Demodulation method based on ultra-weak fiber grating OFDR

Abstract

The demodulation method based on the ultra-weak fiber grating OFDR includes: performing fast Fourier transform on the time domain reflection signal collected by the OFDR system to obtain a frequency domain spectrum; setting an amplitude threshold, identifying the UW-FBG array reflection peak in the frequency domain spectrum, calibrating the spatial position of the sensing unit, and intercepting the window segment spectrum signal corresponding to each UW-FBG; performing inverse Fourier transform on the intercepted window segment spectrum signal to restore the spectrum signal of a single UW-FBG; for the reconstructed spectrum signal, selecting a fitting region containing the Bragg reflection peak, iteratively optimizing the Gaussian function fitting parameters by the least square method, and demodulating the peak Bragg wavelength; traversing the window segment spectrum signals of all UW-FBGs and repeating the above steps to obtain the Bragg wavelength shift distribution of the whole sensing region. The demodulation method based on the ultra-weak fiber grating OFDR improves the high-precision detection characteristics of the OFDR, realizes dynamic demodulation, significantly improves the sensing demodulation rate, and simplifies the algorithm complexity.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing demodulation technology, and in particular to a demodulation method based on an ultra-weak fiber grating OFDR. Background Technology

[0002] Traditional optical frequency domain reflectance (OFDR) systems use ordinary single-mode optical fibers as the sensing element. These fibers have poor directionality and low backscattered Rayleigh light intensity, making them susceptible to environmental interference and limiting the system's measurement accuracy and dynamic range. Furthermore, factors such as nonlinear sweep of the light source and phase noise degrade the actual system parameters. To overcome these problems, recent research has focused on diversified technical approaches to improve system performance.

[0003] In 2022, Fang et al. published a phase-domain-based resampling method in “Spatial Resolution Enhancement of OFDR Sensing System Using Phase-Domain-Interpolation Resampling Method[J]. IEEE SensorsJournal, 2022, 22(4): 3202-3210.” This method directly uses the phase of the auxiliary interferometer signal to complete nonlinear compensation, achieving a spatial resolution of 0.15 mm when measuring a distance of 302 m with single-mode fiber.

[0004] In 2023, Zhong et al. proposed a single interferometer scheme with self-compensation method in “High-spatial-resolution OFDR with single interferometer using self-compensation method[J]. Optics and Lasers in Engineering, 2023, 161.” This scheme replaces the auxiliary interferometer of traditional optical frequency domain reflection (OFDR) with the arc end of the fiber under test, eliminating the phase noise of optical frequency domain reflection (OFDR) and achieving temperature sensing with a spatial resolution of 3 mm at a measurement distance of 108 m.

[0005] In 2024, Zou et al. proposed the spectral shift adjacent point difference method in "Distributed ultra large strain measurement range sensing based on spectral shift adjacent point difference method in OFDR[J].Optics and Laser Technology,2024,176111003." This method uses an algorithm to identify and remove false peaks in cross-correlation noise to achieve large strain measurement, achieving a strain range of 10800με at a spatial resolution of 7.84mm.

[0006] In the same year, Li et al. proposed an iterative birefringence calibration algorithm in “Performance improvement of a distributed temperaturesensor with kilometer length and centimeter spatial resolution based on polarization-sensitive OFDR[J]. Sensors and Actuators A: Physical,2024,373:115430.”, which achieved a spatial resolution of 5 cm at a sensing distance of 1.5 km and a temperature measurement uncertainty of ±0.2℃.

[0007] In 2025, Liu et al. proposed a spectral segmented normalized cross correlation algorithm in “Optical frequency domain reflectometer based on spectral segmented normalized cross correlation[J]. Optics&Laser Technology,2025,191.”, which achieved a measurement with a spatial resolution of 3.2 mm at 3000 με.

[0008] The aforementioned work has achieved some results, but as the sensing distance of the system increases, the spatial resolution deteriorates sharply, and the optical path structure and algorithm are complex, resulting in high system costs. Regarding the commercial development of OFDRs, the French company APEX's OFDR-AP6 series can achieve high-precision detection of fiber optic links, with a sampling resolution of 42μm on 244m of fiber, but it cannot achieve sensing detection; the American company LUNA's ODiSI7100 series can achieve a temperature / strain resolution higher than 0.1℃ / 1με and a spatial resolution of 10mm on 50m of fiber, but its price, often exceeding one million, limits its widespread application in the sensing field.

[0009] Domestic universities and enterprises have also made significant progress in the commercialization research and development of OFDR. Tianjin University, Shanghai Jiao Tong University, and others have successively launched patents such as "High-speed distributed strain measurement system and method based on optical frequency domain reflection: CN202110907914.6 [P]. 2022-08-23." and "Double-sideband optical frequency domain reflectometer: CN202210559130.3 [P]. 2023-03-14." In 2024, Professor Dong Yongkang's team at Harbin Institute of Technology released a high spatial resolution fiber optic sensing system, achieving a spatial resolution of 0.5 mm under a maximum measurement distance of 100 m. Wuhan Haoheng Technology Co., Ltd. launched the OSI series of commercial equipment, which can achieve a static temperature measurement accuracy of ±0.1℃ and a strain measurement accuracy of ±1με within a 100 m testing range. Although the performance of domestically produced OFDRs has approached or even surpassed that of similar international products, the core light source and key electronic components still rely on imports. Furthermore, the large size and poor portability of the system restrict its application potential in scenarios such as field testing and mobile platform deployment. Therefore, achieving the miniaturization and integration of OFDR instruments has become the key to promoting the application of this new technology. Summary of the Invention

[0010] This invention provides a demodulation method based on ultra-weak fiber Bragg grating (OFDR), which improves the high-precision detection characteristics of OFDR while achieving dynamic demodulation; it significantly improves the sensing demodulation rate and simplifies the algorithm complexity.

[0011] The technical solution adopted in this invention is as follows:

[0012] The demodulation method based on ultra-weak fiber grating OFDR includes the following steps: Step 1: Time-frequency conversion: The frequency domain spectrum is obtained by performing a Fast Fourier Transform (FFT) on the time-domain reflection signal acquired by the OFDR system. Step 2: Threshold localization and spectrum extraction: By setting an amplitude threshold, the reflection peaks of the UW-FBGs array in the frequency domain spectrum are identified, the spatial position of the sensing unit is accurately calibrated, and the window segment spectrum signal corresponding to each UW-FBG is extracted. Step 3: Spectral Reconstruction Perform an inverse Fourier transform (IFFT) on the window segment spectrum signal captured in step 2 to reconstruct the spectrum signal of a single UW-FBG. Step 4: Wavelength demodulation optimization: For the reconstructed spectral signal, a fitting region containing the Bragg reflection peak is selected, and the Gaussian function fitting parameters are iteratively optimized using the least squares method to demodulate the peak Bragg wavelength. Step 5: Global Demodulation Traverse all window segment spectrum signals of UW-FBG and repeat steps 3 to 4 above to obtain the Bragg wavelength offset distribution of the entire sensing area.

[0013] In step 1, in the optical frequency domain reflectometry (OFDR) system, the continuous light emitted by the linearly swept frequency source is divided into reference light and sensing light. After the sensing light enters the optical fiber, its Rayleigh scattering or ultra-weak grating reflection serves as the signal light, which merges with the reference light at the coupler to undergo coherent mixing. The intensity of the time-domain interference signal (photocurrent) received by the photodetector can be expressed as: (1); In equation (1), Represents a time-domain signal; The sign indicates that the light intensity is directly proportional to the expression on the right side of the equals sign; and These are the electric field amplitudes of the reference light and the signal light, respectively; The beat frequency; Phase noise; beat frequency It is linearly proportional to the position of the reflection point in the optical fiber, that is... v = 2nγ / c, where γ is the linear sweep rate of the light source in Hz / s; n is the effective refractive index of the optical fiber; and c is the speed of light in vacuum.

[0014] The time-domain signal is obtained by formula (2). By performing a Fast Fourier Transform (FFT), the signal can be transformed from the time domain to the frequency domain, yielding the frequency spectrum S(m): (2); In equation (2), Time-domain signal The discrete sampling sequence is given by: n = 0, 1, 2, ..., N-1, where N is the number of signal points; m is the frequency domain index, m = 0, 1, 2, ..., N-1; each frequency component m in S(m) corresponds to a specific position z in the optical fiber, and its amplitude corresponds to the reflection or scattering intensity at that position.

[0015] In step 2, threshold calibration is performed on the distance domain signal, assuming the system sampling rate interval is... z, the grating length of the ultra-weak fiber grating is L uw It can calculate the number of sampling points N corresponding to a single grating in the range domain signal. uw = L uw / Δz.

[0016] Based on the statistical characteristics of the power spectral density in the local space near the location point, and the length L of the ultra-weak fiber grating region... uw With grating spacing length Suw Parameters, dynamically matched with weighted adaptive power spectral density (PSD) thresholds Its expression is: (3); In equation (3), and These are the statistical mean and standard deviation of the power spectral density (PSD) amplitude, respectively. For adjustment coefficients; For and The weight function is a parameter.

[0017] The weight function expression is: (4); In equation (4), The spacing-to-gate length ratio; α represents the gate length duty cycle; β represents the weighting coefficients.

[0018] Searching along the range domain signal sequence, the first signal with a power spectral density (PSD) greater than [value missing] will be found. The sampling point index is denoted as FBG1 and used as the starting point of the ultra-weak fiber grating array; Starting from the initial point, if the number of consecutive sampling points N is equal to the number of sampling points N corresponding to a single grating in the range domain signal... uw The relation satisfies N>N uw / 2, and at this time the power spectral density at N points all exceeds the threshold. If so, it is determined to be a raster point UW-FBG n And record location information.

[0019] In step 2, the specific spectral signal extraction of the window segment is as follows: UW-FBG of the identified raster points n center frequency Based on this, the spectrum signal truncation range is: f uw = (5); In equation (5), The half-width frequency offset parameter represents the frequency offset when the spectrum is truncated, and is determined by the spectral resolution corresponding to the minimum physical spacing of the UW-FBG.

[0020] In step 3, since the light source in optical frequency domain reflection (OFDR) is linearly swept, the optical frequency ν is linearly related to time t: ν = ν0 + γt; Where: ν0 represents the initial optical frequency, and γ represents the sweep rate; therefore, the sweep signal directly reflects the wavelength change relationship of the UW-FBG reflectance, that is, it restores the reflectance spectrum S(λ) of a single UW-FBG.

[0021] The inverse Fourier transform (IFFT) is performed on the truncated window segment of the spectrum signal, as shown in the following formula: (6); In equation (6), This is the inverse fast Fourier transform function.

[0022] In step 4, the maximum amplitude R is located on the reconstructed reflection spectrum S(λ) of a single UW-FBG. max And its corresponding initial wavelength λ0. Using the initial wavelength λ0 as the center, search both sides of the spectral curve until the spectral amplitude first decreases to 0.2. R max The wavelength points are denoted as λ. left and λ right Wavelength range [λ] left ,λ right This is the region selected as the Gaussian function fitting region.

[0023] In step 4, the Gaussian function fitting parameters are iteratively optimized using the least squares method to demodulate the peak Bragg wavelength. This specifically includes the following steps: S4.1: Establish the UW-FBG spectral Gaussian function model: (7); In equation (7), Represents the reflectance spectrum of a single UW-FBG; Peak intensity; It is the independent variable, representing wavelength; The wavelength of the Bragg center; Spectral width; It is a natural exponential function.

[0024] S4.2: Taking the natural logarithm of the UW-FBG spectral Gaussian function model, we expand it into a quadratic polynomial: (8); S4.3: Solve the parameters using the least squares method to obtain the optimized center wavelength peak value. : (9); In equation (8), This represents the total number of fitted points; This represents the wavelength value represented by the i-th sampling point in the UW-FBG reflectance spectrum; Indicates at wavelength The UW-FBG reflectance spectral intensity was measured at [location].

[0025] In step 4, the Bragg wavelength is optimized. The initial value is set as the wavelength corresponding to the peak value of the UW-FBG spectrum within the Gaussian function fitting region, that is, the maximum intensity value in the UW-FBG reflection spectrum is taken as the Bragg center wavelength. .

[0026] In step 5, after completing the identification and spectral window truncation of the ultra-weak fiber Bragg grating array (UW-FBG), the processing of each grating in steps 3 to 4 is independent. This is achieved by processing the spectral data of N window segments corresponding to N UW-FBGs in the host computer. uwi The i=1,...,N} are allocated to N parallel processing units (threads or computing cores) to achieve parallel processing and improve the demodulation rate.

[0027] In step 5, after completing the wavelength demodulation of each grating in the ultra-weak fiber grating array (UW-FBGs), a Bragg wavelength array {λ} corresponding to the spatial position order of the gratings is obtained. i , i=1,...,N}, where λ i λ is the center wavelength of the grating, and i is the grating number.

[0028] To obtain sensing information reflecting the distribution of external physical fields such as temperature and strain, the reference Bragg wavelength array {λ} measured under default conditions is saved. i_ref , i=1,...,N},λ i_ref The array {λ} represents the center wavelength of the grating in the reference state and the measured Bragg wavelength array in the sensing state. i Subtracting the values ​​of i=1,...,N} gives the wavelength change. λ i .

[0029] This invention provides a demodulation method based on an ultra-weak fiber grating OFDR, with the following technical advantages: 1) While maintaining the high-precision detection characteristics of OFDR, this invention achieves dynamic demodulation, significantly improves the sensing demodulation rate, and simplifies the algorithm complexity; 2) This invention uses ultra-weak fiber optic grating sensing technology, which can not only achieve accurate dynamic demodulation in complex environments, but also has durability and stability, making it suitable for high dynamic scenarios such as early warning of thermal runaway in new energy batteries and monitoring of wing structure damage. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and examples: Figure 1This is a flowchart of a demodulation method based on an ultra-weak fiber grating OFDR.

[0031] Figure 2 This is a schematic diagram of grating threshold calibration.

[0032] Figure 3 A comparison of the improved Gaussian demodulation method with the original spectrum peaks.

[0033] Figure 4(a) shows the temperature sensing effect of the demodulation method based on the ultra-weak fiber grating OFDR. Figure 4(b) shows the strain sensing effect of the demodulation method based on the ultra-weak fiber grating OFDR. Detailed Implementation

[0034] To address the issues of low accuracy and large-range nonlinearity in traditional fiber OFDR, this invention provides a demodulation method based on ultra-weak fiber grating OFDR. By performing real-time threshold calibration on the optical frequency domain reflectance (OFDR) signal in the distance domain, the position information of the grating array is accurately located. A parallelized IFFT spectral reconstruction architecture is adopted, combined with a Gaussian fitting algorithm, to achieve rapid peak extraction of the grating array spectrum.

[0035] Based on ultra-weak fiber Bragg grating OFDR systems, such as Figure 1 As shown, the system includes a linearly swept narrow-linewidth laser (TLS), an optical fiber coupler (OC), a time-delay fiber (DF), a photodetector (PD), an optical circulator (ICR), a polarization beamsplitter (PBS), a balanced optical detector (BPD), an ultra-weak fiber grating array (UW-FBGs), an embedded data acquisition card (Zynq7100), and a host computer (PC). The TLS laser is connected to the input of the PBS. The output of the PBS is connected to the reference arm and the sensing arm, respectively. A mirror is connected to the end of the reference arm, and the sensing arm is connected to the UW-FBG array. The two return beams converge at the coupler (OC) / circulator (ICR) and are then input to the photodetector (PD). The electrical output of the photodetector (PD) is acquired by the DAQ and transmitted to the processing unit.

[0036] The flowchart of the demodulation method based on ultra-weak fiber grating OFDR is as follows: Figure 2 As shown.

[0037] The demodulation method and the original spectrum peak effect are compared in the figure below. Figure 3 As shown, by Figure 3 It can be seen that the average jump of the center wavelength demodulated by the maximum value method is ≥5pm, while the average jump of the improved Gaussian fitting method of this invention is ≤2pm, showing a significant optimization effect. Figures 4(a) and 4(b) show the temperature sensing effect of the demodulation method based on ultra-weak fiber Bragg grating (OFDR). Figure 4(a) shows the calibration curve of the demodulation method based on ultra-weak fiber Bragg grating (OFDR) in the temperature sensing experiment. The horizontal axis represents the temperature change ΔT, and the vertical axis represents the wavelength shift Δλ. This figure verifies that there is an excellent linear relationship between the demodulation result and the temperature change, R² = 0.99989. Figure 4(b) shows the calibration curve of the demodulation method based on ultra-weak fiber Bragg grating (OFDR) in the strain sensing experiment. The horizontal axis represents the load G, and the vertical axis represents the strain demodulation amount με. This figure verifies that there is an excellent linear relationship between the demodulation result and the strain change, R² = 0.99989. 2 =0.99994. Figures 4(a) and 4(b) verify that the method of the present invention has distributed measurement capabilities and good dynamic response characteristics, and can accurately and synchronously acquire the status information of each point on the sensing link, meeting the real-time monitoring requirements; In summary, this invention accurately locates the position information of the grating array through threshold calibration, employs a parallelized IFFT spectral reconstruction architecture, and combines a Gaussian fitting algorithm to achieve rapid peak extraction of the grating array spectrum, thus overcoming the technical bottleneck of ultra-weak fiber grating OFDR systems in dynamic measurements. Experiments verify that the demodulation method based on ultra-weak fiber grating OFDR achieves a temperature sensing linearity of 0.99989 and a strain sensing linearity of 0.99994, with an accuracy of ±0.1℃ / 1με. The demodulation rate is 22.26% higher than that of traditional OFDR systems, providing a cost-effective solution for high-dynamic scenarios such as thermal runaway early warning in new energy batteries.

Claims

1. A demodulation method based on ultra-weak fiber grating OFDR, characterized in that... Includes the following steps: Step 1: Perform a Fast Fourier Transform on the time-domain reflection signal acquired by the OFDR system to obtain the frequency domain spectrum; Step 2: Set the amplitude threshold, identify the reflection peaks of the UW-FBGs array in the frequency domain spectrum, calibrate the spatial position of the sensing unit, and extract the window segment spectrum signal corresponding to each UW-FBG; Step 3: Perform an inverse Fourier transform on the window segment spectrum signal extracted in Step 2 to reconstruct the spectral signal of a single UW-FBG; Step 4: For the reconstructed spectral signal, select the fitting region containing the Bragg reflection peak, and iteratively optimize the Gaussian function fitting parameters using the least squares method to demodulate the peak Bragg wavelength. Step 5: Traverse the window segment spectrum signal of all UW-FBG and repeat steps 3 to 4 above to obtain the Bragg wavelength offset distribution of the entire sensing area.

2. The demodulation method based on ultra-weak fiber grating OFDR according to claim 1, characterized in that: In step 1, in the optical frequency domain reflectometry (OFDR) system, the continuous light emitted by the linearly swept frequency source is divided into reference light and sensing light. After the sensing light enters the optical fiber, its Rayleigh scattering or ultra-weak grating reflection light serves as the signal light, which merges with the reference light at the coupler to undergo coherent mixing. The intensity of the time-domain interference signal received by the photodetector is expressed as: （1）； In equation (1), Represents a time-domain signal; The sign indicates that the light intensity is directly proportional to the expression on the right side of the equals sign; and These are the electric field amplitudes of the reference light and the signal light, respectively; The beat frequency; Phase noise; beat frequency It is linearly proportional to the position of the reflection point in the optical fiber, that is... v = 2nγ / c, where γ is the linear sweep rate of the light source; n is the effective refractive index of the optical fiber; and c is the speed of light in vacuum. The time-domain signal is obtained by formula (2). Performing a Fast Fourier Transform converts the signal from the time domain to the frequency domain, yielding the frequency spectrum S(m): （2）； In equation (2), Time-domain signal The discrete sampling sequence is given by: n = 0, 1, 2, ..., N-1, where N is the number of signal points; m is the frequency domain index, m = 0, 1, 2, ..., N-1; each frequency component m in S(m) corresponds to a specific position z in the optical fiber, and its amplitude corresponds to the reflection or scattering intensity at that position.

3. The demodulation method based on ultra-weak fiber grating OFDR according to claim 2, characterized in that: In step 2, threshold calibration is performed on the distance domain signal, assuming the system sampling rate interval is... z, the grating length of the ultra-weak fiber grating is L uw Calculate the number of sampling points N corresponding to a single grating in the range domain signal. uw = L uw / Δz; Based on the statistical characteristics of the power spectral density in the local space near the location point, and the length L of the ultra-weak fiber grating region... uw With grating spacing length S uw Parameters, dynamically matched with weighted adaptive power spectral density (PSD) thresholds Its expression is: （3）； In equation (3), and These are the statistical mean and standard deviation of the power spectral density (PSD) amplitude, respectively. For adjustment coefficients; For and Weighting function for parameters; The weight function expression is: （4）； In equation (4), The spacing-to-gate length ratio; α is the gate length duty cycle; β are weighting coefficients. Searching along the range domain signal sequence, the first signal with a power spectral density (PSD) greater than [value missing] will be found. The sampling point index is denoted as FBG1 and used as the starting point of the ultra-weak fiber grating array; Starting from the initial point, if the number of consecutive sampling points N is equal to the number of sampling points N corresponding to a single grating in the range domain signal... uw The relation satisfies N>N uw / 2, and at this time the power spectral density at N points all exceeds the threshold. If so, it is determined to be a raster point UW-FBG n And record location information.

4. The demodulation method based on ultra-weak fiber grating OFDR according to claim 3, characterized in that: In step 2, the specific spectral signal extraction of the window segment is as follows: UW-FBG of the identified raster points n center frequency Based on this, the spectrum signal truncation range is: f uw = （5）； In equation (5), The half-width frequency offset parameter represents the frequency offset when the spectrum is truncated, and is determined by the spectral resolution corresponding to the minimum physical spacing of the UW-FBG.

5. The demodulation method based on ultra-weak fiber grating OFDR according to claim 4, characterized in that: In step 3, since the light source in the optical frequency domain reflector (OFDR) is linearly swept, the optical frequency ν is linearly related to time t: ν = ν0 + γt; ν0 represents the initial optical frequency, and γ represents the sweep rate; therefore, the sweep signal directly reflects the wavelength change relationship of the UW-FBG reflectance, that is, it reconstructs the reflectance spectrum S(λ) of a single UW-FBG. The inverse Fourier transform of the truncated window segment spectrum signal is shown in the following formula: （6）； In equation (6), This is the inverse fast Fourier transform function.

6. The demodulation method based on ultra-weak fiber grating OFDR according to claim 5, characterized in that: In step 4, the maximum amplitude R is located on the reconstructed reflection spectrum S(λ) of a single UW-FBG. max And its corresponding initial wavelength λ0; with the initial wavelength λ0 as the center, search both sides of the spectral curve, and find the point where the spectral amplitude first drops to 0.

2. R max The wavelength points are denoted as λ. left and λ right Wavelength range [λ] left ,λ right This is the region selected as the Gaussian function fitting region.

7. The demodulation method based on ultra-weak fiber grating OFDR according to claim 6, characterized in that: In step 4, the Gaussian function fitting parameters are iteratively optimized using the least squares method to demodulate the peak Bragg wavelength. This specifically includes the following steps: S4.1: Establish the UW-FBG spectral Gaussian function model: （7）； In equation (7), Represents the reflectance spectrum of a single UW-FBG; Peak intensity; It is the independent variable, representing wavelength; The wavelength of the Bragg center; Spectral width; It is a natural exponential function; S4.2: Taking the natural logarithm of the UW-FBG spectral Gaussian function model, we expand it into a quadratic polynomial: （8）； S4.3: Solve the parameters using the least squares method to obtain the optimized center wavelength peak value. : （9）； In equation (8), This represents the total number of fitted points; This represents the wavelength value represented by the i-th sampling point in the UW-FBG reflectance spectrum; Indicates at wavelength The UW-FBG reflectance spectral intensity was measured at [location].

8. The demodulation method based on ultra-weak fiber grating OFDR according to claim 7, characterized in that: In step 4, the Bragg wavelength is optimized. The initial value is set as the wavelength corresponding to the peak value of the UW-FBG spectrum within the Gaussian function fitting region, that is, the maximum intensity value in the UW-FBG reflection spectrum is taken as the Bragg center wavelength. .

9. The demodulation method based on ultra-weak fiber grating OFDR according to claim 8, characterized in that: In step 5, after completing the identification and spectral window truncation of the ultra-weak fiber Bragg grating array (UW-FBG), the processing of each grating in steps 3 to 4 is independent; by transferring the spectral data of the N window segments corresponding to the N UW-FBGs to the host computer {f uwi The i=1,...,N} groups are assigned to N parallel processing units to achieve parallel processing and improve the demodulation rate.

10. The demodulation method based on ultra-weak fiber grating OFDR according to claim 9, characterized in that: In step 5, after completing the wavelength demodulation of each grating in the ultra-weak fiber grating array (UW-FBGs), a Bragg wavelength array {λ} corresponding to the spatial position order of the gratings is obtained. i , i=1,...,N}, where λ i λ is the center wavelength of the grating, and i is the grating number. To obtain sensing information reflecting the distribution of external physical fields such as temperature and strain, the reference Bragg wavelength array {λ} measured under default conditions is saved. i_ref , i=1,...,N},λ i_ref The array {λ} represents the center wavelength of the grating in the reference state and the measured Bragg wavelength array in the sensing state. i Subtracting the values ​​of i=1,...,N} gives the wavelength change. λ i .

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