particular, different types of single frequency seed lasers 101 may be employed as desired.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the carrier-suppressed single-sideband modulator 102 is one of a lithium niobate modulator or a silicon optical modulator, and a carrier suppression ratio of the carrier-suppressed single-sideband modulator 102 is greater than 10dB.
In particular, carrier-suppressed single sideband modulator 102 made of different materials may be used as desired.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the sweep frequency source 103 is one of a DDS, a DAC, or a phase-locked feedback voltage-controlled oscillator, and a sweep frequency bandwidth of the sweep frequency source 103 is greater than or equal to 1GHz. The carrier-suppressed single sideband modulator 102 may be an In-phase Quadrature (IQ) modulator.
Specifically, a Direct Digital Frequency synthesizer (DDS) has a full Digital structure, and has the advantages of a relatively wide Frequency band of a synthesized signal, a short Frequency conversion time, a high Frequency resolution, phase connection of the synthesized signal, and the like. Digital-to-Analog Converter (DAC)
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the acousto-optic frequency shift module includes:
an acousto-optic modulator 106, located in the emitting direction of the first beam of the swept laser of the laser beam splitter 105, or located in the emitting direction of the second beam of the swept laser;
and a driving source 107 connected to the acousto-optic modulator 106.
Specifically, the acousto-optic modulator 106 may shift the frequency of one of the first and second swept laser beams.
In a preferred implementation of the embodiment of the present invention, as shown in fig. 1-2, the acousto-optic modulator 106 is one of a fiber-coupled or free-space modulator, and the acousto-optic modulator 106 is used for detecting the frequency shift of light; the output frequency of the driving source 107 is a radio frequency signal of 30MHz to 500MHz. Specifically, the frequency of the drive source 107 is set as needed, and the frequency of the drive source 107 needs to be sufficiently large so that a phenomenon of frequency aliasing does not occur. It should be noted here that the size of the acousto-optic shift frequency is selected to satisfy the shift frequency f AOM Greater than the sum f of the Doppler frequency shift due to velocity and the frequency shift due to distance Doppler + α τ, i.e. frequency aliasing of the beat signal is better avoided, i.e. f AOM >f Doppler + α τ, i.e.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the laser beam splitter 105 is one of a fiber coupler, a lens coated with a light splitting film, and a spatial polarization beam splitter, and a power ratio of the first swept laser beam to the second swept laser beam is greater than 9.
Specifically, the power ratio of the first beam of swept laser to the second beam of swept laser is greater than 9, for example, the power ratio of the first beam of swept laser to the second beam of swept laser may be 99. 99% of the swept laser enters the acousto-optic frequency shift module for frequency shift, and 1% of the swept laser enters the laser beam combiner 110 as local oscillation laser.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the laser beam combiner 110 is one of an optical fiber or a free space beam combiner, and a beam combining power ratio of the laser beam combiner 110 is 1. Specifically, the power ratio of the laser beam combiner 110 may be set as needed.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, a laser power amplifier 104 is disposed between the modulation frequency sweep module and the laser beam splitter 105, and is used for performing power amplification on the frequency sweep laser. Specifically, the laser power amplifier 104 power-amplifies the weak swept laser.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, a laser circulator 108 and a laser beam expander 109 are disposed between the acousto-optic frequency shift module and the target, the laser circulator 108 is configured to separate a first beam of swept laser and echo laser reflected by the target, and the laser beam expander 109 is configured to compress a divergence angle of the first beam of swept laser and irradiate the first beam of swept laser onto the target. Specifically, a first beam of swept laser passes through the first port 1 of the laser circulator 108, the second port 2 of the laser circulator 108, and the laser beam expander 109, then enters the air, and irradiates the target, the laser is reflected on the surface of the target, the reflected echo laser passes through the laser beam expander 109 and then reaches the second port 2 of the laser circulator 108, and the laser circulator 108 transmits the reflected echo laser from the third port 3 of the laser circulator 108 to the laser beam combiner 110.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the laser power amplifier 104 is one of an EDFA and an EYDFA semiconductor laser amplifier (SOA), the input power of the laser power amplifier 104 is-50 dBm to 10dBm, and the output power is 0dBm to 30dBm.
Specifically, an Erbium Doped Fiber Amplifier (EDFA) is an optical Fiber, and rare earth elements such as Erbium (Er) are injected into a Fiber core, so that an optical signal with a certain wavelength can be directly amplified under the action of a pump light source. Erbium-yttrium-Doped Fiber Amplifier (EYDFA) is also a Fiber, and two rare earth elements of Erbium (Er) and yttrium (Y) are injected into a Fiber core.
In a preferred implementation of the embodiment of the present invention, as shown in fig. 1-2, the laser circulator 108 is one of a fiber optic circulator or a spatial laser circulator 108.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1 to fig. 2, the laser beam expander 109 is one of a transmissive beam expander and a reflective beam expander, and a diameter of a laser spot emitted by the laser beam expander 109 is greater than 2mm. Specifically, after the beam is expanded by the laser beam expander 109, the diameter of the laser beam is increased, which is beneficial to irradiating the target.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the data acquisition and analysis module includes:
a photoelectric balance detector 111 for converting the combined laser light into an electrical signal;
a data acquisition module 112 for acquiring the electrical signal;
and the data processing module 113 is configured to process the acquired electrical signals to output the speed and/or distance of the target.
Specifically, beat signals of the combined laser beams are detected by the photoelectric balance detector 111, and the speed and/or the distance of the target are acquired and processed.
In a preferred implementation manner of the embodiment of the present invention, as shown in fig. 1-2, the photo balance detector 111 is one of a PIN balance detector and an APD balance detector;
the data acquisition module 112 is an ADC analog-to-digital converter;
the data processing module 113 is an FPGA or DSP module.
Specifically, the PIN balance detector is a photoelectric detector with an intrinsic layer added between a P-type region and an N-type region. The APD balance detector obtains photocurrent gain by using avalanche effect of photo-generated carriers in a high electric field region, has the advantages of high sensitivity, quick response and the like, and is generally used for laser ranging, laser radar and weak light detection (nonlinearity). An ADC (Analog-to-Digital Converter) Analog-to-Digital Converter converts an Analog quantity into a Digital quantity. An FPGA module (Field-Programmable Gate Array) is a Field Programmable Gate Array. The data processing module 113 performs fourier transform on the acquired signals and analyzes the speed and distance information of the targets carried in the signals. The DSP module (Digital Signal Processing) is Digital Signal Processing.
The invention also provides a preferred embodiment of the speed and distance measuring method of the frequency modulation continuous wave laser radar, which comprises the following steps:
as shown in fig. 3, the method for measuring speed and distance by using frequency modulated continuous wave lidar according to the embodiment of the present invention includes the following steps:
s100, modulating laser emitted by a single-frequency seed laser, performing frequency sweeping treatment, and splitting the laser into a first beam of frequency sweeping laser and a second beam of frequency sweeping laser; the first beam of sweep-frequency laser and the second beam of sweep-frequency laser are both triangular wave type sweep-frequency lasers.
Specifically, laser emitted by a single-frequency seed laser is modulated and swept into triangular wave type swept laser through a modulation sweep frequency module, and the triangular wave type swept laser is divided into two beams through a laser beam splitter, namely a first beam of swept laser and a second beam of swept laser.
S200, performing frequency shift on the first beam of sweep frequency laser and irradiating a target; wherein the target is in a moving state relative to the single frequency seed laser.
Specifically, the frequency of the first beam of sweep frequency laser is shifted through the acousto-optic frequency shift module, and the target is irradiated. Of course, the frequency shift of the first beam of sweep-frequency laser may be omitted, and the target may be directly irradiated, and the frequency shift of the second beam of sweep-frequency laser may be performed by the acousto-optic frequency shift module.
And S300, combining the second beam of sweep-frequency laser and the echo laser reflected by the target.
Specifically, the first beam of sweep-frequency laser is irradiated to the target and then reflected to form echo laser, and the second beam of sweep-frequency laser and the echo laser reflected by the target are combined by the laser beam combiner.
And S400, obtaining the speed and/or distance of the target according to the combined laser.
Specifically, the speed and/or distance of the target is obtained through the data acquisition and analysis module according to the combined laser.
Compared with the traditional FMCW laser radar speed measurement algorithm, the method needs to respectively perform Fourier transform (FFT) calculation on the upper frequency sweep and the lower frequency sweep of the triangular wave, extract the peak value and calculate the difference value of the peak value and the lower frequency sweep to obtain the speed and the direction of the target. In the implementation case, the speed and direction information of the target can be obtained only by performing Fourier transform on the signal of one triangular wave period, so that multiple operations are avoided. The specific treatment steps are as follows:
step S400 includes:
and S410, collecting the laser beam to obtain a beat frequency signal of a triangular wave period, and determining the slope and the frequency of the sweep frequency triangular wave.
Specifically, a beat frequency signal of a triangular wave period is acquired through the data acquisition module, and the size of the triangular wave period can be determined according to the first beam of sweep laser or the second beam of sweep laser. The slope alpha and frequency lambda of the sweep-frequency triangular wave can also be determined by the beat signal of one triangular wave period.
Step S420, performing an FFT calculation on the beat signal of one triangular wave period to obtain a processed beat signal.
Specifically, the method only needs to acquire a beat frequency signal of one triangular wave period and perform Fourier transform only once.
Step S430, performing denoising processing on the processed beat signal, and determining two peak values of the processed beat signal.
Specifically, a threshold algorithm is used to remove noise interference, and then a peak searching algorithm is used to find the maximum two peaks within a range specified by a program.
As shown in fig. 2, the frequency shift f due to the acousto-optic modulator AOM Greater than targetThe frequency shift caused by the speed can identify the peak value f with larger frequency 2 The beat signal of the laser beam is a frequency component swept by a triangular wave, and the second peak value f 1 The beat signal of the combined laser is the frequency component swept on a triangular wave. In addition, the accuracy of the two peaks can be improved through denoising processing.
Step S440, calculating the distance of the target according to the two peak values and the slope of the sweep triangular wave; and/or calculating the speed of the target according to the two peaks and the frequency of the combined laser.
The distance of the target is as follows:
where D represents the distance of the target, f 1 、f 2 Respectively representing two peak values, alpha represents the slope of the sweep triangular wave of the laser of the combined beam, and c represents the speed of light;
the speed of the target is:
where upsilon denotes the velocity of the target, lambda denotes the frequency of the combined laser light, f AOM The frequency shift of the first beam of sweep laser is shown, specifically, the frequency shift of the laser signal caused by the acousto-optic frequency shift module.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (13)
1. The utility model provides a frequency modulation continuous wave laser radar speed measuring range unit which characterized in that includes:
a single-frequency seed laser;
the modulation frequency sweep module is positioned in the emergent direction of the single-frequency seed laser;
the laser beam splitter is positioned in the emergent direction of the modulation frequency sweeping module and is used for splitting the frequency sweeping laser into two beams;
the acousto-optic frequency shift module is positioned in the emergent direction of the first beam of sweep laser and is used for carrying out frequency shift on the first beam of sweep laser and then irradiating a target, or is positioned in the emergent direction of the second beam of sweep laser and is used for carrying out frequency shift on the second beam of sweep laser;
the laser beam combiner is used for combining the second beam of sweep frequency laser and the echo laser reflected by the target;
the data acquisition and analysis module is used for acquiring the laser of the set beam to output the speed and/or distance of the target;
the modulation frequency sweep module modulates and sweeps laser emitted by the single-frequency seed laser into triangular-wave type swept laser;
the target is in a moving state relative to the single frequency seed laser.
2. A frequency modulated continuous wave lidar speed and distance measuring device according to claim 1, wherein the modulating sweep module comprises:
the carrier suppression type single-side band modulator is positioned in the emergent direction of the single-frequency seed laser;
a swept frequency source connected to the carrier suppressed single sideband modulator.
3. A frequency modulated continuous wave lidar speed and distance measuring device as defined in claim 2 wherein the carrier-suppressed single-sideband modulator is one of a lithium niobate modulator or a silicon optical modulator;
the sweep frequency source is one of DDS, DAC or phase-locked feedback voltage-controlled oscillator, and the sweep frequency bandwidth of the sweep frequency source is greater than or equal to 500MHz.
4. A fm cw lidar speed and distance measuring device as claimed in claim 1, wherein the acousto-optic frequency shift module comprises:
the acousto-optic modulator is positioned in the emergent direction of the first beam of sweep frequency laser of the laser beam splitter or in the emergent direction of the second beam of sweep frequency laser;
and the driving source is connected with the acousto-optic modulator.
5. A frequency modulated continuous wave lidar speed and distance measuring apparatus according to claim 4, wherein said acousto-optic modulator is one of a fiber-coupled and a free-space modulator, said acousto-optic modulator being configured to detect a frequency shift of light;
the output frequency of the driving source is a radio frequency signal of 30MHz to 500MHz.
6. A frequency modulated continuous wave lidar speed and distance measuring device as defined in claim 1 wherein the single frequency seed laser is a 1.5 μm or 1.3 μm laser with a linewidth less than or equal to 500 kHz;
the single-frequency seed laser is one of a semiconductor laser, a fiber laser or a solid gain medium laser;
the laser beam splitter is one of an optical fiber coupler, a lens plated with a light splitting film and a spatial polarization beam splitter, and the power ratio of the first beam of sweep laser to the second beam of sweep laser is more than 8;
the laser beam combiner is one of an optical fiber or a free space beam combiner.
7. A frequency modulated continuous wave lidar speed and distance measuring device according to any of claims 1-6, characterized in that a laser power amplifier is arranged between the modulation sweep module and the laser beam splitter for power amplification of the sweep laser;
and a laser circulator and a laser beam expander are arranged between the acousto-optic frequency shift module and the target, the laser circulator is used for separating the first beam of the sweep-frequency laser and the echo laser reflected by the target, and the laser beam expander is used for compressing the divergence angle of the first beam of the sweep-frequency laser and irradiating the first beam of the sweep-frequency laser to the target.
8. A frequency modulated continuous wave lidar speed and distance measuring device according to claim 7, wherein the laser power amplifier is one of an EDFA, EYDFA and a semiconductor laser amplifier;
the laser circulator is one of an optical fiber circulator or a space laser circulator;
the laser beam expander is one of a transmission type beam expander or a reflection type beam expander.
9. A frequency modulated continuous wave lidar speed and distance measuring device according to any of claims 1 to 6, wherein the data acquisition and analysis module comprises:
the photoelectric balance detector is used for converting the combined laser into an electric signal;
the data acquisition module is used for acquiring the electric signals;
and the data processing module is used for processing the acquired electric signals so as to output the speed and/or the distance of the target.
10. A frequency modulated continuous wave lidar speed and distance measuring device according to claim 9, wherein the photo balance detector is one of a PIN balance detector or an APD balance detector;
the data acquisition module is an ADC (analog-to-digital converter);
the data processing module is an FPGA module or a DSP module.
11. A speed and distance measuring method of a frequency modulation continuous wave laser radar is characterized by comprising the following steps:
the method comprises the following steps of modulating laser emitted by a single-frequency seed laser, carrying out frequency sweep treatment, and splitting into a first beam of frequency sweep laser and a second beam of frequency sweep laser; the first beam of sweep-frequency laser and the second beam of sweep-frequency laser are both triangular wave type sweep-frequency lasers;
carrying out frequency shift on the first beam of sweep frequency laser and then irradiating a target; wherein the target is in a moving state relative to the single frequency seed laser;
combining the second beam of sweep-frequency laser and the echo laser reflected by the target;
and obtaining the speed and/or distance of the target according to the combined laser.
12. A frequency modulated continuous wave lidar speed and distance measuring method according to claim 11, wherein the obtaining of the speed and/or distance of the target from the combined laser comprises:
acquiring a beat frequency signal of a triangular wave period by adopting the laser of the beam set, and determining the slope of the sweep frequency triangular wave and/or the frequency of the laser of the beam combination;
performing FFT calculation on the beat frequency signal of one triangular wave period to obtain a processed beat frequency signal;
denoising the processed beat frequency signal, and determining two peak values of the processed beat frequency signal;
calculating the distance of the target according to the two peak values and the slope of the sweep-frequency triangular wave; and/or calculating the speed of the target according to the two peaks and the frequency of the combined laser.
13. A frequency modulated continuous wave lidar speed and distance measuring method according to claim 12, wherein the range of the target is:
where D represents the distance of the target, f 1 、f 2 Respectively representing two peak values, alpha represents the slope of the sweep triangular wave of the laser of the combined beam, and c represents the speed of light;
the speed of the target is:
where upsilon denotes the velocity of the target, lambda denotes the frequency of the combined laser light, f AOM Representing the frequency shift, f, of the first beam of swept laser doppler Indicating the doppler shift caused by the velocity.
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