Pulse compression dual-comb frequency-modulated continuous-wave laser ranging device and ranging method

Abstract

A pulse compression double optical comb frequency modulation continuous wave laser ranging device and method, the device comprises a FMCW light source, a beam splitter, a probe light channel, a reference light channel, a beam combiner and a processing module, the FMCW light source outputs bidirectional linear sweep frequency laser with sweep bandwidth B and sweep period 2T, which is divided into probe light and reference light by the beam splitter.The probe light channel generates a first optical comb with comb interval f R , the reference light channel generates a second optical comb with comb interval f R +Δf R , the two signals are combined by the beam combiner and input to the photoelectric detector to generate beat signals, the processing module performs backend data processing on the beat signals, the time domain signal splicing is realized by using the phase correlation of the double optical comb, and the ranging accuracy is improved.The present application uses pulse compression technology to reduce the duty cycle of the probe light pulse and improve the ranging resolution;at the same time, the beat signal is generated by the double optical comb technology, the time domain signal splicing is realized by using the phase correlation between different combs, the equivalent sweep bandwidth is improved, and the ranging accuracy is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser ranging, in particular to a pulse compression double optical comb frequency-modulated continuous wave laser ranging device and method, which can avoid atmospheric turbulence and other path interference in the ranging path, and realize a practical high-precision ranging system. BACKGROUND

[0002] Laser ranging can achieve high-precision ranging of target objects and has wide application value in automatic driving, remote sensing detection, three-dimensional modeling, etc. By combining frequency-modulated continuous wave (FMCW) technology with double optical comb technology, millimeter-level measurement accuracy can be achieved with relatively low system complexity. The prior application patent CN202410559087.X proposes a frequency-modulated continuous wave laser radar measurement device based on double optical frequency combs, which uses the phase correlation of signal spectrum to improve the equivalent sweep bandwidth through phase correlation splicing, thereby improving the ranging accuracy. However, this scheme faces a challenge that cannot be ignored in actual application: the continuity of the measurement signal in time. This continuity causes disturbances such as atmospheric turbulence on the measurement path to continuously affect the amplitude and phase of the signal, introducing errors. As a complex natural phenomenon, the randomness and unpredictability of atmospheric turbulence make it difficult for traditional signal processing techniques to effectively suppress its impact on laser ranging accuracy.

[0003] Therefore, although the existing frequency-modulated continuous wave laser radar measurement device based on double optical frequency combs can exhibit excellent ranging accuracy and sensitivity in laboratory environments, in actual application scenarios, especially in complex and variable atmospheric environments, its performance is often significantly affected, resulting in ranging accuracy and sensitivity that cannot reach the level of laboratory environments. This situation seriously restricts the widespread application and in-depth development of laser ranging technology in key fields such as automatic driving and remote sensing detection.

[0004] Therefore, it is urgent to develop a new laser ranging scheme that can effectively suppress path interference factors such as atmospheric turbulence and ensure that the ranging accuracy and sensitivity of the ranging system in actual application can be consistent with the performance in laboratory environments. SUMMARY

[0005] The problem to be solved by the present application is the deficiency that the continuous existence of signals in time in the existing FMCW combined with double optical comb laser ranging scheme makes it susceptible to path interference in actual application, and a laser ranging device and method based on optical comb pulse compression are provided, which can effectively suppress path interference and avoid reduction in ranging performance.

[0006] To achieve the above-mentioned objectives, the technical solutions of the present application are as follows:

[0007] A pulse compression double optical comb frequency modulation continuous wave laser ranging device, comprising:

[0008] An FMCW light source outputs bidirectional linear sweep frequency laser with sweep bandwidth B and sweep period 2T;

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

[0010] In the probe light channel, the optical signal sequentially passes through a first optical comb generator, a pulse compressor, a measured target and a pulse stretcher. The first optical comb generator generates a first optical comb with a comb tooth interval f R for detecting the target object; the first optical comb enters the pulse compressor and is then emitted to the target object, the echo light of the target object enters the pulse stretcher and enters the beam combiner;

[0011] In the reference light channel, the optical signal sequentially passes through a second optical comb generator and a filter. The second optical comb generator generates a second optical comb with a comb tooth interval f R +Δf R , and Δf R is the repetition frequency difference between the double optical combs; the filter filters out the spectrum on one side of the center wavelength of the second optical comb to avoid mirror interference after beat with the probe light;

[0012] The beam combiner combines the two signals of the above-mentioned probe light channel and reference light channel and enters the photodetector to generate a beat signal;

[0013] The processing module performs back-end data processing on the beat signal, utilizes the phase correlation between the beat signals generated by different comb teeth, realizes time domain signal splicing, equivalently increases the sweep bandwidth, and further improves the ranging accuracy;

[0014] Further, the first optical comb generator and the second optical comb generator generate the required optical frequency comb through cascading intensity modulators and phase modulators, and apply microwave modulation signals to generate the required repetition frequency; the generated optical frequency comb should have a square time domain phase, i.e. a linear time domain frequency chirp;

[0015] Further, the pulse compressor is a dispersion device for compensating for the linear time domain frequency chirp of the first optical comb, and the dispersion amount of the pulse compressor should make the compressed output optical pulse be transform limited;

[0016] Further, the pulse stretcher is a dispersion device for restoring the optical pulse to a time domain continuous signal, and the dispersion amount of the pulse stretcher should be equal in absolute value and opposite in sign to the dispersion amount of the pulse compressor;

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

[0018] S1. The beat signal is divided into two parts, up-sweeping and down-sweeping, in the sweeping direction, and is processed respectively, and the up-sweeping part is processed first;

[0019] S2. The beat signal spectrum is segmented by Fourier transform with comb tooth interval Δf R , i.e. the range of the i-th frequency band is [(i-1)Δf R , iΔf R ];

[0020] S3. The [(i-1)Δf R , iΔf R ] spectrum of the i-th frequency band is moved to the baseband [0, Δf R ];

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

[0022] S5. In the time domain, all signals are processed for phase continuity, i.e. the phase at the end time of the previous signal is equal to the phase at the start time of the next signal, and amplitude compensation processing is performed, and time domain signal splicing is performed;

[0023] S6. The same processing is performed on the down-sweeping signal by repeating S2-S5;

[0024] S7. The up-sweeping spliced signal and the down-sweeping spliced signal after Fourier transform are compared 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 reflection DBR laser, a vertical cavity surface emitting VCSEL laser or an external cavity laser ECL.

[0026] Preferably, the comb tooth interval (i.e. the repetition frequency) of the optical comb is slightly smaller than the sweeping bandwidth of the FMCW light source, i.e. f R <B.

[0027] Preferably, the pulse compressor and the pulse stretcher are realized by using optical fibers, fiber gratings, bulk gratings or other devices with dispersion characteristics.

[0028] In principle, the application utilizes the characteristics 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 pulses, the narrowest of which can be compressed to the transform limited pulse, and the duty cycle (i.e. pulse width divided by pulse period) is equal to the comb tooth spacing (i.e. the repetition rate of the optical comb) divided by the spectral width, and the typical value is 5%~1%. When the compressed pulse signal is transmitted to the free space for ranging, only the interference in the path (such as atmospheric turbulence) can be felt in the time when the pulse exists, so the intensity of the disturbance is only 5%~1% of the whole path disturbance, and the influence of the path disturbance on the ranging can be significantly inhibited. And after receiving the echo signal, the pulse signal is restored to the time domain continuous signal by using a pulse stretcher with opposite dispersion, so that when coherent detection is performed with the local reference optical comb, the time domain overlap is the largest, and the beat frequency efficiency is improved. At the same time, the transmittance of the dispersion device can almost reach 100%, so the loss introduced is very small. In summary, the path disturbance can be suppressed, and the efficiency loss of local coherent detection can be avoided.

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

[0030] Compared with the prior application patent CN202410559087.X, the application avoids the noise accumulation of the path disturbance on the probe light by compressing the probe light into pulses before transmission, and restores the echo light to a time domain continuous signal, ensuring the detection efficiency of local coherent detection.

[0031] Compared with the traditional frequency modulated continuous wave (FMCW) scheme, the application realizes multi-channel parallel measurement by using double optical combs, and the ranging accuracy is significantly improved.

[0032] Compared with the double optical comb ranging scheme based on mode-locked lasers, the system structure of the application is simpler and the reliability is higher BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the pulse compression double optical comb frequency modulated continuous wave laser ranging device embodiment of the application.

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

[0035] Figure 2 is a frequency domain and time domain waveform schematic diagram of the optical signal of the measurement channel in the application. DETAILED DESCRIPTION

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

[0037] Please refer to Figure 1 , Figure 1 is a structural schematic diagram of an embodiment of the pulse compression double optical comb frequency modulation continuous wave laser ranging device of the application, as shown in the figure, a pulse compression double optical comb frequency modulation continuous wave laser ranging device, comprising:

[0038] an FMCW light source 1 for generating bidirectional linear sweep frequency laser with a sweep bandwidth of B and a sweep period of 2T;

[0039] a beam splitter 2 for splitting the sweep frequency laser generated by the FMCW light source 1 into two paths of probe light and reference light, respectively for detecting a target object and as a local reference.

[0040] Among them, along the transmission direction of the probe light, a first optical comb generator 3, a pulse compressor 4, a measured target 5 and a pulse stretcher 6 are sequentially arranged. The first optical comb generator 3 generates a first optical comb with a comb tooth interval f R , which is used to detect the target object; each comb tooth of the optical comb is synchronously swept, forming a plurality of parallel sweep frequency signals. The pulse compressor 4, as a dispersion device, compensates for the linear time domain frequency chirp of the first optical comb, compresses the time domain signal into a pulse. The first optical comb enters the pulse compressor 4, and the compressed pulse has a transform limit, that is, the ratio of the pulse width to the pulse period (duty cycle) is equal to the comb tooth interval divided by the spectral width in the frequency domain. Then it is emitted to the measured target object 5, and the echo light of the measured target object enters the pulse stretcher 6. The pulse stretcher 6 also serves as a dispersion device, but the dispersion amount is opposite to that of the pulse compressor, which 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] Along the transmission direction of the reference light, a second optical comb generator 7 and a filter 8 are sequentially arranged. The second optical comb generator 7 generates a second optical comb with a comb tooth interval f R +Δf R , and Δf R is the repetition frequency difference between the double optical combs. The filter 8 is used to filter out the spectrum on one side of the center wavelength of the second optical comb to avoid mirror interference after beat with the probe light.

[0042] After the probe light and the reference light are combined by a combiner 9, a beat signal is generated by a photodetector 10;

[0043] A processing module 11 performs back-end data processing on the beat signal, uses the phase correlation between the beat signals generated by different comb teeth to realize time domain signal splicing, equivalently increases the sweep bandwidth, and further improves the ranging accuracy.

[0044] The application utilizes the characteristics of the electro-optical frequency comb that can realize linear chirp signals, and through pulse compression technology, the time domain signals are compressed into pulses, which significantly reduces 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, to ensure the coherence detection efficiency with the local reference optical comb. This method not only suppresses the path interference, but also avoids the efficiency loss of coherent detection, thereby realizing high-precision and high-sensitivity laser ranging.

[0045] Figure 2 is the schematic diagram of the instantaneous frequency and instantaneous power of the optical signal of the measurement channel in the time domain in the application. The time domain instantaneous frequency of 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, the frequency domain generates an optical frequency comb, and each comb tooth of the optical frequency comb is synchronously swept, so the time domain instantaneous frequency is a multi-parallel swept signal with the optical frequency comb repetition frequency 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 is still an optical frequency comb with synchronous comb tooth sweeping, and the time domain power becomes a pulse sequence with 1 / f R After the measurement light is emitted, reflected by the target object, and then passes through the pulse stretcher, the instantaneous frequency waveform is frequency-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: The application relates to a frequency-modulated continuous-wave (FMCW) ranging system and a ranging method thereof. The FMCW light source is used for outputting bidirectional linear sweep frequency laser with a sweep bandwidth B and a sweep period 2T. The beam splitter is used for receiving the FMCW light source and splitting the FMCW light source into probe light and reference light. The detection light channel comprises, in sequence along a transmission direction of the detection light, a first optical comb generator, a pulse compressor, a target to be detected, and a pulse stretcher; wherein the first optical comb generator is configured to generate a first optical comb with a comb interval f R Each comb tooth of the first optical comb is synchronously swept; the pulse compressor is configured as a dispersion device to compensate for a linear time-domain frequency chirp of the first optical comb and compress a time-domain signal into a pulse; and the pulse stretcher is configured as a dispersion device with an absolute value of dispersion equal to that of the pulse compressor but with an opposite sign to restore a 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 a reference light transmission direction, wherein the second optical comb generator is configured to generate a second optical comb with comb teeth spaced by f R + Δf R , Δf R being a repetition frequency difference between the two optical combs; and the filter is configured to filter out a spectrum on one side of a center wavelength of the second optical comb. The beam combiner is used for combining two signals of the probe light channel and the reference light channel and inputting the two signals into a photoelectric detector to generate a beat signal. The processing module is used for performing back-end data processing on the beat signal, realizing time-domain signal splicing by using the phase correlation between beat signals generated by different combs, equivalently improving the sweep bandwidth, and further improving the ranging precision. The first optical comb generator and the second optical comb generator generate the required optical frequency comb 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, namely a linear time-domain frequency chirp. The pulse compressor compresses the time-domain signal into a pulse with a duty cycle equal to the comb spacing divided by the spectral width.

2. The pulse-compressed dual-optical-comb frequency-modulated continuous-wave laser ranging device of claim 1, wherein, 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).

3. The pulse-compressed double optical comb frequency-modulated continuous wave laser ranging device of claim 1, wherein, The optical comb tooth spacing f R Slightly less than the FMCW light source sweep bandwidth B.

4. A method for distance measurement using the laser distance measuring device according to any one of claims 1 to 3, characterized in that The application relates to a frequency-modulated continuous-wave (FMCW) ranging system and a ranging method thereof. The beat signal is divided into upward sweep frequency and downward sweep frequency according to the sweep direction, and the two parts are processed respectively. - for each partial signal, the spectrum of the beat signal is segmented by a comb spacing Δf R of length 2N, i.e. the i-th segment ranges from [(i-1)Δf R , iΔf R ] - shifting the spectrum of each frequency band into baseband [0, Δf R ] ; Inverse Fourier transform is performed on all frequency bands. Phase continuous processing and amplitude compensation processing are performed on all signals in the time domain, and time-domain signal splicing is performed. The upward sweep splicing signal and the downward sweep splicing signal are compared to obtain the speed and distance information of the target object.

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