A method for parallel ranging of a chirp continuous wave lidar based on electro-optic comb

Abstract

The application discloses a kind of linear frequency modulation continuous wave laser radar parallel ranging methods based on electro-optical comb, its steps include:1) seed light source is input modulator and modulated to generate single sideband signal;2) single sideband signal light is input electro-optical comb generator to generate multi-wavelength FMCW laser;3) multi-wavelength FMCW laser is divided into two-way output;One way as local oscillator light input to multi-channel dense optical wave multiplexing device;Another way as probe light is output through circulator;4) multi-wavelength FMCW laser output by circulator is collimated and incident to spatial grating to carry out first dimension direction on the light splitting;After light splitting, each light beam is scanned to second dimension direction by control unit;5) when scanning, the reflected light of object returns to input to multiplexing device, and the light output by each channel of multiplexing device is received by a photoelectric detector and then input data processing unit;6) data processing unit draws the three-dimensional image of object according to input signal and marks speed.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics, specifically to a parallel ranging method and system for linear frequency modulated continuous wave lidar based on an electro-optical comb. This invention is applicable to scene detection in fields such as autonomous driving and robotics, enabling rapid large-scale scanning and image formation at the receiving end. Background Technology

[0002] With the development of the information age, autonomous driving technology has become a major demand, and vehicle-mounted radar, as a key technology for autonomous driving, determines its performance. By installing millimeter-wave radar or lidar on a vehicle, the radar emits signals, obstacles reflect these signals, and the vehicle receives them. Analysis of the reflected signals detects the distance and speed of obstacles in front of the vehicle. Combined with scanning devices to change the direction of the radar signal, three-dimensional imaging is achieved through point-by-point scanning. Compared to millimeter-wave radar, lidar has advantages such as high resolution, good concealment, strong resistance to active interference, good low-altitude detection performance, small size, and light weight. Based on the ranging method, lidar can be divided into two main categories: Time-of-Flight (ToF) and Linear Frequency Modulated Continuous Wave (FMCW). ToF technology uses the flight time of a light pulse between an obstacle and the lidar to calculate the distance, but it is susceptible to stray light. FMCW technology, on the other hand, uses mixing technology to detect the frequency difference between the local light and the returned light to calculate the target distance.

[0003] FMCW lidar utilizes coherent detection technology to detect frequency differences for ranging, is unaffected by stray light interference, and is more suitable for vehicle-mounted lidar, making it a research hotspot. The ranging resolution of FMCW lidar depends on the sweep frequency range; the larger the sweep frequency range, the higher the ranging resolution. In recent years, several studies have used FMCW lidar to achieve three-dimensional imaging. For example, E. Baumann et al. used FMCW lidar to detect obstacle distances and combined it with a mode-locked optical frequency comb for frequency correction to achieve three-dimensional physical imaging [Reference: E. Baumann, et al. "Comb-calibrated laser ranging for three-dimensional surface profiling with micrometer-level precision at a distance," Opt. Express 22, 24914-24928 (2014)]. With the development of optical frequency combs, lidar that combines high-repetition-frequency optical frequency combs to achieve parallel ranging has also become a research hotspot. The repetition frequency of a Kerr optical frequency comb depends on the micro-ring radius; using FMCW lasers as seed light for Kerr optical frequency combs can achieve multi-wavelength FMCW lasers with equal frequency intervals. By combining spatial gratings to separate beams of different frequencies, multi-channel parallel ranging can be achieved [Reference: Riemensberger, J., et al. "Massively parallel coherent laser ranging using a soliton microcomb," Nature 581, 164–170 (2020).]. However, due to the stringent generation conditions of the Kerr frequency comb, the above scheme can only realize FMCW lidar with a narrow sweep range and low ranging resolution, leaving room for improvement in both sweep range and ranging resolution. Summary of the Invention

[0004] To improve the frequency sweep range of FMCW lidar while ensuring parallel ranging and to enhance ranging resolution to meet the requirements of scanning imaging, this invention provides a parallel ranging method and system for linear frequency modulated continuous wave lidar based on an electro-optical comb. This invention uses a continuous wave laser as the light source and achieves single-sideband modulation to obtain a single-wavelength FMCW laser by driving an electro-optical modulator through an arbitrary waveform generator (AWG). The single-wavelength FMCW laser is then fed into an electro-optical comb generator composed of a single intensity modulator and several phase modulators to obtain M (e.g., M=31) multi-wavelength FMCW lasers with equal frequency intervals. This allows for simultaneous measurement of the distance to M points, achieving an efficiency M times that of traditional single-wavelength FMCW lidar.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A parallel ranging method for linear frequency modulated continuous wave lidar based on an electro-optical comb, comprising the following steps:

[0007] 1) Input the seed light source into the modulator; use a waveform generator to drive the modulator to modulate the seed light source to generate a single-sideband signal; wherein, the frequency range of the linear sweep wave output by the waveform generator is B;

[0008] 2) The single-sideband signal light is input into an electro-optical comb generator to generate multi-wavelength FMCW lasers with equal frequency intervals; wherein, the FMCW laser is a linear frequency modulated continuous wave laser;

[0009] 3) The multi-wavelength FMCW laser is split into two outputs; one output is used as the local oscillator light input to a multi-channel dense optical multiplexing device; the other output is used as the probe light output through a circulator.

[0010] 4) The multi-wavelength FMCW laser output from the circulator is collimated by a collimator and converted into spatial light before being incident on a spatial grating for beam splitting in the first dimension. Each beam after beam splitting by the spatial grating is scanned in the second dimension by a beam scanning control unit. The first dimension is perpendicular to the second dimension.

[0011] 5) During scanning, the reflected light from the object returns along the original path and is input to the multi-channel dense optical wave multiplexing device through the circulator; the multi-channel dense optical wave multiplexing device mixes the reflected light and local oscillator light of the same frequency band in the same channel and outputs them. The light output from each channel is received by a corresponding photodetector and then input to the data processing unit.

[0012] 6) The data processing unit draws a three-dimensional image of the object and labels the velocity information based on the signal input from the photodetector.

[0013] Furthermore, the data processing unit includes an electron spectrometer and a host computer; the electron spectrometer measures the beat frequency signal based on the signal input from the photodetector and transmits it to the host computer; the host computer calculates distance information based on the beat frequency signal to achieve imaging.

[0014] Furthermore, the data processing unit processes the signal input from the photodetector to obtain the distance to the object. speed Among them, f u and f d These represent the higher and lower beat frequency values ​​in the beat frequency signal, respectively, where T is the sweep signal period of the waveform generator, and f... c To detect the frequency of light.

[0015] Furthermore, the modulator is an electro-optic modulator; the single-sideband signal output by the electro-optic modulator is amplified by an EDFA and then input into an electro-optic comb generator to generate multi-wavelength lasers with equal frequency intervals.

[0016] Furthermore, the electro-optical comb generator includes an intensity modulator and several cascaded phase modulators; both the intensity modulator and the phase modulator are powered by the same radio frequency f. r The radio frequency signal source drives the comb; wherein the intensity modulator is used to control the flatness of the comb teeth of the electro-optical frequency comb, and the phase modulator is used to expand the spectrum to obtain a multi-tooth electro-optical frequency comb.

[0017] Furthermore, the electro-optical comb generator is a cascaded modulator type electro-optical frequency comb generator, a cavity-enhanced electro-optical frequency comb generator with a Fabry-Perot cavity built-in phase modulator, or an electro-optical comb generator integrated on a thin-film lithium niobate sheet.

[0018] Furthermore, the multi-wavelength FMCW laser is amplified by an erbium-doped fiber amplifier and then split into two outputs, one of which serves as the local oscillator and the other as the probe light.

[0019] Furthermore, the wavelength of the seed light source is 1550nm; the grating has a line density greater than or equal to 1000 lines per mm and a working wavelength of 1550nm.

[0020] Furthermore, the beam scanning control unit is a microelectromechanical system galvanometer or a rapid steering mirror.

[0021] A parallel ranging system for linear frequency modulated continuous wave lidar based on an electro-optical comb is characterized by comprising a laser, a modulator, a waveform generator, an electro-optical comb generator, a multi-channel dense optical multiplexing device, a circulator, a collimator, a spatial grating, a beam scanning control unit, and a data processing unit; wherein...

[0022] The laser is used to generate a seed light source;

[0023] The modulator is connected to the waveform generator and is used to modulate the input seed light source using the drive signal of the waveform generator to generate a single-sideband signal; wherein, the frequency range of the linear sweep wave output by the waveform generator is B;

[0024] The electro-optic comb generator is used to generate multi-wavelength FMCW lasers with equal frequency intervals based on the input single-sideband signal light and split them into two outputs; one output is used as the local oscillator light input to a multi-channel dense optical multiplexing device; the other output is used as the probe light output through a circulator; wherein the FMCW laser is a linear frequency modulated continuous wave laser.

[0025] The multi-wavelength FMCW laser output from the circulator is collimated by a collimator and converted into spatial light before being incident on a spatial grating for beam splitting in the first dimension. The beams split by the spatial grating are then scanned in the second dimension by the beam scanning control unit. The first dimension is perpendicular to the second dimension.

[0026] During scanning, the reflected light from the object returns along the original path and is input to the multi-channel dense optical wave multiplexing device through the circulator; the multi-channel dense optical wave multiplexing device is used to mix the reflected light and the local oscillator light of the same frequency band in the same channel and output them. The light output from each channel is received by a corresponding photodetector and then input to the data processing unit.

[0027] The data processing unit draws a three-dimensional image of the object and labels its speed information based on the signal input from the photodetector.

[0028] This invention uses a continuous-wave laser as the light source. A single-sideband modulation is achieved by driving an electro-optic modulator through an arbitrary waveform generator (AWG) to obtain a single-wavelength FMCW laser. After power loss is compensated using an erbium-doped fiber amplifier (EDFA), the laser beam passes through an electro-optic comb generator composed of a single intensity modulator and several phase modulators to obtain M multi-wavelength FMCW lasers with equal frequency intervals. After further power loss compensation using an EDFA, the fiber light is collimated into spatial light by a collimator. The multi-wavelength beams pass through a high-line-count spatial grating to form M beams that simultaneously illuminate M points. The return light from the M points is mixed with M local signal lights, and the distances to the M points are obtained through dense wavelet multiplexing (DWDM). Combining this with a microelectromechanical system (MEMS) galvanometer or a fast-steering mirror (FSM) allows for scanning in another dimension.

[0029] The beneficial effects of this invention are:

[0030] This invention provides a parallel ranging FMCW lidar implementation method with high sweep frequency range and high measurement accuracy, which is applicable to applications such as vehicle-mounted lidar, enabling rapid scanning and accurate ranging, and greatly improving the performance of vehicle-mounted lidar. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the parallel ranging linear frequency modulated continuous wave lidar system based on electro-optical frequency comb of the present invention.

[0032] Figure 2 This is a single-wavelength FMCW laser obtained by single-sideband modulation, taking a sideband modulation frequency of 10GHz as an example;

[0033] Figure 3 The multi-wavelength laser spectrum generated after passing through the electro-optic frequency comb generator is shown here, taking a sideband modulation frequency of 10 GHz as an example.

[0034] Figure 4 The image shown is an image created using this method. Here, we take a complete obstacle and a perforated obstacle that are 20cm apart as examples.

[0035] Among them, 1. Continuous wave laser, 2. Electro-optic modulator, 3. Arbitrary waveform generator, 4. Erbium-doped fiber amplifier, 5. M-comb electro-optic frequency comb generator, 6. Erbium-doped fiber amplifier, 7. Optical circulator, 8. Collimator, 9. Spatial grating, 10. Beam scanning control unit, 11. Obstacle, 12. M-channel dense optical wave multiplexing device, 13. Electro-spectrometer and host. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings.

[0037] The principle of the present invention is as follows: Figure 1 As shown. A 1550nm laser 1 serves as the seed light source, generating a single-sideband signal through an electro-optic modulator 2 driven by an arbitrary waveform generator (AWG) 3. The AWG and the electro-optic modulator are connected via a K-connector RF cable for modulating and generating the single-sideband signal. The linear sweep frequency range of the AWG output is f0 to (f0+B), so the sweep range is B. We use a sweep from 5GHz to 14.728GHz, resulting in a sweep range of 9.728GHz. The output of the electro-optic modulator 2 is amplified by an EDFA to compensate for losses, such as... Figure 2 The image shows the spectrum when the frequency is swept to 10 GHz. The single-sideband signal light is then passed through an electro-optical comb generator 5 to generate multi-wavelength FMCW lasers with equal frequency intervals. The electro-optical comb generator consists of one intensity modulator and two phase modulators connected in series. All three modulators are powered by the same radio frequency f. r A 25GHz radio frequency (RF) signal source drives the signal. The RF signal source output signal is split into three paths by a power divider, each driving a modulator via a phase shifter and an RF amplifier. The intensity modulator controls the flatness of the electro-optical frequency comb teeth, and the phase modulator is used for spectral expansion to obtain a multi-tooth electro-optical frequency comb. Therefore, the electro-optical comb generator 5 generates a frequency interval of f. r =25GHz 31-wavelength FMCW laser. For example... Figure 3The image shows a multi-wavelength spectrum when the frequency is swept to 10 GHz. Note that the sweep range is not limited to the parameters mentioned above; any setting is acceptable as long as the scanning beams do not overlap. Therefore, the maximum sweep range is close to the electro-optical comb driving frequency of 25 GHz. Furthermore, the electro-optical comb generator 5 described above is a cascaded modulator type, and the number of phase modulators is not limited to two. The main function of the phase modulators is to broaden the spectrum; more phase modulators result in a wider spectrum and allow for more scanning points. A cavity-enhanced electro-optical comb generator using a Fabry-Perot cavity with a built-in phase modulator can achieve the same effect. Both types of electro-optical comb generators can also use electro-optical comb generators integrated on a thin-film lithium niobate sheet. To compensate for the power loss of the electro-optical comb generator 5 and ensure sufficient power detection for each comb tooth, an erbium-doped fiber amplifier 6 amplifies the optical power. One amplified optical signal is used as the local oscillator, and the other is connected to the collimator 8 via a circulator 7 for detection.

[0038] The multi-wavelength FMCW laser is converted into spatial light by collimator 8 and then passes through a spatial grating 9 with a scribe density of 1000 lines per mm, operating at a wavelength of 1550 nm. During use, the incident angle of the laser is controlled at the Littrow angle, at which point the beam transmittance through the grating is highest. After passing through the spatial grating, the multi-wavelength laser beam is split horizontally. After propagating a certain distance, the beams no longer overlap, allowing for independent measurement of distance information at different locations. Note that the higher the scribe density of the spatial grating, the stronger the beam splitting effect, and the less likely beam overlap will occur, allowing for a larger sweep frequency range. The beam is then scanned vertically by a beam scanning control unit 10 (such as a microelectromechanical system galvanometer or a fast-turning mirror). Combining these two-dimensional scans enables three-dimensional stereoscopic detection.

[0039] A single-sideband signal light is generated into M frequency bands by an electro-optical comb generator 5. The reflected light returns along the original path and is mixed with the local oscillator light by a circulator 7. After passing through an M-channel (channel spacing 25 GHz) dense optical wave multiplexing device 12, the local oscillator light and 31 different frequencies of the reflected light enter different channels, with the same channel containing light of the same frequency band. Each channel's light is received by a different photodetector to obtain a beat frequency signal reflecting distance information. The beat frequency signal is measured by an electrospectrometer and transmitted to the host computer. The host computer calculates the obstacle distance and velocity information at the corresponding point using a set FMCW ranging formula and records it in an array. After the measurement is completed, a three-dimensional image of the obstacle is drawn and the velocity information is labeled. Thus, the electrospectrometer and the host computer 13 process the beat frequency signals from the photodetectors to achieve 31-channel parallel ranging. Distance D, velocity v, and beat frequency signal f are used to calculate the distance, velocity v, and beat frequency signal f. u f d Relationship (where f) u and f dThe higher and lower frequency beat frequencies in the beat frequency signal are respectively represented by the following formula, where T is the period of the AWG sweep signal, and f c To detect the frequency of light.

[0040]

[0041]

[0042] Figure 4 The image shown is an image created using this method. Here, we take a complete obstacle and a perforated obstacle that are 20cm apart as examples.

[0043] Let the speed of light be c, then the longitudinal resolution of the FMCW lidar is:

[0044]

[0045] In the above parameter settings, ΔR = 1.54cm.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention. The scope of protection of the present invention should be determined by the claims.

Claims

1. A parallel ranging method for linear frequency modulated continuous wave lidar based on an electro-optical comb, comprising the following steps: 1) Input the seed light source into the modulator; A waveform generator drives the modulator to modulate the seed light source, generating a single-sideband signal; wherein the frequency range of the linear sweep wave output by the waveform generator is [missing information]. B ; 2) The single-sideband signal is input into the electro-optical comb generator to generate multi-wavelength FMCW lasers with equal frequency intervals; wherein, the FMCW laser is a linear frequency modulated continuous wave laser; 3) The multi-wavelength FMCW laser is split into two outputs; one output is used as the local oscillator light input to a multi-channel dense optical multiplexing device; the other output is used as the probe light output through a circulator. 4) The multi-wavelength FMCW laser output from the circulator is collimated by a collimator and converted into spatial light before being incident on a spatial grating for beam splitting in the first dimension. Each beam after beam splitting by the spatial grating is scanned in the second dimension by a beam scanning control unit. The first dimension is perpendicular to the second dimension. 5) During scanning, the reflected light from the object returns along the original path and is input to the multi-channel dense optical wave multiplexing device through the circulator; the multi-channel dense optical wave multiplexing device mixes the reflected light and local oscillator light of the same frequency band in the same channel and outputs them. The light output from each channel is received by a corresponding photodetector and then input to the data processing unit. 6) The data processing unit draws a three-dimensional image of the object and labels the velocity information based on the signal input from the photodetector.

2. The method according to claim 1, characterized in that, The data processing unit includes an electron spectrometer and a host computer; the electron spectrometer measures the beat frequency signal based on the signal input from the photodetector and transmits it to the host computer; the host computer calculates distance information based on the beat frequency signal to achieve imaging.

3. The method according to claim 2, characterized in that, The data processing unit processes the signal input from the photodetector to obtain the distance to the object. ,speed ;in, f u and f d These represent the higher and lower frequency beat frequency values ​​in the beat frequency signal, respectively. T The period of the sweep frequency signal of the waveform generator is given. To detect the frequency of light.

4. The method according to claim 1, 2, or 3, characterized in that, The modulator is an electro-optic modulator; the single-sideband signal output by the electro-optic modulator is amplified by the first erbium-doped fiber amplifier and then input into the electro-optic comb generator to generate multi-wavelength lasers with equal frequency intervals.

5. The method according to claim 1, 2, or 3, characterized in that, The electro-optical comb generator includes an intensity modulator and several cascaded phase modulators; both the intensity modulator and the phase modulator operate at the same radio frequency. f r The radio frequency signal source drives the comb; wherein the intensity modulator is used to control the flatness of the comb teeth of the electro-optical frequency comb, and the phase modulator is used to expand the spectrum to obtain a multi-tooth electro-optical frequency comb.

6. The method according to claim 1, 2, or 3, characterized in that, The electro-optical comb generator is a cascaded modulator type electro-optical frequency comb generator, a cavity-enhanced electro-optical frequency comb generator with a built-in phase modulator in a Fabry-Perot cavity, or an electro-optical comb generator integrated on a thin-film lithium niobate sheet.

7. The method according to claim 1, 2, or 3, characterized in that, The multi-wavelength FMCW laser is amplified by the second erbium-doped fiber amplifier and then split into two outputs, one of which is used as the local oscillator and the other as the probe light.

8. The method according to claim 1, characterized in that, The wavelength of the seed light source is 1550 nm; the grating has a line density greater than or equal to 1000 lines per mm and a working wavelength of 1550 nm.

9. The method according to claim 1, characterized in that, The beam scanning control unit is a microelectromechanical system galvanometer or a rapid steering mirror.

10. A parallel ranging system for linear frequency modulated continuous wave lidar based on an electro-optical comb, characterized in that, It includes a laser, modulator, waveform generator, electro-optical comb generator, multi-channel dense optical multiplexing device, circulator, collimator, spatial grating, beam scanning control unit, and data processing unit; among which, The laser is used to generate a seed light source; The modulator is connected to the waveform generator and is used to modulate the input seed light source using the drive signal of the waveform generator to generate a single-sideband signal; wherein, the frequency range of the linear sweep wave output by the waveform generator is [missing information]. B ; The electro-optic comb generator is used to generate multi-wavelength FMCW lasers with equal frequency intervals according to the input single-sideband signal and split them into two outputs; one output is used as the local oscillator light input to a multi-channel dense optical multiplexing device; the other output is used as the probe light output through a circulator; wherein the FMCW laser is a linear frequency modulated continuous wave laser. The multi-wavelength FMCW laser output from the circulator is collimated by a collimator and converted into spatial light before being incident on a spatial grating for beam splitting in the first dimension. The beams split by the spatial grating are then scanned in the second dimension by the beam scanning control unit. The first dimension is perpendicular to the second dimension. During scanning, the reflected light from the object returns along the original path and is input to the multi-channel dense optical wave multiplexing device through the circulator; the multi-channel dense optical wave multiplexing device is used to mix the reflected light and the local oscillator light of the same frequency band in the same channel and output them. The light output from each channel is received by a corresponding photodetector and then input to the data processing unit. The data processing unit draws a three-dimensional image of the object and labels its speed information based on the signal input from the photodetector.

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