CN100419480C - Distributed tapered fiber grating sensor and its bandwidth demodulation device and detection method - Google Patents

Abstract

A distributed tapered fiber grating sensor and its bandwidth demodulation device and detection method relate to the field of fiber Bragg grating sensing technology and spectrum analysis technology, and it solves the existing problem of power measurement based on the reflected light of a tapered fiber grating. Obtain the sensed stress/strain information, so that the tapered grating can no longer be used to realize the distributed sensing method, and add sensor devices and multiple sets of separate demodulation to distinguish the influence of temperature and stress changes on the fiber grating The instrument thus leads to the problem of complex structure of the sensing instrument. The distributed tapered fiber grating sensor is composed of multiple fiber segments (1) with the same diameter, and each fiber segment (1) contains a tapered Bragg grating (2) with a length of L; it provides a The reflection light bandwidth demodulation device of the tapered grating of the linear array can realize the measurement of the reflection spectrum bandwidth of the tapered fiber grating and the calculation and recording of the bandwidth change, and then realize the simultaneous measurement of temperature and stress.

Description

Distributed tapered fiber grating sensor and its bandwidth demodulation device and detection method

technical field

The invention relates to the fields of optical fiber Bragg grating sensing technology and spectrum analysis technology.

Background technique

As a wavelength modulation sensor, Fiber Bragg Grating (FBG) has many outstanding advantages such as light weight, corrosion resistance, anti-electromagnetic interference, high sensitivity, and compact structure. has a wide range of applications. At the same time, due to the wavelength modulation characteristics of fiber gratings, fiber gratings can be used for distributed measurement of physical quantities, and are not affected by factors such as coupling loss and light source output power fluctuations on the accuracy and stability of the measurement system. However, there is a huge problem in the practical engineering application of FBG sensors, that is, the change of temperature and stress can cause the drift of its central reflection wavelength, but it is difficult for us to distinguish their respective ones only by measuring the FBG reflection wavelength. This is the temperature-stress cross-sensitivity problem of fiber gratings. This problem has always been one of the hot spots in the field of fiber grating sensing. Aiming at this problem, a lot of researches have been done at home and abroad, and many solutions have been proposed. However, most of these solutions use multiple fiber gratings or multiple light sources, and some even require multiple sets of separate demodulation instruments, resulting in the increase of the overall cost of the sensing system and the complexity of the implementation, which is not conducive to the development of fiber grating sensing technology. Promotion in practical engineering. In recent years, there have been reports on the use of tapered fiber gratings to achieve temperature-insensitive stress/strain measurement methods. These methods have solved the "cross-sensitivity problem" with a simple structure and low cost, but these methods are Based on the power measurement of the reflected light of the tapered fiber grating, and then through the change of the power to obtain the sensed stress/strain information, they deviate from the most significant characteristics of the fiber grating as a wavelength modulation sensor, so that the tapered grating cannot It is then used to implement a distributed sensing method. At the same time, factors such as the fluctuation of the output power of the light source and the coupling loss in the optical system will affect the accuracy and stability of the sensing system. To overcome these effects will inevitably lead to an increase in the overall cost of the system.

Contents of the invention

In order to solve the existing stress/strain information based on the power measurement of the reflected light of the tapered fiber grating, the tapered grating can no longer be used to realize the distributed sensing method, and to distinguish between temperature and stress The influence of the change of the fiber grating on the influence of the sensor device and multiple sets of separate demodulation instruments will lead to the problem of complex structure of the sensor instrument. The invention provides a distributed tapered fiber grating sensor and its reflected light bandwidth demodulation device ,Detection method.

The distributed tapered fiber grating sensor of the present invention is composed of multiple fiber segments with the same diameter. Each fiber segment contains a tapered Bragg grating with a length L. The tapered Bragg grating contained in each fiber segment is tapered by linear erosion along the fiber axis, and the cross-sectional area of the tapered Bragg grating along the grating direction changes linearly.

The reflected light bandwidth demodulation device of the above-mentioned distributed tapered fiber grating sensor is composed of collimating optics, plane diffraction grating, converging optics, linear array CCD, CCD control and reading circuit, A/D conversion circuit and central processing unit Composition, the reflected light of the tapered grating output by the distributed tapered fiber grating sensor is incident on the light input end of the collimating optics. Above, the beams of different wavelengths will be scattered along different angles after being split by the plane diffraction grating. The beams of different wavelengths scattered at different angles will be converged by the converging optics and then irradiated to the photosensitive side of the line array CCD. The photosensitive side of the line array CCD will obtain One or several sections of illumination area formed by beams of different wavelengths; CCD control and reading circuit is connected with linear array CCD for the control of linear array CCD and reading of analog electrical signals output by each pixel, CCD control and reading circuit The output end of the A/D conversion circuit is connected to the input end of the A/D conversion circuit, and the output end of the A/D conversion circuit is connected to the CCD signal input end of the central processing unit.

Using the above-mentioned distributed tapered fiber grating sensor and based on the detection method of the stress/temperature change of the above-mentioned reflected light bandwidth demodulation device, it is carried out in the following steps:

Step 1. Calibrate the reflected light bandwidth demodulation device of the above-mentioned distributed tapered fiber grating sensor: ① Determine the respective stress sensitivity K _ε and temperature by applying rated stress and temperature to each tapered grating sensor Sensitivity K _T ; ②Apply the rated stress variation to the distributed tapered fiber grating sensor along the axial direction, and then use the reflected light bandwidth demodulation device to obtain one or several sections of illumination areas formed by beams of different wavelengths on the linear array CCD Width, and then establish the relationship between the stress induced by the distributed tapered fiber grating sensor and the width of the illumination area corresponding to different wavelengths on the linear array CCD;

Step 2. Embed the above-mentioned distributed tapered fiber grating sensor inside the object to be monitored or adhere to the surface of the component to be measured. A tapered Bragg grating is located at a measurement point that needs to be monitored. The distributed tapered fiber grating sensor The central wavelengths of the plurality of tapered Bragg gratings are different from each other, and the distance between the central reflection wavelengths of adjacent tapered Bragg gratings must ensure that the reflected light of adjacent tapered Bragg gratings does not interfere with each other;

Step 3: Make the reflected light of the tapered grating output by the distributed tapered fiber Bragg grating sensor incident into the reflected light bandwidth demodulation device of the above-mentioned distributed tapered fiber Bragg grating sensor through the collimation optics, from the distributed tapered fiber Bragg grating sensor The obtained reflected light beam is a light pulse with a certain bandwidth and different central wavelengths containing the temperature and stress change information of each measurement point. Or several sections of illumination area, use CCD control and reading circuit, A/D conversion circuit to collect the image information of linear array CCD, use the central processor to analyze and calculate the reflection spectrum information of distributed tapered fiber grating sensor and the upper section of linear array CCD Or the width of several segments of the illuminated area;

Step 4. According to the width of one or several sections of the illumination area on the linear array CCD obtained by the analysis and calculation of the central processing unit in step 3, the stress induced by the distributed tapered fiber grating sensor obtained in step 1 corresponds to the different wavelengths on the linear array CCD. The change relationship of the width of the illuminated area, determine the stress value ε corresponding to each measurement point at this time;

Step 5. Determine the drift of the Bragg grating center reflection wavelength at each point according to the reflection spectrum information obtained through the analysis and calculation of the central processing unit in step 3;

Step 6. For each measurement point, use the stress sensitivity K _ε and temperature sensitivity K _T obtained in step 1, the drift of the Bragg grating center reflection wavelength obtained in step 5, and the stress value ε of the measurement point obtained in step 4, press The following formula can obtain the amount of change in temperature, thereby distinguishing temperature from stress:

$\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}$

In the above formula, Δλ _B is the drift of the Bragg grating center reflection wavelength obtained in step 5; K _ε is the stress sensitivity coefficient of the conical grating obtained in step 1; ε is the stress value measured in step 4; K _T is the step - the obtained temperature sensitivity coefficient of the tapered grating; ΔT is the temperature variation.

Working principle: The present invention is proposed on the basis of the feasibility of measuring the spectral width (hereinafter referred to as "bandwidth") of the reflected light of the tapered grating to obtain the measured stress/strain information.

It is known that the Bragg (Bragg) reflection wavelength λ _B (z) along the axis of the reflective fiber grating is

λ _B (z)=2n _eff (z)Λ(z) (1)

In the formula, both the grating period Λ and the effective refractive index n _eff are functions of the axial stress value ε of the grating:

Λ(ε)＝ _Λ0 (1+ε) (2)

n _eff (ε)＝n _eff0 +κ ^ε ε (3)

In the formula, κ ^ε represents the factor of the influence of strain on the refractive index, and Λ ₀ and n _eff0 are the grating period and effective refractive index when ε=0, respectively. The stress value ε at point z on the grating axis can be expressed as

ε(z)=F/EA(z)(4)

In the formula, F is the tension applied to both ends of the grating, E is the Young's modulus of the fiber, and A(z) is the cross-sectional area of the grating at point z.

According to equations (2) and (3), the Bragg wavelength of the grating axial point z in the strained state is

λ _B ＝2n _eff (ε _z )Λ(ε _z )≈2n _eff0 Λ ₀ +2(n _eff0 Λ ₀ +k ^ε Λ ₀ )ε _z (5)

It can be seen that the bandwidth of the grating is

Δλ=λ _B (L)-λ _B (0)+Δλ(δn)(6)

In the formula, λ _B (0), λ _B (L) are the Bragg reflection wavelengths at the first and last ends of the grating, respectively, and Δλ(δn) is the grating bandwidth caused by the change of the refractive index of the grating. After the grating is fabricated, δn(z) will not change, and the resulting bandwidth Δλ(δn) will not change either.

When the Bragg grating is etched linearly along the axial direction, the cross-sectional area along the direction of the grating changes linearly, assuming that one end is A(0) and the other end is A(L), and A(L)<A(0 ). From formulas (4), (5), and (6), it can be deduced that when the tension at both ends of the grating is F, the bandwidth of the grating is

$\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="eff"\; filenames="C20061001052700131.png"\; state="\{\{state\}\}">eff</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}^{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\frac{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&delta;n</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (7) that after being linearly etched, the bandwidth of the grating changes linearly with the stress, as shown in Figures 3 and 4. For a strong grating, when the grating is corroded and subjected to tension, the bandwidth of the grating is widened, but the reflection power of each point on the grating remains unchanged, so the total reflection power P within the bandwidth of the grating increases linearly, then the total reflection power within the bandwidth of the grating P also varies linearly with stress, which can be expressed as

P＝kF+B (8)

In the formula, k and B are constants of proportionality.

When the temperature changes, the change of the Bragg wavelength at each point on the grating is

Δλ _B ＝(ξ _s +α _s )ΔT (9)

Among them, ξ _s and α _s are the thermo-optic coefficient (-7×10 ^-6 K ^-1 ) and thermal expansion coefficient of the fiber material, respectively. From formula (9), it can be known that the change of temperature will not affect the change of grating reflection bandwidth or power, as shown in Figures 5 and 6

Based on the above theoretical basis, the present invention uses the bandwidth of the reflected light of the tapered grating to determine the stress variation, thereby distinguishing the temperature from the stress variation, solving the problem of cross sensitivity, and realizing the simultaneous measurement of temperature and stress; and This measurement method also retains the most remarkable characteristics of the fiber grating as a wavelength modulation sensor, and can realize a distributed sensing method. Since the bandwidth of the grating varies linearly with the stress, the width of one or several illumination areas formed by the beams of different wavelengths obtained on the linear CCD also varies linearly with the stress; then, ① determine the illumination area by pre-calibration The linear relationship between the width and the applied stress, and then the stress value can be obtained by referring to the calibration result during actual measurement; ② By using a specific data processing method for the above-mentioned one or several sections of the illumination area, the reflected light of the tapered fiber grating can be obtained The drift of the central wavelength of different beams contained in , the joint influence caused by the stress and temperature change at a specific position can be known, and then the stress value obtained in ① is removed from this common influence, and the temperature change can be obtained .

Effect of the invention: the present invention provides a reflection light bandwidth demodulation device using a tapered grating of a plane diffraction grating-CCD linear array, which can realize the measurement of the reflection spectrum bandwidth of a tapered fiber grating and the calculation and recording of the bandwidth change , and then on the basis of using different functional software modules, the following purposes can be achieved: temperature-insensitive stress/strain measurement, simultaneous measurement of temperature and stress, distributed measurement of stress/strain, distributed simultaneous measurement of temperature and stress, etc. . Based on the demodulation device of the present invention, the sensing of the stress of the tapered grating no longer depends on the measurement of the reflected light power of the tapered grating, and the wavelength modulation characteristics of the fiber grating sensor are restored, so that the tapered fiber grating can be used for distributed sensing , at the same time, this sensing method is no longer affected by light source fluctuations, coupling loss, etc., and has a simple and easy-to-implement demodulation method, which has a good application prospect. The demodulation device proposed by the present invention has simple structure, clear functions of each part, and is easy to realize; and it can be further developed into a general-purpose instrument with a smaller volume, whose input end is directly connected with an optical fiber, and whose output end can be directly connected with a computer for further data processing. processing (or directly use DSP chips to solve the problem of signal processing without the computer), and then output the temperature or stress/strain value to be measured.

Description of drawings

Fig. 1 is a schematic structural diagram of a distributed tapered fiber grating sensor of the present invention. Fig. 2 is a structural schematic diagram of the reflected light bandwidth demodulation device of the distributed tapered fiber grating sensor of the present invention. Figure 3 is a schematic diagram of the reflection spectrum change of the tapered grating under stress, the abscissa represents the central wavelength λ (nm) of the light reflected by the tapered grating, and the ordinate represents the pulse amplitude R (dB) of the light reflected by the tapered grating. Figure 4 is a schematic diagram of the relationship between the bandwidth of the reflection spectrum of the tapered grating and the stress change. The abscissa indicates the central wavelength (nm) of the reflected light of the tapered grating, and the vertical axis indicates the bandwidth change (nm) of the reflected light of the tapered grating. -◆- indicates Stress points. Fig. 5 is a schematic diagram of the reflection spectrum change of the tapered grating when the temperature changes, the abscissa represents the central wavelength λ (nm) of the light reflected by the tapered grating, and the ordinate represents the pulse amplitude R (dB) of the light reflected by the tapered grating. Figure 6 is a schematic diagram of the relationship between the bandwidth of the tapered grating reflection spectrum and the temperature change. The abscissa represents the central wavelength (nm) of the light reflected by the tapered grating, and the ordinate represents the bandwidth change (nm) of the light reflected by the tapered grating. -○- indicates Temperature change measurement point.

Detailed ways

Specific embodiment one: referring to Fig. 1, the distributed tapered fiber grating sensor of this specific embodiment, the optical fiber segment 1 of the same diameter of mountain multi-section is formed, and each segment optical fiber segment 1 contains the tapered Bragg grating 2 that length is L, and multi-section optical fiber segment The first end and the end of 1 are serially connected together in sequence. The tapered Bragg grating 2 contained in each fiber segment 1 is tapered by linear erosion along the fiber axis, and the cross-sectional area of the tapered Bragg grating 2 changes linearly along the grating direction. Fiber segment 1 is a single-mode fiber. The preparation method of each section of optical fiber segment 1 of this specific embodiment is: utilize the phase mask method to write uniform Bragg (Bragg) fiber grating on the upper side of the single-mode optical fiber treated by high-pressure hydrogen loading, and the reflectivity of the grating is all higher than 99%; after the grating is annealed at high temperature, the bandwidth and reflectivity of the grating will no longer change with temperature and time; then the annealed grating is immersed in the HF acid solution and pulled out from the HF acid at a uniform speed. Since the etching speed is proportional to the time, the cross-section of the grating changes linearly after the grating is etched. In this specific embodiment, we etched the diameter of the fiber segment from D(0)=125 μm to D(L)=90 μm, where L represents the length of the Bragg grating.

Specific embodiment two: referring to Fig. 2, the reflected light bandwidth demodulation device of the described distributed tapered fiber grating sensor of specific embodiment one is made up of collimating optics 4, plane diffraction grating 6, converging optics 5, line array Composed of CCD 7, CCD control and reading circuit 8, A/D conversion circuit 9 and central processing unit 10, the tapered grating reflected light output by the distributed tapered fiber grating sensor 3 is incident on the light input end of the collimating optical device 4 , the reflected light of the tapered grating is collimated by the collimating optics 4 and becomes a parallel beam and irradiates on the plane diffraction grating 6, after being split by the plane diffraction grating 6, beams of different wavelengths scattered along different angles are obtained. The light beams of different wavelengths are converged by the converging optics 5 and then incident on the photosensitive side of the line array CCD 7, and one or several sections of illumination areas formed by the light beams of different wavelengths are obtained on the photosensitive side of the line array CCD 7; CCD control and reading circuit 8 is connected with the linear array CCD 7 for the control of the linear array CCD 7 and the reading of the analog electrical signal output by each pixel, the output end of the CCD control and reading circuit 8 is connected to the input end of the A/D conversion circuit 9, and the A/D The output end of the conversion circuit 9 is connected to the CCD signal input end of the CPU 10 . The collimating optics 4 adopts a collimating lens group. The converging optical device 5 adopts a convex lens.

The plane diffraction grating 6 adopts a plane grating with 600 lines/mm. Generally speaking, the higher the number of lines, the higher the precision. The linear array CCD 7 can adopt the linear array CCD device of 2048 picture elements, as the TCD142D that Toshiba Corporation of Japan produces; The longer it is, the larger the spectral range it can demodulate, so the number of gratings that can be multiplexed in the sensing system increases. The CCD control and reading circuit 8 realizes the driving of the linear array CCD 7 and the reading of the output signal. It provides the working sequence for the CCD and reads the photoelectric conversion output signal of the CCD according to a certain sequence, and adopts general technology. The A/D conversion circuit 9 adopts a 12-bit A/D conversion card, such as the PCI-7422 produced by Beijing Hongtuo Measurement and Control Company. The central processing unit 10 performs data processing of the demodulation device to obtain the required sensing information, which can be realized by computer programming or DSP chip (digital signal processor), such as TMS320 series of TI company.

Specific embodiment three: Referring to Figures 1 and 2, using the distributed tapered fiber grating sensor described in specific embodiment one and based on the reflected light bandwidth demodulation device of the distributed tapered fiber grating sensor described in specific embodiment two The detection method of stress/temperature change is carried out in the following steps:

Step 1. Calibrate the reflected light bandwidth demodulation device of the distributed tapered fiber grating sensor 3 described in the second embodiment: 1. determine its respective Stress sensitivity K _ε and temperature sensitivity K _T ; ② Apply a rated stress variation to the distributed tapered fiber grating sensor 3 along the axial direction, and then use the reflected light bandwidth demodulator to know the formation of beams of different wavelengths on the linear array CCD 7 One or several sections of the width of the illumination area, and then establish the relationship between the stress induced by the distributed tapered fiber grating sensor 3 and the width of the illumination area corresponding to the different wavelengths on the linear array CCD 7;

Step 2. Embedding the distributed tapered fiber grating sensor 3 described in Embodiment 1 into the object to be monitored or adhered to the surface of the member to be measured. A tapered Bragg grating is located at a measurement point to be monitored, distributed The central wavelengths of multiple tapered Bragg gratings in the type tapered fiber grating sensor 3 are different from each other, and the distance between the center reflection wavelengths of adjacent tapered Bragg gratings should ensure that the reflected light of adjacent tapered Bragg gratings is different from each other. interference;

Step 3, make the tapered grating reflected light output by the distributed tapered fiber grating sensor 3 incident into the reflected light bandwidth demodulation device of the above-mentioned distributed tapered fiber grating sensor 3 through the collimating optics 4, from the distributed tapered fiber grating sensor The reflected light beam obtained by the fiber grating sensor 3 is an optical pulse with a certain bandwidth and different central wavelengths containing information on temperature and stress changes at each measurement point. One or several sections of illumination areas formed on the photosensitive side of the array CCD 7, use the CCD control and reading circuit 8, and the A/D conversion circuit 9 to collect the image information of the linear array CCD 7, and use the central processing unit 10 to analyze and calculate the distributed cone The reflection spectrum information of the fiber grating sensor 3 and the width of one or several sections of illumination areas on the linear array CCD 7;

Step 4, analyze and calculate according to the width of one or more sections of the illumination area on the linear array CCD 7 obtained by the central processing unit 10 in step 3, and use the stress and the induced stress of the distributed tapered fiber grating sensor 3 obtained in the step 1 on the linear array CCD 7 The change relationship of the width of the illumination area corresponding to different wavelengths determines the stress value ε corresponding to each measurement point at this time;

Step 5. Determine the drift of the Bragg grating center reflection wavelength at each point according to the reflection spectrum information obtained by the analysis and calculation of the central processing unit 10 in step 3;

Step 6. For each measurement point, use the stress sensitivity K _ε and temperature sensitivity K _T obtained in step 1, the drift of the Bragg grating center reflection wavelength obtained in step 5, and the stress value ε of the measurement point obtained in step 4, The temperature change can be obtained according to the following formula, so as to distinguish the temperature from the stress:

$\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}$

In the above formula, Δλ _B is the drift of the Bragg grating center reflection wavelength obtained in step 5; K _ε is the stress sensitivity coefficient of the conical grating obtained in step 1; ε is the stress value measured in step 4; K _T is the step - the obtained temperature sensitivity coefficient of the tapered grating; ΔT is the temperature variation. The method of the present invention is designed on the basis of the second specific embodiment, and is simple and practical.

Claims (7)

1. A distributed tapered fiber grating sensor is characterized in that said distributed tapered fiber grating sensor is made of many sections of fiber optic sections (1) with the same diameter, and each section of fiber optic section (1) contains a taper with a length of L The Bragg grating (2), the head end and the end end of a plurality of optical fiber segments (1) are sequentially connected together in series. 2. Distributed tapered fiber grating sensor according to claim 1, it is characterized in that the tapered Bragg grating (2) that every segment of fiber segment (1) contains is by the taper that corrodes linearly along the optical fiber axis, The cross-sectional area of the tapered Bragg grating (2) along the grating direction changes linearly. 3. distributed tapered fiber grating sensor according to claim 1, is characterized in that optical fiber section (1) adopts single-mode optical fiber. 4. comprise the reflected light bandwidth demodulation device of a kind of distributed tapered fiber grating sensor claimed in claim 1, it is characterized in that described reflected light bandwidth demodulation device is made of collimating optics (4), plane diffraction grating ( 6), converging optics (5), linear array CCD (7), CCD control and reading circuit (8), A/D conversion circuit (9) and central processing unit (10), distributed tapered fiber grating The reflected light of the conical grating output by the sensor (3) is incident on the light input end of the collimator (4), and the reflected light of the conical grating is collimated by the collimating optical device (4) and becomes a parallel beam and irradiates the plane diffraction On the grating (6), light beams of different wavelengths scattered along different angles are obtained after splitting light by the plane diffraction grating (6). 7) on the photosensitive side, obtain one or several sections of illumination areas formed by light beams of different wavelengths on the photosensitive side of the line array CCD (7); the CCD control and reading circuit (8) is connected with the line array CCD (7) for line The control of the array CCD (7) and the reading of the analog electrical signal output by each picture element, the output end of the CCD control and the reading circuit (8) is connected to the input end of the A/D conversion circuit (9), and the A/D conversion circuit ( 9) The output terminal is connected to the CCD signal input terminal of the central processing unit (10). 5. the reflected light bandwidth demodulation device of distributed tapered fiber grating sensor according to claim 4, it is characterized in that described collimating optical device (4) adopts collimating lens group. 6. the reflected light bandwidth demodulation device of distributed tapered fiber grating sensor according to claim 4, it is characterized in that described converging optics (5) adopts convex lens. 7. A detection method of the reflected light bandwidth mediation device of distributed tapered fiber grating sensor, use the method for the sensor reflected light of claim 1 to detect the device described in claim 1, it is characterized in that described method follows the steps successively conduct: Step 1, calibration is carried out to the reflected light bandwidth demodulation device of distributed tapered fiber grating sensor (3) described in claim 4: 1. determine its respective stress and temperature by respectively applying rated stress and temperature to each tapered grating sensor Stress sensitivity K _ε and temperature sensitivity K _T ; ② Apply a rated stress variation to the distributed tapered fiber grating sensor (3) along the axial direction, and then use the reflected light bandwidth demodulator to obtain the different values on the linear array CCD (7) The width of one or more sections of the illumination area formed by the light beam of the wavelength, and then establish the relationship between the stress induced by the distributed tapered fiber grating sensor (3) and the width of the illumination area corresponding to the different wavelengths on the linear array CCD (7); Step 2, embedding the distributed tapered fiber grating sensor (3) according to claim 1 inside the object to be monitored or adhered to the surface of the member to be measured, a tapered Bragg grating is located at a measuring point that needs to be monitored, The central wavelengths of multiple tapered Bragg gratings in the distributed tapered fiber grating sensor (3) are different from each other, and the distance between the central reflection wavelengths of adjacent tapered Bragg gratings must ensure that the reflection of adjacent tapered Bragg gratings Light does not interfere with each other; Step 3, make the tapered grating reflected light output by the distributed tapered fiber grating sensor (3) incident into the reflected light bandwidth demodulation device of the above-mentioned distributed tapered fiber grating sensor (3) through the collimating optics (4) , the reflected light beam obtained from the distributed tapered fiber grating sensor (3) is an optical pulse with a certain bandwidth and different central wavelengths containing the temperature and stress change information of each measurement point. The optical pulse passes through the collimating optical device (4), Plane diffraction grating (6), converging optics (5) form one or several sections of illumination area on the light-sensitive side of line array CCD (7), utilize CCD control and readout circuit (8), A/D conversion circuit (9) Collect the image information of the linear array CCD (7), and use the central processing unit (10) to analyze and calculate the reflectance spectrum information of the distributed tapered fiber grating sensor (3) and the width of one or more illumination areas on the linear array CCD (7) ; Step 4. According to the width of the linear array CCD (7) on one or several sections of the illuminated area obtained by analyzing and calculating the central processing unit (10) in step 3, use the stress induced by the distributed tapered fiber grating sensor (3) obtained in step 1. Determine the stress value ε corresponding to each measurement point at this time according to the relationship between the variation of the width of the illuminated area corresponding to the different wavelengths on the linear array CCD (7); Step 5, determine the drift of the Bragg grating center reflection wavelength at each point according to the reflection spectrum information obtained by the analysis and calculation of the central processing unit (10) in step 3; Step 6. For each measurement point, use the stress sensitivity K _ε and temperature sensitivity K _T obtained in step 1, the drift of the Bragg grating center reflection wavelength obtained in step 5, and the stress value ε of the measurement point obtained in step 4, press The following formula can obtain the amount of change in temperature, thereby distinguishing temperature from stress: $\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}$ In the above formula, Δλ _B is the drift of the Bragg grating center reflection wavelength obtained in step 5; K _ε is the stress sensitivity coefficient of the conical grating obtained in step 1; ε is the stress value measured in step 4; K _T is the step - the obtained temperature sensitivity coefficient of the tapered grating; ΔT is the temperature variation.

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