Frequency-shifted dual-comb based frequency-modulated continuous-wave laser ranging device

Abstract

The application provides a frequency-shifted double optical comb-based frequency-modulated continuous wave laser ranging device, which combines frequency-modulated continuous wave and double optical comb technology and comprises an FMCW light source, a beam splitter, a detection and reference light channel, a beam combiner, a photoelectric detector and a processing module. The FMCW light source outputs linear sweep laser, which is divided into two paths by the beam splitter, the detection light channel uses a first optical comb generator and a circulator to detect a target, and the reference light channel increases the frequency f FS by a frequency shifter and generates an optical comb with different comb tooth intervals by a second optical comb generator, wherein f FS and the repetition frequency difference Δf R are not integer multiples, thereby effectively avoiding interference. After the two paths of signals are combined by the beam combiner, the photoelectric detector converts the signals into beat signals, and the processing module splices the time domain signals by using the phase correlation, thereby improving the ranging accuracy. The frequency-shifted double optical comb technology improves the accuracy and anti-interference performance, and the efficient data processing algorithm ensures fast measurement and wide application range.

Description

Technical Field

[0001] This invention relates to the field of laser ranging, specifically to a frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb, which fully utilizes the optical frequency comb spectrum and improves ranging accuracy. Background Technology

[0002] Laser ranging utilizes the high resolution of lasers to achieve high-precision ranging of target objects, and has wide application value in fields such as autonomous driving and remote sensing. By combining frequency-modulated continuous wave (FMCW) technology with dual-comb technology, millimeter-level measurement accuracy can be achieved with low system complexity. A prior patent application, CN202410559087.X, discloses a measurement device for a frequency-modulated continuous wave lidar based on dual-comb technology. It utilizes the coherence of the signal spectrum and improves the equivalent sweep bandwidth through coherent splicing, thereby enhancing ranging accuracy. However, in this scheme, to avoid image beat interference introduced by the symmetrical comb spectrum during coherent detection, one of the combs filters out half of the spectrum. Although this method alleviates the interference problem to some extent, it inevitably sacrifices effective detection power, adversely affecting ranging accuracy.

[0003] Given the aforementioned limitations, the industry urgently needs a more efficient and innovative solution designed to more fully utilize the comb line power of the optical comb, thereby significantly improving the sensitivity of the ranging system without compromising ranging accuracy. This will not only drive laser ranging technology towards higher precision and efficiency but also lay a solid foundation for further development in fields such as autonomous driving and remote sensing. Summary of the Invention

[0004] The problem this invention aims to solve is the deficiency in existing FMCW laser ranging schemes that combine dual optical combs and require sacrificing half of the optical frequency comb spectrum, resulting in reduced sensitivity. This invention provides an FMCW laser ranging device and method based on frequency-shifting dual optical frequency combs, which can more effectively utilize the optical comb spectral power and improve ranging sensitivity.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb includes:

[0007] FMCW light source, outputting bidirectional linear sweeping laser with a sweep bandwidth of B and a sweep period of 2T;

[0008] A beam splitter receives the FMCW light source and splits it into probe light and reference light;

[0009] In the probe optical channel, the optical signal passes sequentially through the first optical comb generator and the circulator. The first optical comb generator produces the comb tooth spacing f. R The first optical comb is used to detect the target object; the first optical comb enters the first port of the circulator and is emitted to the target object from the second port of the circulator; the echo light from the target object enters the second port of the circulator and is output from the third port of the circulator.

[0010] In the reference optical path, the optical signal sequentially passes through a frequency shifter and a second optical comb generator. The frequency shifter increases the frequency of the optical signal by f. FS The second optical comb generator produces the comb tooth spacing f. R +Δf R The second optical comb, where Δf R The repetition rate difference between the two optical combs; the frequency shifting frequency f FS It cannot be the frequency repetition rate difference Δf R Integer multiples of;

[0011] The beam combiner combines the two signals from the probe optical channel and the reference optical channel and sends them to the photodetector to generate a beat frequency signal.

[0012] The processing module performs backend data processing on the beat frequency signal, and utilizes the coherence between the beat frequency signals generated by different comb teeth to realize time-domain signal splicing, effectively increasing the sweep frequency bandwidth, thereby improving the ranging accuracy.

[0013] Furthermore, the frequency shift frequency f generated by the frequency shifter FS The values ​​should be chosen to ensure that the signals generated by the beat frequencies of the left half (i.e., the part with frequencies less than the center frequency) and the right half (i.e., the part with frequencies greater than the center frequency) of the optical comb do not interleave in the spectrum, so as to facilitate spectrum segmentation.

[0014] Furthermore, the backend time-domain splicing data processing specifically includes the following steps:

[0015] S1. Divide the beat frequency signal into two parts, upward sweep frequency and downward sweep frequency, according to the sweep frequency direction, and process them separately. First, process the upward sweep frequency part.

[0016] S2. Using Fourier transform with comb-tooth spacing Δf R The length of the beat frequency signal spectrum is used to divide the spectrum, that is, the range of the i-th frequency band is [(i-1)Δf R ,iΔf R ];

[0017] S3. [(i-1)Δf] of the i-th frequency band R ,(i-0.5)Δf R The sub-band spectrum is shifted to the baseband [0, 0.5Δf]. R Within ], [(i-0.5)ΔfR ,iΔf R After the sub-band spectrum is flipped, it is moved to the baseband [0, 0.5Δf]. R [Inside (i.e., iΔf)] R Moved to baseband 0 frequency, (i-0.5)Δf R Moved to baseband 0.5Δf R ); where the spectrum generated by the beat frequency of the right half of the optical comb (i.e., the part greater than the center frequency) corresponds to [(i-1)Δf R ,(i-0.5)Δf R The sub-band, the spectrum generated by the beat frequency of the left half of the optical comb (i.e., the part smaller than the center frequency) corresponds to [(i-0.5)Δf]. R ,iΔf R Sub-band;

[0018] S4. Repeat S3, shifting N frequency bands, resulting in a total of 2N bands [0, 0.5Δf]. R The sub-bands of ] are then subjected to inverse Fourier transform of all 2N sub-bands;

[0019] S5. Perform phase continuity processing on all signals in the time domain, that is, the phase of the end time of the previous signal is equal to the phase of the start time of the next signal, and perform amplitude compensation processing, and then splice the time domain signals.

[0020] S6. Repeat S2-S5 to perform the same processing on the signal of the downward frequency sweep section;

[0021] S7. Compare the up-scanned frequency spliced ​​signal and the down-scanned frequency spliced ​​signal after Fourier transform to obtain the velocity and distance information of the target object.

[0022] Preferably, the FMCW light source is a distributed feedback DFB laser, a distributed Bragg reflector (DBR) laser, a vertical cavity surface emitter (VCSEL) laser, or an external cavity laser (ECL).

[0023] Preferably, the optical comb generator is an electro-optical comb or a Kerr optical comb.

[0024] Preferably, the spacing between the comb teeth is slightly smaller than the bandwidth of the seed light sweep frequency, i.e., f R <B。

[0025] Preferably, the frequency shifter is an acousto-optic frequency shifter or a frequency shifter based on a single-sideband electro-optic modulator.

[0026] Preferably, the frequency shift frequency f generated by the frequency shifter FS The value range is within the frequency repetition rate difference Δf R 10% to 40%.

[0027] This invention eliminates image interference in the beat frequency between the reference and measurement optical combs by applying a frequency shift to the local reference optical comb, allowing all teeth of all optical combs to provide ranging information. Simultaneously, by appropriately selecting the frequency shift f... FS and the frequency difference Δf R The value of allows the signals obtained from the beat frequencies of the left and right halves of the optical comb to be distinguishable in the spectrum. This significantly increases the number of comb teeth available for time-domain stitching, thereby substantially improving ranging accuracy.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] Compared to the earlier patent application CN202410559087.X, this invention eliminates the need to filter out half of the spectrum from one optical comb, thus doubling the number of comb teeth available for splicing and doubling the ranging accuracy.

[0030] Compared to the traditional frequency modulated continuous wave (FMCW) scheme, this invention utilizes dual optical combs to achieve multi-channel parallel measurement, which significantly improves ranging accuracy.

[0031] Compared to dual-comb ranging schemes based on mode-locked lasers, the system structure of this invention is simpler and more reliable.

[0032] By utilizing dual-optical-comb technology and introducing frequency repetition difference and frequency shift, the accuracy of ranging is effectively improved. Dual-optical-comb technology fully leverages the high spectral resolution and pulse rate advantages of optical frequency combs to achieve high-precision measurements. The back-end data processing module performs coherent processing on the beat frequency signal to achieve time-domain signal stitching, effectively increasing the sweep bandwidth and further improving ranging accuracy. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an embodiment of the frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to the present invention.

[0034] 1-FMCW light source, 2-beam splitter, 3-first optical comb generator, 4-circulator, 5-target under test, 6-frequency shifter, 7-second optical comb generator, 8-beam combiner, 9-photodetector, 10-processing module

[0035] Figure 2 This is a schematic diagram of the beat frequency of the measuring optical comb (first optical comb) and the reference optical comb (second optical comb) in this invention.

[0036] Where the frequency shift f FS =25MHz, frequency repetition rate difference Δf R =100MHz. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention. Embodiments of the present invention include, but are not limited to, the following embodiments.

[0038] Please see Figure 1 , Figure 1 This is a schematic diagram of an embodiment of the frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to the present invention. As shown in the figure, a frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb includes:

[0039] The FMCW light source 1 outputs a bidirectional linearly swept laser with a specific sweep bandwidth B and a sweep period of 2T. In this embodiment, the FMCW light source can be a distributed feedback DFB laser, a distributed Bragg reflector (DBR) laser, a vertical cavity surface emitter (VCSEL) laser, or an external cavity laser (ECL), etc.

[0040] Beam splitter 2 splits the laser beam output from the FMCW light source into two paths: a probe beam and a reference beam.

[0041] In the detection optical channel, the optical signal passes sequentially through the first optical comb generator 3 and the circulator 4. The first optical comb generator 3 generates the comb tooth spacing f. R The first optical comb is used to detect the target object; the circulator 4 enables the detection light to be transmitted unidirectionally to the target object and receives the echo light from the target object. The first optical comb enters the first port of the circulator, is emitted to the target object from the second port of the circulator, and the echo light from the target object enters the second port of the circulator and is output from the third port of the circulator. The first optical comb generator is an electro-optical comb or a Kerr optical comb, and the comb tooth spacing is slightly smaller than the bandwidth of the seed light sweep frequency, i.e., f. R <B。

[0042] In the reference optical path, the optical signal sequentially passes through frequency shifter 6 and second optical comb generator 7. Frequency shifter 6 increases the frequency of the optical signal by f. FS The second optical comb generator produces the comb tooth spacing f. R +Δf R The second optical comb, where Δf R The repetition rate difference between the two optical combs; the frequency shifting frequency f FS It cannot be the frequency repetition rate difference Δf R The frequency shift frequency is an integer multiple of the specified frequency to ensure interference elimination. The second optical comb generator uses an electro-optical comb or a Kerr optical comb to generate the frequency. The frequency shifter employs an acousto-optic frequency shifter or a frequency shifter based on a single-sideband electro-optic modulator. The frequency shifter generates a frequency shift frequency f. FS The value range is within the frequency repetition rate difference Δf R 10% to 40% of the signal is used to ensure the elimination of interference and the effective differentiation of signals.

[0043] The beam combiner 8 combines the two signals from the probe optical channel and the reference optical channel.

[0044] Photodetector 9: Converts the combined optical signal into an electrical signal, namely a beat frequency signal. The beat frequency signal contains distance information of the target object.

[0045] Processing module 10 performs backend data processing on the beat frequency signal, and utilizes the coherence between the beat frequency signals generated by different comb teeth to realize time domain signal splicing, effectively increasing the sweep frequency bandwidth, thereby improving the ranging accuracy.

[0046] When the probe light shines on the target object, some of the light is reflected back, forming an echo. This echo and the reference light are combined at a beam combiner and then enter a photodetector. The photodetector converts the combined optical signal into an electrical signal, namely a beat frequency signal. The frequency of the beat frequency signal is related to the distance to the target object.

[0047] The key to backend data processing lies in distinguishing and processing the signals obtained from the beat frequencies of the left and right halves of the optical comb. The specific steps are as follows:

[0048] S1. Frequency Division Processing: The received beat frequency signal is divided into two parts according to the sweep direction: upward sweep and downward sweep, and processed separately; the upward sweep part is processed first.

[0049] S2. Spectrum Segmentation: Through Fourier transform, the spectrum of the beat frequency signal is segmented into comb-tooth intervals Δf. R The length is divided, that is, the range of the i-th frequency band is [(i-1)Δf R ,iΔf R ];

[0050] S3. Spectrum shifting and flipping: [(i-1)Δf] of the i-th frequency band R ,(i-0.5)Δf R The sub-band spectrum is shifted to the baseband [0, 0.5Δf]. R Within ], [(i-0.5)Δf R ,iΔf R After the sub-band spectrum is flipped, it is moved to the baseband [0, 0.5Δf]. R [Inside (i.e., iΔf)] R Moved to baseband 0 frequency, (i-0.5)Δf R Moved to baseband 0.5Δf R ); where the spectrum generated by the beat frequency of the right half of the optical comb (i.e., the part greater than the center frequency) corresponds to [(i-1)Δf R ,(i-0.5)Δf R The sub-band, the spectrum generated by the beat frequency of the left half of the optical comb (i.e., the part smaller than the center frequency) corresponds to [(i-0.5)Δf]. R ,iΔfR Sub-band;

[0051] S4. Inverse Fourier Transform: Repeat S3, shifting N frequency bands, resulting in 2N bands [0, 0.5Δf]. R The sub-bands are then divided into 2N sub-bands, and then inverse Fourier transforms are performed on all 2N sub-bands to convert them from the frequency domain back to the time domain.

[0052] S5. Time Domain Stitching: In the time domain, all signals are phase-continuously processed to ensure that the phase of the previous signal's end time is equal to the phase of the next signal's start time. Simultaneously, amplitude compensation is performed to eliminate amplitude distortion caused by segmentation and shifting. Finally, these processed time-domain signals are stitched together to form a complete upward sweep frequency signal.

[0053] S6. Repeat steps S2 to S5 for the downward frequency sweep portion of the signal to obtain the complete downward frequency sweep splicing signal.

[0054] S7. Compare the up-scanned and down-scanned spliced ​​signals after Fourier transform to obtain the velocity and distance information of the target object. That is, by measuring the phase difference and time delay between the two spliced ​​signals, the relative velocity and absolute distance of the target object can be calculated.

[0055] This embodiment eliminates image interference in the beat frequency between the reference optical comb and the measurement optical comb by applying a frequency shift to the local reference optical comb. Simultaneously, by appropriately selecting the frequency shift frequency f... FS and the frequency difference Δf R The value of allows the signals obtained from the beat frequencies of the left and right halves of the optical comb to be distinguishable in the spectrum. This significantly increases the number of comb teeth available for time-domain stitching, thereby substantially improving ranging accuracy.

[0056] Figure 2 This is a schematic diagram of the beat frequency of the measuring optical comb (first optical comb) and the reference optical comb (second optical comb) in this invention.

[0057] Where the frequency shift f FS =25MHz, frequency repetition rate difference Δf R=100MHz. When there is no target, the beat frequency signals of the two optical combs are a series of spectral lines such as 25MHz, 75MHz, 125MHz, and 175MHz, with a frequency band interval of 100MHz. Each 100MHz band contains two spectral lines: +25MHz and +75MHz. When there is a target, the +25MHz spectral line shifts to the right (e.g., to +26MHz), and the +75MHz spectral line shifts to the left (e.g., to +74MHz), with equal shift amounts (e.g., both 1MHz). Therefore, taking the first frequency band 0-100MHz as an example, the 50MHz-100MHz sub-band is mirrored around 50MHz. At this point, the original 74MHz spectral line becomes 26MHz, which can be coherently spliced ​​with the original 26MHz spectral line in the 0-50MHz sub-band. Similarly, the second frequency band 100MHz-200MHz can also be first shifted to 0-100MHz, and then divided into two 50MHz wide sub-bands for similar processing. Finally... Figure 2 The 0-300MHz band includes three 100MHz frequency bands or six 50MHz sub-bands. After the frequency shifting and mirror reversal processes described above, a total of six spectral lines located at 26MHz are obtained, which can be phase-splitting to effectively increase the measurement time and achieve higher ranging accuracy.

Claims

1. A frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb, characterized in that, include: FMCW light source, used to output bidirectional linear sweep laser with sweep bandwidth B and sweep period 2T; A beam splitter is used to receive the laser output from the FMCW light source and split it into probe light and reference light; The probe optical channel includes a first optical comb generator and a circulator, wherein the first optical comb generator is used to generate a comb tooth spacing of f. R The first optical comb is used to detect the target object, and the circulator is used to emit the first optical comb to the target object and receive its echo light; A reference optical channel includes a frequency shifter and a second optical comb generator, wherein the frequency shifter is used to increase the frequency of the reference optical signal by f. FS The second optical comb generator is used to generate a comb tooth spacing of f. R +Δf R The second optical comb, where Δf R The frequency shift frequency f is the repetition frequency difference between the first and second optical combs. FS It cannot be the frequency repetition rate difference Δf R Integer multiples of; A beam combiner is used to combine two signals from the probe optical channel and the reference optical channel. A photodetector is used to receive the combined optical signal output by the beam combiner and convert it into a beat frequency signal; The processing module is used to perform back-end data processing on the beat frequency signal, and to realize time-domain signal splicing by utilizing the coherence between the beat frequency signals generated by different comb teeth, so as to effectively increase the sweep frequency bandwidth B, thereby improving the ranging accuracy. The backend data processing includes: S1. Frequency division processing: The received beat frequency signal is divided into two parts, upward sweep frequency and downward sweep frequency, according to the sweep frequency direction, and processed separately; S2. Spectrum Segmentation: Through Fourier transform, the spectrum of the beat frequency signal is segmented into comb-tooth intervals Δf. R Divide the length into segments; S3. Spectrum Shifting and Flipping: The segmented spectrum sub-bands are shifted and flipped so that the spectra generated by the beat frequencies of the left and right halves of the optical comb are shifted to the baseband [0, 0.5Δf]. R ]Inside; The frequency shift frequency f generated by the frequency shifter FS The frequency repetition rate difference Δf between the two optical combs R 10% to 40%.

2. The frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to claim 1, characterized in that, The processing module includes a Fourier transform unit, a spectrum segmentation unit, a spectrum shifting and flipping unit, an inverse Fourier transform unit, a phase continuity processing unit, and an amplitude compensation processing unit, which are used to perform fine processing on the beat frequency signal to improve the accuracy of time-domain signal splicing and ranging.

3. The laser ranging device according to claim 2, characterized in that, The processing module also includes a signal comparison unit, which is used to compare the upper frequency splicing signal and the lower frequency splicing signal to obtain the speed and distance information of the target object.

4. The frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to claim 1, characterized in that, The FMCW light source employs a distributed feedback DFB laser, a distributed Bragg reflector (DBR) laser, a vertical cavity surface emitter (VCSEL) laser, or an external cavity laser (ECL).

5. The frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to claim 4, characterized in that, The sweep period 2T of the bidirectional linear sweep laser output by the FMCW light source is a preset value to ensure that the echo light from the target object can be received within the sweep period.

6. The frequency-modulated continuous wave laser ranging device based on frequency-shifting dual optical combs according to claim 1, characterized in that, The optical combs generated by the first and second optical comb generators have stable comb tooth spacing and phase relationship to ensure the coherence of the beat frequency signal.

7. The frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to claim 6, characterized in that, Both the first optical comb generator (3) and the second optical comb generator (7) are electro-optical combs or Kerr optical combs, and f R <B。 8. The frequency-modulated continuous wave laser ranging device based on frequency-shifting dual optical combs according to claim 1, characterized in that, The frequency shifter increases the frequency of the optical signal through electro-optic, acousto-optic, or thermo-optic effects.

9. The frequency-modulated continuous wave laser ranging device based on a frequency-shifting dual optical comb according to claim 1, characterized in that, The backend data processing also includes: S4. Inverse Fourier Transform: Perform an inverse Fourier transform on all processed sub-bands to convert them back from the frequency domain to the time domain; S5. Time Domain Stitching: In the time domain, all signals are processed for phase continuity and amplitude compensation. Then, the processed time domain signals are stitched together to form complete upward and downward frequency sweep signals respectively. S6. Comparison Processing: Compare the upward frequency-scanned spliced ​​signal and the downward frequency-scanned spliced ​​signal after Fourier transform to obtain the speed and distance information of the target object.

Images