An optical frequency domain reflectometry system and a dynamic sweep range compensation method and a demodulation method thereof
By constructing a time-wavenumber mapping relationship and using the phase information of an auxiliary interferometer for resampling, the problem of frequency sweep range drift in the optical frequency domain reflection sensing system was solved, improving measurement accuracy and system stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN UNIV
- Filing Date
- 2026-03-31
- Publication Date
- 2026-07-14
AI Technical Summary
In existing optical frequency domain reflection sensing technology, random drift and fluctuations in the sweep frequency range lead to a decrease in measurement accuracy and system stability. Existing nonlinear compensation methods have failed to effectively cope with the dynamic changes of tunable lasers.
By reading the actual beat frequency sequences of the main interferometer and the auxiliary interferometer, a mapping relationship between time and wavenumber is constructed. The phase information of the auxiliary interferometer is used for resampling to compensate for the sweep frequency range offset of the tunable laser, ensuring that the sweep frequency range covers the theoretical range, and thus realizing the resampling of the beat frequency sequence of the main interferometer.
It effectively compensates for random drift in the frequency sweep range, reduces demodulation error, and improves measurement accuracy and system stability.
Smart Images
Figure CN122384871A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to optical frequency domain reflection sensing technology, and more particularly to an optical frequency domain reflection sensing system and its dynamic frequency sweep range compensation and demodulation method. Background Technology
[0002] Optical frequency domain reflectometry (OFDR) technology uses a tunable laser to continuously sweep frequencies to analyze Rayleigh scattering interference signals in sensing optical fibers, thereby enabling distributed strain or temperature measurement. Frequency sweep nonlinearity is the main factor affecting the accuracy of OFDR measurements. Existing techniques typically use an auxiliary interferometer to resample the beat frequency signal of the main interferometer to establish a linear mapping relationship between frequency and time, thus compensating for frequency sweep nonlinearity errors.
[0003] However, existing nonlinear compensation methods are all based on the assumption that the sweep frequency range of the tunable laser is constant. In actual dynamic sensing, the tunable laser is affected by its own operating state and environmental factors, and its sweep frequency range may drift or fluctuate randomly, causing the pre-calibrated frequency-time mapping relationship to fail, thereby introducing spatial positioning errors and demodulation deviations, which seriously affect the measurement accuracy and system stability. Summary of the Invention
[0004] To address the shortcomings of the prior art, this invention provides an optical frequency domain reflection sensing system and its dynamic frequency sweep range compensation and demodulation method, which can adapt to dynamic changes in the frequency sweep range for compensation.
[0005] The technical problem to be solved by the present invention is achieved through the following technical solution: A method for dynamic frequency sweep range compensation in an optical frequency domain reflection sensing system includes the following steps: Step 1: Read the actual beat frequency sequence of the main interferometer and the auxiliary interferometer. The actual beat frequency sequence is obtained by initial sampling of the actual beat frequency sequence of the main interferometer and the auxiliary interferometer under the preset sweep frequency range. The preset sweep frequency range is larger than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario. Step 2: Determine the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer; Step 3: Based on the mapping relationship between time and wavenumber, map the resampled wavenumber sequence with equal wavenumber intervals to the time domain to obtain the resampled time sequence. The resampled wavenumber sequence is constructed based on the theoretical frequency sweep range. Step 4: Based on the resampling time series, resample the actual beat frequency sequence of the main interferometer to obtain the theoretical beat frequency sequence of the main interferometer within the theoretical sweep frequency range.
[0006] Furthermore, in step 2, the steps for determining the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer are as follows: Step 21: Perform phase demodulation on the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer; Step 22: Based on the linear relationship between phase and wavenumber, map the phase axis of the phase information to the wavenumber axis to obtain the mapping relationship between time and wavenumber.
[0007] Furthermore, the mapping relationship between time and wavenumber is as follows: in, The wavenumber information of the auxiliary interferometer, The phase information of the auxiliary interferometer, The initial phase of the auxiliary interferometer, The optical path difference of the auxiliary interferometer is given.
[0008] Furthermore, in step 21, the step of performing phase demodulation on the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer is as follows: Step 211: Perform Hilbert transform on the actual beat frequency sequence of the auxiliary interferometer to obtain the complex signal of the auxiliary interferometer; Step 212: Perform arctangent and unwinding processing on the complex signal of the auxiliary interferometer in sequence to obtain the phase information of the auxiliary interferometer.
[0009] Furthermore, in step 4, the steps for resampling the actual beat frequency sequence of the main interferometer according to the resampling time sequence to obtain the theoretical beat frequency sequence of the main interferometer under the theoretical sweep frequency range are as follows: Step 41: For each resampling time point in the resampling time series, search for the two adjacent initial sampling time points and the signal strength of these two initial sampling time points in the actual beat frequency sequence of the main interferometer; Step 42: Based on the two initial sampling time points and their signal strengths, determine the signal strength of the resampling time point using a one-dimensional linear interpolation method.
[0010] Furthermore, the signal strength at the m-th resampling time point is as follows: in, This refers to the m-th resampling time point in the resampling time series. and These are the two initial sampling time points adjacent to the m-th resampling time point in the actual beat frequency sequence of the main interferometer. and These represent the signal strengths at the two initial sampling time points mentioned above.
[0011] A demodulation method for an optical frequency domain reflectance sensing system includes the following steps: Step S1: Set the preset sweep frequency range of the tunable laser, wherein the preset sweep frequency range is greater than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario; Step S2: Based on the theoretical sweep frequency range, construct a resampled wavenumber sequence with equal wavenumber intervals; Step S3: When the sensing fiber is in the reference state, control the tunable laser to emit continuous sweeping light to the main interferometer and the auxiliary interferometer using the preset sweeping frequency range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the reference beat frequency signals output by the main interferometer and the auxiliary interferometer respectively, so as to obtain the actual reference beat frequency sequence of the main interferometer and the auxiliary interferometer. Step S4: Using the above-described dynamic frequency sweep range compensation method, the actual reference beat frequency sequence of the main interferometer is resampled according to the actual reference beat frequency sequence of the auxiliary interferometer to obtain the theoretical reference beat frequency sequence of the main interferometer; Step S5: When the sensing fiber is in the measurement state, control the tunable laser to emit continuous frequency sweep light to the main interferometer and the auxiliary interferometer using the preset frequency sweep range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the measurement beat frequency sequence output by the main interferometer and the auxiliary interferometer to obtain the actual measurement beat frequency sequence of the main interferometer and the auxiliary interferometer; Step S6: Using the above-described dynamic frequency sweep range compensation method, the actual measured beat frequency sequence of the main interferometer is resampled according to the actual measured beat frequency sequence of the auxiliary interferometer to obtain the theoretical measured beat frequency sequence of the main interferometer; Step S7: Perform wavelength drift demodulation on the theoretical reference beat frequency sequence and the theoretical measured beat frequency sequence of the master interferometer to obtain the cross-correlation spectrum of the sensing fiber.
[0012] Furthermore, in step S2, the steps for constructing a resampled wavenumber sequence with equal wavenumber intervals based on the theoretical sweep frequency range are as follows: Step S21: Calculate the resampling start wavenumber and resampling end wavenumber of the resampling wavenumber sequence based on the starting and ending sweep wavelengths of the theoretical sweep range. Step S22: Calculate the resampling interval wavenumber based on the resampling start wavenumber and resampling end wavenumber, combined with the set number of resampling points; Step S23: Starting with the resampling start wavenumber or resampling end wavenumber, and using the resampling interval wavenumber as the step size, the resampling interval wavenumber is incremented or decremented to obtain the resampling wavenumber sequence.
[0013] Furthermore, the initial wavenumber for resampling is as follows: The resampling termination wavenumber is as follows: in, and These are, in order, the starting and ending sweep wavelengths of the theoretical sweep range; The resampling interval wavenumber is as follows: The resampled wavenumber sequence is as follows: Or as follows: Where N is the set number of resampling points.
[0014] An optical frequency domain reflectance sensing system includes a data processing device, which is used to execute the above-described dynamic frequency sweep range compensation method or the above-described demodulation method.
[0015] The present invention has the following beneficial effects: The dynamic sweep frequency range compensation method of the present invention controls the tunable laser to sweep frequency within a preset sweep frequency range greater than the theoretical sweep frequency range, so that even if the actual sweep frequency range of the tunable laser deviates from the preset sweep frequency range, it can still completely cover the theoretical sweep frequency range. Then, the actual beat frequency sequence of the auxiliary interferometer is used to construct a mapping relationship between time and wavenumber, so as to use this mapping relationship to map the actual beat frequency sequence of the main interferometer to the theoretical sweep frequency range for resampling, effectively compensating for the random drift of the sweep frequency range and avoiding demodulation error. Attached Figure Description
[0016] Figure 1 The schematic diagram of the optical frequency domain reflection sensing system provided by the present invention.
[0017] Figure 2 This is a flowchart illustrating the steps of the dynamic frequency sweep range compensation method provided by the present invention.
[0018] Figure 3 A flowchart illustrating the steps of the demodulation method provided by this invention.
[0019] Figure 4The image shows a comparison of the distance domain spectrum and strain demodulation results of the optical frequency domain reflection sensing system provided by this invention with and without dynamic frequency sweep range compensation. Detailed Implementation
[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0021] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0022] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.
[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0024] Example 1 like Figure 1 As shown, an optical frequency domain reflectance sensing system includes a data processing device 1, an ADC acquisition card 2, an interference optical path module 3, and a sensing optical fiber 4. The sensing end of the interference optical path module 3 is connected to the sensing optical fiber 4, and the output end of the interference optical path module 3 is connected to the ADC acquisition card 2. The ADC acquisition card 2 is connected to the data processing device 1.
[0025] During operation, the continuous sweeping light emitted by the interference optical path module 3 enters the sensing optical fiber 4, and the Rayleigh scattered light generated by the sensing optical fiber 4 re-enters the interference optical path module 3. The interference optical path module 3 converts the Rayleigh scattered light into a beat frequency signal and outputs it to the ADC acquisition card 2. The ADC acquisition card 2 acquires the beat frequency signal at equal time intervals and outputs the beat frequency sequence obtained from the initial sampling to the data processing device 1. The data processing device 1 demodulates the beat frequency sequence and finally obtains the measurement distribution curve of the sensing optical fiber 4.
[0026] The interference optical path module 3 includes a tunable laser 31, a first fiber coupler 32, an auxiliary interferometer, a main interferometer, a first photoelectric balance detector 313, a second photoelectric balance detector 314, and a third photoelectric balance detector 315. The tunable laser 31 is connected to the auxiliary interferometer and the main interferometer respectively through the first fiber coupler 32. The auxiliary interferometer is connected to the first photoelectric balance detector 313. The main interferometer is connected to the second photoelectric balance detector 314 and the third photoelectric balance detector 315 respectively. The first photoelectric balance detector 313, the second photoelectric balance detector 314, and the third photoelectric balance detector 315 are all connected to the ADC acquisition card 2.
[0027] The auxiliary interferometer includes a second fiber coupler 33, a time-delay fiber 34, a first Faraday rotator mirror 35, and a second Faraday rotator mirror 36. The first port of the second fiber coupler 33 is connected to the first fiber coupler 32, the second port of the second fiber coupler 33 is connected to the first photoelectric balance detector 313, the third port of the second fiber coupler 33 is connected to the first Faraday rotator mirror 35 via the time-delay fiber 34, and the fourth port of the second fiber coupler 33 is connected to the second Faraday rotator mirror 36.
[0028] The main interferometer includes a third fiber coupler 37, a polarization controller 38, a fiber circulator 39, a fourth fiber coupler 310, a first polarization beam splitter 311, and a second polarization beam splitter 312. The first port of the third fiber coupler 37 is connected to the first fiber coupler 32, and the second port of the third fiber coupler 37 is connected to the first port of the fourth fiber coupler 310 via the polarization controller 38. The third port of the third fiber coupler 37 is connected to the first port of the fiber circulator 39. The second port of the fiber circulator 39 is connected to the sensing fiber 4, and the third port of the fiber circulator 39 is connected to the second port of the fourth fiber coupler 310. The third port of the fourth fiber coupler 310 is connected to the second photoelectric balance detector 314 and the third photoelectric balance detector 315 via the first polarization beam splitter 311, and the fourth port of the fourth fiber coupler 310 is connected to the second photoelectric balance detector 314 and the third photoelectric balance detector 315 via the second polarization beam splitter 312.
[0029] In use, the continuously swept light emitted by the tunable laser 31 is split at a ratio of 10:90 after passing through the first fiber coupler 32. 10% of the continuously swept light enters the auxiliary interferometer, and the remaining 90% enters the main interferometer. In the auxiliary interferometer, the continuously swept light is split into two beams after passing through the second fiber coupler 33. One beam passes through the time-delay fiber 34 and reaches the first Faraday rotator mirror 35, while the other beam directly reaches the second Faraday rotator mirror 36. After being reflected by the first and second Faraday rotator mirrors 35 and 36 respectively, the two beams return to the second fiber coupler 33, generating a first beat frequency interference beam. This first beat frequency interference beam is ultimately input to the first photoelectric balance detector 313 for photoelectric signal conversion to form the auxiliary interferometer. The beat frequency signal of the interferometer; in the main interferometer, after the continuous sweep light is split by the third fiber coupler 37, one continuous sweep light enters the fourth fiber coupler 310 through the polarization controller 38, and the other continuous sweep light enters the sensing fiber 4 after passing through the fiber circulator 39. Rayleigh scattered light is formed in the sensing fiber 4 and then enters the fourth fiber coupler 310 through the fiber circulator 39. The Rayleigh scattered light and the continuous sweep light generate a second beat frequency interference light in the fourth fiber coupler 310. After the second beat frequency interference light is split by the fourth fiber coupler 310, it is then polarized and split by the first polarization beam splitter 311 and the second polarization beam splitter 312, respectively. Finally, it is input to the second photoelectric balance detector 314 and the third photoelectric balance detector 315 for photoelectric signal conversion to form the beat frequency signal of the main interferometer.
[0030] The ADC acquisition card 2 simultaneously samples the beat frequency signals of the main interferometer and the auxiliary interferometer at equal time intervals, obtaining the beat frequency sequences of the main interferometer and the auxiliary interferometer respectively. These two sets of beat frequency sequences are then provided to the data processing device 1 for measurement and demodulation. When the environment surrounding the sensing fiber 4 does not experience changes in parameters such as temperature or strain, the beat frequency signal output by the main interferometer is the reference beat frequency signal, and the beat frequency sequence obtained by the ADC acquisition card 2 during the initial sampling is the reference beat frequency sequence. When the environment surrounding the sensing fiber 4 experiences changes in parameters such as temperature or strain, the beat frequency signal output by the main interferometer is the measurement beat frequency, and the beat frequency sequence obtained by the ADC acquisition card 2 during the initial sampling is the measurement beat frequency sequence.
[0031] Theoretically, the continuously swept light emitted by the tunable laser 31 should be linear, meaning the swept wavelength changes linearly with time. However, regardless of how the manufacturing process of the tunable laser 31 is improved, the continuously swept light emitted by the tunable laser 31 inevitably contains a small amount of nonlinear swept light. Furthermore, existing technologies do not consider that the actual swept range of the tunable laser 31 may randomly drift or fluctuate during each sweep when performing nonlinear compensation. This results in the reference beat frequency signal and the measured beat frequency signal being generated under different sweep frequency ranges. Therefore, when performing wavelength offset demodulation on the reference beat frequency signal and the measured beat frequency signal, spatial positioning errors and demodulation deviations are introduced, severely affecting measurement accuracy and system stability.
[0032] Example 2 like Figure 2 As shown, a dynamic frequency sweep range compensation method is used in the optical frequency domain reflection sensing system described in Embodiment 1; the dynamic frequency sweep range compensation method includes the following steps: Step 1: Read the actual beat frequency sequences of the main interferometer and the auxiliary interferometer. The actual beat frequency sequences are obtained by initial sampling of the actual beat frequency sequences of the main interferometer and the auxiliary interferometer within a preset sweep frequency range. The preset sweep frequency range is greater than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario.
[0033] In step 1, the actual beat frequency sequence refers to the original beat frequency sequence obtained by the ADC acquisition card initially sampling the beat frequency signals output by the main interferometer and the auxiliary interferometer at equal time intervals. The data processing device includes a processor and a memory. The ADC acquisition card first stores the initially sampled actual beat frequency sequence in the memory, and then the processor reads the actual beat frequency sequence from the memory according to the first-in-first-out principle.
[0034] The beat frequency signal of the main interferometer is represented as: The beat frequency signal of the auxiliary interferometer is represented as: That is, the signal strength of the beat frequency signals output by the main interferometer and the auxiliary interferometer changes over time; after the initial sampling by the ADC acquisition card, the actual beat frequency sequence of the main interferometer is represented as follows: The actual beat frequency sequence of the auxiliary interferometer is represented as follows: , where n is the number of initial sampling points.
[0035] The preset sweep frequency range being greater than the theoretical sweep frequency range means that the starting sweep wavelength of the preset sweep frequency range is greater than the starting sweep wavelength of the theoretical sweep frequency range, and the ending sweep wavelength of the preset sweep frequency range is also greater than the ending sweep wavelength of the theoretical sweep frequency range. By controlling the tunable laser to emit continuous sweep light to the main interferometer and auxiliary interferometer with a larger preset sweep frequency range, it can be ensured that even if the actual sweep frequency range of the tunable laser deviates from the preset sweep frequency range, it can still completely cover the theoretical sweep frequency range. Since the sweep frequency offset of the tunable laser is small, only tens of pm, and will not exceed 1 nm, a preset sweep frequency range that is about 1 nm larger than the theoretical sweep frequency range is sufficient to meet the requirements.
[0036] The theoretical frequency sweep range required by the optical frequency domain reflection sensing system varies depending on different application scenarios, mainly depending on the spatial resolution required by different application scenarios. The theoretical frequency sweep range and spatial resolution satisfy the following formula: in, The spatial resolution is [the value of the space resolution]. The theoretical frequency sweep range is... λ is the center wavelength of the theoretical sweep frequency range, and n is the effective refractive index of the sensing fiber.
[0037] Step 2: Determine the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer.
[0038] In step 2, by analyzing the actual beat frequency sequence of the auxiliary interferometer and utilizing the linear relationship between its phase and wavenumber, a mapping relationship between time and wavenumber can be constructed, thereby determining the actual sweep frequency range of the tunable laser after the sweep frequency shift. Furthermore, since the auxiliary interferometer and the main interferometer sweep frequencies simultaneously, the constructed mapping relationship between time and wavenumber can be applied to the actual beat frequency sequence of the main interferometer for time-domain and wavenumber-domain conversion.
[0039] Specifically, in step 2, the steps for determining the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer are as follows: Step 21: Perform phase demodulation on the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer.
[0040] In step 21, the phase information reflects the change of noise phase in the actual beat frequency sequence of the auxiliary interferometer over time under the actual frequency sweep range. Therefore, the phase information of the auxiliary interferometer can change with the frequency sweep offset of the tunable laser. The mapping relationship between time and wavenumber during each frequency sweep of the tunable laser can be constructed through the phase information.
[0041] Specifically, in step 21, the step of performing phase demodulation on the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer is as follows: Step 211: Perform Hilbert transform on the actual beat frequency sequence of the auxiliary interferometer to obtain the complex signal of the auxiliary interferometer.
[0042] In step 211, the actual beat frequency sequence of the auxiliary interferometer is converted from a one-dimensional time-domain signal into a rotating vector on a two-dimensional complex plane by Hilbert transform, so as to facilitate subsequent phase extraction.
[0043] Specifically, a Hilbert transform is used to perform a 90° phase shift on the actual beat frequency sequence of the auxiliary interferometer to generate an imaginary part signal orthogonal to the actual beat frequency sequence of the auxiliary interferometer. Then, the actual beat frequency sequence of the auxiliary interferometer is used as the real part signal to construct the following complex signal: in, This is the actual beat frequency sequence of the auxiliary interferometer. The result is the Hilbert transform of the actual beat frequency sequence of the auxiliary interferometer.
[0044] Step 212: Perform arctangent and unwinding processing on the complex signal of the auxiliary interferometer in sequence to obtain the phase information of the auxiliary interferometer.
[0045] In step 212, the instantaneous phase is extracted from the complex signal of the auxiliary interferometer by arctangent operation, so as to map the complex signal of the auxiliary interferometer into the angular domain, and the phase unwinding process is used to eliminate the phase jump problem during instantaneous phase extraction, thereby restoring the true continuous phase curve.
[0046] The phase curve after arctangent operation is as follows: Here, atan2 is the arctangent function in the fourth quadrant, with an output range of (-π, π).
[0047] The phase curve after phase unwinding is as follows: in, It is an integer compensation value calculated based on the phase transition.
[0048] Step 22: Based on the linear relationship between phase and wavenumber, map the phase axis of the phase information to the wavenumber axis to obtain the mapping relationship between time and wavenumber.
[0049] In step 22, the mapping relationship between time and wavenumber is as follows: in, The wavenumber information of the auxiliary interferometer, The phase information of the auxiliary interferometer, The initial phase of the auxiliary interferometer, The optical path difference of the auxiliary interferometer is given.
[0050] Step 3: Based on the mapping relationship between time and wavenumber, map the resampled wavenumber sequence with equal wavenumber intervals onto the time domain to obtain the resampled time sequence. The resampled wavenumber sequence is constructed based on the theoretical frequency sweep range.
[0051] In step 3, the resampled wavenumber sequence contains a series of resampled wavenumber points used to resample the actual beat frequency sequence of the master interferometer. The resampled wavenumber sequence is represented as follows: N represents the number of resampling points. Since the actual beat frequency sequence of the main interferometer is a time-domain sequence, it cannot be directly resampled. Therefore, each resampled wavenumber point in the resampled wavenumber sequence needs to be mapped to the time domain to obtain the resampled time sequence. The resampled time sequence contains a series of resampled time points used to resample the actual beat frequency sequence of the main interferometer. The resampled time sequence is represented as follows: Due to the nonlinearity of the tunable laser, the time intervals between each resampling time point in the resampling time series are not equal after the mapping from the time domain to the wavenumber domain.
[0052] Step 4: Based on the resampling time series, resample the actual beat frequency sequence of the main interferometer to obtain the theoretical beat frequency sequence of the main interferometer within the theoretical sweep frequency range.
[0053] In step 4, the actual beat frequency sequence of the main interferometer is resampled by using the mapping relationship between time and wavenumber and combining the resampled wavenumber sequence of the theoretical sweep frequency range. This ensures that no matter how the actual sweep frequency range of the main interferometer deviates, it can be remapped back to the theoretical sweep frequency range, thereby obtaining the theoretical beat frequency sequence of the main interferometer within the theoretical sweep frequency range.
[0054] Specifically, in step 4, the steps of resampling the actual beat frequency sequence of the main interferometer according to the resampling time sequence to obtain the theoretical beat frequency sequence of the main interferometer under the theoretical sweep frequency range are as follows: Step 41: For each resampling time point in the resampling time series, search for the two adjacent initial sampling time points and the signal strength of these two initial sampling time points in the actual beat frequency sequence of the main interferometer; Step 42: Based on the two initial sampling time points and their signal strengths, determine the signal strength of the resampling time point using a one-dimensional linear interpolation method.
[0055] In step 42, the signal strength at the m-th resampling time point is as follows: in, This refers to the m-th resampling time point in the resampling time series. and These are the two initial sampling time points adjacent to the m-th resampling time point in the actual beat frequency sequence of the main interferometer. and These represent the signal strengths at the two initial sampling time points mentioned above.
[0056] Example 3 like Figure 3 As shown, a demodulation method is used in the optical frequency domain reflection sensing system described in Embodiment 1; the demodulation method includes the following steps: Step S1: Set the preset sweep frequency range of the tunable laser, wherein the preset sweep frequency range is greater than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario; Step S2: Based on the theoretical sweep frequency range, construct a resampled wavenumber sequence with equal wavenumber intervals; Step S3: When the sensing fiber is in the reference state, control the tunable laser to emit continuous sweeping light to the main interferometer and the auxiliary interferometer using the preset sweeping frequency range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the reference beat frequency signals output by the main interferometer and the auxiliary interferometer respectively, so as to obtain the actual reference beat frequency sequence of the main interferometer and the auxiliary interferometer. Step S4: Using the dynamic frequency sweep range compensation method described in Example 2, the actual reference beat frequency sequence of the main interferometer is resampled according to the actual reference beat frequency sequence of the auxiliary interferometer to obtain the theoretical reference beat frequency sequence of the main interferometer; Step S5: When the sensing fiber is in the measurement state, control the tunable laser to emit continuous frequency sweep light to the main interferometer and the auxiliary interferometer using the preset frequency sweep range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the measurement beat frequency sequence output by the main interferometer and the auxiliary interferometer to obtain the actual measurement beat frequency sequence of the main interferometer and the auxiliary interferometer; Step S6: Using the dynamic sweep frequency range compensation method described in Example 2, the actual measured beat frequency sequence of the main interferometer is resampled according to the actual measured beat frequency sequence of the auxiliary interferometer to obtain the theoretical measured beat frequency sequence of the main interferometer; Step S7: Perform wavelength drift demodulation on the theoretical reference beat frequency sequence and the theoretical measured beat frequency sequence of the master interferometer to obtain the cross-correlation spectrum of the sensing fiber.
[0057] Depend on Figure 4 (a) It can be seen that without dynamic frequency sweep range compensation, the inconsistency between the actual frequency sweep ranges of the reference state Ref and the measurement state Mea leads to a significant shift in their response positions in the distance domain, especially exhibiting a noticeable non-overlapping phenomenon at the fiber end region. As a result, such as Figure 4 As shown in (c), compared to the actual strain distribution (green curve), the strain demodulation result (purple curve) exhibits more abnormal demodulation points and error fluctuations, severely affecting the demodulation accuracy. Figure 4 (b) It can be seen that after adopting the dynamic frequency sweep range compensation method proposed in this invention, the range domain signal under the reference state Ref and the measurement state Mea can be well overlapped, and at the same time... Figure 4 As shown in (d), the strain demodulation results after compensation (purple curve) are more consistent with the actual strain distribution (green curve), the number of abnormal jump points is significantly reduced, and the strain demodulation results are more stable.
[0058] In step S3, the reference state refers to the environment in which the sensing fiber 4 is located, where no changes have occurred in the measured parameters such as temperature and strain. In step S5, the measurement state refers to the environment in which the sensing fiber is located, where changes have occurred in the measured parameters such as temperature and strain. In step S7, the wavelength shift demodulation specifically involves first performing a Fast Fourier Transform on the theoretical reference beat frequency sequence and the theoretical measurement beat frequency sequence of the main interferometer, respectively, to transform the theoretical reference beat frequency sequence and the theoretical measurement beat frequency sequence from the time domain to the range domain, obtaining the reference range domain spectrum of the theoretical reference beat frequency sequence and the measurement range domain spectrum of the theoretical measurement beat frequency sequence, and then... The distance domain spectrum and the measured distance domain spectrum are respectively subjected to sliding window values to obtain the local reference distance domain spectrum and the local measured distance domain spectrum corresponding to each measurement point. Then, the local reference distance domain spectrum and the local measured distance domain spectrum are subjected to inverse fast Fourier transform to transform the local reference distance domain spectrum and the local measured distance domain spectrum from the distance domain to the frequency domain, to obtain the local reference frequency domain spectrum and the local measured frequency domain spectrum corresponding to each measurement point. Next, the local reference frequency domain spectrum and the local measured frequency domain spectrum of the same measurement point are cross-correlated to obtain the cross-correlation spectrum corresponding to each measurement point. Finally, the cross-correlation spectra are spliced according to the measurement point positions to obtain the cross-correlation spectrum of the sensing fiber.
[0059] In addition, the steps in step S2 for constructing the resampled wavenumber sequence based on the theoretical sweep range are as follows: Step S21: Calculate the resampling start wavenumber and resampling end wavenumber of the resampling wavenumber sequence based on the starting and ending sweep wavelengths of the theoretical sweep range.
[0060] In step S21, the initial wavenumber for resampling is as follows: The resampling termination wavenumber is as follows: in, and These are, in order, the starting and ending sweep wavelengths of the theoretical sweep range.
[0061] Step S22: Calculate the resampling interval wavenumber based on the resampling start wavenumber and resampling end wavenumber, combined with the set number of resampling points.
[0062] In step S22, the resampling interval wavenumber is as follows: Where N is the set number of resampling points.
[0063] Step S23: Starting with the resampling start wavenumber or resampling end wavenumber, and using the resampling interval wavenumber as the step size, the resampling interval wavenumber is incremented or decremented to obtain the resampling wavenumber sequence.
[0064] In step 23, the resampled wavenumber sequence is as follows: Or as follows: Where N is the set number of resampling points.
[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for dynamic frequency sweep range compensation in an optical frequency domain reflection sensing system, characterized in that, Includes the following steps: Step 1: Read the actual beat frequency sequence of the main interferometer and the auxiliary interferometer. The actual beat frequency sequence is obtained by initial sampling of the actual beat frequency sequence of the main interferometer and the auxiliary interferometer under the preset sweep frequency range. The preset sweep frequency range is larger than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario. Step 2: Determine the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer; Step 3: Based on the mapping relationship between time and wavenumber, map the resampled wavenumber sequence with equal wavenumber intervals to the time domain to obtain the resampled time sequence. The resampled wavenumber sequence is constructed based on the theoretical frequency sweep range. Step 4: Based on the resampling time series, resample the actual beat frequency sequence of the main interferometer to obtain the theoretical beat frequency sequence of the main interferometer within the theoretical sweep frequency range.
2. The dynamic frequency sweep range compensation method according to claim 1, characterized in that, In step 2, the steps for determining the mapping relationship between time and wavenumber based on the actual beat frequency sequence of the auxiliary interferometer are as follows: Step 21: Perform phase demodulation on the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer; Step 22: Based on the linear relationship between phase and wavenumber, map the phase axis of the phase information to the wavenumber axis to obtain the mapping relationship between time and wavenumber.
3. The dynamic frequency sweep range compensation method according to claim 1 or 2, characterized in that, The mapping relationship between time and wavenumber is as follows: in, The wavenumber information of the auxiliary interferometer, The phase information of the auxiliary interferometer, The initial phase of the auxiliary interferometer, The optical path difference of the auxiliary interferometer is given.
4. The dynamic frequency sweep range compensation method according to claim 2, characterized in that, In step 21, the phase demodulation of the actual beat frequency sequence of the auxiliary interferometer to obtain the phase information of the auxiliary interferometer is performed as follows: Step 211: Perform Hilbert transform on the actual beat frequency sequence of the auxiliary interferometer to obtain the complex signal of the auxiliary interferometer; Step 212: Perform arctangent and unwinding processing on the complex signal of the auxiliary interferometer in sequence to obtain the phase information of the auxiliary interferometer.
5. The dynamic frequency sweep range compensation method according to claim 1, characterized in that, In step 4, the steps for resampling the actual beat frequency sequence of the main interferometer according to the resampled time sequence to obtain the theoretical beat frequency sequence of the main interferometer under the theoretical sweep frequency range are as follows: Step 41: For each resampling time point in the resampling time series, search for the two adjacent initial sampling time points and the signal strength of these two initial sampling time points in the actual beat frequency sequence of the main interferometer; Step 42: Based on the two initial sampling time points and their signal strengths, determine the signal strength of the resampling time point using a one-dimensional linear interpolation method.
6. The dynamic frequency sweep range compensation method according to claim 5, characterized in that, The signal strength at the m-th resampling time point is as follows: in, This refers to the m-th resampling time point in the resampling time series. and These are the two initial sampling time points adjacent to the m-th resampling time point in the actual beat frequency sequence of the main interferometer. and These represent the signal strengths at the two initial sampling time points mentioned above.
7. A demodulation method for an optical frequency domain reflectance sensing system, characterized in that, Includes the following steps: Step S1: Set the preset sweep frequency range of the tunable laser, wherein the preset sweep frequency range is greater than the theoretical sweep frequency range required by the optical frequency domain reflection sensing system in the target application scenario; Step S2: Based on the theoretical sweep frequency range, construct a resampled wavenumber sequence with equal wavenumber intervals; Step S3: When the sensing fiber is in the reference state, control the tunable laser to emit continuous sweeping light to the main interferometer and the auxiliary interferometer using the preset sweeping frequency range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the reference beat frequency signals output by the main interferometer and the auxiliary interferometer respectively, so as to obtain the actual reference beat frequency sequence of the main interferometer and the auxiliary interferometer. Step S4: Using the dynamic frequency sweep range compensation method of claim 1, the actual reference beat frequency sequence of the main interferometer is resampled according to the actual reference beat frequency sequence of the auxiliary interferometer to obtain the theoretical reference beat frequency sequence of the main interferometer; Step S5: When the sensing fiber is in the measurement state, control the tunable laser to emit continuous frequency sweep light to the main interferometer and the auxiliary interferometer using the preset frequency sweep range, and control the ADC acquisition card to perform initial sampling and analog-to-digital conversion on the measurement beat frequency sequence output by the main interferometer and the auxiliary interferometer to obtain the actual measurement beat frequency sequence of the main interferometer and the auxiliary interferometer; Step S6: Using the dynamic sweep frequency range compensation method of claim 1, the actual measured beat frequency sequence of the main interferometer is resampled according to the actual measured beat frequency sequence of the auxiliary interferometer to obtain the theoretical measured beat frequency sequence of the main interferometer; Step S7: Perform wavelength drift demodulation on the theoretical reference beat frequency sequence and the theoretical measured beat frequency sequence of the master interferometer to obtain the cross-correlation spectrum of the sensing fiber.
8. The dynamic frequency sweep range compensation method according to claim 7, characterized in that, In step S2, the steps for constructing a resampled wavenumber sequence with equal wavenumber intervals based on the theoretical sweep frequency range are as follows: Step S21: Calculate the resampling start wavenumber and resampling end wavenumber of the resampling wavenumber sequence based on the starting and ending sweep wavelengths of the theoretical sweep range. Step S22: Calculate the resampling interval wavenumber based on the resampling start wavenumber and resampling end wavenumber, combined with the set number of resampling points; Step S23: Starting with the resampling start wavenumber or resampling end wavenumber, and using the resampling interval wavenumber as the step size, the resampling interval wavenumber is incremented or decremented to obtain the resampling wavenumber sequence.
9. The demodulation method according to claim 8, characterized in that, The initial wavenumber for resampling is as follows: The resampling termination wavenumber is as follows: in, and These are, in order, the starting and ending sweep wavelengths of the theoretical sweep range; The resampling interval wavenumber is as follows: The resampled wavenumber sequence is as follows: Or as follows: Where N is the set number of resampling points.
10. An optical frequency domain reflectance sensing system, characterized in that, It includes a data processing device, which is used to execute the dynamic frequency sweep range compensation method of claim 1 or the demodulation method of claim 6.