Array grating addressing device and addressing method based on median filter

Abstract

The invention relates to an array grating addressing device and addressing method based on a median filter, the device comprises a sweep frequency light source, a first optical fiber 1 * 2 coupler, a main interferometer module, an auxiliary interferometer module and a data acquisition module, the input end of the first optical fiber 1 * 2 coupler is connected with the output end of the sweep frequency light source, and the input end of the first optical fiber 1 * 2 coupler is connected with the output end of the sweep frequency light source; two output ends, a second end and a third end of the first optical fiber 1 * 2 coupler are respectively connected with the main interferometer module and the auxiliary interferometer module, the first optical fiber 1 * 2 coupler divides laser output by a frequency sweeping light source into two beams, and the two beams are respectively output to the main interferometer module and the auxiliary interferometer module. According to the invention, the accurate addressing of the array grating in the optical frequency domain reflection system is realized, and the spectrum demodulation precision and the distributed measurement precision can be improved.

Description

Technical Field

[0001] The present application relates to the field of distributed optical fiber sensing technology, and in particular to an array grating addressing and addressing method based on a median filter. Background Art

[0002] A fiber Bragg grating (FBG) is a passive optical device fabricated within the core of an optical fiber with a unique reflection spectrum. It reflects only light at the Bragg wavelength, the center wavelength of the grating spectrum, and reflects virtually no light at other wavelengths. By monitoring the shift in the center wavelength of the grating spectrum, changes in external physical quantities can be detected. Arrayed FBGs, fabricated consecutively on the same optical fiber, form a FBG array, enabling distributed sensing.

[0003] However, accurately locating the position of each grating in an array grating, known as grating addressing, has long been a challenge in array grating applications. Positioning methods based on optical time-domain reflectometry (OTDR) have poor spatial resolution, typically measured in meters, and are unable to obtain the actual position of each grating. While positioning methods based on optical frequency-domain reflectometry (OFDR) can achieve millimeter-level spatial resolution, they still lack an efficient and accurate method for obtaining the position of each grating. Summary of the Invention

[0004] The embodiment of the present application provides an array grating addressing and addressing method based on a median filter, which realizes accurate addressing of the array grating in an optical frequency domain reflection system, which is beneficial to improving the spectral demodulation accuracy and distributed measurement accuracy.

[0005] To achieve the above objectives, this application provides the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides an array grating addressing device based on a median filter, comprising a swept-frequency light source, a first fiber 1x2 coupler, a main interferometer module, an auxiliary interferometer module, and a data acquisition module, wherein the input end of the first fiber 1x2 coupler is connected to the output end of the swept-frequency light source, and the two output ends of the first fiber 1x2 coupler, the second end and the third end, are respectively connected to the main interferometer module and the auxiliary interferometer module. The first fiber 1x2 coupler divides the laser output of the swept-frequency light source into two beams, which are output to the main interferometer module and the auxiliary interferometer module respectively; the main interferometer module is used to measure the distributed reflection signal of the optical fiber to be tested, i.e., the array grating; the auxiliary interferometer module is used to measure and compensate for the nonlinear scanning phase noise of the swept-frequency light source; and the input end of the data acquisition module is respectively connected to the trigger end of the swept-frequency light source, the output end of the main interferometer module, and the output end of the auxiliary interferometer module.

[0007] The main interferometer module includes a second fiber 1x2 coupler, an optical circulator, a first fiber 2x2 coupler, a first balanced photodetector and an array grating. The input end of the second fiber 1x2 coupler is connected to the second end of the first fiber 1x2 coupler, the first end of the optical circulator is connected to the second end of the second fiber 1x2 coupler, the second end of the optical circulator is connected to the array grating, the third end of the optical circulator is connected to the first end of the first fiber 2x2 coupler, the third end of the second fiber 1x2 coupler is connected to the second end of the first fiber 2x2 coupler, and the third and fourth ends of the first fiber 2x2 coupler are respectively connected to the two input ports of the first balanced photodetector.

[0008] The auxiliary interferometer module includes a third optical fiber 1x2 coupler, a delay optical fiber, a second optical fiber 2x2 coupler and a second balanced photodetector. The input end of the third optical fiber 1x2 coupler is connected to the third end of the first optical fiber 1x2 coupler, the two ends of the delay optical fiber are respectively connected to the third end of the third optical fiber 1x2 coupler and the second end of the second optical fiber 2x2 coupler, the second end of the third optical fiber 1x2 coupler is connected to the first end of the second optical fiber 2x2 coupler, and the third end and fourth end of the second optical fiber 2x2 coupler are respectively connected to the two input ports of the second balanced photodetector.

[0009] The splitting ratio between the second end and the third end of the first optical fiber 1x2 coupler is 99:1, the splitting ratio between the second optical fiber 1x2 coupler and the third optical fiber 1x2 coupler is 1:1, and the splitting ratio between the first optical fiber 2x2 coupler and the second optical fiber 2x2 coupler is 1:1.

[0010] The laser output by the frequency-sweeping light source is continuous light with linearly varying frequency, and the function expression of the light field is:

[0011]

[0012] Where t represents the time variable, E(t) represents the output light field that changes with time t, f0 represents the initial frequency, γ represents the frequency scanning rate, exp{} represents the natural exponential function, j represents the imaginary unit, and E0(t) represents the light field amplitude that changes with time t. represents the nonlinear swept phase noise that varies with time t.

[0013] The function expression of the beat frequency interference signal output by the main interferometer module is:

[0014]

[0015] τ i =2n·li / c

[0016] Among them, E m (t) represents the functional expression of the beat frequency interference signal output by the main interferometer module, τ i represents the optical delay of the reflected light of the i-th grating in the array grating, l i represents the spatial position of the i-th grating, R i (t) represents the reflection intensity of the i-th grating that varies with time, and is also the reflection spectrum of the i-th grating. n represents the refractive index of the optical fiber, and c represents the speed of light in vacuum.

[0017] The function expression of the beat frequency interference signal output by the auxiliary interferometer module is:

[0018]

[0019] τ a =n·l a / c

[0020] Among them, E a (t) represents the functional expression of the beat frequency interference signal output by the auxiliary interferometer module, τ a Indicates the optical delay of the delay fiber, l a Indicates the length of the delay fiber.

[0021] The wavelength scanning range of the frequency-sweeping light source should cover the spectral range of all gratings in the array grating.

[0022] In a second aspect, an embodiment of the present application provides an array grating addressing method based on a median filter, which uses a median filter to smooth the distributed reflection signal of the array grating obtained by the optical frequency domain reflection system, and combines the minimum algorithm to obtain the position coordinates of each fiber grating.

[0023] The beat frequency interference signal output by the main interferometer module is Fourier transformed to obtain the distributed reflection signal of the array grating. The distributed reflection signal is then smoothed using a median filter. The smoothed signal is then searched for its minimum value using a minimum algorithm. The position of each grating is located between two adjacent minimum positions. By performing an inverse Fourier transform on the distributed reflection signal between two adjacent minimum positions, the spectrum of a single fiber Bragg grating at that position can be obtained.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Compared with positioning devices based on optical time-domain reflectometry, the spatial positioning resolution is higher. This is because the spatial positioning resolution of the optical time-domain reflectometry system is limited by the output pulse width of the light source. The interval between two adjacent gratings in the array grating needs to be greater than the laser pulse width to distinguish a single grating, and the actual position information of each grating cannot be obtained. However, positioning devices using optical frequency-domain reflectometry technology can achieve millimeter-level spatial resolution because the system's spatial positioning resolution depends only on the frequency scanning range of the swept light source, and can accurately locate the actual position of each grating.

[0026] 2. Ability to obtain accurate position information of each grating. The traditional method of using optical frequency domain reflection technology to realize array grating positioning requires manual identification and recording of the position of each grating. This method is inefficient and inaccurate, and is obviously not applicable to the application scenarios of large-scale array gratings. The array grating addressing method based on the median filter uses a median filter to smooth the distributed reflection signal of the array grating, thereby eliminating the reflection noise and obtaining a more accurate distributed reflection signal; the minimum value algorithm is used to accurately locate the weak reflection area between two adjacent gratings, thereby achieving accurate addressing of each grating position. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 The array grating addressing device based on the median filter provided by the present invention;

[0029] Figure 2 The array grating distributed reflection signal obtained by the array grating addressing device based on the median filter provided by the present invention;

[0030] Figure 3 The present invention provides a smooth signal obtained by using a median filter-based array grating addressing method. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings. It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0032] The terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0033] The terms "first," "second," etc. are only used to distinguish one entity or operation from another entity or operation, and are not to be understood as indicating or implying relative importance, nor are they to be understood as requiring or implying any actual relationship or order between these entities or operations.

[0034] like Figure 1 As shown, an array grating addressing device based on a median filter, such as Figure 1 As shown, it includes a swept frequency light source 1, a first optical fiber 1x2 coupler 11, a main interferometer module 2 and an auxiliary interferometer module 3, and a data acquisition module 4, wherein:

[0035] The swept frequency light source 1 is used to output laser light with a light frequency that changes with time. The wavelength scanning range is set to 1540nm to 1560nm, and the wavelength scanning speed is 20nm / s.

[0036] Furthermore, the light field function expression output by the frequency-sweeping light source 1 in one scanning cycle is:

[0037]

[0038] Where t represents the time variable, E(t) represents the output light field that varies with time t, f0 represents the initial frequency, γ represents the frequency sweep rate, exp{} represents the natural exponential function, j represents the imaginary unit, E0(t) represents the light field amplitude that varies with time t, and φ(t) represents the nonlinear sweep phase noise that varies with time t.

[0039] The input port of the first fiber 1x2 coupler 11 is connected to the swept-frequency light source 1, and the two output ports are connected to the main interferometer module 2 and the auxiliary interferometer module 3, respectively. The first fiber 1x2 coupler 11 splits the laser output from the swept-frequency light source 1 into two beams, outputting them to the main interferometer module 2 and the auxiliary interferometer module 3, respectively.

[0040] Furthermore, the splitting ratio of the first optical fiber 1x2 coupler 11 is 99:1, so that most of the power output by the laser enters the main interferometer module 2, thereby increasing the intensity of the main interference signal. A small part of the power enters the auxiliary interferometer module 3. Such optical power distribution is sufficient to obtain the phase information of the auxiliary interference signal.

[0041] In this embodiment, the main interferometer module 2 includes a second optical fiber 1x2 coupler 21, an optical circulator 22, a first optical fiber 2x2 coupler 23, a first balanced photodetector 24 and an array grating 25. The input end of the second optical fiber 1x2 coupler 21 is connected to the second end of the first optical fiber 1x2 coupler 11, the first end of the optical circulator 22 is connected to the second end of the second optical fiber 1x2 coupler 21, the second end of the optical circulator 22 is connected to the array grating 25, the third end of the optical circulator 22 is connected to the first end of the first optical fiber 2x2 coupler 23, the third end of the second optical fiber 1x2 coupler 21 is connected to the second end of the first optical fiber 2x2 coupler 23, and the third and fourth ends of the first optical fiber 2x2 coupler 23 are respectively connected to the two input ports of the first balanced photodetector 24.

[0042] The laser light entering the main interferometer module 2 then passes through the second fiber 1x2 coupler 21 and optical circulator 22 into the array grating 25, where it is reflected at the center wavelength corresponding to each grating in the array grating 25. The reflected light then returns to the main interferometer module 2 through the optical circulator 22 and undergoes beat frequency interference with another signal in the main interferometer module 2 in the first fiber 2x2 coupler 23. The main interference signal is then converted into an electrical signal by the first balanced photodetector 24.

[0043] Furthermore, the function expression of the beat frequency interference signal output by the main interferometer module 2 is:

[0044]

[0045] τ i =2n·l i / c

[0046] Among them, E m (t) represents the functional expression of the beat frequency interference signal output by the main interferometer module, τ i represents the optical delay of the reflected light of the i-th grating in the array grating, l i represents the spatial position of the i-th grating, R i (t) represents the reflection intensity of the i-th grating that varies with time, and is also the reflection spectrum of the i-th grating. n represents the refractive index of the optical fiber, and c represents the speed of light in vacuum.

[0047] Furthermore, the array grating 25 is an identical grating array, all gratings have the same central wavelength of 1550 nm, the size of each grating is 10 mm, and the interval between adjacent gratings is 10 mm.

[0048] Furthermore, the second fiber 1x2 coupler 21 has a 1:1 splitting ratio, ensuring that the two beams entering the main interferometer module 2 have equal power, thus maximizing the intensity of the output main interference signal. The first fiber 2x2 coupler 23 also has a 1:1 splitting ratio, ensuring that the optical power entering the two input ports of the first balanced photodetector 24 is equal, effectively eliminating the DC component and noise in the main interference signal.

[0049] In this embodiment, the auxiliary interferometer module 3 includes a third optical fiber 1x2 coupler 31, a delay optical fiber 32, a second optical fiber 2x2 coupler 33 and a second balanced photodetector 34. The input end of the third optical fiber 1x2 coupler 31 is connected to the third end of the first optical fiber 1x2 coupler 11, the two ends of the delay optical fiber 32 are respectively connected to the third end of the third optical fiber 1x2 coupler 31 and the second end of the second optical fiber 2x2 coupler 33, the second end of the third optical fiber 1x2 coupler 31 is connected to the first end of the second optical fiber 2x2 coupler 33, and the third end and the fourth end of the second optical fiber 2x2 coupler 33 are respectively connected to the two input ports of the second balanced photodetector 34.

[0050] Furthermore, the two signals in the auxiliary interferometer module 3 will generate beat frequency interference in the second optical fiber 2×2 coupler 33 , and the auxiliary interference signal will be converted into an electrical signal by the second balanced photodetector 34 .

[0051] Furthermore, the function expression of the beat frequency interference signal output by the auxiliary interferometer module 3 is:

[0052]

[0053] τ a =n·l a / c

[0054] Among them, E a (t) represents the functional expression of the beat frequency interference signal output by the auxiliary interferometer module, τ a Indicates the optical delay of the delay fiber, l a Indicates the length of the delay fiber.

[0055] Furthermore, the auxiliary interferometer module 3 is used to measure and compensate for the nonlinear scanning phase noise of the swept frequency light source 1. The compensation process is as follows: the auxiliary interference signal E is converted into a (t) is converted into an analytical signal in the complex domain, the inverse tangent function arctan{} is used to extract the azimuth of the analytical signal, and the unwrap algorithm unwrap{} is used to calculate the phase information φ(t) that changes with time:

[0056] φ(t)=unwrap{arctan{H{E a (t)}}}

[0057] Due to the nonlinear scanning phase noise of the swept light source 1, the phase information φ(t) does not change completely linearly with time, and the main interference signal E m (t) is not a sampling of uniform frequency intervals. The maximum value of φ(t) is found by the maximum function max(), and then the phase information φ(t) is normalized to obtain φ n (t):

[0058] φ n (t) = φ(t) / max(φ(t))

[0059] Use φ n (t) replaces the main interference signal E m (t) time variable t:

[0060]

[0061] The main interference signal E is interpolated using a cubic interpolation function. m (φ n (t)) performs interpolation resampling with uniform frequency intervals:

[0062]

[0063] Thus, the main interference signal E originally sampled at non-uniform frequency intervals is converted to m (t), resampled to a signal with uniform frequency spacing Thereby, the nonlinear scanning phase noise of the swept-frequency light source 1 is compensated.

[0064] Furthermore, the third fiber 1x2 coupler 31 has a 1:1 splitting ratio, ensuring that the two beams entering the auxiliary interferometer module 3 have equal power, thus maximizing the intensity of the output auxiliary interference signal. The second fiber 2x2 coupler 33 also has a 1:1 splitting ratio, ensuring that the optical power entering the two input ports of the second balanced photodetector 34 is equal, effectively eliminating the DC component and noise in the auxiliary interference signal.

[0065] In this embodiment, the input end of the data acquisition module 4 is respectively connected to the trigger end of the swept light source 1, the output end of the first balanced photodetector 24 in the main interferometer module 2 and the output end of the second balanced photodetector 34 in the auxiliary interferometer module 3.

[0066] Furthermore, when the swept frequency light source 1 starts emitting laser light, it also outputs a synchronization trigger signal to the data acquisition module 4. After receiving the synchronization trigger signal, the data acquisition module 4 starts to collect data. The collected data comes from the main interference signal output by the first balanced photodetector 24 and the auxiliary interference signal output by the second balanced photodetector 34.

[0067] The array grating addressing method based on the median filter is as follows:

[0068] For signals resampled to uniform frequency intervals Perform Fourier transform F{} to obtain the spectrum distribution

[0069]

[0070] Use the distance variable l instead of the spectrum distribution The operational relationship between the frequency variable f, distance variable l and frequency variable f in is:

[0071] f=2n·l / c

[0072] Thus, the distributed reflection signal of the array grating is obtained like Figure 2 As shown. Distributed reflection signal Whether in the strong reflection area of the grating or other weak reflection areas in the optical fiber, there is severe high-frequency reflection noise. N ,L} for distributed reflection signal To smooth:

[0073]

[0074] Among them, L FBG is the length of a single fiber Bragg grating. The smoothed distributed reflection signal like Figure 3 As shown. After the median filter MF{y N ,L} Smoothed distributed reflection signal High-frequency reflection noise is eliminated, which is beneficial to the accurate addressing of the grating.

[0075] Furthermore, the median filter MF{y N ,L} is used to convert the array y with N elements into N The value y of the i-th element in N [i] is changed to the median of the values of the L elements on the left and right sides of the i-th element.

[0076] Furthermore, using the median filter MF{y N ,L} distributed reflection signal of array grating The advantage of smoothing is that it can remove high-frequency reflection noise at all positions while preserving the sharp intensity changes at the start and end positions of the grating, thereby achieving more accurate grating positioning.

[0077] Using the minimum algorithm MIN{y N ,L}, for the smoothed distributed reflection signal Perform a minimum search:

[0078]

[0079] Among them, L spacing is the interval between the gratings. L[M] is the coordinate of M minimum points. The actual position of the grating is between the coordinates of two adjacent minimum points, such as Figure 3 As shown in the dots in , accurate grating addressing is achieved.

[0080] Furthermore, the inverse Fourier transform F -1 {}By filtering out the distributed reflection signal between two adjacent minimum positions, the spectrum of a single fiber Bragg grating at that position can be obtained, which is conducive to more accurate distributed sensing.

[0081] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An array grating addressing device based on a median filter, characterized in that: The invention comprises a frequency sweeping light source (1), a first optical fiber 1x2 coupler (11), a main interferometer module (2), an auxiliary interferometer module (3), and a data acquisition module (4), wherein the input end of the first optical fiber 1x2 coupler (11) is connected to the output end of the frequency sweeping light source (1), the second end and the third end of the two output ends of the first optical fiber 1x2 coupler (11) are connected to the main interferometer module (2) and the auxiliary interferometer module (3), respectively, and the first optical fiber 1x2 coupler (11) connects the frequency sweeping light source ( 1) output laser light is divided into two beams, and the two beams are output to the main interferometer module (2) and the auxiliary interferometer module (3) respectively; the main interferometer module (2) is used to measure the distributed reflection signal of the optical fiber to be measured, that is, the array grating; the auxiliary interferometer module (3) is used to measure and compensate for the nonlinear scanning phase noise of the swept-frequency light source (1); the input end of the data acquisition module (4) is respectively connected to the trigger end of the swept-frequency light source (1), the output end of the main interferometer module (2), and the output end of the auxiliary interferometer module (3).

2. The array grating addressing device based on a median filter according to claim 1, characterized in that: The main interferometer module (2) comprises a second optical fiber 1x2 coupler (21), an optical circulator (22), a first optical fiber 2x2 coupler (23), a first balanced photodetector (24) and an array grating (25); the input end of the second optical fiber 1x2 coupler (21) is connected to the second end of the first optical fiber 1x2 coupler (11); the first end of the optical circulator (22) is connected to the second end of the second optical fiber 1x2 coupler (21); the second end of the optical circulator (22) is connected to the array grating (25); the third end of the optical circulator (22) is connected to the first end of the first optical fiber 2x2 coupler (23); the third end of the second optical fiber 1x2 coupler (21) is connected to the second end of the first optical fiber 2x2 coupler (23); and the third end and the fourth end of the first optical fiber 2x2 coupler (23) are respectively connected to the two input ports of the first balanced photodetector (24).

3. The array grating addressing device based on a median filter according to claim 2, characterized in that: The auxiliary interferometer module (3) comprises a third optical fiber 1x2 coupler (31), a time-delay optical fiber (32), a second optical fiber 2x2 coupler (33) and a second balanced photodetector (34); the input end of the third optical fiber 1x2 coupler (31) is connected to the third end of the first optical fiber 1x2 coupler (11); the two ends of the time-delay optical fiber (32) are respectively connected to the third end of the third optical fiber 1x2 coupler (31) and the second end of the second optical fiber 2x2 coupler (33); the second end of the third optical fiber 1x2 coupler (31) is connected to the first end of the second optical fiber 2x2 coupler (33); and the third end and the fourth end of the second optical fiber 2x2 coupler (33) are respectively connected to the two input ports of the second balanced photodetector (34).

4. The median filter-based array grating addressing device according to claim 3, wherein: The splitting ratio between the second end and the third end of the first optical fiber 1x2 coupler (11) is 99:1, the splitting ratio between the second optical fiber 1x2 coupler (21) and the third optical fiber 1x2 coupler (31) is 1:1, and the splitting ratio between the first optical fiber 2x2 coupler (23) and the second optical fiber 2x2 coupler (33) is 1:

1.

5. The array grating addressing device based on a median filter according to claim 1, characterized in that: The laser output by the frequency sweeping light source (1) is continuous light with linearly varying frequency, and the function expression of the light field is: Where t represents the time variable, E(t) represents the output light field that changes with time t, f0 represents the initial frequency, γ represents the frequency scanning rate, exp{} represents the natural exponential function, j represents the imaginary unit, and E0(t) represents the light field amplitude that changes with time t. represents the nonlinear swept phase noise that varies with time t.

6. The array grating addressing device based on a median filter according to claim 1, characterized in that: The function expression of the beat frequency interference signal output by the main interferometer module (2) is: τ i =2n·l i / c Among them, E m (t) represents the functional expression of the beat frequency interference signal output by the main interferometer module (2), τ i represents the optical delay of the reflected light of the i-th grating in the array grating (25), l i represents the spatial position of the i-th grating, R i (t) represents the reflection intensity of the i-th grating that varies with time, and is also the reflection spectrum of the i-th grating. n represents the refractive index of the optical fiber, and c represents the speed of light in vacuum.

7. The array grating addressing device based on a median filter according to claim 1, characterized in that: The function expression of the beat frequency interference signal output by the auxiliary interferometer module (3) is: t a =n·l a / c Among them, E a (t) represents the functional expression of the beat frequency interference signal output by the auxiliary interferometer module (3), τ a represents the optical delay of the delay fiber (32), l a represents the length of the delay optical fiber (32).

8. The array grating addressing device based on a median filter according to claim 1, characterized in that: The wavelength scanning range of the frequency-sweeping light source (1) should cover the spectral range of all gratings in the array grating (25).

9. A method for addressing an array grating based on a median filter, characterized in that: The distributed reflection signal of the array grating obtained by the optical frequency domain reflection system is smoothed by a median filter, and the position coordinates of each fiber Bragg grating are obtained by combining the minimum algorithm.

10. The array grating addressing method based on a median filter according to claim 9, characterized in that: The beat frequency interference signal output by the main interferometer module (2) is subjected to Fourier transform to obtain the distributed reflection signal of the array grating (25), and then the distributed reflection signal is smoothed by using a median filter. After that, the smoothed signal is subjected to a minimum search using a minimum algorithm, and the position of each grating is located between two adjacent minimum positions. By performing an inverse Fourier transform on the distributed reflection signal between two adjacent minimum positions, the spectrum of a single fiber grating at that position can be obtained.

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