Pulse compression double-optical comb frequency modulation continuous wave laser ranging device and ranging method

Abstract

The invention discloses a pulse compression double-optical comb frequency modulation continuous wave laser ranging device and method, the device comprises an FMCW light source, a beam splitter, a detection light channel, a reference light channel, a beam combiner and a processing module, the FMCW light source outputs bidirectional linear frequency sweeping laser with the frequency sweeping bandwidth B and the frequency sweeping period 2T, and the bidirectional linear frequency sweeping laser is divided into detection light and reference light through the beam splitter. The detection optical channel, the first optical comb generating the comb tooth interval of fR, the reference optical channel and the second optical comb generating the comb tooth interval of fR + delta fR are used, two paths of signals are combined through the beam combiner and then input to the photoelectric detector to generate beat frequency signals, the processing module carries out rear-end data processing on the beat frequency signals, time domain signal splicing is achieved through the coherence of the double optical combs, and time domain signals are obtained. And the ranging precision is improved. According to the invention, the pulse compression technology is used to reduce the duty ratio of the detection light pulse and improve the ranging resolution; meanwhile, beat frequency signals are generated through the double-optical comb technology, time domain signal splicing is achieved through coherence between different comb teeth, the frequency sweeping bandwidth is equivalently improved, and the distance measuring precision is further improved.

Description

Technical Field

[0001] The present invention relates to the field of laser ranging, and in particular to a pulse compression dual-comb frequency-modulated continuous wave laser ranging device and ranging method, which can avoid path interference such as atmospheric turbulence in the ranging path and realize a practical high-precision ranging system. Background Art

[0002] Laser ranging can achieve high-precision ranging of target objects and has wide application value in the fields of autonomous driving, remote sensing detection, three-dimensional modeling, etc. By combining frequency-modulated continuous wave (FMCW) technology with dual optical comb technology, millimeter-level measurement accuracy can be obtained with low system complexity. The previously applied patent CN202410559087.X proposes a measurement device for frequency-modulated continuous wave lidar based on dual optical frequency combs, which uses the coherence of the signal spectrum to improve the equivalent sweep bandwidth through coherent splicing, thereby improving the ranging accuracy. However, this solution faces a challenge that cannot be ignored in practical applications: the continuity of the measurement signal in time. This continuity leads to interference on the measurement path, such as atmospheric turbulence, which will continuously affect the amplitude and phase of the signal and introduce errors. As a complex natural phenomenon, the randomness and unpredictability of atmospheric turbulence make it difficult for traditional signal processing technology to effectively suppress its impact on the accuracy of laser ranging.

[0003] Therefore, although the existing FMCW laser radar measurement device based on dual optical frequency comb can show excellent ranging accuracy and sensitivity in laboratory environment, in actual application scenarios, especially in the face of complex and changeable atmospheric environment, its performance is often significantly affected, resulting in ranging accuracy and sensitivity can not reach the level of laboratory environment. This situation seriously restricts the wide application and in-depth development of laser ranging technology in key fields such as autonomous driving and remote sensing detection.

[0004] In view of this, there is an urgent need to develop a new laser ranging scheme that should be able to effectively suppress path interference factors such as atmospheric turbulence, and ensure that the ranging accuracy and sensitivity of the ranging system in practical applications can be consistent with the performance in laboratory environments. Summary of the invention

[0005] The problem to be solved by the present invention is that the signal in the existing FMCW combined with dual optical comb laser ranging solution persists in time, resulting in the deficiency of being susceptible to path interference in practical applications. A laser ranging device and method based on optical frequency comb pulse compression are provided, which can effectively suppress path interference and avoid degradation of ranging performance.

[0006] In order to achieve the above objectives, the technical solutions of the present invention are as follows:

[0007] A pulse compression dual-comb frequency modulated continuous wave laser ranging device, comprising:

[0008] FMCW light source, outputting bidirectional linear frequency sweeping laser with frequency sweeping bandwidth B and frequency sweeping period 2T;

[0009] A beam splitter receives the FMCW light source and splits it into a detection light and a reference light;

[0010] In the detection optical channel, the optical signal passes through the first optical comb generator, the pulse compressor, the target to be detected and the pulse stretcher in sequence. Among them, the first optical comb generator generates a comb tooth interval f R The first optical comb is used to detect the target object; the first optical comb enters the pulse compressor and then is emitted to the target object, and the echo light of the target object enters the pulse stretcher and enters the beam combiner;

[0011] In the reference optical channel, the optical signal passes through the second optical comb generator and the filter in sequence. The second optical comb generator generates a comb tooth interval f R +Δf R The second optical comb, Δf R is the repetition frequency difference between the two optical combs; the filter filters out the spectrum on one side of the central wavelength of the second optical comb to avoid image interference after beating with the detection light;

[0012] A beam combiner combines the two signals of the detection optical channel and the reference optical channel and sends them into a photodetector to generate a beat frequency signal;

[0013] A processing module performs back-end data processing on the beat frequency signal, utilizes the coherence between the beat frequency signals generated by different comb teeth, realizes time domain signal splicing, equivalently improves the sweep bandwidth, and thus improves the ranging accuracy;

[0014] Furthermore, the first optical comb generator and the second optical comb generator generate an optical frequency comb with a desired repetition rate by cascading an intensity modulator and a phase modulator and applying a microwave modulation signal; the generated optical frequency comb should have a square time domain phase, that is, a linear time domain frequency chirp;

[0015] Furthermore, the pulse compressor is a dispersion device used to compensate for the linear time-domain frequency chirp of the first optical comb, and its dispersion amount should make the optical pulse output after compression to be transformation-limited;

[0016] Furthermore, the pulse stretcher is a dispersive device used to restore the optical pulse to a continuous signal in the time domain, and its dispersion amount should be equal to the absolute value of the dispersion amount of the pulse compressor, but with an opposite sign;

[0017] Furthermore, the back-end time domain splicing data processing specifically includes the following steps:

[0018] S1. The beat frequency signal is divided into two parts, an upward sweep and a downward sweep, according to the sweep direction, and processed separately, first processing the upward sweep part;

[0019] S2. Through Fourier transform with comb teeth spacing Δf R The beat frequency signal spectrum is divided by the length of R ,iΔf R ];

[0020] S3. Set [(i-1)Δf R ,iΔf R ] spectrum is moved to baseband [0,Δf R ]Inside;

[0021] S4. Repeat S3 to move N frequency bands, and then perform inverse Fourier transform on all N frequency bands;

[0022] 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 perform time domain signal splicing;

[0023] S6. Repeat S2-S5 to perform the same processing on the signal of the downward sweep portion;

[0024] S7. Compare the upper frequency sweep stitching signal and the lower frequency sweep stitching signal after Fourier transformation to obtain the speed and distance information of the target object.

[0025] Preferably, the FMCW light source adopts a distributed feedback DFB laser, a distributed Bragg reflector DBR laser, a vertical cavity surface emitting VCSEL laser or an external cavity laser ECL.

[0026] Preferably, the optical comb teeth spacing (i.e., repetition frequency) is slightly smaller than the FMCW light source sweep bandwidth, i.e., f R <B。

[0027] Preferably, the pulse compressor and pulse stretcher are implemented using optical fiber, fiber grating, volume grating or other devices with dispersion characteristics.

[0028] In principle, the present invention utilizes the characteristic that the electro-optical frequency comb can realize linear chirp signals, and uses a pulse compressor with corresponding dispersion to compress the time domain signal into a pulse, which can be compressed to the narrowest transformation limit pulse, and its duty cycle (i.e., pulse width divided by pulse period) is equal to the comb tooth spacing in the frequency domain (i.e., optical comb repetition rate) divided by the spectrum width, and the typical value is 5% to 1%. When the compressed pulse signal is transmitted to the free space for ranging, the interference in the path (such as atmospheric turbulence) can be felt only during the time when the pulse exists, so the intensity of the disturbance is only 5% to 1% of the total disturbance of the entire path, which can significantly suppress the influence of path interference on ranging. After receiving the echo signal, the pulse signal is restored to a time domain continuous signal by using a pulse stretcher with opposite dispersion, so that when coherently detected with the local reference optical comb, it has the maximum time domain overlap, and improves the beat frequency efficiency. At the same time, the transmittance of the dispersion device can reach almost 100%, so the loss introduced is extremely small. In summary, the suppression of path interference can be achieved at the same time, and the efficiency loss of local coherent detection can be avoided.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] Compared with the previously applied patent CN202410559087.X, the present invention avoids the noise accumulation of path interference on the detection light by compressing the detection light into pulses before emitting it, and then broadens the echo light into a time-domain continuous signal, thereby ensuring the detection efficiency of local coherent detection.

[0031] Compared with the traditional frequency modulated continuous wave (FMCW) scheme, the present invention uses dual optical combs to achieve multi-channel parallel measurement, and the ranging accuracy is significantly improved.

[0032] Compared with the dual-comb ranging solution based on mode-locked laser, the system structure of the present invention is simpler and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of an embodiment of a pulse compression dual-comb frequency-modulated continuous wave laser ranging device of the present invention.

[0034] 1-FMCW light source, 2-beam splitter, 3-first optical comb generator, 4-pulse compressor, 5-target, 6-pulse stretcher, 7-second optical comb generator, 8-filter, 9-beam combiner, 10-photodetector, 11-processing module.

[0035] Figure 2 It is a schematic diagram of the frequency domain and time domain waveforms of the optical signal of the measurement channel in the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and examples, but the protection scope of the present invention shall not be limited thereto. The embodiments of the present invention include but are not limited to the following examples.

[0037] See also Figure 1 , Figure 1 1 is a schematic diagram of the structure of an embodiment of a pulse compression dual-comb frequency modulated continuous wave laser ranging device according to the present invention. As shown in the figure, a pulse compression dual-comb frequency modulated continuous wave laser ranging device comprises:

[0038] FMCW light source 1, used to generate a bidirectional linear frequency sweeping laser with a frequency sweeping bandwidth of B and a frequency sweeping period of 2T;

[0039] The beam splitter 2 is used to split the frequency-sweeping laser light generated by the FMCW light source 1 into two paths: a detection light and a reference light, which are used to detect the target object and serve as a local reference, respectively.

[0040] Among them, a first optical comb generator 3, a pulse compressor 4, a target 5 and a pulse stretcher 6 are sequentially arranged along the transmission direction of the detection light. The first optical comb generator 3 generates a comb tooth interval f R The first optical comb is used to detect the target object; each comb tooth of the optical comb is synchronously swept to form a multi-channel parallel swept signal. The pulse compressor 4, as a dispersion device, compensates for the linear time-domain frequency chirp of the first optical comb and compresses the time-domain signal into a pulse. The first optical comb enters the pulse compressor 4, and the compressed pulse has a transformation limit, that is, the ratio of the pulse width to the pulse period (duty cycle) is equal to the comb tooth spacing in the frequency domain divided by the spectral width. It is then emitted to the target object 5 to be measured, and the echo light of the target object to be measured enters the pulse stretcher 6. The pulse stretcher 6 also acts as a dispersion device, but the dispersion amount is opposite to that of the pulse compressor. It is used to restore the received echo pulse signal to a time-domain continuous signal for coherent detection with the local reference optical comb.

[0041] A second optical comb generator 7 and a filter 8 are sequentially arranged along the reference light transmission direction. The second optical comb generator 7 generates a comb tooth interval f R +Δf R The second optical comb, Δf R The filter 8 is used to filter out the spectrum on one side of the central wavelength of the second optical comb to avoid image interference after beating with the detection light.

[0042] The detection light and the reference light are combined by the beam combiner 9 and enter the photodetector 10 to generate a beat frequency signal;

[0043] The processing module 11 performs back-end 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, which is equivalent to improving the sweep bandwidth, thereby improving the ranging accuracy.

[0044] The present invention utilizes the characteristic that the electro-optical frequency comb can realize linear chirp signals, and compresses the time domain signal into pulses through pulse compression technology, which significantly reduces the impact of path interference on ranging. After receiving the echo signal, the pulse stretcher is used to restore the pulse signal to a time domain continuous signal to ensure the coherent detection efficiency with the local reference optical comb. This method not only suppresses path interference, but also avoids the efficiency loss of coherent detection, thereby realizing high-precision and high-sensitivity laser ranging.

[0045] Figure 2 It is a schematic diagram of the instantaneous frequency and instantaneous power of the optical signal of the measurement channel in the time domain in the present invention. The instantaneous frequency in the time domain generated by the FMCW light source is a linearly swept signal, and the time domain power corresponds to a constant continuous wave. After passing through the first optical comb generator, an optical frequency comb is generated in the frequency domain, and each comb tooth of the optical frequency comb is synchronously swept. Therefore, the instantaneous frequency in the time domain is a multi-channel parallel swept signal with the repetition frequency of the optical frequency comb as the interval, and the time domain power still corresponds to a constant continuous wave. After passing through the pulse compressor, the instantaneous frequency waveform remains unchanged, and it is still an optical frequency comb with synchronous sweeping of the comb teeth. The time domain power becomes a 1 / f R After the measurement light is emitted, it is reflected by the target object and then passes through the pulse stretcher. The instantaneous frequency waveform is shifted on the time axis, and the time domain power waveform is restored to a constant continuous wave.

Claims

1. A pulse compression dual-comb frequency modulated continuous wave laser ranging device, characterized in that: include: FMCW light source, used to output bidirectional linear frequency sweeping laser with frequency sweeping bandwidth B and frequency sweeping period 2T; A beam splitter, used for receiving the FMCW light source and splitting it into a detection light and a reference light; The detection light channel comprises a first optical comb generator, a pulse compressor, a target to be detected and a pulse stretcher which are sequentially arranged along the transmission direction of the detection light; wherein the first optical comb generator is used to generate a comb tooth interval f R A first optical comb is used, and each comb tooth of the first optical comb is synchronously swept; the pulse compressor is used as a dispersion device to compensate for the linear time-domain frequency chirp of the first optical comb and compress the time-domain signal into a pulse; the pulse stretcher is used as a dispersion device with an absolute value equal to that of the pulse compressor but an opposite sign, and is used to restore the received echo pulse signal into a time-domain continuous signal; The reference light channel comprises a second optical comb generator and a filter arranged in sequence along the reference light transmission direction, wherein the second optical comb generator is used to generate a comb tooth interval f R +Δf R The second optical comb, Δf R is the repetition frequency difference between the two optical combs; the filter is used to filter out the spectrum on one side of the central wavelength of the second optical comb; A beam combiner, used to combine the two signals of the detection light channel and the reference light channel, and input the combined signals into a photodetector to generate a beat frequency signal; The processing module is used to perform back-end data processing on the beat frequency signal, and utilize the coherence between the beat frequency signals generated by different comb teeth to realize time domain signal splicing, equivalently improve the sweep bandwidth, and thus improve the ranging accuracy.

2. The pulse compression dual-comb frequency modulated continuous wave laser ranging device according to claim 1, characterized in that: The first optical comb generator and the second optical comb generator generate an optical frequency comb with a desired repetition rate by cascading an intensity modulator and a phase modulator and applying a microwave modulation signal; the generated optical frequency comb has a square time domain phase, that is, a linear time domain frequency chirp.

3. The pulse compression dual-comb frequency modulated continuous wave laser ranging device according to claim 1, characterized in that: The pulse compressor compresses the time domain signal into a pulse duty cycle that is equal to the comb tooth spacing in the frequency domain divided by the spectrum width.

4. The pulse compression dual-comb frequency modulated continuous wave laser ranging device according to claim 1, characterized in that: The FMCW light source adopts a distributed feedback DFB laser, a distributed Bragg reflector DBR laser, a vertical cavity surface emitting VCSEL laser or an external cavity laser ECL.

5. The pulse compression dual-comb frequency modulated continuous wave laser ranging device according to claim 1, characterized in that: The optical comb teeth spacing f R Slightly smaller than the FMCW light source sweep bandwidth B.

6. A method for measuring distance using the laser distance measuring device according to any one of claims 1 to 5, characterized in that: include: -The beat frequency signal is divided into two parts, upward sweep and downward sweep, according to the sweep direction, and processed separately; -For each part of the signal, the comb spacing Δf is calculated by Fourier transform R The length of the beat frequency signal spectrum is divided into two parts, that is, the range of the i-th frequency band is [(i-1)Δf R ,iΔf R ]; - Move the spectrum of each frequency band to the baseband [0,Δf R ]Inside; - Perform inverse Fourier transform on all frequency bands; -Perform phase continuity and amplitude compensation processing on all signals in the time domain, and perform time domain signal splicing; -Compare the processed upward sweep stitching signal and downward sweep stitching signal to obtain the speed and distance information of the target object.

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