阅读说明：本技术 一种密集光纤光栅阵列解调的装置和方法 (Device and method for demodulating dense fiber bragg grating array ) 是由 周斌 郭昌建 季戌涛 安倩 于 2020-06-03 设计创作，主要内容包括：本发明公开了一种密集光纤光栅阵列解调的装置和方法,该装置包括上位机、控制采集板卡、用于发射不同波长的激光发射装置、m×n式光纤耦合器、1×2式光纤耦合器、光纤光栅阵列、光探测器。其中,光纤光栅阵列为光纤光栅链路多通道排列的复合结构,其单链光纤上刻有不同波长的弱反射光纤光栅,形成密集光纤光栅阵列。该方法是光纤光栅阵列中的光纤光栅受环境变化影响导致反射谱中心波长位移,发生位移的偏移量引起反射信号功率的变化,通过分析回波信号中光纤光栅阵列的中心波长,与校准的光纤光栅阵列中心波长对比从而实现快速解调。本发明实现了数量巨大的光纤光栅传感器快速解调,拓宽了光纤光栅传感的应用领域,应用场合广泛。(The invention discloses a device and a method for demodulating a dense fiber grating array, wherein the device comprises an upper computer, a control acquisition board card, a laser emitting device for emitting different wavelengths, an mxn type fiber coupler, a 1 × 2 type fiber coupler, a fiber grating array and a light detector. The fiber grating array is a composite structure with fiber grating links arranged in a multi-channel mode, weak reflection fiber gratings with different wavelengths are engraved on single-chain fibers of the fiber grating array, and a dense fiber grating array is formed. The method is characterized in that the central wavelength of a reflection spectrum is displaced due to the influence of environmental changes on the fiber bragg grating in the fiber bragg grating array, the power of a reflected signal is changed due to the offset of the displacement, and the central wavelength of the fiber bragg grating array in an echo signal is analyzed and compared with the central wavelength of the calibrated fiber bragg grating array, so that the rapid demodulation is realized. The invention realizes the rapid demodulation of the fiber grating sensors with huge number, widens the application field of the fiber grating sensors and has wide application occasions.)

1. A device for demodulating a dense fiber grating array is characterized by comprising an upper computer, a control acquisition board card, a laser emitting device for emitting different wavelengths, an mxn type fiber coupler, a 1 × 2 type fiber coupler, a fiber grating array and a light detector, wherein in the mxn type fiber coupler, m is more than or equal to 1, and n is more than 1;

the laser emission device and the 1 x 2 type optical fiber coupler are respectively connected with the mxn type optical fiber coupler, N sensing optical fiber links in the optical fiber grating array are respectively connected with the 1 x 2 type optical fiber coupler, the 1 x 2 type optical fiber coupler and the control acquisition board card are respectively connected with the optical detector, the laser emission device and the upper computer are respectively connected with the control acquisition board card, the optical fiber grating array is a composite structure formed by multi-channel arrangement of the optical fiber grating links, and a plurality of weak reflection optical fiber gratings are engraved on a single optical fiber chain and arranged to form the optical fiber grating array.

2. The apparatus according to claim 1, wherein the laser emitting device is a laser array, the laser wavelength of each laser of the laser array is in different wavelength channels, and the central wavelength interval between adjacent wavelength channels is above 1 nm.

3. The apparatus according to claim 2, wherein each laser of the laser array can change wavelength within a small range by changing temperature or current, and the wavelength tunable range is a wavelength channel range in which each laser is located.

4. The apparatus for demodulating dense fiber grating array according to claim 1, wherein the laser emitting device is a wavelength tunable laser, the laser wavelength of the wavelength tunable laser can change the wavelength in a wide range, and the wavelength tunable range includes the wavelengths of all the fiber gratings on the fiber grating array.

5. The apparatus according to claim 1, wherein the fiber grating is a broad-spectrum weak-reflection fiber grating with a maximum reflectivity of 1% and a minimum full width at half maximum of 0.5 nm.

6. The apparatus for demodulating dense fiber grating array as claimed in claim 1, wherein the fiber grating array on the single fiber chain is divided into multiple groups, the fiber gratings in the same group have different bragg wavelengths and are located on different wavelength channels, and the bragg wavelengths of the fiber gratings in other groups are their repetitions; the fiber gratings in the same group are distributed on the sensing optical fiber at positions adjacent to each other and located at the same section of the sensing optical fiber, and the fiber gratings in different groups are located at different sections of the sensing optical fiber.

7. The method for adjusting the device for dense fiber grating array demodulation according to claim 2, wherein the method is based on a pulsed laser time division multiplexing and wavelength division multiplexing method, and specifically comprises:

step one, fiber grating array spectrum calibration:

(1) placing the fiber grating array in a calibration environment with known temperature and strain;

(2) each laser in the laser array is controlled to sequentially emit pulse laser, the pulse laser is incident to the sensing optical fiber, the pulse laser is reflected by each fiber grating to form a reflected light signal, the reflected light signal is converted into an electric signal by the optical detector through the 1 x 2 type fiber coupler, the reflecting moments of the fiber gratings at different positions are different, the positions of the fiber gratings in the fiber grating array can be distinguished, and the intensity of the electric signal is acquired through the control acquisition board card;

(3) driving each laser in the laser array one by one to scan and change the wavelength in the adjustable range of the laser array, repeating the step (2), obtaining the spectrum of each fiber grating in the fiber grating array, recording the spectrum, and simultaneously recording the environmental temperature and the strain value of each fiber grating to realize spectrum calibration;

step two, fast demodulation of the fiber grating array:

(4) placing the fiber bragg grating array in an environment to be measured;

(5) fixing the wavelength of each laser in the laser array, enabling the wavelength to be positioned on the bevel edge of the sensing fiber grating, obtaining the reflection intensity of each fiber grating in a time division multiplexing working mode, and comparing the obtained reflection intensity of each fiber grating with the reflection spectrum of each fiber grating recorded in the first step to obtain the spectrum drift value of each fiber grating so as to realize a rapid demodulation process;

(6) pausing (5) at intervals, repeating (3) to perform spectrum calibration to obtain the maximum reflection value of each fiber grating in the fiber grating array, taking the obtained maximum reflection value of each fiber grating as the reflection value of each fiber grating Bragg wavelength, modifying the fiber grating spectrum recorded in (3) according to the obtained maximum reflection value, and then entering the second step again;

(7) and the acquisition board card is controlled to acquire signals of different channels, so that simultaneous measurement of the multi-fiber link is finally realized.

8. The method of claim 7, wherein the intensity of each laser of the laser array is sinusoidally modulated and the frequency of the sinusoidal modulation varies linearly.

9. The method of claim 7, wherein each laser of the laser array is a pulsed laser.

10. The method for adjusting the device for dense fiber grating array demodulation according to claim 2, wherein the method is based on a frequency division multiplexing and wavelength division multiplexing method of sine-modulated laser, and specifically comprises:

step one, fiber grating array spectrum calibration:

(1) placing the fiber grating array in a calibration environment with known temperature and strain;

(2) the lasers in the laser array are controlled to work in sequence, the intensity of the lasers is modulated in a sine mode when the lasers work, and the frequency of the sine modulation changes linearly. The modulated laser enters the sensing optical fiber, is reflected by each fiber grating to form a reflected light signal, is converted into an electric signal by the optical detector through the 1 x 2 type fiber coupler, is reflected by the fiber gratings at different positions, and can be distinguished by detecting that the frequency difference between the frequency of the reflected light signal and the local modulation frequency is different. The intensity of the electric signal is acquired by controlling the acquisition board card. The acquired signals are subjected to frequency spectrum transformation to obtain frequency and intensity information, and the frequency and intensity information is recorded;

(3) driving each laser in the laser array one by one to scan the variable wavelength within the adjustable range of the laser and repeating the step (2); acquiring and recording the spectrum of each fiber grating in the fiber grating array, and simultaneously recording the environmental temperature and the strain value of each fiber grating to realize spectrum calibration;

step two, fast demodulation of the fiber grating array:

(4) placing the fiber bragg grating array in an environment to be measured;

(5) fixing the wavelength of each laser in the laser array, enabling the wavelength to be positioned on the bevel edge of the sensing fiber grating, obtaining the reflection intensity of each fiber grating in a frequency division multiplexing working mode, and comparing the obtained reflection intensity of each fiber grating with the reflection spectrum of each fiber grating recorded in the first step to obtain the spectrum drift value of each fiber grating so as to realize a rapid demodulation process;

(6) pausing (5) at intervals, repeating (3) to perform spectrum calibration to obtain the maximum reflection value of each fiber grating in the fiber grating array, taking the obtained maximum reflection value of each fiber grating as the reflection value of each fiber grating Bragg wavelength, modifying the fiber grating spectrum recorded in (3) according to the obtained maximum reflection value, and then entering the second step again;

(7) the signals of different channels are collected by controlling the collection board card, and simultaneous measurement of multiple sensing optical fiber links is finally realized.

Technical Field

The invention relates to the field of fiber grating demodulation technology research, in particular to a device and a method for dense fiber grating array demodulation.

Background

Fiber Bragg Gratings (FBGs) are very sensitive to changes in temperature and strain, and thus become a very important sensing device in the industry. At present, the quasi-distributed fiber grating temperature demodulation technology is widely applied to a plurality of fields such as petroleum transmission pipelines, transmission lines, transformer substations, tunnels, large buildings, rails and the like, the traditional demodulation technology mainly utilizes the wavelength division multiplexing principle to realize the demodulation of the fiber gratings, however, the number of the fiber gratings which can be multiplexed on a single fiber is at most dozens at present due to the limited number of wavelength channels, and the quasi-distributed fiber grating temperature demodulation technology is not suitable for a plurality of applications which need mass sensors.

To overcome the above problems, the academia and the industry have started to research dense fiber grating arrays. The demodulation mode of the dense fiber grating array in the academic world and the industrial world is still more preliminary, and the existing research results and patents include: invention patent application No.: 201611039334.5 perimeter intrusion system of fiber grating array, high reflectivity fiber grating array is divided into groups, the wavelength of each fiber grating in each group is identical, and the wavelength can be displayed on spectrum as long as there is a fiber grating wavelength change in the group. The method improves the number of the fiber gratings which can be connected in series on a single sensing fiber to a certain extent, but the change of any one fiber grating cannot be demodulated, so the application is limited; the invention patent application No. 201510297907.3, high resolution dense fiber grating layout method, proposes that multiple fibers of staggered inscribing fiber gratings are placed in parallel, and the fiber gratings on adjacent fibers are spaced at a proper distance, thereby improving the fiber grating number and spatial resolution of the whole fiber cluster, belonging to the space division multiplexing and wavelength division multiplexing mode. 2012, a Large Serial Time-division multiplexed Fiber Bragg Grating Sensor Network proposes to realize Fiber Grating multiplexing based on a Time division multiplexing technology, and 2016, an interconnection of a Sensor Array of an identified Fiber Bragg Grating using Dispersive coherent OFDR based on a frequency division multiplexing technology proposes to realize Fiber Grating multiplexing based on a frequency division multiplexing technology.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a device and a method for demodulating a dense fiber grating array.

In order to achieve the purpose, the invention adopts the following technical scheme:

a device for demodulating a dense fiber grating array comprises an upper computer, a control acquisition board card, a laser emission device for emitting different wavelengths, an mxn type fiber coupler, a 1 × 2 type fiber coupler, a fiber grating array and a photodetector, wherein in the mxn type fiber coupler, m is more than or equal to 1, and n is more than 1;

the laser emission device and the 1 x 2 type optical fiber coupler are respectively connected with the mxn type optical fiber coupler, N sensing optical fiber links in the optical fiber grating array are respectively connected with the 1 x 2 type optical fiber coupler, the 1 x 2 type optical fiber coupler and the control acquisition board card are respectively connected with the optical detector, the laser emission device and the upper computer are respectively connected with the control acquisition board card, the optical fiber grating array is a composite structure formed by multi-channel arrangement of the optical fiber grating links, and a plurality of weak reflection optical fiber gratings are engraved on a single optical fiber chain and arranged to form the optical fiber grating array.

As a preferred technical solution, the laser emitting device is a laser array, the laser wavelength of each laser of the laser array is in a different wavelength channel, and the center wavelength interval between adjacent wavelength channels is more than 1 nm.

As a preferred technical solution, each laser of the laser array can change the wavelength within a small range by changing the temperature or the current, and the wavelength tunable range is the wavelength channel range in which each laser is located.

As a preferred technical solution, the laser emitting device is a wavelength tunable laser, the wavelength of the laser wavelength of the wavelength tunable laser can be changed in a wide range, and the wavelength tunable range includes the wavelengths of all fiber gratings on the fiber grating array.

As a preferable technical solution, the fiber grating is a wide-spectrum weak reflection fiber grating, the maximum reflectivity of the fiber grating is 1%, and the minimum spectrum full width at half maximum is 0.5 nm.

As a preferred technical scheme, the fiber grating arrays on the single fiber chains are divided into a plurality of groups, the fiber gratings in the same group have different bragg wavelengths and are located on different wavelength channels, and the bragg wavelengths of the fiber gratings in other groups are the repetition thereof; the fiber gratings in the same group are distributed on the sensing optical fiber at positions adjacent to each other and located at the same section of the sensing optical fiber, and the fiber gratings in different groups are located at different sections of the sensing optical fiber.

A method for adjusting a device for dense fiber grating array demodulation is based on a method of pulse laser time division multiplexing and wavelength division multiplexing, and specifically comprises the following steps:

step one, fiber grating array spectrum calibration:

(1) placing the fiber grating array in a calibration environment with known temperature and strain;

(2) each laser in the laser array is controlled to sequentially emit pulse laser, the pulse laser is incident to the sensing optical fiber, the pulse laser is reflected by each fiber grating to form a reflected light signal, the reflected light signal is converted into an electric signal by the optical detector through the 1 x 2 type fiber coupler, the reflecting moments of the fiber gratings at different positions are different, the positions of the fiber gratings in the fiber grating array can be distinguished, and the intensity of the electric signal is acquired through the control acquisition board card;

(3) driving each laser in the laser array one by one to scan and change the wavelength in the adjustable range of the laser array, repeating the step (2), obtaining the spectrum of each fiber grating in the fiber grating array, recording the spectrum, and simultaneously recording the environmental temperature and the strain value of each fiber grating to realize spectrum calibration;

step two, fast demodulation of the fiber grating array:

(4) placing the fiber bragg grating array in an environment to be measured;

(5) fixing the wavelength of each laser in the laser array, enabling the wavelength to be positioned on the bevel edge of the sensing fiber grating, obtaining the reflection intensity of each fiber grating in a time division multiplexing working mode, and comparing the obtained reflection intensity of each fiber grating with the reflection spectrum of each fiber grating recorded in the first step to obtain the spectrum drift value of each fiber grating so as to realize a rapid demodulation process;

(6) pausing (5) at intervals, repeating (3) to perform spectrum calibration to obtain the maximum reflection value of each fiber grating in the fiber grating array, taking the obtained maximum reflection value of each fiber grating as the reflection value of each fiber grating Bragg wavelength, modifying the fiber grating spectrum recorded in (3) according to the obtained maximum reflection value, and then entering the second step again;

(7) and the acquisition board card is controlled to acquire signals of different channels, so that simultaneous measurement of the multi-fiber link is finally realized.

As a preferred solution, the intensity of each laser of the laser array is sinusoidally modulated, and the frequency of the sinusoidal modulation varies linearly.

Preferably, each laser of the laser array is a pulsed laser.

A method for adjusting a device for demodulating a dense fiber grating array is based on a frequency division multiplexing and wavelength division multiplexing method of sine modulation laser, and specifically comprises the following steps:

step one, fiber grating array spectrum calibration:

(1) placing the fiber grating array in a calibration environment with known temperature and strain;

(2) the lasers in the laser array are controlled to work in sequence, the intensity of the lasers is modulated in a sine mode when the lasers work, and the frequency of the sine modulation changes linearly. The modulated laser enters the sensing optical fiber, is reflected by each fiber grating to form a reflected light signal, is converted into an electric signal by the optical detector through the 1 x 2 type fiber coupler, is reflected by the fiber gratings at different positions, and can be distinguished by detecting that the frequency difference between the frequency of the reflected light signal and the local modulation frequency is different. The intensity of the electric signal is acquired by controlling the acquisition board card. The acquired signals are subjected to frequency spectrum transformation to obtain frequency and intensity information, and the frequency and intensity information is recorded;

(3) driving each laser in the laser array one by one to scan the variable wavelength within the adjustable range of the laser and repeating the step (2); acquiring and recording the spectrum of each fiber grating in the fiber grating array, and simultaneously recording the environmental temperature and the strain value of each fiber grating to realize spectrum calibration;

step two, fast demodulation of the fiber grating array:

(4) placing the fiber bragg grating array in an environment to be measured;

(5) fixing the wavelength of each laser in the laser array, enabling the wavelength to be positioned on the bevel edge of the sensing fiber grating, obtaining the reflection intensity of each fiber grating in a frequency division multiplexing working mode, and comparing the obtained reflection intensity of each fiber grating with the reflection spectrum of each fiber grating recorded in the first step to obtain the spectrum drift value of each fiber grating so as to realize a rapid demodulation process;

(6) pausing (5) at intervals, repeating (3) to perform spectrum calibration to obtain the maximum reflection value of each fiber grating in the fiber grating array, taking the obtained maximum reflection value of each fiber grating as the reflection value of each fiber grating Bragg wavelength, modifying the fiber grating spectrum recorded in (3) according to the obtained maximum reflection value, and then entering the second step again;

(7) the signals of different channels are collected by controlling the collection board card, and simultaneous measurement of multiple sensing optical fiber links is finally realized.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the invention is suitable for fiber grating demodulation, and compared with the traditional fiber grating demodulation system, the demodulation target of the invention is a sensing array formed by dense weak reflection fiber gratings. The fiber gratings in the sensing array are arranged according to a specific mode, and the number of the fiber gratings which can be multiplexed on the single-chain fiber is increased to the maximum by adopting time division multiplexing, frequency division multiplexing and wavelength division multiplexing modes.

2. The invention adopts the method of fixing the laser wavelength to the position of the optical fiber grating spectrum bevel edge and detecting the reflection intensity, thereby realizing the demodulation of the highest speed.

3. The invention adopts an optical fiber structure, monitoring signals can be transmitted for a long distance, and remote online monitoring can be realized.

4. The fiber bragg grating adopted by the invention is easy to realize the parallel connection of the multi-channel fiber links and realize the simultaneous multi-point detection.

Drawings

FIG. 1 is a schematic diagram of the structure of the apparatus of the present invention;

FIG. 2 is a schematic diagram of a structure after replacing part of the device

Fig. 3 is a schematic structural diagram of a fiber grating array in the device of the present invention.

Detailed Description

In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.