阅读说明：本技术 光纤光栅边缘叠加滤波的波长解调方法 (Wavelength demodulation method for fiber grating edge superposition filtering ) 是由 王永皎 黄真 徐一旻 周益平 闻益 于 2020-07-03 设计创作，主要内容包括：本发明公开了一种光纤光栅边缘叠加滤波的波长解调方法,包括以下步骤：S1、宽带光源发出的宽谱光入射到光纤光栅,该光纤光栅为包含多个等间距峰的倾斜光纤光栅,其反射光为多峰梳状光；S2、将经光纤光栅反射的多峰梳状光经过梳状滤波器,每个光纤光栅的反射光谱峰的中心波长位于每个梳状滤波器的透射光谱梳状峰的斜边上,反射光谱和透射光谱的斜边部分重叠,通过该梳状滤波器对多峰梳状光的每个峰进行边缘滤波；S3、将光纤光栅的反射谱函数和经过梳状滤波器边缘滤波的透射谱函数拟合,计算光纤光栅的波长变化量；S4、重复执行步骤S2和S3进行波长的连续解调。本发明实现了高灵敏度边缘滤波及波长解调,增强了系统的信噪比。(The invention discloses a wavelength demodulation method for fiber grating edge superposition filtering, which comprises the following steps: s1, wide spectrum light emitted by the broadband light source is incident to the fiber grating, the fiber grating is an inclined fiber grating comprising a plurality of equally spaced peaks, and the reflected light of the fiber grating is multi-peak comb-shaped light; s2, passing the multi-peak comb light reflected by the fiber bragg grating through a comb filter, wherein the center wavelength of the reflection spectrum peak of each fiber bragg grating is located on the oblique side of the transmission spectrum comb peak of each comb filter, the reflection spectrum and the oblique side of the transmission spectrum are partially overlapped, and edge filtering is carried out on each peak of the multi-peak comb light through the comb filter; s3, fitting the reflection spectrum function of the fiber grating and the transmission spectrum function filtered by the edge of the comb filter, and calculating the wavelength variation of the fiber grating; and S4, repeatedly executing the steps S2 and S3 to continuously demodulate the wavelength. The invention realizes high-sensitivity edge filtering and wavelength demodulation and enhances the signal-to-noise ratio of the system.)

1. A wavelength demodulation method of fiber grating edge superposition filtering is characterized by comprising the following steps:

s1, wide spectrum light emitted by the broadband light source is incident to the fiber grating, the fiber grating is an inclined fiber grating comprising a plurality of equally spaced peaks, and the reflected light of the fiber grating is multi-peak comb-shaped light;

s2, passing the multi-peak comb light reflected by the fiber grating through a comb filter, wherein the transmission spectrum of the comb filter and the adjacent spectrum peaks of the reflection spectrum of the fiber grating have the same wavelength interval, the center wavelength of the reflection spectrum peak of each fiber grating is positioned on the bevel edge of the transmission spectrum comb peak of each comb filter, the reflection spectrum and the bevel edge of the transmission spectrum are partially overlapped, and edge filtering is carried out on each peak of the multi-peak comb light through the comb filter;

s3, fitting the reflection spectrum function of the fiber grating and the transmission spectrum function filtered by the edge of the comb filter, and calculating the wavelength variation of the fiber grating;

and S4, repeatedly executing the steps S2 and S3 to continuously demodulate the wavelength.

2. The method of claim 1, wherein the peak-to-peak separation of the comb filter transmission spectrum and the fiber grating reflection spectrum is equal.

3. The method of claim 1, wherein each comb-peak spectrum in the transmission spectrum of the comb filter is a Gaussian spectrum.

4. The method of claim 1, wherein each reflection peak in the reflection spectrum of the fiber grating is a Gaussian spectrum.

5. The method of claim 1, wherein the intersection point where the peak of the comb filter and the peak edge of the fiber grating coincide is at the midpoint of the hypotenuse of the peak.

6. The method for wavelength demodulation of fiber grating edge-add filtering according to any one of claims 1-5, further comprising step S5: the optical power of the optical signal after edge filtering is corrected by eliminating the change of the optical power of the broadband light source, and the wavelength variation of the fiber bragg grating is recalculated.

7. The method for wavelength demodulation of fiber grating edge superposition filtering according to claim 6, wherein the step S5 specifically comprises the steps of:

dividing the multimodal comb-shaped light reflected by the fiber bragg grating into two paths, wherein one path is probe light, and the other path is reference light;

the detection light passes through a comb filter, the transmission light of the detection light is subjected to photoelectric conversion to generate a first electric signal, the first electric signal is subjected to analog-to-digital conversion to obtain the optical power of the detection light, and the change rate of the optical power of the detection light is calculated;

generating a second electric signal after the reference light is subjected to photoelectric conversion, performing analog-to-digital conversion on the second electric signal to obtain the optical power of the reference light, and calculating the change rate of the optical power of the reference light;

subtracting the change rate of the optical power of the reference light from the change rate of the optical power of the detection light to obtain a corrected optical power value of the detection light;

and after the transmission spectrum function is fitted, the wavelength variation of the fiber tilt grating is calculated by combining the corrected optical power value of the detection light.

Technical Field

The invention belongs to the technical field of optical fiber sensing, and particularly relates to a wavelength demodulation method based on high-sensitivity edge filtering.

Background

The fiber grating is an important device for fiber sensing due to the advantages of specific fiber internal sensitivity, wavelength coding, easiness in multiplexing, networking and the like. Wavelength demodulation of the grating is one of the key technologies for grating sensing. The existing grating wavelength demodulation technology includes a spectrum method, a wavelength scanning method and a traditional edge filtering method.

The wavelength scanning method is classified into a broad spectrum light pass tunable filter scanning method and a scanning laser method. Tunable filter demodulation is severely limited by the response speed of the mechanical tuning mechanism in the filter, which is slow and expensive.

In the conventional scanning wavelength demodulation method, if a single sensor is used, only one path of wide-spectrum light emitted by a scanning laser reaches the sensing grating, the reflected light of the wide-spectrum light reaches a narrow-band light centered on the central wavelength of the sensing grating, and the other path of wide-spectrum light passes through an etalon and is received by a photoelectric detector. Only when the center wavelength of the reflected light coincides with the center wavelength of the FFP will the photodetector detect a pulse signal, and the same rational etalon detect a train of pulses that represent the peaks of the etalon transmission peaks. The time of the maximum light intensity of the sensing grating detected by the photoelectric detector is recorded, the time is compared with each peak time of a series of pulses of the etalon (the etalon mainly has the function of correcting the wavelength value), the central wavelength value of the sensing grating can be calculated through a peak demodulation algorithm, and wavelength demodulation is realized. In the case of multiple sensors, the light reflected from the sensors is a comb-like pulse spectrum having multiple peaks, and multiple center wavelength values of the multiple sensors can be calculated at a time by demodulating the peak wavelengths with the respective peak wavelengths of the etalon. However, the sensors are independent and incoherent, and the sensors can be used to measure different quantities, such as temperature sensors, pressure sensors, etc. However, in either a single sensor or a plurality of sensors, the wavelength demodulated by the scanning wavelength demodulation method is not accurate, and the mode hopping of the laser causes a discontinuity in wavelength scanning, so that the output laser is wavelength-hopped, which complicates laser control, signal processing, and speed. The spectrum method generally adopts a CCD detection module, and because the inside adopts a diffraction grating and the back end of the diffraction grating receives signals by a linear array CCD, the spectrum method is not only expensive, but also precise in structure and difficult to adapt to vibration and high-temperature occasions.

The edge filtering demodulation technology is simple in structure, high in reliability and high in speed, the traditional edge filtering is formed by a filter with a single-peak spectrum and a traditional single-peak Bragg grating, the traditional edge filtering is limited by the side band gradient of the grating and the gradient of the edge of the transmission spectrum of the filter, the single-peak edge is steep, the width is narrow, the strength is low, the sensitivity is limited, high-sensitivity occasions such as vibration and sound waves are difficult to meet, and the practicability is not enough.

Disclosure of Invention

The invention aims to overcome the defects of the conventional grating wavelength demodulation technology and provides a wavelength demodulation method for realizing high sensitivity of the inclined grating wavelength by using a comb filter.

The technical scheme adopted by the invention for achieving the purpose of the invention is as follows:

the wavelength demodulation method for the fiber grating edge superposition filtering is characterized by comprising the following steps of:

s1, wide spectrum light emitted by the broadband light source is incident to the fiber grating, the fiber grating is an inclined fiber grating comprising a plurality of equally spaced peaks, and the reflected light of the fiber grating is multi-peak comb-shaped light;

s2, passing the multi-peak comb light reflected by the fiber bragg grating through a comb filter, wherein the center wavelength of the reflection spectrum peak of each fiber bragg grating is located on the oblique side of the transmission spectrum comb peak of each comb filter, the reflection spectrum and the oblique side of the transmission spectrum are partially overlapped, and edge filtering is carried out on each peak of the multi-peak comb light through the comb filter;

s3, fitting the reflection spectrum function of the fiber grating and the transmission spectrum function filtered by the edge of the comb filter, and calculating the wavelength variation of the fiber grating;

and S4, repeatedly executing the steps S2 and S3 to continuously demodulate the wavelength.

According to the technical scheme, the peak distance between the transmission spectrum of the comb filter and the reflection spectrum of the fiber grating is equal.

According to the technical scheme, in the transmission spectrum of the comb filter, the spectrum of each comb peak is a Gaussian spectrum.

According to the technical scheme, in the reflection spectrum of the fiber grating, each reflection peak is a Gaussian spectrum.

According to the technical scheme, the intersection point of the peak of the comb filter and the coincidence of the peak edges of the fiber bragg gratings is located at the middle point of the oblique side of the peak.

In connection with the above technical solution, the method further includes step S5: the optical power of the edge-filtered optical signal is corrected by eliminating variations in the optical power of the broadband light source itself.

In connection with the above technical solution, step S5 specifically includes the steps of:

dividing the multimodal comb-shaped light reflected by the fiber bragg grating into two paths, wherein one path is probe light, and the other path is reference light;

the detection light passes through a comb filter, the transmission light of the detection light is subjected to photoelectric conversion to generate a first electric signal, the first electric signal is subjected to analog-to-digital conversion to obtain the optical power of the detection light, and the change rate of the optical power of the detection light is calculated;

generating a second electric signal after the reference light is subjected to photoelectric conversion, performing analog-to-digital conversion on the second electric signal to obtain the optical power of the reference light, and calculating the change rate of the optical power of the reference light;

subtracting the change rate of the optical power of the reference light from the change rate of the optical power of the detection light to obtain a corrected optical power value of the detection light;

in step S3, after the transmission spectrum function is fitted, the wavelength variation of the fiber bragg grating is calculated by combining the corrected optical power value of the probe light.

The invention has the following beneficial effects: the invention adopts the comb filter to carry out edge demodulation on the inclined grating, compared with the traditional edge demodulation method, the invention has the advantages that a plurality of peaks of the comb filter and a plurality of peaks matched with the inclined grating form a plurality of edge filters, the plurality of peaks are adopted to carry out edge filtering at the same time, the reflection area is increased when one peak is added, the light intensity is increased, the response of the system is improved under the condition that the dynamic range is unchanged, and the demodulation sensitivity is increased. The invention has higher sensitivity and signal-to-noise ratio for detecting high-frequency weak signals, such as sound waves, weak vibration signals and the like.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a flowchart of a wavelength demodulation method of fiber grating edge-add filtering according to a first embodiment of the present invention;

FIG. 2 is a flowchart of a wavelength demodulation method of fiber grating edge-add filtering according to a second embodiment of the present invention;

FIG. 3 is a first schematic structural diagram of a wavelength demodulation system for fiber grating edge add-on filtering according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a transmission spectrum of the comb filter and a reflected light spectrum of the measured tilted grating in the detection light path according to the embodiment of the present invention;

fig. 5 is a schematic structural diagram of a wavelength demodulation system for fiber grating edge add-on filtering according to an embodiment of the present invention.

In the figure: 1-a broadband light source, 2 a-an optical circulator, 201 a-an optical circulator first port, 202 a-an optical circulator second port, 203 a-an optical circulator third port, 2 b-a first optical circulator, 201 b-a first optical circulator first port, 202 b-a first optical circulator second port, 203 b-a first optical circulator third port, 3 a-an optical fiber tilt grating, 3 b-a first optical fiber tilt grating, 4-an optical fiber coupler, 401-an optical fiber coupler first port, 402-an optical fiber coupler second port, 403-an optical fiber coupler third port, 5-a comb filter, 6-a first optical detector, 7-a second optical detector, 8-a signal processor, 801-a signal processor first port, 802-a second port of the signal processor, 803-a third port of the signal processor, 9-an upper computer, 10-a second optical circulator, 1001-a first port of the second optical circulator, 1002-a second port of the second optical circulator, 1003-a third port of the second optical circulator and 11-a second fiber tilt grating.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in fig. 1, the wavelength demodulation method of fiber grating edge add-on filtering according to embodiment 1 of the present invention includes the following steps:

s1, wide spectrum light emitted by the broadband light source is incident to the fiber grating, the fiber grating is an inclined fiber grating comprising a plurality of equally spaced peaks, and the reflected light of the fiber grating is multi-peak comb-shaped light;

s2, passing the multi-peak comb light reflected by the fiber bragg grating through a comb filter, wherein the center wavelength of the reflection spectrum peak of each fiber bragg grating is positioned on the oblique side of the transmission spectrum comb peak of each comb filter, an overlapping part is formed, and the comb filter is used for carrying out edge filtering on each peak of the multi-peak comb light;

s3, fitting the reflection spectrum function of the fiber grating and the transmission spectrum function filtered by the edge of the comb filter, and calculating the wavelength variation of the fiber grating;

s4, determining whether to perform continuous demodulation of the wavelength, if yes, repeating steps S2 and S3 to perform continuous demodulation of the wavelength.

In a preferred embodiment of the present invention, the peak pitches of the transmission spectrum of the comb filter and the reflection spectrum of the fiber grating are set to be equal (theoretically unequal, the most essential requirement is that the peaks of the tilted grating and the comb filter can be matched, if the pitches are unequal, only the two peaks are arranged at the same pitch, that is, if the pitches of the gratings are unequal, the pitches of the comb filter are also arranged at the same unequal pitches, which can also be realized). The present invention preferably performs multiple reflection peak simultaneous edge filtering on the reflected light of the tilted grating by using a comb filter having a comb peak interval that is the same as the tilted grating peak interval.

Further, in the transmission spectrum of the comb filter, each comb peak spectrum is a gaussian spectrum.

Further, in the reflection spectrum of the fiber grating, each reflection peak is a gaussian spectrum.

Further, the center wavelength of the reflection spectrum peak of the fiber-tilted grating is located on the hypotenuse of the comb peak of the transmission spectrum of the comb filter, and the two peaks have an overlapping portion. The intersection point of the bevel edges of the two peaks is close to the middle point of the bevel edge as much as possible, so that the demodulation dynamic range is large and the linearity is good.

As shown in fig. 2, a wavelength demodulation method of fiber grating edge overlap filtering according to another embodiment of the present invention mainly includes the following steps:

s101, wide-spectrum light emitted by a broadband light source enters a fiber grating;

s102, dividing the multi-peak comb light reflected by the fiber bragg grating into two paths, wherein one path is probe light, and the other path is reference light;

s103, the detection light passes through a comb filter, and the transmission light of the detection light is subjected to photoelectric conversion to generate a first electric signal;

s104, generating a second electric signal after the reference light is subjected to photoelectric conversion;

s105, performing analog-to-digital conversion on the first electric signal to obtain the optical power of the detection light, and calculating the change rate of the optical power of the detection light; the change rate is the ratio of the current sampling value to the initial sampling value of the detection light path;

s106, performing analog-to-digital conversion on the second electric signal to obtain the optical power of the reference light, and calculating the change rate of the optical power of the reference light, wherein the change rate is the ratio of the current sampling value to the initial sampling value of the reference light path;

s107, subtracting the change rate of the optical power of the reference light from the change rate of the optical power of the detection light to obtain a corrected optical power value of the detection light;

s108, fitting the reflection spectrum function of the fiber grating and the transmission spectrum function of the comb filter, and calculating the wavelength variation of the fiber grating by combining the corrected optical power value of the detection light;

s109, repeating the steps S105-S108 to continuously demodulate the wavelength.

In step S108, each peak function of the tilted grating and the comb filter is a gaussian function, and a plurality of peaks are the superposition of the gaussian functions and are directly fitted by the gaussian functions. The correction optical power is obtained by subtracting the change rate of the optical power of the second photodetector from the change rate of the optical power of the first photodetector, and since the change rate of the optical power of the second photodetector is the change of the light source itself and the optical power of the first photodetector is the sum of the change of the light source power added to the change of the sensor itself, the correction optical power may be obtained by directly subtracting the change rates thereof.

The multi-peak comb light is subjected to edge filtering by overlapping a plurality of peaks of the comb filter with edge parts of a plurality of peaks of the fiber grating; the comb filter can perform simultaneous edge filtering on a plurality of reflection peaks of the reflected light of the fiber bragg grating, so that the sensitivity of the system is improved on the premise of not improving the complexity and the cost of the system, and the signal-to-noise ratio of the system is enhanced.

Fig. 3 is a schematic structural diagram of a wavelength demodulation system based on high-sensitivity edge filtering according to an embodiment of the present invention, which can implement the wavelength demodulation method based on high-sensitivity edge filtering according to the embodiment. The edge filtering wavelength demodulation system comprises a broadband light source 1, an optical circulator 2a, an optical fiber grating 3a, an optical fiber coupler 4, a comb filter 5, a first photoelectric detector 6, a second photoelectric detector 7, a signal processor 8 and an upper computer 9.

The output of the broadband light source 1 is connected to the first port 201a of the optical circulator, and provides a wide spectrum light source for the demodulation device, and the effective wavelength range of the wide spectrum light source is larger than the measurement range of the device. The optical circulator second port 202a is connected with the fiber grating 3 a. The optical circulator third port 203a is connected to the fiber coupler first port 401.

The second port 402 of the optical fiber coupler is connected to the input port of the comb filter 5, the comb filter 5 is an optical waveguide comb filter, the adjacent spectral peaks of the transmission spectrum of the comb filter 5 and the reflection spectrum of the fiber grating 3a have the same wavelength interval, and the shape of each spectral peak satisfies the gaussian spectrum type.

An output port of the comb filter 5 is connected to an optical input port of the first photodetector 6, an electrical output port of the first photodetector 6 is connected to a first port 801 of the signal processor, and the first port 801 of the signal processor is connected to the upper computer 9.

The third port 403 of the optical fiber coupler is connected to the optical input port of the second photodetector 7, and the electrical output port of the second photodetector 7 is connected to the second port 802 of the signal processor; the third port 803 of the signal processor is connected to the upper computer 9. The host computer can be a terminal of the system, a personal PC and the like, and mainly receives data of the sensor and then performs various applications, such as storage, display and the like.

The method for realizing wavelength demodulation by using the high-sensitivity edge filtering-based wavelength demodulation system comprises the following steps:

s201: the broad spectrum light emitted from the broadband light source 1 is first coupled to the first port 201a of the optical circulator and then is incident into the fiber grating 3a through the second port 202a of the optical circulator. The multi-peak comb light with a specific wavelength reflected by the fiber grating 3a further returns to the second port 202a of the optical circulator, and then enters the first port 401 of the fiber coupler through the third port 203a of the optical circulator, and is then divided into two paths of light, namely, probe light and reference light.

S202: the detection light is input into the fiber-optic comb filter 5 through the second port 402 of the fiber-optic coupler, the reflection spectrum of the part of the fiber grating 3a branched out by the fiber-optic coupler 4 is, as shown in fig. 4, filtered by the fiber-optic comb filter 5, the transmission light thereof is coupled into the first photodetector 6, as shown by the shaded portion in fig. 4, and the electrical signal converted by the photodetector is connected to the first port 801 of the signal processor. The respective spectrums of the comb filter and the inclined grating are provided with a plurality of peaks, so that edge filtering is better realized, the inclined edges of two peaks with similar wavelengths need to meet a certain condition, the peaks of the comb filter and one peak of the inclined grating are close to each other in wavelength and partially overlapped, and the intersection point of the overlapped edges is close to the middle point of the inclined edge as much as possible, so that better linearity and dynamic range are realized.

The fiber grating 3a reflects part of the light split out through the third port 403 of the fiber coupler as reference light, and after the reference light is coupled to the second photodetector 7 through the third port 403 of the fiber coupler, an electrical signal converted by the photodetector is connected to the second port 802 of the signal processor.

S203: the signal processor 8 performs analog-to-digital conversion on the electrical signal output by the second photodetector 7, and calculates and obtains a change rate of optical power of output optical power (i.e., a reference optical path) of the broadband light source 1, which is a ratio of a current sampling value to an initial sampling value of the reference optical path.

S204: the signal processor 8 performs analog-to-digital conversion on the electrical signal output by the first photodetector 6, and calculates and obtains the optical power of the detection light obtained by filtering part of the reflected light of the fiber grating 3a output by the second port 402 of the fiber coupler by the comb filter 5.

S205: the change rate of the optical power of the reference optical path acquired in step S203 is calculated by subtracting the change rate of the probe optical power acquired in step S204, and the optical power value of the corrected probe light is obtained.

S6: the wavelength variation of the fiber grating 3a is calculated by fitting the reflection spectrum function of the fiber grating 3a and the transmission spectrum function of the comb filter 5 in combination with the optical power value of the corrected probe light obtained in step S5.

S207: the signal processor 8 transmits the wavelength variation acquired in step S206 to the upper computer 9.

S208: repeating steps S203, S204, S205, S206 and S207 realizes continuous demodulation of the wavelength of the fiber grating 3 a.

Fig. 5 is a schematic structural diagram of a wavelength demodulation system based on high-sensitivity edge filtering according to a second embodiment of the present invention, which includes a broadband light source 1, a first optical circulator 2b, a first fiber grating 3b, an optical fiber coupler 4, a comb filter 5, a first photodetector 6, a second photodetector 7, a signal processor 8, an upper computer 9, a second optical circulator 10, and a second fiber grating 11.

The output of the broadband light source 1 is connected to the first port 201b of the first optical circulator, and provides a wide spectrum light source for the demodulation device, and the effective wavelength range of the wide spectrum light source is larger than the measurement range of the device. The second port 202b of the first optical circulator is connected with the first fiber grating 3 b; the first optical circulator third port 203b is connected to the fiber coupler first port 401 and the fiber coupler second port 402 is connected to the input port of the comb filter 5.

The comb filter 5 comprises a second optical circulator 10 and a second fiber grating 11, the second optical circulator 10 comprises a first port 1001 of the second optical circulator, a second port 1002 of the second optical circulator and a third port 1003 of the second optical circulator, the first port 1001 of the second optical circulator is an input port of the comb filter device 5, the second port 1002 of the second optical circulator is connected with the second fiber grating 11, and the third port 1003 of the second optical circulator is an output port of the comb filter 5. In the embodiment, the comb filter device 5 is realized by the fiber grating, so that the cost is reduced.

In addition, in order to realize higher-quality edge filtering, the peak pitches of two multi-peak devices can be set to be equal, and the devices with the same peak pitch are easy to manufacture when the inclined grating is manufactured in batches, so that the manufacture is more convenient.

The output port of the comb filter 5 is connected to the optical input port of the first photodetector 6, and adjacent peaks of the transmission spectrum of the comb filter 5 and the reflection spectrum of the first fiber grating 3b have the same wavelength interval. The shape of each peak of the transmission spectrum of the comb filter 5 and the reflection spectrum of the first fiber grating 3b satisfies the gaussian spectrum type. The electrical output port of the first photodetector 6 is connected to the signal processor first port 801. The third port 403 of the optical fiber coupler is connected to the optical input port of the second photodetector 7, and the electrical output port of the second photodetector 7 is connected to the second port 802 of the signal processor; the third port 803 of the signal processor is connected to the upper computer 9.

The method for realizing wavelength demodulation by using the demodulation system based on the high-sensitivity edge filtering of the embodiment comprises the following steps:

s301, coupling wide-spectrum light emitted by a broadband light source 1 to a first port 201b of a first optical circulator, and then entering a first fiber grating 3b through a second port 202b of the first optical circulator; the multi-peak comb light with a specific wavelength reflected by the first fiber grating 3b further returns to the second port 202b of the first optical circulator, and then enters the first port 401 of the fiber coupler through the third port 203b of the first optical circulator, and is then split into two paths of light, which are probe light and reference light, respectively.

S302, the detection light is input into the fiber comb filter 5 through the second port 402 of the fiber coupler, the reflection spectrum of the first fiber grating 3b branched by the fiber coupler 4, as shown in fig. 4, is filtered by the fiber comb filter 5, and then the transmission light is coupled to the first photodetector 6, as shown by the shaded portion in fig. 4, and the electrical signal converted by the photodetector is connected to the first port 801 of the signal processor.

The first fiber grating 3b reflects part of the light split out through the third port 403 of the fiber coupler as reference light, and after the reference light is coupled to the second photodetector 7 through the third port 403 of the fiber coupler, an electrical signal converted by the photodetector is connected to the second port 802 of the signal processor.

S303, the signal processor 8 performs analog-to-digital conversion on the electrical signal output by the second photodetector 7, and calculates and obtains a fluctuation coefficient k of the output power of the broadband light source 1 (i.e. a change rate of the optical power of the reference optical path), where the size of k is a ratio of the current sampling value to the initial sampling value of the reference optical path.

S304, the signal processor 8 performs analog-to-digital conversion on the electrical signal output by the first photodetector 6, calculates and obtains the optical power of the detection light, which is obtained by filtering part of the reflected light of the first fiber grating 3b output by the second port 402 of the fiber coupler by the comb filter 5, and calculates the change rate of the optical power of the detection light, specifically, the ratio of the current sampling value to the initial sampling value of the detection light path.

S305, the fluctuation coefficient k of the broadband light source 1 calculated in step S303 is subtracted from the change rate of the optical power of the probe light acquired in step S304, and the optical power value of the probe light is corrected.

S306, the wavelength variation of the first fiber grating 3b is calculated by fitting the reflection spectrum function of the first fiber grating 3b and the transmission spectrum function of the comb filter 5 in combination with the corrected detection light power obtained in the step S305.

And S307, the signal processor 8 sends the wavelength variation acquired in the step S306 to the upper computer 9.

S308, repeating steps S303, S304, S305, S306 and S307 realizes continuous demodulation of the wavelength of the first fiber grating 3 b.

In summary, the invention utilizes the comb filter to demodulate the wavelength of the fiber grating to realize the wavelength demodulation based on the high-sensitivity edge filtering, and the comb filter with the comb peak interval matched with the peak value of the inclined grating is adopted to simultaneously perform the edge filtering on a plurality of reflection peaks on the reflected light of the inclined grating, thereby realizing the edge filtering demodulation of the wavelength change of the inclined grating. Because the comb filter is adopted to match a plurality of reflection peaks of the inclined grating for filtering simultaneously, the sensitivity of the system is improved on the premise of not improving the complexity and the cost of the system, the signal-to-noise ratio of the system is enhanced, and the comb filter is beneficial to the application in the high-sensitivity detection fields of sound waves, vibration and the like.

It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.