CN102818531A - Dynamic strain measurement instrument based on multiple overlapped gratings - Google Patents

Abstract

A dynamic strain gauge based on overlapping multi-gratings, including overlapping multi-gratings, broadband light sources, tunable filters, directional couplers, etalons, photodetectors, demodulation and control circuits, etc. The overlapping multi-gratings are selected from different The phase template overlaps and writes multiple sensing gratings with central wavelengths distributed at equal intervals on the same area of the sensing fiber, where the central wavelengths of multiple overlapping and written optical fiber gratings are within the wavelength scanning range of the tunable filter and are continuous. Interval distribution, so that the sensing information of the same measured physical quantity can be continuously obtained multiple times in each wavelength scanning period, and the original dynamic strain signal can be reconstructed by recording the peak position and wavelength change of each sensing grating in the overlapping multi-grating. The purpose of improving the measurement bandwidth of the dynamic strain signal based on the tunable filter grating demodulation system is achieved. The invention effectively improves the measurement bandwidth based on the tunable filter fiber grating sensor, and can meet the simultaneous measurement requirements of high speed and high precision for dynamic strain signals.

Description

A Dynamic Strain Measuring Instrument Based on Overlapping Multiple Gratings

technical field

The invention relates to a dynamic strain measuring instrument based on overlapping multiple gratings, which is mainly used for sensing and measuring dynamic strain signals and belongs to the field of sensing technology.

Background technique

Fiber Bragg gratings can convert changes in the external environment (such as stress, strain, vibration, temperature changes, etc.) Sensors have been widely used in the fields of long-distance optical sensing and optical communication due to their characteristics of being immune to electromagnetic radiation interference, small size, simple fabrication, and wavelength sensitivity.

At present, the technologies for demodulating the center wavelength of fiber gratings usually include the following types, which are spectral analysis technology, wavelength scanning technology based on tunable filters, edge filter technology, unbalanced M-Z interferometer demodulation technology and matched grating demodulation method, etc. Due to the need for a large number of mathematical calculations, the spectral analysis technology has a low wavelength demodulation speed and cannot adapt to the measurement of large bandwidth signals; the unbalanced M-Z interferometer demodulation technology is currently only suitable for the measurement of dynamic signals due to the problem of zero point drift. Filtering technology needs to configure a separate edge filter and detector for each sensing grating, which is not convenient for the multiplexing of multiple grating sensors, and the cost is high; the wavelength scanning technology based on tunable filters has high wavelength resolution , wide measurement range, and strong multiplexing capability have been widely used in engineering applications. However, the grating demodulation system based on this method currently on the market has the problem of low wavelength scanning rate, so it cannot meet the measurement requirements of large bandwidth dynamic signals.

The reasons affecting the measurement bandwidth of the tunable filter grating demodulation system mainly include the following two aspects:

(1) The tunable speed of the tunable filter itself is limited. In order to ensure the long-term stability and reliability of the laser, the tuning speed of the existing fiber laser based on the tunable filter is usually on the order of 1 Hz to several kHz.

(2) The limitation of signal acquisition and processing speed. Under the condition of keeping the scanning wavelength resolution unchanged, the conversion rate of A/D and D/A is proportional to the wavelength scanning rate of the tunable filter, and the demodulation system The data processing capability limits the improvement of the A/D sampling frequency, and under the condition that the A/D sampling frequency remains unchanged, the wavelength scanning range and wavelength resolution can only be reduced to increase the wavelength scanning rate, but this will affect the demodulation Multiplexing capability and demodulation accuracy of the system.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art, and propose a dynamic strain measuring instrument based on overlapping multi-gratings to meet the measurement requirements of a large-bandwidth dynamic strain signal by a grating demodulation system based on a tunable filter.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a dynamic strain gauge based on overlapping multi-gratings, which is characterized in that the sensor fiber grating 5 or Various fiber grating-based stress, strain or shock vibration sensors are designed by connecting multiple overlapping multi-gratings in parallel. Multiple fiber gratings overlapped together can sense the same measured physical quantity at the same time. The center wavelength of each grating The amount of change is proportional to the size of the measured physical quantity, and the grating demodulation system based on the broadband light source 1 and the tunable filter 2 outputs continuous narrow-linewidth wavelengths under the action of the triangular wave D/A converter 11 and the high-voltage driver 12, The output wavelength enters the overlapping multi-grating 5 and the etalon 6 after passing through the coupler 3, the isolator 4 is used to isolate the reflection signal of the etalon 6, and the reflection spectrum of the overlapping multi-grating 5 and the transmission spectrum of the etalon 6 respectively enter the photodetector 7 , and finally through the multi-channel synchronous serial A/D converter 8 real-time synchronous acquisition of the electrical signal output by the photodetector 7; FPGA-based demodulation and control circuit 10 is used to control the A/D converter 8 and the D/A converter 11 working sequence and output waveform, while receiving and processing the signal of the A/D converter 8 in real time, and sending the real-time processed data to the computer 9 through the interface (PCI, USB or network interface) for further processing, and the computer 9 It mainly completes the calculation and reconstruction of the peak wavelength of each sensing grating in the overlapping multi-grating of each wavelength scanning period; the FPGA-based demodulation and control circuit 10 can use the peak extraction algorithm to calculate in real time the overlapping multi-grating in each wavelength scanning period The D/A control value of the scanning voltage corresponding to each peak wavelength of the etalon, because the center wavelength of each output peak of the etalon is fixed, and the peak wavelength of the overlapping multi-grating output will shift to the long-wave or short-wave direction under the action of dynamic strain Move, computer 9 can solve the change of each sensing grating center wavelength in the overlapping multi-grating by calculating the variation of each peak position of the overlapping multi-grating 5 with respect to each peak center position of the etalon 6; The central wavelengths of each sensing grating are evenly distributed in the frequency domain, and the output wavelength of the tunable filter 2 is continuously and linearly distributed in the time domain, so the solution results of the central wavelengths of each sensing grating in the overlapping multi-grating are in the time domain It is also continuously distributed at equal intervals, and the dynamic strain information can be reconstructed by combining the calculation results of the center wavelength of each sensing grating in the overlapping multi-grating according to the scanning order of the wavelength.

Since the overlapping multi-gratings have sensor grating response spectrum output during the forward and reverse wavelength scanning process of the tunable filter, in order to achieve the purpose of collecting dynamic strain signals at equal intervals, each wavelength scanning cycle needs to simultaneously solve the positive and negative Sensing grating response spectra in two directions, and in order to achieve uniform distribution of central wavelengths of each grating in the overlapping multi-grating, the central wavelength of each sensing grating in the overlapping multi-grating should be selected according to the calculation results of the following formula:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: λ _B[i] is the center wavelength of the i-th sensing grating;

λ _S is the wavelength scanning starting point of the tunable filter;

λ _E is the wavelength scanning end point of the tunable filter;

n is the total number of sensing gratings.

Since it is impossible to ensure that the central wavelengths of each sensing grating are distributed at equal intervals in the wavelength scanning range of the tunable filter during the manufacturing process of overlapping multiple gratings, and the central wavelengths of the sensing gratings will be skewed under the action of dynamic strain. The short-wave and long-wave directions move back and forth. In addition, the nonlinear scanning of the tunable filter will also cause the output spectrum of the sensing grating to be distributed at non-equal intervals. In order to correctly reconstruct the dynamic strain signal of the measured physical quantity, the FPGA-based demodulation and control circuit (10) It is necessary to calculate the peak position of the overlapping multi-grating and etalon in each wavelength scanning period in real time, and send the calculation result to the computer (9). The calculation result should include the wavelength scanning period n, each sensing grating in the overlapping multi-grating The position t _ni of the central wavelength and the peak position of the etalon, since the central wavelength corresponding to the peak position of the etalon is fixed, the computer (9) can compare the position of the central wavelength of each sensing grating in the overlapping multi-grating with respect to the standard The change of the central wavelength of each sensing grating is calculated by the position change of the sensor Δλ _ni , and then the dynamic strain information of the measured physical quantity can be reconstructed according to the dynamic strain sensitivity coefficient k _i of the central wavelength of each sensing grating in the overlapping multi-grating, The dynamic strain signal of the nth scanning period should be reconstructed as follows:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \{</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="t\; no"\; filenames="HDA00002126194500011.png"\; state="\{\{state\}\}">t</figure-callout></span><figure-callout\; id="2"\; label="t\; no"\; filenames="HDA00002126194500011.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; ,</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; ni</span>}}<span\; class="notranslate">\; ,</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; ni</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</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">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula: Δε _n is the dynamic strain information obtained in the nth scanning cycle;

t _ni is the peak position of the ith sensing grating in the overlapping multi-grating of the nth scanning period;

Δλ _ni is the change in the central wavelength of the i-th sensing grating in the n-th scanning cycle overlapping multiple gratings;

k _i is the dynamic strain sensitivity coefficient of the ith sensing grating in the overlapping multi-grating.

Principle of the present invention: The overlapping multi-grating used in the present invention is made by repeatedly writing phase templates with different central wavelengths on the same position of the sensing fiber, and it mainly has the following characteristics: (1) Time synchronization, namely All the overlapping sensing gratings can sense the sensing information of the measured physical quantity at the same time; (2) The structure is compact, because all the sensing gratings are written on the same sensitive position of the sensing fiber. The measuring instrument based on the overlapping multi-grating is mainly composed of two parts: the overlapping multi-grating for dynamic strain measurement and the grating demodulation system based on tunable filter and broadband light source. The overlapping multi-grating for dynamic strain measurement is in the same On the same sensing area of the optical fiber, a plurality of fiber gratings whose center wavelength is uniformly distributed within the wavelength scanning range are repeatedly written. Since each additional grating will affect the central wavelength and reflectivity of the already written grating in the process of manufacturing overlapping multi-gratings, this requires a higher writing process for overlapping multi-gratings, thus limiting the number of overlapping gratings. To further improve the measurement bandwidth of dynamic strain and ensure the demodulation accuracy, the number of sensing gratings per wavelength scanning period can be increased by connecting multiple overlapping multi-gratings in parallel, so as to achieve the purpose of simultaneous sensing of more gratings. In each wavelength scanning period, the sensor based on the above overlapping multi-grating can continuously obtain multiple sensing grating output spectra at equal intervals, by solving the change of the central wavelength of each sensing grating in real time and according to the output spectrum of the sensing grating After the time sequence is reconstructed, more dynamic strain sensing information can be obtained, so that the measurement purpose of the large bandwidth signal can be realized under the condition of keeping the scan rate of the tunable filter unchanged, and the present invention does not need to improve the tunable filter The scanning rate and scanning step are not required to reduce the wavelength scanning range of the tunable filter, so the sensing and measurement of large bandwidth dynamic strain signals can be realized on the basis of the existing wavelength resolution and multiplexing capability.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention uses overlapping multi-gratings with multiple center wavelengths evenly distributed at equal intervals within the wavelength scanning range of the tunable filter to design a dynamic strain sensing device, which can effectively improve the existing tunable filter grating demodulation system At the same time, it has the advantages of high wavelength resolution, wide measurement range and strong multiplexing ability of the demodulation system.

(2) The dynamic strain sensor based on overlapping multiple gratings of the present invention can be connected with multiple sensors designed with a single grating through the same optical fiber for combined sensing, so that it can satisfy both low-frequency small signals and high-frequency dynamic strain signals. Simultaneous measurement requirements can effectively improve the application range and flexibility of grating sensing.

Description of drawings

Fig. 1 is the composition of the dynamic strain measuring instrument system based on overlapping multi-grating of the present invention;

Fig. 2 is the demodulation principle of the dynamic strain measuring instrument based on overlapping and writing two central wavelength overlapping multi-gratings of the present invention, wherein: (a) is the sensing grating output spectrum under the action of dynamic strain of overlapping multi-gratings; (b) is the comb output spectrum of the etalon; (c) is the scanning voltage of the tunable filter;

Fig. 3 Dynamic strain sensing principle of overlapping and writing multiple sampling gratings on a single sensing fiber;

Figure 4 adopts the principle of dynamic strain sensing with parallel connection of two engraved overlapping multi-grating optical fibers;

Fig. 5 The reflectance spectrum of each period sensing grating under the action of the overlapping multi-grating of the present invention under the action of 100 Hz sinusoidal dynamic strain;

Fig. 6 is the wavelength-varying reflectance spectrum of each period of the 100 Hz sinusoidal dynamic strain signal reconstructed by the present invention.

In the figure: 1-width light source; 2-tunable filter; 3-fiber coupler; 4-isolator; 5-overlapping multiple gratings; 6-etalon; 7-photodetector; 8-A/D converter ; 9-computer; 10-demodulation and control circuit based on FPGA; 11-D/A converter; 12-high voltage driver.

Detailed ways

The present invention will be further described in detail below in conjunction with accompanying drawings and examples.

As shown in Figure 1, the dynamic strain gauge based on overlapping multiple gratings mainly includes broadband light source 1, tunable filter 2, fiber coupler 3, isolator 4, overlapping multiple gratings 5, etalon 6, photodetector 7, A/D converter 8, computer 9, FPGA-based demodulation and control circuit 10, D/A converter 11 and high-voltage drive amplifier circuit 12; among the figure, broadband light source 1 can be selected as a high-power light source with higher gain flatness (The bandwidth is greater than 40nm, the wavelength range is 1520nm~1560nm, and the total power is greater than 10mW). After the broadband light source passes through the tunable filter 2, it will become a laser with a narrow linewidth. The output linewidth of the selected tunable filter should be better than 0.01nm , to ensure the demodulation accuracy of the demodulation system, the tunable filter 2 will periodically output a narrow linewidth laser that changes linearly under the action of the triangular wave scanning voltage, and the wavelength of the narrow linewidth laser is periodically in the range of 1520nm~1560nm change, the triangular wave scanning voltage is generated by the FPGA-based demodulation and control circuit 10 through the D/A converter 11 and the high-voltage driver 12, and the narrow linewidth output wavelength enters the overlapping multi-grating 5 and the etalon 6 respectively after passing through the coupler 3, The isolator 4 is used to isolate the reflected signal of the etalon 6; the reflected wave through the overlapping multi-grating 5 and the transmitted wave of the etalon 6 respectively enter the photodetector 7, and then the output of the photodetector 7 is collected synchronously by the A/D converter 8 in real time The A/D converter 8 adopts multi-channel high-speed synchronous serial A/D, which can effectively improve the multi-channel parallel data processing capability of the FPGA-based demodulation and control circuit 10, and reduce the A/D conversion The FPGA-based demodulation and control circuit 10 input and output pin requirements facilitate the expansion of more demodulation channels. FPGA-based demodulation and control circuit 10 is used to control the working sequence and output waveform of A/D converter 8 and D/A converter 1, simultaneously receive and process the signal of A/D converter 8 in real time, and finally process the signal in real time The completed data is sent to the computer 9 for further processing through the interface (PCI, USB or network interface), and the computer 9 mainly completes the calculation and reconstruction of the peak wavelength of each sensor grating in the overlapping multi-grating of each wavelength scanning period; based on FPGA The demodulation and control circuit 10 can use the peak advance algorithm to calculate in real time the position of the scanning voltage corresponding to each peak wavelength in the overlapping multi-grating and etalon in each wavelength scanning period, because the central wavelength of each output peak of the etalon is fixed , and the peak wavelength output by each sensing grating in the overlapping multi-grating will move to the long-wave or short-wave direction under the action of dynamic strain, the computer 9 calculates the amount of change of each peak position of the overlapping multi-grating 5 relative to each peak center position of the etalon 6 , the change of the center wavelength of each overlapping multi-grating can be calculated.

The overlapping multi-gratings used in Figure 1 need to determine the number of sensing gratings and the interval between the center wavelengths according to the requirements of the dynamic strain measurement bandwidth and the scanning rate of the tunable filter, and then use the formula (1) to calculate each of the overlapping multi-gratings The central wavelength of the grating is finally written by selecting the corresponding grating to make a template. Since the overlapping multi-grating needs to be fixed by pre-tension before dynamic strain sensing, the central wavelength of each grating will be under the action of pre-tension. Direction movement, so that the top and bottom of the triangular wave scanning voltage of the tunable filter will be relatively pulled closer and farther away, resulting in non-equally spaced sampling at the junction. This problem can be eliminated by adjusting the sweep bias voltage of the tunable filter .

As shown in Figure 2, it is the demodulation principle of the dynamic strain gauge based on overlapping multiple gratings. Figure 2(a) shows the output of the overlapping multiple gratings with two center wavelengths in a single tunable filter wavelength scanning period. A sensing grating reflectance spectrum, in which two sensing grating reflectance spectra are generated during forward scanning and reverse scanning, and the central wavelength of the sensing grating reflective spectrum is the same as that of the two sensing grating central wavelengths in the overlapping multi-grating Correspondingly, since the overlapping multi-gratings are written in the same area of the sensing fiber, they have similar sensing sensitivities. The demodulation results of the reflection spectra of the 4 sensing gratings in each scanning cycle are consistent with the range of dynamic strain, but each sensing The occurrence time of the grating reflection spectrum is distributed at equal intervals in turn. Under the dynamic stress of overlapping multiple gratings, the reflection spectrum of the four sensing gratings will move to the short-wave or long-wave direction at the same time. The demodulation results of the reflection spectrum of the four sensing gratings are according to the formula ( 2) After recombining the order of time and time, the measurement of dynamic strain signals four times faster than the wavelength scanning rate can be realized, so as to achieve the purpose of improving the measurement bandwidth of the grating demodulation system based on tunable filters. Figure 2(b) shows the comb-shaped output spectrum of the etalon. The interval of each comb-shaped output spectrum is fixed at 800pm. Since the central wavelength of each output spectrum of the etalon is slightly affected by temperature, it can be used as a reference wavelength. Based on the real-time dynamic calibration of overlapping multiple gratings, the demodulation accuracy of the central wavelength of the gratings can be effectively improved. Figure 2(c) is the scanning voltage of the tunable filter. By changing the bias voltage of the scanning waveform and the amplitude of the scanning voltage, the range of the scanning wavelength of the tunable filter can be changed.

As shown in Figure 3, in order to select different phase masks at the same position of the sensing fiber to overlap and write multiple sensing gratings, the sensing fiber is kept still during the writing process of overlapping multiple gratings, and the first phase mask is written. After sensing the grating, switch to a phase mask with a different central wavelength for the second writing, or directly select a phase mask with multiple sensing gratings for writing to complete the writing of multiple sensing gratings, The central wavelength of the reflection spectrum of each sensing grating in the overlapping multi-grating will move left and right under the action of tension and compression of dynamic stress, and the result of the movement is shown in the small picture in Fig. 2(a).

As shown in Figure 4, the design method of connecting two dynamic strain sensors with overlapping multi-gratings in parallel can reduce the negative impact caused by overlapping and writing multiple sensing gratings on the same optical fiber, so as to improve the dynamic strain sensor. The number of sensing gratings used in strain sensing, the reflection spectrum signals of two overlapping multi-gratings can enter independent photodetectors, or enter the same photodetector through a directional coupler for signal acquisition and processing, because all used The central wavelength of the sensing grating is evenly distributed at equal intervals within the wavelength scanning range of the tunable filter, and it needs to be uniformly distributed according to the requirements of formula (1), and there is no problem of wavelength overlap.

Example 1

The following mainly illustrates the measurement method of a dynamic sinusoidal strain signal that is 4 times faster than the scan rate of a tunable filter by overlapping multiple gratings with two sensing gratings written on top of each other. Figure 2 shows the dynamic strain measurement based on overlapping multiple gratings The demodulation principle of the instrument, taking the wavelength scanning range of the tunable filter from 1535nm to 1555nm as an example, the center wavelength of the two sensing gratings in the overlapping multi-grating can be selected according to the formula (1), corresponding to the center wavelength of the two sensing gratings The wavelengths are 1540nm and 1550nm respectively, and the center wavelength interval of each sensing grating is 10nm. Taking the wavelength scanning rate of the tunable filter as 500Hz as an example, the dynamic strain sensing device with overlapping multi-grating design is in each tunable filter The forward and reverse scanning processes of the wavelength scanning cycle of the sensor can obtain the measured physical quantity of the same sensing point twice in a row, which is 4 times the measurement bandwidth of the measured physical quantity that can be obtained by a single sensing grating, corresponding to a large overlap The actual information acquisition frequency obtained by the grating dynamic strain sensing measurement device should be 2kHz, that is, the measurement bandwidth of the measured signal is increased by 4 times. The scanning wavelength and the output power spectrum of the overlapping multi-grating are shown in Figure 2. The reflection spectrum of the overlapping multi-grating and the triangular wave scanning voltage of the tunable filter in the forward and reverse scanning process of the demodulation system are shown, and the wavelength scanning range is 1535nm～1555nm. Figure 5 shows four 100 Hz sinusoidal dynamic strain reflection spectra of overlapping multi-gratings under the action of 500 Hz forward and reverse scanning voltages. The peak position of the output reflection spectrum of the grating presents a periodic sinusoidal change. Figure 6 shows the wavelength-varying reflection spectra of the four sinusoidal dynamic strain reflection spectra in Figure 5 reconstructed according to formula (2). The output reflection spectra of the sensing grating have changed from 5 of a single sensing grating to 20, that is, The number of dynamic strain signal acquisition points that is 4 times that of the scan rate of the tunable filter is increased, thereby effectively improving the measurement bandwidth of the dynamic strain signal.

In a word, the present invention does not need to select expensive high-speed tunable filters, and does not need to reduce the wavelength scanning range, so it can realize the measurement of higher bandwidth signals without affecting the original wavelength resolution and multiplexing capability. This method can effectively improve the measurement bandwidth based on tunable filter fiber grating sensing, and can meet the simultaneous measurement requirements of high-speed and high-precision dynamic strain signals.

Parts not described in detail in the present invention belong to the known techniques of those skilled in the art.

Claims (6)

1. dynamic strain measurement appearance based on overlapping many gratings is characterized in that: comprise wideband light source (1), tunable optic filter (2), fiber coupler (3), isolator (4), overlapping many gratings (5), etalon (6), photodetector (7), A/D converter (8), computing machine (9), based on demodulation and control circuit (10), D/A converter (11) and the high drive amplifying circuit (12) of FPGA; Said overlapping many gratings (5) are to repeat to inscribe a plurality of sensing gratings with different centre wavelengths at sensor fibre the same area, and each centre wavelength of overlapping many gratings (5) is spacedly distributed tunable optic filter (2) wavelength scanning range planted agent; Demodulation and control circuit (10) based on FPGA pass through D/A converter (11) and high-voltage drive (12) control wideband light source (1) and the continuous wavelength of tunable optic filter (2) output, get into overlapping many gratings (5) and etalon (6) respectively behind this output wavelength process coupling mechanism (3); Isolator (4) is used for the reflected signal of isolation standard tool (6); Get into photodetection (7) respectively through the reflection wave of the many gratings of lap over (5) and the transmitted wave of etalon (6), deliver in the demodulation and control circuit (10) based on FPGA through the electric signal of A/D converter (8) synchronous acquisition photodetector (7) output in real time again; The signal that receives A/D converter (8) in real time based on demodulation and the control circuit (10) of FPGA; The peak of overlapping many gratings of each length scanning cycle (5) and etalon (6) in the signal calculated; And result of calculation sent to computing machine (9), be used to control the work schedule and the output waveform of A/D converter (8) and D/A converter (11) simultaneously based on the demodulation of FPGA and control circuit (10); Because the centre wavelength of each output peak value of etalon (6) immobilizes; And the peak wavelength of overlapping many gratings (5) output will move to long wave or shortwave direction under the dynamic strain effect; Computing machine (9) can calculate the variation of each sensing grating centre wavelength in overlapping many gratings (5) through calculating the variable quantity of each peak of peak relative standard tool (6) of each sensing grating in overlapping many gratings (5); In addition because each centre wavelength of overlapping many gratings (5) uniformly-spaced evenly distribution on frequency domain; And the output wavelength of tunable optic filter (2) is continuous linear distribution on time domain; The result that resolves of each centre wavelength of overlapping many gratings (5) also is spacedly distributed on time domain continuously, with each centre wavelength of overlapping many gratings (5) to resolve that the result combines by the scanning sequency of wavelength be restructural dynamic strain information.

2. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings, it is characterized in that: a plurality of sensing gratings with different centre wavelengths are chosen according to following formula in said overlapping many gratings (5):

${\mathrm{\&lambda;}}_{B\left[i\right]}={\mathrm{\&lambda;}}_S+[i-\frac{1}{2}]\&times;\frac{{\mathrm{\&lambda;}}_E-{\mathrm{\&lambda;}}_S}{n}$

In the formula: λ _{B [i]}Be the centre wavelength of i sensing grating;

λ _SLength scanning starting point for tunable optic filter;

λ _ELength scanning terminal point for tunable optic filter;

N is the total number of sensing grating.

3. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: in order further to improve the measurement bandwidth of dynamic strain; In said overlapping many gratings (5), also can promptly overlapping many gratings have all been inscribed on every sensor fibre through the parallel production method that connects many overlapping many gratings; Again with the parallel stiff end that is connected to the dynamic strain measurement device of many sensor fibres; Be used for the purpose of the synchronous sensing of same measurand with the more gratings of realization, but all sensing grating centre wavelengths of using need be unified to choose in the many overlapping many gratings of connection that walk abreast, choosing method is:

${\mathrm{\&lambda;}}_{B\left[i\right]}={\mathrm{\&lambda;}}_S+[i-\frac{1}{2}]\&times;\frac{{\mathrm{\&lambda;}}_E-{\mathrm{\&lambda;}}_S}{n}$

In the formula: λ _{B [i]}Be the centre wavelength of i sensing grating;

λ _SLength scanning starting point for tunable optic filter;

λ _ELength scanning terminal point for tunable optic filter;

N is the total number of sensing grating.

4. a kind of dynamic strain measurement appearance based on overlapping many gratings according to claim 1 is characterized in that: the process of said computing machine (9) reconstruct dynamic strain information is: the variation delta λ that calculates each sensing grating centre wavelength according to each sensing grating peak in overlapping many gratings with respect to the change in location of etalon output peak value _Ni, again according to each sensing grating centre wavelength dynamic strain sensitivity coefficient k in overlapping many gratings _iBe the dynamic strain information of restructural measurand, n scan period dynamic strain signal should be by reconstruct shown in the following formula:

$\mathrm{\&Delta;}{\mathrm{\&epsiv;}}_n=\{(t_{n1},\frac{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_{n1}}{k_1}),(t_{n2},\frac{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_{n2}}{k_2}),\&CenterDot;\&CenterDot;\&CenterDot;,(t_{\mathrm{ni}},\frac{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_{\mathrm{ni}}}{k_i})\}$

In the formula: Δ ε _nBe n the dynamic strain information that the scan period obtained;

t _NiBe i sensing grating peaks of n overlapping many gratings of scan period;

Δ λ _NiIt is the wavelength change of i sensing grating of n overlapping many gratings of scan period;

k _iDynamic strain sensitivity coefficient for i sensing grating of overlapping many gratings.

5. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: said A/D converter (8) adopts multipath high-speed synchronous serial A/D; Can effectively improve based on the demodulation of FPGA and the multi-channel parallel data-handling capacity of control circuit (10) through this design; Reduce the A/D conversion to based on the demodulation of FPGA and the demand of control circuit (10) input and output pin, be convenient to the expansion of more demodulation passages.

6. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: said tunable optic filter (2) adopts the mode of triangular wave or sinusoidal wave symmetrical scanning; And can change output wavelength through the bias voltage and the peak-to-peak value scope of adjustment sweep waveform, on frequency domain so that the output wavelength of each sensing grating is spacedly distributed in overlapping many gratings (5) as far as possible.

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