A high-precision ranging method and device based on a double auxiliary interferometer time-stretch swept-frequency interference

Abstract

The application discloses a high-precision ranging method and device based on a double-assistant interferometer time stretching sweep frequency interference, and relates to the technical field of absolute distance measurement of non-cooperative targets. In order to solve the technical defects of the prior art, such as the large ranging result drift caused by the initial wavelength fluctuation of a light source and the sweep frequency nonlinearity, and the interference signal interference by zero frequency noise, the technical scheme provided by the application comprises the following steps: obtaining a linear frequency modulation light signal output by a common source sweep frequency laser, and transmitting the linear frequency modulation light signal to a measurement interferometer, an assistant interferometer and a resampling assistant interferometer respectively to form a common source three-interference structure; introducing a dispersive medium through a reference arm to make reference light generate time stretching, and forming a chirp beat signal by interference with measurement light; and performing k-domain resampling and cross-correlation processing on the beat signal to extract target distance information. The application is suitable for absolute distance measurement of non-cooperative targets with high precision and large range, and is especially suitable for the fields of laser radar three-dimensional modeling, precision industrial detection and robot calibration.

Description

Technical Field

[0001] It involves technical fields such as absolute distance measurement of non-cooperative targets, fiber optic sensing, OFDR, frequency sweep interferometry, OCT, and lidar three-dimensional measurement, specifically involving high-precision ranging based on time-stretched frequency sweep interferometry using a dual-auxiliary interferometer. Background Technology

[0002] Frequency scanning interferometry (FSI) is a core technology in the fields of non-cooperative target absolute distance measurement and lidar 3D measurement. It typically uses a high-bandwidth, narrow-linewidth linear frequency-modulated laser as the light source. The target's scattered light is interfered with the local reference light in the time domain. The target distance is demodulated by analyzing the spectrum of the beat signal. This technology can currently achieve distance resolution and ranging accuracy at the micrometer or even sub-micrometer level, meeting the needs of fields such as large-size workpiece 3D shape measurement, laser trackers, 3D rapid scanning and inspection, reverse engineering, robot calibration, and automated production.

[0003] The basic process of frequency sweeping interferometric ranging technology is as follows: Figure 1 As shown, the time delay difference is... The complex form of the beat signal from the interference of two frequency-modulated continuous beams can be expressed as: (1) in, Indicates the amplitude of the beat signal. Represents the angular frequency of light. This represents the frequency of light that changes over time. This represents the initial optical frequency. It is typically determined using an FFT. Perform quickly Domain spectral analysis, where the computational resolution (range bin) of the distance spectrum is... : (2) It is only related to the sweep bandwidth. In the field of precision measurement with FMCW lidar, due to limitations in laser and data processing efficiency, the sweep bandwidth of the light source is generally <10nm. For precision requirements ranging from tens to even a few micrometers, direct FFT is clearly insufficient. The Zoom FFT using complex modulation-downsampling and the Chirp-Z Transform (CZT) algorithm using spiral sampling are classic methods for achieving higher frequency resolution within specific narrow spectral ranges. Both require prior information from a pre-executed FFT to plan the frequency range to be subdivided before performing frequency subdivision. Therefore, high time complexity is their main problem. Yongwoo Park et al. proposed a cross-chirped interferometry system and method for ranging. This method uses a dispersive medium to slightly change the sweep slope of the reference light, interfering with it against the measuring arm. Due to the target time delay, the light frequencies of the two beams cross at a certain moment. The zero-frequency position of the interference signal is then searched to achieve distance demodulation. This process is as follows: Figure 2 As shown.

[0004] However, this method has a serious problem: fluctuations in the initial wavelength of the light source cause drift in the measurement results. The initial wavelength stability varies considerably among different swept-frequency lasers. For a wide-bandwidth external cavity swept-frequency laser, assuming its initial wavelength fluctuation... The wavelength is 0.01 nm, and the dispersion D of the fiber grating used is approximately 100. This corresponds to a 150μm drift in the ranging result ( This is absolutely unacceptable in precision measurement.

[0005] In summary, existing technologies suffer from technical defects such as large drift in ranging results caused by fluctuations in the initial wavelength of the light source and nonlinearity of the sweep frequency, high complexity of high-resolution algorithms, and interference of interference signals by zero-frequency noise. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as large drift in ranging results due to initial wavelength fluctuations of the light source, high complexity of high-resolution algorithms, and interference from zero-frequency noise in the interference signal, the technical solution provided by this invention is as follows: A high-precision ranging method based on time-stretched sweep interferometry using a dual-auxiliary interferometer includes: The steps include acquiring the linear frequency-modulated optical signal output from the common-source swept-frequency laser and transmitting it to the measurement interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer to form a common-source three-interference structure; The steps involve introducing a dispersive medium through a reference arm to cause time stretching of the reference light, which then interferes with the measurement light to form a chirped beat frequency signal. The steps involve k-domain resampling and cross-correlation processing of the beat frequency signal to extract target distance information.

[0007] Furthermore, a preferred embodiment is provided in which the optical signal output by the swept laser is simultaneously injected into a three-way interferometer via an optical splitter.

[0008] Furthermore, a preferred embodiment is provided in which the dispersive medium in the reference arm is a chirped fiber Bragg grating, used to achieve group delay dispersion to achieve time stretching.

[0009] Furthermore, a preferred embodiment is provided in which the measuring interferometer and the auxiliary interferometer adopt an unbalanced heterodyne structure, wherein only the reference arm introduces dispersion and sets an optical path difference, so that the frequency of the interference signal is far from zero frequency.

[0010] Furthermore, a preferred embodiment is provided in which a resampling auxiliary interferometer is used to output an equal-frequency-interval interference signal, which is processed by a comparator and used as an external clock signal to drive the data acquisition module to perform k-domain resampling of the beat frequency signal.

[0011] A time-stretched sweep interferometric high-precision ranging device based on dual-auxiliary interferometers is also provided, comprising: A module that acquires the linear frequency-modulated optical signal output from a common-source swept-frequency laser and transmits it to a measurement interferometer, an auxiliary interferometer, and a resampling auxiliary interferometer to form a common-source three-interference structure; A module that introduces a dispersive medium through a reference arm to cause time stretching of the reference light, which then interferes with the measurement light to form a chirped beat frequency signal; A module that performs k-domain resampling and cross-correlation processing on the beat frequency signal to extract target distance information.

[0012] A time-stretched sweep interferometry high-precision ranging system based on dual-auxiliary interferometers is also provided to implement the method, including: A swept-frequency laser is used to emit linearly frequency-modulated optical signals; An optical splitter structure is used to divide an optical signal into three paths; The time stretching module is used to perform dispersion stretching on two reference beams; The measuring interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer each receive the split optical signal. The measuring interferometer and the auxiliary interferometer form a beat frequency interference signal through the time stretching module, and the resampling auxiliary interferometer provides an equal optical frequency interval interference signal. The detector module is used to receive the interference signals output by each interferometer and convert them into electrical signals.

[0013] A computer storage medium is also provided for storing a computer program, which, when read by the computer, executes the method.

[0014] A computer is also provided, including a processor and a storage medium, wherein the computer executes the method when the processor reads a computer program stored in the storage medium.

[0015] A computer program product is also provided, which, when executed, implements the method described.

[0016] Compared with the prior art, the advantages of the technical solution provided by the present invention are as follows: A common-source dual-auxiliary interferometer structure is adopted to solve the distance drift problem caused by initial frequency fluctuations of the light source in existing swept-frequency interferometric ranging systems. Since the measuring interferometer and the auxiliary interferometer use the same light source and share a time-stretching module, the errors caused by initial optical frequency fluctuations in their generated interference signals are essentially the same. By cross-correlation processing of the two interference signals, this common-mode error can be canceled, thereby effectively suppressing fluctuations in the ranging results and improving the repeatability and stability of the measurement system. Compared with the cross-chirped interferometry method proposed by Yongwoo Park et al., this method significantly reduces the drift error caused by initial wavelength instability, maintaining stable ranging even with sub-micron level accuracy requirements.

[0017] The interference pattern is improved from the traditional zero-frequency cross-interference method to an unbalanced heterodyne interference structure. In this structure, the reference arm introduces dispersion for time stretching, while the measuring arm is not stretched, creating an unbalanced state. Furthermore, by delaying the interference signal spectrum away from the zero-frequency point, zero-frequency noise and image interference problems are avoided. Compared to the traditional structure, this method improves the signal-to-noise ratio and stability of the interference signal, providing a clearer and more reliable signal foundation for subsequent high-precision distance demodulation.

[0018] A resampling-assisted interferometer is used to provide an equal-frequency sampling clock, solving the problem of non-uniform signal sampling caused by the nonlinear frequency modulation of the swept laser. By measuring the time delay difference between the interferometer and the resampling interferometer, a k-domain resampling mechanism is constructed to achieve data reconstruction with uniform optical frequency distribution, thereby improving the frequency matching accuracy and distance demodulation accuracy.

[0019] By utilizing a dispersive medium CFBG to map target delay information from the time domain to the optical frequency domain, the delay estimation problem is transformed into a frequency estimation problem. Range demodulation is then performed through frequency cross-correlation analysis. This frequency domain mapping strategy improves demodulation sensitivity and anti-interference capability compared to traditional time-domain methods that directly process chirped signals. Especially under the influence of CFBG with high dispersion, it effectively achieves frequency "zoom" amplification, increasing delay resolution by thousands of times. This enables higher-precision ranging within a limited sampling bandwidth, far exceeding the accuracy level achievable by existing FMCW radars limited by a 10nm bandwidth.

[0020] It is suitable for high-precision, large-range non-cooperative target absolute distance measurement, especially for fields such as lidar 3D modeling, precision industrial inspection and robot calibration. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the basic FSI ranging process; Figure 2 This is a schematic diagram of a ranging method based on cross-chirped interferometry. Figure 3 This is a schematic diagram illustrating the principle of a large-range ranging method based on common-source dual-optical time-stretched sweeping interferometry. Figure 4 This is a schematic diagram of the optical path structure of the ranging system; Figure 5 This is a schematic diagram of the time stretching module. Detailed Implementation

[0022] To make the advantages and benefits of the technical solution provided by the present invention clearer, the technical solution provided by the present invention will now be described in further detail with reference to the accompanying drawings, specifically: Implementation Method 1: This implementation method provides a high-precision ranging method based on time-stretched sweep interferometry using a dual-auxiliary interferometer, including: The steps include acquiring the linear frequency-modulated optical signal output from the common-source swept-frequency laser and transmitting it to the measurement interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer to form a common-source three-interference structure; The steps involve introducing a dispersive medium through a reference arm to cause time stretching of the reference light, which then interferes with the measurement light to form a chirped beat frequency signal. The steps involve k-domain resampling and cross-correlation processing of the beat frequency signal to extract target distance information.

[0023] The optical signal output by the swept laser is simultaneously injected into the three interferometers through an optical splitter.

[0024] The dispersive medium in the reference arm is a chirped fiber Bragg grating, used to achieve group delay dispersion to achieve time stretching.

[0025] The measuring interferometer and the auxiliary interferometer adopt an unbalanced heterodyne structure, in which only the reference arm introduces dispersion and sets the optical path difference, so that the frequency of the interference signal is far away from zero frequency.

[0026] The resampling-assisted interferometer is used to output an equal-frequency-interval interference signal, which, after being processed by a comparator, serves as an external clock signal to drive the data acquisition module to perform k-domain resampling of the beat frequency signal.

[0027] A time-stretched sweep interferometry high-precision ranging system based on dual-auxiliary interferometers is also provided to implement the method, including: A swept-frequency laser is used to emit linearly frequency-modulated optical signals; An optical splitter structure is used to divide an optical signal into three paths; The time stretching module is used to perform dispersion stretching on two reference beams; The measuring interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer each receive the split optical signal. The measuring interferometer and the auxiliary interferometer form a beat frequency interference signal through the time stretching module, and the resampling auxiliary interferometer provides an equal optical frequency interval interference signal. The detector module is used to receive the interference signals output by each interferometer and convert them into electrical signals.

[0028] Implementation Method Two: This implementation method further describes the technical solution provided in Implementation Method One in more detail, specifically: This embodiment provides a time-stretched sweep frequency interferometry high-precision ranging method and device based on dual-auxiliary interferometers. It is suitable for absolute distance measurement of non-cooperative targets, has sub-micron ranging accuracy and tens of meters range, and is especially suitable for scenarios such as precision measurement, lidar 3D modeling, and robot calibration.

[0029] Step 1: Constructing a common-source interferometric ranging system First, a three-channel interferometric system is constructed, comprising a measurement interferometer, an auxiliary interferometer, and a resampling interferometer. The three interferometers share a single swept-frequency laser source and time-stretching module to achieve signal synchronization. Specifically, the measurement interferometer acquires the beat frequency signal related to the target distance; the auxiliary interferometer cross-correlates with the measurement interferometer signal to compensate for errors caused by initial frequency fluctuations of the light source; and the resampling interferometer provides a clock signal of equal optical frequency for resampling the beat frequency signal.

[0030] Step 2: Build the time stretching module and connect it to the interferometer A dispersive medium, such as a dispersion-compensated fiber grating (CFBG), is inserted into the reference arm of both the measuring interferometer and the auxiliary interferometer, and unidirectional transmission is achieved through a circulator. The group delay dispersion characteristics of the dispersive medium compress the reference arm signal in the optical frequency domain, achieving time stretching. At this point, the interference signal is transformed from a traditional single-frequency modulated signal into a chirped signal, and the target distance information is mapped to frequency variation characteristics.

[0031] Step 3: Generate unbalanced interference signals By adjusting the optical path lengths of the measuring arm and the reference arm to create a certain length difference, an unbalanced structure is formed. Furthermore, the reference arm introduces dispersion while the measuring arm remains unstretched, resulting in unbalanced time-stretched interference. Because the interference signal frequency is far from zero, low-frequency noise and image interference are avoided, thus improving signal quality.

[0032] Step 4: Cross-correlation processing of auxiliary interferometer signal and measurement signal The beat frequency signal acquired by the co-source auxiliary interferometer and the beat frequency signal of the measuring interferometer are cross-correlated. Since the two interferometers share a common light source, the initial frequency fluctuations of the light source have almost the same impact on the two signals. Therefore, the common-mode error can be effectively canceled through cross-correlation calculation, resulting in a more stable and interference-resistant target range response. This cross-correlation result serves as the basis for subsequent range calculations.

[0033] Step 5: The k-domain resampling clock is provided by the resampling interferometer. The nonlinearity of frequency variation in swept-frequency lasers over time leads to uneven sampling intervals in the beat frequency signal in the optical frequency domain, affecting the accuracy of spectrum processing. A resampling interferometer obtains interference signals with equal optical frequency intervals. This signal, through a comparator and shaping circuit, outputs a uniform clock pulse signal, which serves as the external clock for the data acquisition card. This clock drives the k-domain resampling operation of the measured interference signal and the auxiliary interference signal, achieving uniform data reconstruction in the optical frequency domain.

[0034] Step Six: Perform adaptive frequency shift cross-correlation matching processing After k-domain equal-interval resampling, adaptive frequency-shifting cross-correlation matching is performed on the measured interference signal and the auxiliary interference signal. This processing method combines the sparsity of the beat frequency signal and the advantages of cross-correlation filtering, allowing direct extraction of the frequency position information corresponding to the target distance from the chirped interference signal without prior coarse FFT analysis. The matching result is represented by a narrow pulse output, the peak position of which corresponds to the target distance.

[0035] Step 7: Calculate the target distance Finally, based on the peak position of the frequency cross-correlation and the system calibration parameters (including dispersion, time stretching coefficient, interference length difference, etc.), the absolute distance value of the target is calculated. Since the cross-correlation processing has offset the drift error caused by the initial wavelength fluctuation of the light source, and combined with the frequency uniformity provided by k-domain resampling, the obtained ranging result has high repeatability and stability, with an accuracy of sub-micrometer level and a range of tens of meters.

[0036] Regarding the optical path structure: Figure 4 The overall optical path structure of the time-stretched sweep interferometric ranging system based on dual-auxiliary interferometers proposed in this invention is demonstrated. The entire system mainly consists of the following parts: 1. TLS (Tunable Laser Source) – Frequency-swept laser Function: Outputs a linearly frequency-modulated, narrow-linewidth laser signal as the unified light source for the system; Requirements: Wide sweep bandwidth and good frequency stability; The output light is simultaneously fed into three interferometers as an input signal.

[0037] 2. Optical Coupler System Function: Splits the optical signal output by TLS into three paths: The signal is fed into the measuring interferometer. The feed is sent directly into the auxiliary interferometer; One path is fed into the resampling-assisted interferometer; Requirements: Consistent splitting ratio, reasonable distribution of signal strength, and all three beams must originate from the same source.

[0038] 3. Time-stretching Module Function: Used to introduce group delay dispersion in the reference optical path, stretching the original optical signal in the time domain to achieve modulation of the chirped signal.

[0039] Location: Located in the reference arm of the measuring interferometer and the auxiliary interferometer, sharing this module.

[0040] Implementation: See details for the specific structure. Figure 5 This can be achieved in two ways.

[0041] 4. Measurement Interferometer Structure: It consists of a measuring arm and a reference arm, which are ultimately combined at the photodetector to form an interference signal; Measuring arm path: Optical signal → OC1 → CIR1 (optical circulator) → Lens → Target (object under test) reflection; Echo → Lens → CIR1 → OC4 → BPD1; Reference arm path: Optical signal → OC1 → OC2 → CIR2 → CFBG (dispersion grating) → CIR2 → OC5 → OC4 → BPD1; Features: The non-equilibrium interference structure is formed by stretching only the reference arm; The output beat frequency signal (a chirped signal) is input to BPD1 for use in main distance demodulation.

[0042] 5. Auxiliary Interferometer Function: To generate a cross-correlation beat frequency signal with the measuring interferometer, used to eliminate initial frequency drift error; Measuring arm path: TLS → OC1 → OC2 → OC3 → DL1 (Delayed Fiber) → OC6 → BPD2; Reference arm path: TLS → OC1 → OC2 → CIR2 → CFBG → CIR2 → OC5 → OC6 → BPD2; Features: The two interfering signals have a common source and are synchronized; the initial frequency fluctuation has a common-mode effect. Cross-correlation can cancel common-mode error and enhance system stability; Output beat frequency signal input BPD2.

[0043] 6. Resampling Auxiliary Interferometer Function: Generates equal-frequency-interval interference signals and outputs an external clock signal for k-domain resampling of beat frequency signals; Measuring arm path: TLS → OC1 → OC2 → OC3 → OC7 → DL2 → OC8 → BPD3; Reference arm path: TLS → OC1 → OC2 → OC3 → OC7 → OC8 → BPD3; Features: Interference fringes are formed using delay fiber DL2; The output is used for an optical frequency clock signal; It provides a precise resampling reference, solving the problem of nonlinear frequency modulation of the light source; The output signal is input to BPD3 and sent to a comparator or shaping circuit as an external clock for the data acquisition card.

[0044] 7. BPD1 / BPD2 / BPD3 (Balanced Photodetector) Function: Used to detect the output optical signal of a three-way interferometer and convert it into an electrical signal; Requirements: High response rate and low noise, for accurate capture of interferometric beat frequencies.

[0045] Figure 5 Detailed Explanation of Two Implementation Methods for the Time Stretching Module The time stretching module is one of the core modules of this system. Its purpose is to introduce group delay dispersion on the reference optical path, generate a chirped signal, and improve the distance demodulation resolution.

[0046] Implementation Method 1: Based on CFBG (Chired Fiber Bragg Grating) structure: Input light → CIR (optical circulator) → CFBG → CIR output; effect: CFBG provides fixed group delay dispersion (GDD), which allows for precise control of the frequency-time mapping. The stretched reference light exhibits a linear frequency change in the frequency domain.

[0047] With a compact structure and high stability, it is suitable for conventional fixed dispersion requirements, has high linearity during stretching, and can be customized to 0 for higher-order dispersion.

[0048] Implementation Method 2: Based on DCF (Dispersion Compensating Fiber) structure: Input light → CIR → DCF → out effect: DCF dispersion-compensated fiber serves the same purpose as CFBG, but with advantages such as lower cost, easier adjustment of dispersion, and the ability to achieve greater bandwidth and group delay dispersion.

[0049] Figure 4 The core innovation of this system, the three-way interference structure and its optical connection method, are demonstrated. Figure 5 The implementation method of the time stretching module is specifically given. The entire structure effectively solves key technical problems such as initial frequency drift of the light source, nonlinear frequency modulation and zero-frequency noise interference through homogeneous design, double interference structure, dispersion stretching and resampling mechanism, and realizes a high-precision, robust and wide-range high-performance absolute ranging system.

[0050] Implementation Method 3: Combination Figure 1-5 This embodiment describes the technical solution provided above in further detail through specific examples. Specifically: A large-range ranging method based on common-source dual-optical time-stretched sweeping interferometry is proposed, the idea of ​​which is as follows: Figure 3 As shown, a dispersive medium is first introduced onto the reference arm to obtain a local oscillator light (stretched light) with a changed frequency modulation slope. This local oscillator light, together with the unstretched measurement light, forms a non-equilibrium time-stretched interference. The beat signal changes from a single-frequency signal in FSI to a chirped signal, and the frequency estimation problem can be transformed into a correlation delay estimation problem for the chirped signal. The group delay dispersion of the dispersive medium... Mapping the target time delay to the optical frequency domain, and Figure 3 The peak positions of the cross-correlation spectrum correspond to each other, because Extremely small The spectral line spacing FSR corresponding to the domain Much smaller than the spectral line spacing in FFT Therefore, this method can more precisely characterize the cross-correlation spectrum and improve the accuracy of time delay estimation. This process can be figuratively described as starting from... Domain FFT spectrum to Domain cross-correlation spectrum zoom magnification, zoom magnification is The system employs a common-source dual-optical time-stretched sweep frequency interference structure to ensure synchronization between the measurement signal and the reference signal, and suppresses the initial frequency drift of the light source through cross-correlation.

[0051] Based on this ranging method, the ranging system designed in this patent is as follows: Figure 4 As shown, the system consists of three parts: a measurement interferometer, an auxiliary interferometer, and a resampling auxiliary interferometer. The measurement interferometer and the auxiliary interferometer share a time stretching module, which can... Figure 5 The two methods shown are used for construction.

[0052] Specifically, the measurement interferometer consists of the measurement arm TLS-OC1-CIR1-Lens-Target-Lens-CIR1-OC4-BPD1 and the reference arm TLS-OC1-OC2-CIR2-CFBG-CIR2-OC5-OC4-BPD1; the auxiliary interferometer consists of the measurement arm TLS-OC1-OC2-OC3-DL1-OC6-BPD2 and the reference arm. Composed of TLS-OC1-OC2-CIR2-CFBG-CIR2-OC5-OC6-BPD2; resampling interferometer measuring arm. The system consists of TLS-OC1-OC2-OC3-OC7-DL2-OC8-BPD3 and reference arms TLS-OC1-OC2-OC3-OC7-OC8-BPD3. Both interferometers employ an unbalanced heterodyne interferometric structure. Unbalanced means that time stretching occurs only in one reference arm, while the measuring arm is not stretched, resulting in an unbalanced structure. Heterodyne refers to the inconsistent lengths of the measuring arm and the reference arm, causing the interference signal frequency to be approximately zero. The measuring interferometer and the auxiliary interferometer share a single TLS light source and the same time stretching module, forming a homogeneous dual-interference structure to suppress the influence of initial wavelength fluctuations of the light source on the ranging results. Since the sweep frequency and time do not satisfy a strict linear relationship, a method of equal optical frequency interval resampling (k-domain resampling) is generally used to resample the non-uniform beat signal. The resampling clock comes from the interference signal of the auxiliary interferometer, and the time delay difference between the measuring arm and the reference arm satisfies the following condition: The optical frequency resampling process can be represented as: (3) Therefore, the total number of sampling points can be obtained. ,in The relative change in the angular frequency of the light source is given by the free spectral range (FSR) of the resampling interferometer. .

[0053] The time stretching module consists of a dispersive medium CFBG and a circulator CIR1, where CFBG can be regarded as a phase filter, and its transfer function can be expressed as: (4) Its phase can be at the CFBG center frequency At this point, through Taylor expansion, we obtain: (5) in, Indicates the initial phase. Indicates the optical path length of the medium. This represents the group delay (GD) at the center frequency. These represent group-delay dispersion (GDD) and third-order dispersion (TOD), respectively. The dispersion of a CFBG is generally determined by... To describe, and there is a relationship The beat frequency signal generated by the measurement interferometer It can be expressed in complex form as: (6) in, This indicates the time delay difference of the measuring interferometer.

[0054] Because a non-equilibrium heterodyne interference form was adopted, i.e. This ensures that the interference signal does not pass through zero frequency, thus avoiding zero-frequency noise interference and image frequency interference.

[0055] Because the initial optical frequency of a frequency-sweeping laser cannot be guaranteed to be exactly the same when performing repeated frequency sweeps, i.e., the initial frequency fluctuates, let's assume that the initial angular frequency of the sweeping light is the same as the center frequency of the CFBG. The difference is ,but It can be represented as: (7) in, This represents the change in angular frequency, with an initial value of 0 and a final value of [missing value]. , Let be the sweep bandwidth. Equation (6) can be converted to about perfect square: (8) in, It is a constant. This represents the change in time delay introduced by the initial optical frequency fluctuation, which will lead to... The distance drift error severely degrades the repeatability and stability of the ranging system.

[0056] To suppress To address the reference drift caused by fluctuations, an additional non-equilibrium time-stretching auxiliary interferometer of the same origin was designed. Since the two interferometers are of the same origin, the fluctuations in the initial optical frequency... They remain basically synchronized. The signal from the auxiliary interferometer can be represented as: (9) in, To assist in understanding the time delay difference between the interferometer's measuring arm and the reference arm, pre-calibration can be performed before the measurement begins. The definitions of the remaining symbols are consistent with those in equation (6).

[0057] The beat signal of the resampling interferometer is used as an external clock for the acquisition card through conditioning circuits such as comparators, and the clock signal is used to adjust the two interference signals mentioned above. and By performing k-domain equal-interval resampling to correct the nonlinearity of the swept-frequency laser, and substituting equation (3) into equations (8) and (9), the resampled signal can be obtained: (10) (11) Cross-correlation of the resampled signals yields a compressed narrow pulse output. : (12) Time delay error caused by initial optical frequency fluctuations in the two interference signals Since they are essentially the same and are common-mode terms, the time delay error in the two interfering signals can be reduced through cross-correlation processing. They cancel each other out, thus suppressing reference drift.

[0058] Finally, searching peak position The distance to be measured can be obtained. : (13) The ranging formula shows that it can suppress the reference drift problem caused by the initial optical frequency fluctuation of the swept frequency light source, and greatly improve the repeatability of the measurement system.

[0059] The above description of several specific embodiments further details the technical solution provided by the present invention in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the above-described specific embodiments are not intended to limit the present invention. Any reasonable modifications and improvements to the present invention, combinations of embodiments, and equivalent substitutions based on the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision ranging method based on time-stretched sweep interferometry using a dual-auxiliary interferometer, characterized in that, include: Step 1: Construct a common-source interferometric ranging system; The linear frequency-modulated optical signal output from the common-source swept-frequency laser is acquired and simultaneously injected into the measurement interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer through an optical splitter to form a three-interference structure with the same source. The measurement interferometer is used to acquire the beat frequency signal related to the target distance. The auxiliary interferometer is used to form a cross-correlation beat frequency signal with the measurement interferometer. Step 2: Construct a time stretching module and connect it to the interferometer; introduce a dispersive medium through the reference arms of the measuring interferometer and the auxiliary interferometer to cause time stretching of the reference light, which interferes with the measuring light to form a chirped beat frequency signal; the dispersive medium is a chirped fiber Bragg grating, used to achieve group delay dispersion to achieve time stretching; the time stretching module is shared in the reference arms of the measuring interferometer and the auxiliary interferometer. Step 3: Generate unbalanced interference signal; by adjusting the optical path lengths of the measuring arm and the reference arm, a certain length difference is made between them to form an unbalanced structure; the measuring interferometer and the auxiliary interferometer adopt an unbalanced heterodyne structure, with only the reference arm introducing a dispersive medium and setting an optical path difference, so that the interference signal frequency is far away from the zero frequency point; Step 4: Cross-correlation processing of auxiliary interferometer signal and measurement signal; By cross-correlation processing of the beat frequency signals acquired by the co-source auxiliary interferometer and the measurement interferometer, common-mode errors and errors caused by the initial frequency fluctuations of the light source can be effectively offset. Step 5: The k-domain resampling clock is provided by the resampling interferometer; the equal optical frequency interval interference signal is obtained by the resampling interferometer, and a uniform clock pulse signal is output by the comparator and shaping circuit as the external clock of the data acquisition card, which is used to drive the k-domain resampling operation of the measurement interference signal and the auxiliary interference signal, so as to realize the uniform reconstruction of data in the optical frequency domain. Step Six: Perform adaptive frequency shift cross-correlation matching processing; After completing the k-domain equal-interval resampling, adaptive frequency-shifting cross-correlation matching processing is performed on the measured interference signal and the auxiliary interference signal; The frequency position information corresponding to the target distance is extracted from the chirped interference signal; the matching result is represented by a narrow pulse output, the peak position of which corresponds to the target distance. Step 7: Calculate the target distance; based on the peak position of the frequency cross-correlation and the system calibration parameters, calculate the absolute distance value of the target; the system calibration parameters include dispersion, time stretching coefficient, and interference length difference.

2. A time-stretched sweep interferometry high-precision ranging device based on a dual-auxiliary interferometer, used to implement the method of claim 1, characterized in that, include: A module that acquires the linear frequency-modulated optical signal output from a common-source swept-frequency laser and transmits it to a measurement interferometer, an auxiliary interferometer, and a resampling auxiliary interferometer to form a common-source three-interference structure; A module that introduces a dispersive medium through the reference arm of the measuring interferometer and the auxiliary interferometer to cause time stretching of the reference light, which then interferes with the measuring light to form a chirped beat frequency signal; A module for generating unbalanced interference signals; A module for cross-correlation processing of auxiliary interferometer signals and measurement signals; A module that provides the k-domain resampling clock via a resampling interferometer; A module for adaptive frequency-shift cross-correlation matching processing; The module that calculates the target distance.

3. A time-stretched sweep interferometric high-precision ranging system based on a dual-auxiliary interferometer, characterized in that, To implement the method of claim 1, the method comprises: A swept-frequency laser is used to emit linearly frequency-modulated optical signals; An optical splitter structure is used to divide an optical signal into three paths; The time stretching module is used to perform dispersion stretching on two reference beams; The measuring interferometer, the auxiliary interferometer, and the resampling auxiliary interferometer each receive the split optical signal. The measuring interferometer and the auxiliary interferometer form a beat frequency interference signal through the time stretching module, and the resampling auxiliary interferometer provides an equal optical frequency interval interference signal. The detector module is used to receive the interference signals output by each interferometer and convert them into electrical signals.

4. A computer storage medium for storing computer programs, characterized in that: When the computer program is read by the computer, the computer executes the method of claim 1.

5. A computer, including a processor and a storage medium, characterized in that, When the processor reads the computer program stored in the storage medium, the computer executes the method of claim 1.

6. A computer program product, as a computer program, is characterized by: When the computer program is executed, it implements the method of claim 1.

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