An optical frequency domain reflectometry signal processing method based on auxiliary interferometer dual-domain joint compensation

Abstract

The present application relates to the field of optical fiber sensing, optical frequency domain reflectometry, swept laser nonlinear correction and digital signal processing, and particularly relates to an optical frequency domain reflectometry signal processing method based on auxiliary interferometer dual-domain joint compensation. The present application establishes a dual-path utilization mechanism of auxiliary interferometer phase information: the nonlinear phase estimation information and the optical frequency coordinate information are obtained from the same auxiliary interferometer phase respectively; the former is used to implement global de-skew compensation on the main interferometer signal in the phase domain, to restore the phase consistency of the signal, and then the latter is used to implement coordinate correction in the optical frequency coordinate domain, to restore the sampling coordinate consistency of the Fourier transform input. Thus, the distance recovery is established on the basis of the equal optical frequency data after the joint correction in the phase domain and the coordinate domain, so as to improve the system distance recovery accuracy, the reflectometry peak quality and the algorithm robustness.

Description

Technical Field

[0001] This invention relates to the fields of fiber optic sensing, optical frequency domain reflectionometry (OFDR), swept-frequency laser nonlinear correction, and digital signal processing. In particular, it relates to a signal processing method that utilizes the phase of the same auxiliary interferometer in a dual-path manner and performs joint compensation in the phase domain and optical frequency coordinate domain, respectively. This method can be applied to systems such as distributed fiber optic sensing, fiber optic device testing, and high-resolution reflection measurement. Background Technology

[0002] Optical frequency domain reflectance measurement (OFDR) systems obtain reflection information along the length of the optical fiber or optical device under test using a swept-frequency laser. Ideally, the laser frequency should change strictly linearly with time, and the collected interference signal can be directly recovered from the distance information through Fourier transform.

[0003] However, practical frequency-sweeping lasers generally exhibit optical frequency nonlinearity, and their instantaneous optical frequency can be expressed as:

[0004]

[0005] in It is a swept-frequency nonlinearity.

[0006] Currently, there are two main types of correction methods:

[0007] (1) Resampling method: The auxiliary interferometer recovers the laser light frequency trajectory, the main interferometer data is remapped to uniform light frequency coordinates, and then FFT is performed. The advantages of this method are: simple theory; easy to implement; and good effect for short to medium distances. The disadvantages of this method are: completely dependent on the accuracy of the light frequency trajectory; errors are introduced in the interpolation process; and the long-distance coherence is significantly affected by laser phase noise.

[0008] (2) Deskewing method: The auxiliary interferometer recovers the nonlinear phase of the laser, and the phase of the main interferometer is directly compensated by the deskewing filter. Advantages of this method: It can effectively compensate for large-scale sweep frequency nonlinearity; its long-distance performance is better than traditional resampling. Disadvantages of this method: Local optical frequency coordinate deviation may still exist after deskewing compensation; the Fourier transform input still corresponds to time sampling, rather than strictly uniform optical frequency sampling.

[0009] Existing technologies include methods that eliminate Doppler errors caused by environmental vibrations by constructing complex dual-tunable lasers and implementing bidirectional positive and negative optical frequency scanning (such as CN118131250A). These methods heavily rely on the strict synchronous tuning of the two light sources and dual-path fixed-delay trigger pulses in terms of hardware, addressing the interference of Doppler frequency shift on absolute ranging. However, these schemes cannot solve the phase walk-off problem of interference signals in OFDR caused by the laser's own sweep frequency nonlinearity and inherent phase noise, nor can they suppress the broadening of the range spectrum reflection peak (point spread function PSF) due to large-scale nonlinearity.

[0010] To address the compatibility and nonlinearity correction issues of OFDR systems at different measurement distances, existing technologies employ methods such as stacking multiple auxiliary interferometers with different delay fiber lengths (e.g., CN214372546U) on hardware and switching the number of hardware channels based on the measurement distance. This approach significantly increases the redundancy, production cost, and system size of the optical hardware. Furthermore, each auxiliary interferometer remains constrained by the inherent physical limitations of single-dimensional resampling or deskewing algorithms when dealing with large-scale high-order nonlinearities and phase noise in lasers (it cannot simultaneously handle long distances and narrow PSF widths).

[0011] Currently, there is a lack of a method that utilizes phase information from the same auxiliary interferometer in a dual-path manner and places phase consistency compensation and optical frequency sampling coordinate consistency correction in the same processing chain. Existing technologies typically only utilize auxiliary interferometer information to perform either phase domain compensation or coordinate domain compensation, making it difficult to simultaneously achieve large-scale nonlinear phase correction and precise Fourier transform coordinate alignment. Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention proposes a method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer. The core of this invention lies in establishing a dual-path utilization mechanism for the phase information of the auxiliary interferometer: nonlinear phase estimation information and optical frequency coordinate information are generated separately from the same auxiliary interferometer phase. The former is used for global deskewing in the phase domain to restore the phase consistency of the main interferometer signal, while the latter is used for optical frequency coordinate correction of the deskewn signal to restore the sampling coordinate consistency of the Fourier transform input. Phase domain compensation and coordinate domain correction each perform independent functions in different mathematical domains and work collaboratively in sequence, thereby further improving the system's distance recovery accuracy, reflection peak quality, and algorithm robustness.

[0013] The technical solution of this invention is: a method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer, characterized by comprising the following steps:

[0014] Step 1: The swept laser outputs swept light, and the data acquisition unit simultaneously acquires the main interferometer signal and the auxiliary interferometer reference interference signal; the optical field of the swept laser is:

[0015]

[0016] Phase

[0017] Instantaneous frequency of laser light field

[0018] Indicates the instantaneous phase of the laser; Represents the laser light field; Indicates the amplitude of the laser light field; Represents the imaginary unit; This indicates the center optical frequency of the swept-frequency laser; Indicates the sampling time; This represents the linear sweep slope of the sweep laser; This indicates the nonlinear phase error of the swept-frequency laser;

[0019] The phase of the auxiliary interferometer is restored as follows:

[0020]

[0021] in, This indicates the optical delay time between the two arms of the auxiliary interferometer; The function representing the change of the instantaneous laser frequency within the integral over time;

[0022] Step 2: Perform dual-path information extraction on the phase of the auxiliary interferometer, and construct the following:

[0023] ① Phase domain information extraction: The phase of the auxiliary interferometer is decomposed into ideal linear time-varying phase components and nonlinear phase components:

[0024]

[0025]

[0026]

[0027] This represents the nonlinear phase component of the auxiliary interferometer; This represents the linear time-varying phase component under ideal conditions of the auxiliary interferometer;

[0028] Higher-order inversion:

[0029]

[0030] Points earned ;

[0031] ② Optical frequency coordinate domain information extraction: Obtain the equivalent relative optical frequency trajectory based on the phase of the auxiliary interferometer and construct a uniform optical frequency axis:

[0032] Optical frequency coordinate domain information extraction:

[0033] Constructing a uniform optical frequency axis:

[0034] get ;

[0035] The uniform, equal-frequency coordinate axes representing the structure; This represents the time-varying instantaneous light frequency trajectory obtained by phase demodulation using an auxiliary interferometer; The starting optical frequency represents the uniform optical frequency axis. Indicates the discrete sampling point index of the uniform optical frequency axis; This represents the optical frequency interval between adjacent sampling points on a uniform optical frequency axis;

[0036] MAIN main interferometer signal; A is the signal amplitude;

[0037] Step 3: Use the nonlinear phase estimation information obtained from the first path to perform global deskewing compensation on the main interferometer signal in order to restore the phase consistency of the signal;

[0038] get: The specific process is as follows:

[0039] First domain: Phase consistency compensation

[0040]

[0041] This represents the intermediate state signal of the master interferometer after high-order nonlinear phase conjugate multiplication. This represents the original master interferometer signal acquired.

[0042] After deskewing / residual video phase (RVP) filtering:

[0043]

[0044] Representing the frequency, we obtain the phase-domain compensated signal: ;

[0045] Step 4: Use the optical frequency trajectory obtained from the second path to perform optical frequency coordinate correction on the de-skewed master interferometer signal;

[0046] The process of establishing uniform optical frequency coordinates and obtaining the master interferometer signal with equal optical frequency sampling is as follows:

[0047] Second domain: Optical frequency coordinate consistency correction

[0048] make ,structure The time is obtained by monotonic mapping. Calculate using interpolation, resampling, or equivalent numerical mapping operators 𝓘 , thus obtaining the main interferometer signal sampled at the same optical frequency;

[0049] Function: To restore the consistency of optical frequency sampling coordinates of the Fourier transform input, so that distance recovery is based on a unified optical frequency coordinate system;

[0050] Step 5: Perform Fourier transform on the unified optical frequency coordinates:

[0051]

[0052] The specific process for recovering the distance spectrum is as follows:

[0053] Distance recovery:

[0054] Fourier transform (discrete implementation can use FFT or equivalent transform): .

[0055] According to the optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described above, the characteristic is that the signal after phase domain compensation is represented as follows:

[0056] .

[0057] According to the optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation of an auxiliary interferometer as described above, the method is characterized by:

[0058] The distance conversion formula is:

[0059] Represents the speed of light in a vacuum. Indicates the effective refractive index of the sensing fiber. Indicates the delay time.

[0060] According to the above-described optical frequency domain reflection measurement signal processing method based on dual-domain joint compensation of an auxiliary interferometer, the method is characterized by: further including step 6, performing Rayleigh scattering correlation analysis, strain demodulation, temperature demodulation, and polarization analysis on the signal acquired by the swept laser.

[0061] According to the above-described optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation of an auxiliary interferometer, the specific process of Rayleigh scattering correlation analysis and strain / temperature demodulation is as follows: continuously acquire the main interferometer signal of the swept laser under different environmental conditions, and recover multiple sets of high-resolution range-domain Rayleigh scattering spectral signals through steps 1 to 5; set a sliding window in the range domain for local truncation, perform cross-correlation calculation on the spectral signals of the test state and the reference state, and obtain the frequency shift of the Rayleigh scattering spectrum; according to the linear coefficient relationship between the frequency shift and the physical quantity, demodulate the distributed temperature change or strain change at each position along the optical fiber sensing link.

[0062] According to the above-described optical frequency domain reflection measurement signal processing method based on dual-domain joint compensation of auxiliary interferometer, the specific process of polarization analysis is as follows: if the system hardware adopts a polarization diversity receiving architecture, then the dual-domain joint compensation of steps 1 to 5 is performed in parallel on the two orthogonal main interferometer signals acquired; after obtaining the range domain complex amplitude data of X and Y channels, the Jones matrix or Stokes vector of each reflection position is constructed, and the polarization state evolution trajectory caused by distributed birefringence, polarization mode dispersion or external disturbance along the optical fiber link is demodulated.

[0063] According to the optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation of auxiliary interferometer as described above, the hardware system of the method consists of a swept laser, a main interferometer, an auxiliary interferometer, multiple couplers, a balanced detector, and a data acquisition unit.

[0064] According to the above-described optical frequency domain reflection measurement signal processing method based on dual-domain joint compensation of an auxiliary interferometer, the characteristic is that: the swept laser is connected to the auxiliary interferometer and the main interferometer through coupler 1, coupler 2 and coupler 3 respectively, and the auxiliary interferometer and the main interferometer are connected to the data acquisition unit through coupler and balanced detector respectively. Attached Figure Description

[0065] Figure 1 This is a system structure diagram of the present invention.

[0066] Figure 2 To facilitate comparisons, the same set of original acquired data, the same distance window, and the same normalization method were used. The blue line represents the traditional resampling algorithm, the red line represents the traditional deskewing algorithm, and the yellow line represents the dual-domain joint compensation algorithm of this invention. The horizontal axis represents the distance to the strongest reflection peak, and the vertical axis represents the normalized amplitude. The main peak of the yellow curve is more concentrated, and the base and system noise floor below the peak are lower.

[0067] Figure 3 A mathematical framework diagram for dual-domain joint compensation to assist in the dual-path utilization of phase information in interferometers and the relationship between phase domain compensation, optical frequency coordinate domain correction, and distance recovery. Detailed Implementation

[0068] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0069] like Figure 1 As shown, the present invention discloses a method for optical frequency domain reflectance measurement signal processing based on dual-domain joint compensation of an auxiliary interferometer. The hardware system mainly includes a swept laser, a main interferometer (Main MZI), and an auxiliary interferometer (Aux MZI). The swept laser is connected to the auxiliary interferometer and the main interferometer through couplers 1, 2, and 3, respectively. The auxiliary interferometer and the main interferometer are connected to the data acquisition unit through couplers and a balanced detector, respectively. The swept laser emits a swept light source.

[0070] like Figure 1 As shown, the optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer according to the present invention includes the following steps:

[0071] like Figure 3 As shown, the phase recovered by the auxiliary interferometer is not used as a single compensation quantity, but rather enters two parallel information extraction paths: the first path estimates the nonlinear phase of the swept laser from the nonlinear components of the auxiliary interferometer phase, used for phase consistency compensation in the first domain; the second path obtains the equivalent relative optical frequency trajectory from the same auxiliary interferometer phase, used for optical frequency coordinate consistency correction in the second domain. These two paths are cascaded at the de-skewed master interferometer signal, decoupling phase error correction and sampling coordinate correction.

[0072] Step 1: The sweep laser outputs sweep beams, and the data acquisition unit simultaneously acquires the main interferometer signal and the auxiliary interferometer reference interference signal.

[0073] It is a momentary optical frequency signal; To restore the phase of the auxiliary interferometer

[0074] The optical field of a swept-frequency laser can be written as:

[0075]

[0076] Phase

[0077] So the instantaneous frequency of the laser light field

[0078] Indicates the instantaneous phase of the laser; Represents the laser light field; Indicates the amplitude of the laser light field; Represents the imaginary unit; This indicates the center optical frequency of the swept-frequency laser; Indicates the sampling time; This represents the linear sweep slope of the sweep laser; This indicates the nonlinear phase error of the swept-frequency laser.

[0079] The phase expression for the recovery interferometer is:

[0080]

[0081]

[0082] in, This indicates the optical delay time between the two arms of the auxiliary interferometer (AUX-MZI); It represents the function that describes the change of the instantaneous laser frequency within the integral over time.

[0083] Step 2: Perform dual-path information extraction on the phase of the auxiliary interferometer to construct nonlinear phase estimation information and optical frequency coordinate information respectively:

[0084] ①Path A – Phase Domain Information Extraction:

[0085]

[0086]

[0087]

[0088] In this process, the phase of the auxiliary interferometer is decomposed into an ideal linear time-varying phase component and a nonlinear phase component; the nonlinear phase component corresponds to the differential response of the nonlinear phase of the swept laser over a fixed delay in the auxiliary interferometer. A nonlinear phase estimate is obtained through high-order inversion and integration, which is then used for subsequent phase domain compensation.

[0089] Higher-order inversion:

[0090]

[0091] Points earned , This represents the laser's inherent nonlinear phase noise curve estimated using Taylor higher-order inversion and integration algorithms.

[0092] ②Path B - Optical frequency coordinate domain information extraction: Obtain the equivalent relative optical frequency trajectory based on the phase of the auxiliary interferometer.

[0093] Optical frequency coordinate domain information extraction:

[0094] Constructing a uniform optical frequency axis:

[0095] This yields the optical frequency trajectory and nonlinear phase estimation; both originate from the same auxiliary interferometer phase data, but serve different mathematical domains.

[0096] The uniform, equal-frequency coordinate axes representing the structure; This represents the time-varying instantaneous light frequency trajectory obtained by phase demodulation (or derivation) using an auxiliary interferometer; This indicates the starting optical frequency of the uniform optical frequency axis (usually corresponding to the minimum value of the sweep frequency range). The discrete sampling point index (or sampling point number (k=0,1,2,..)) represents the uniform optical frequency axis; It represents the optical frequency interval (or optical frequency sampling step size) between adjacent sampling points on a uniform optical frequency axis.

[0097] MAIN main interferometer signal; A represents the signal amplitude, which may include, under non-ideal conditions, [signal amplitude].

[0098] Step 3: Use the nonlinear phase estimation information obtained from path A to perform global deskewing compensation on the master interferometer signal in order to restore the phase consistency of the signal.

[0099] get: The specific process is as follows:

[0100] First domain: Phase consistency compensation

[0101]

[0102] This represents the intermediate state signal of the master interferometer after high-order nonlinear phase conjugate multiplication (primary deskewing). This represents the original master interferometer signal acquired.

[0103] After deskewing / residual video phase (RVP) filtering:

[0104]

[0105] Representing the frequency (specifically, the electronic frequency coordinates conjugate with the time variable after performing a Fourier transform on the signal), we obtain the phase-domain compensated signal: ;

[0106] The master interferometer signal is composed of the superposition of reflections at different distances. When the laser sweep frequency is nonlinear, a residual video phase (RVP) is introduced into the signal. This RVP causes severe broadening of the reflection peak at long distances. To eliminate it, it is not possible to simply perform a simple summation. The multiplication must be performed by a descrambling filter in the frequency domain.

[0107]

[0108] Eliminate large-scale nonlinear phase errors in frequency-sweeping lasers.

[0109] Step 4: Use the optical frequency trajectory obtained from path B to perform optical frequency coordinate consistency correction on the de-skewed master interferometer signal.

[0110] The optical-frequency coordinate refinement establishes uniform optical-frequency coordinates and obtains equal-frequency sampling signals. The specific process is as follows:

[0111] Second domain: Optical frequency coordinate consistency correction

[0112] The optical frequency trajectory recovered by the auxiliary interferometer is represented as: And construct a uniform optical frequency axis . This represents the equal optical frequency step size of the uniform optical frequency axis. This indicates the starting point of the uniform optical frequency axis, i.e., the minimum optical frequency;

[0113] when When monotonic, determine Then, interpolation, resampling, or equivalent numerical mapping operators are used. calculate , This indicates the time position corresponding to sampling point k.

[0114] This step converts the deskewed master interferometer signal from an equal-time sampling representation to an equal-optical-frequency sampling representation, restoring the coordinate consistency of the Fourier transform input; and makes the master interferometer signal form an equal-optical-frequency sampling sequence; where k=0,1,2,…,N−1, and N represents the total number of discrete sampling points on the equal-optical-frequency coordinate axis (i.e., the number of points in the FFT transform).

[0115] This step involves optical frequency coordinate domain compensation, rather than repeated compensation for the same phase error. The combination of steps 3 and 4 constitutes the core innovation of this scheme: the same auxiliary interferometer phase, after dual-path processing, is used to restore phase consistency and optical frequency sampling coordinate consistency, respectively. Traditional resampling directly processes the un-deskessed master interferometer signal, while this invention performs optical frequency coordinate correction after global deskewing. Figure 2 In the embodiment shown, the reflection peak quality (point spread function PSF) of the distance spectrum obtained by dual-domain joint compensation is closer to the theoretical limit, and the sub-peak floor and system noise floor are significantly reduced.

[0116] Step 5: Perform Fourier transform on the unified optical frequency coordinates:

[0117]

[0118] The specific process for recovering the distance spectrum is as follows:

[0119] Distance recovery:

[0120] Fourier transform (discrete implementation can use FFT or equivalent transform):

[0121] Distance conversion:

[0122] Where c represents the speed of light in a vacuum, n represents the group refractive index of the sensing fiber or the calibrated equivalent refractive index, z represents the measurement distance, and τ represents the time delay between the corresponding reflection positions of the two arms of the main interferometer.

[0123] This step performs a Fourier transform on the equal-frequency signal after dual-domain joint compensation, converting the optical frequency variable to a time delay variable. In the discrete implementation, a Fast Fourier Transform (FFT) or an equivalent discrete transform with the same mathematical effect can be used. The transformation result is physically mapped to the distance axis using z = cτ / 2n. The sign convention of the Fourier transform can be selected according to the definition of the complex signal of the master interferometer, both of which are equivalent implementations of this invention.

[0124] In one embodiment, the measurement distance is 1 km, and the effective sweep frequency range of the sweep laser is approximately 100 GHz; based on the relationship between optical bandwidth and spatial resolution, a theoretical spatial resolution on the order of approximately 1 mm can be obtained. This invention is not limited to the aforementioned distance and sweep frequency range.

[0125] The present invention may also include step 6, performing Rayleigh scattering correlation analysis, strain demodulation, temperature demodulation, and polarization analysis on the signal acquired by the swept laser.

[0126] (1) Rayleigh scattering correlation analysis and strain / temperature demodulation: The main interferometer signal of the swept laser under different environmental conditions was continuously acquired, and multiple sets of high-resolution range-domain Rayleigh scattering spectral signals were recovered through the aforementioned steps 1 to 5; a sliding window was set in the range domain for local truncation, and the cross-correlation of the spectral signals of the test state and the reference state was calculated to obtain the frequency shift of the Rayleigh scattering spectrum. Based on the linear relationship between frequency shift and physical quantity ( Demodulate the distributed temperature changes at various locations along the fiber optic sensing link. or strain change .

[0127] (2) Polarization analysis (P-OFDR extension): If the system hardware adopts a polarization diversity receiving architecture, the dual-domain joint compensation of the two orthogonal main interferometer signals (X polarization state and Y polarization state) is performed in parallel from step 1 to step 5. After obtaining the range domain complex amplitude data of the X and Y channels, the Jones matrix or Stokes vector of each reflection position is constructed, and then the distributed birefringence distribution, polarization mode dispersion (PMD) or polarization state (SOP) evolution trajectory caused by external disturbance along the optical fiber link is demodulated.

[0128] The present invention has the following features: (1) It proposes a dual-domain joint compensation framework for the dual-path utilization of phase information of the auxiliary interferometer. The phase of the same auxiliary interferometer is used for phase domain compensation and optical frequency coordinate domain compensation respectively, avoiding the use of only one type of information in the prior art. (2) It decouples the two types of compensation functions: the deskewing process is responsible for restoring the phase consistency of the main interferometer signal and obtaining the measurement capability beyond the laser coherence length; the optical frequency coordinate correction is responsible for restoring the sampling coordinate consistency of the Fourier transform input and improving the accuracy of reflection peak recovery. The two types of compensation are cascaded and coordinated after acting on different mathematical domains respectively. (3) It establishes a unified equal optical frequency Fourier transform input coordinate to improve the consistency of distance axis, peak position and repeated measurement results. (4) The technical solution has good compatibility and can be compatible with traditional resampling system, traditional deskewing system, phase diversity system, polarization diversity system and various auxiliary interferometer structures.

[0129] The technical effects of this invention are as follows: Figure 2 As shown, under the same original acquired data, the same distance window, and the same normalization conditions, the dual-domain joint compensation result exhibits a more concentrated reflection peak, a lower sub-peak floor, and a lower system noise floor compared to traditional resampling and traditional deskewing results. This invention can improve the frequency sweep nonlinear compensation capability, establish unified optical frequency coordinates, improve the consistency of Fourier transform distance recovery and the stability of long-distance OFDR measurements, and provide a unified dual-domain joint compensation framework for ultracoherent length OFDR.

[0130] This invention does not involve Doppler vibration error compensation, but focuses on addressing the spatial resolution degradation caused by laser sweep frequency nonlinearity and phase noise during long-distance measurements using software methods within a standard single-source hardware system. This invention can be implemented based on a single-channel standard auxiliary interferometer, eliminating the need for hardware stacking and switching of multiple auxiliary interferometers with different delays. Through a dual-domain cascade algorithm that combines large-scale deskewing in the phase domain and fine alignment in the coordinate domain, it effectively balances long-distance measurement capability with high spatial resolution.

[0131] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer, characterized in that: Includes the following steps: Step 1: The swept laser outputs swept light, and the data acquisition unit simultaneously acquires the main interferometer signal and the auxiliary interferometer reference interference signal; the optical field of the swept laser is: Phase instantaneous frequency of laser light field Indicates the instantaneous phase of the laser; Represents the laser light field; Indicates the amplitude of the laser light field; Represents the imaginary unit; This indicates the center optical frequency of the swept-frequency laser; Indicates the sampling time; This represents the linear sweep slope of the sweep laser; This indicates the nonlinear phase error of the swept-frequency laser; The phase of the auxiliary interferometer is restored as follows: in, This indicates the optical delay time between the two arms of the auxiliary interferometer; The function representing the change of the instantaneous laser frequency within the integral over time; Step 2: Perform dual-path information extraction on the phase of the auxiliary interferometer to construct nonlinear phase estimation information for phase domain compensation and optical frequency trajectory information for optical frequency coordinate domain correction. ① Phase domain information extraction: The phase of the auxiliary interferometer is decomposed into ideal linear time-varying phase components and nonlinear phase components: This represents the nonlinear phase component of the auxiliary interferometer; This represents the linear time-varying phase component under ideal conditions of the auxiliary interferometer; Higher-order inversion: Points earned ; ② Optical frequency coordinate domain information extraction: Obtain the equivalent relative optical frequency trajectory based on the phase of the auxiliary interferometer, and construct a uniform optical frequency coordinate axis: Optical frequency coordinate domain information extraction: Constructing a uniform optical frequency axis: get ; The uniform, equal-frequency coordinate axes representing the structure; This represents the time-varying instantaneous light frequency trajectory obtained by phase demodulation using an auxiliary interferometer; The starting optical frequency represents the uniform optical frequency axis; Indicates the discrete sampling point index of the uniform optical frequency axis; This represents the optical frequency interval between adjacent sampling points on a uniform optical frequency axis; MAIN main interferometer signal; A is the signal amplitude; Step 3: Use the nonlinear phase estimation information obtained from the first path to perform global deskewing compensation on the master interferometer signal in order to restore the phase consistency of the master interferometer signal; get: The specific process is as follows: First domain: Phase consistency compensation This represents the intermediate state signal of the master interferometer after high-order nonlinear phase conjugate multiplication. This represents the original master interferometer signal acquired. After deskewing / residual video phase (RVP) filtering: Representing the frequency, we obtain the phase-domain compensated signal: ; Step 4: Use the optical frequency trajectory obtained from the second path to perform optical frequency coordinate correction on the de-skewed master interferometer signal; The process of establishing uniform optical frequency coordinates and obtaining the master interferometer signal with equal optical frequency sampling is as follows: Second domain: Optical frequency coordinate consistency correction Let the optical frequency trajectory recovered by the auxiliary interferometer be Constructing a uniform optical frequency axis Determine the time position corresponding to each optical frequency sampling point. Equal-frequency sampling signals are obtained through interpolation, resampling, or equivalent numerical mapping. ; Step 5: Perform Fourier transform on the unified optical frequency coordinates: The specific process for recovering the distance spectrum is as follows: Distance recovery: , Discrete implementations of the Fourier transform employ FFT or equivalent transformations: .

2. The optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described in claim 1, characterized in that: The signal after phase domain compensation is represented as: 。 3. The optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described in claim 1 or 2, characterized in that: The expression for the equal-frequency sampling signal is: .

4. A method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer, as described in claim 1 or 2, characterized in that: The distance conversion formula is: Represents the speed of light in a vacuum. Indicates the effective refractive index of the sensing fiber. Indicates the delay time.

5. A method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer, as described in claim 1 or 2, characterized in that: It also includes step 6, which performs Rayleigh scattering correlation analysis, strain demodulation, temperature demodulation, and polarization analysis on the signal acquired by the swept laser.

6. The optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described in claim 5, characterized in that: The specific process of Rayleigh scattering correlation analysis and strain / temperature demodulation is as follows: continuously acquire the master interferometer signal of the swept laser under different environmental conditions, and recover multiple sets of high-resolution range-domain Rayleigh scattering spectral signals through steps 1 to 5; set a sliding window in the range domain for local truncation, and perform cross-correlation calculation on the spectral signals of the test state and the reference state to obtain the frequency shift of the Rayleigh scattering spectrum; based on the linear coefficient relationship between the frequency shift and the physical quantity, demodulate the distributed temperature change or strain change at each location along the fiber optic sensing link.

7. The optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described in claim 5, characterized in that: The specific process of polarization analysis is as follows: If the system hardware adopts a polarization diversity receiving architecture, the dual-domain joint compensation of steps 1 to 5 is performed in parallel on the two orthogonal main interferometer signals acquired. After obtaining the range domain complex amplitude data of the X and Y channels, the Jones matrix or Stokes vector of each reflection position is constructed, and the polarization state evolution trajectory caused by the distributed birefringence distribution, polarization mode dispersion or external disturbance along the optical fiber link is demodulated.

8. A method for processing optical frequency domain reflectance measurement signals based on dual-domain joint compensation using an auxiliary interferometer, as described in claim 1 or 2, characterized in that: The hardware system of the method consists of a swept laser, a main interferometer, an auxiliary interferometer, multiple couplers, a balanced detector, and a data acquisition unit.

9. The optical frequency domain reflectance measurement signal processing method based on dual-domain joint compensation using an auxiliary interferometer as described in claim 8, characterized in that: The swept laser is connected to the auxiliary interferometer and the main interferometer via coupler 1, coupler 2 and coupler 3 respectively. The auxiliary interferometer and the main interferometer are connected to the data acquisition unit via coupler and balanced detector respectively.

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