CN201242451Y - Equipment for demodulating optical fiber grating sensing array - Google Patents

Abstract

The utility model relates to an optical fiber raster sensing array demodulating device. In the device, the input port of a four-port 3-d B optical fiber coupler is connected with a semiconductor laser through an optical fiber isolator, and the output port thereof is connected with a photodiode, a data acquisition card and a FFT analyzer in sequence; the other two ports of the four-port 3-d B optical fiber coupler are connected through a single mode fiber, the single mode fiber is divided into two sections through an electro-optic modulator, namely, a measuring section single mode fiber and a connecting section single mode fiber , and the electrical driving signal port of the electro-optic modulator is electrically connected with a sinusoidal signal generator; a three-port 3-d B optical fiber coupler is inserted in the measuring section single mode fiber, wherein the two ports of the input end are respectively connected with the measuring section single mode fiber, the other port is optically connected with the optical fiber bragg grating sensing array formed through a way that a plurality of optical fiber bragg gratings with the same wavelength with that of the laser light source are connected in series. The optical fiber raster sensing array demodulating device has very fast response speed, thereby meeting real-time sensing requirements and having relatively low cost.

Description

A kind of optical fibre optical grating sensing array demodulation device

Technical field

The utility model belongs to technical field of optical fiber sensing, has related to a kind of optical fibre optical grating sensing array demodulation device.

Background technology

Fiber Bragg Grating FBG (FBG) owing to its distinctive inside of optical fibre sensitivity, Wavelength-encoding, be easy to a kind of important devices that advantages such as networking become Fibre Optical Sensor.Based on wavelength-division multiplex that has grown up (WDM) and Time Division Multiplexing technology, optical fiber optical grating array is widely used in the quasi-distributed sensing of optical fiber, as: the health monitoring of railway, bridge, dam etc., the monitoring temperature that the trunk power transmission line is along the line.Wherein, WDM requires each FBG sensor to have different bragg wavelengths, need a wideband light source (bandwidth is often greater than 40nm) as the input light source, also need the wavelength sensitive system of a cover relative complex to carry out the demultiplexing of multiplexed signals, as: adjustable Fabry Perot wave filter, Fourier spectrometer, wavelength sensitive coupling mechanism etc.And in TDM, generally adopt burst pulse light source input, the reflected light signal of each FBG sensor to utilize different time-delays to realize signal multiplexing, receive the pulse of reflection with the high speed optoelectronic probe, and by the high-speed door treatment circuit demultiplexing of demodulating end.This two covers multiplex technique all needs higher light source of cost and complicated demodulating system, has directly caused the cost of FBG sensing network high, has limited its a lot of practical applications.

Electrooptic modulator utilizes nonlinear effect, can accurately change the frequency through the light wave of modulator within the specific limits; Sarnia gram (Sagnac) ring is because the symmetry of its structure, temperature variation to external world, and mechanical vibration etc. are disturbed insensitive, and at Fibre Optical Sensor, fields such as optical fiber detection are used very extensive; The quasi-distributed sensor array of FBG that use realizes based on the Sagnac ring of electrooptic modulator optical frequency translation, simple in structure, strong interference immunity does not need photovalve at a high speed, and cost is very low, therefore is highly suitable for practical application.

Summary of the invention

The purpose of this utility model is exactly at the deficiencies in the prior art, and a kind of optical fibre optical grating sensing array demodulation device that adopts electrooptic modulator optical frequency translation technology is provided.

Concrete scheme of the present utility model is: semiconductor laser is connected by the input port light of fibre optic isolater with four port 3-dB fiber couplers, the output port of four port 3-dB fiber couplers is connected with the input end light of photodiode, photodiode output is electrically connected with the input end of data collecting card, and the output terminal of data collecting card is electrically connected with the fast fourier transform analyser.

The centre wavelength of described LASER Light Source is at communication band, and its 3dB live width is smaller or equal to 0.1nm.

Two other port of four port 3-dB fiber couplers connects by single-mode fiber, and single-mode fiber is divided into two sections by electrooptic modulator, is respectively measuring section single-mode fiber and linkage section single-mode fiber, and length is respectively L _aAnd L _b, L _aL _b, the electric drive signal mouth of electrooptic modulator is electrically connected with sinusoidal signal generator; Insert three port 3-dB fiber couplers in the measuring section single-mode fiber, the two-port of the input end of three port 3-dB fiber couplers is connected with the measuring section single-mode fiber respectively, and another port is connected with optical fiber Bragg grating sensing array light.

Described optical fiber Bragg grating sensing array is in series by a plurality of Fiber Bragg Grating FBGs consistent with LASER Light Source centre wavelength, and the reflectivity of Fiber Bragg Grating FBG is less than 3%.

In the utility model, electrooptic modulator utilizes nonlinear effect, can accurately change the frequency through the light wave of modulator within the specific limits.Simultaneously, it is insensitive that the Sarnia gram encircles the interference of temperature variation, mechanical vibration etc. to external world.The utility model is applicable to the quasi-distributed sensor array of general Fiber Bragg Grating FBG, compare with traditional scheme, adopted electronic frequency scanning, rather than use the Wavelength scanning device of the machinery control of low speed, can accomplish high response speed, satisfy the requirement of real-time sensing; And owing to do not need short-pulse laser, high-speed photodiode and high-speed data acquisition card, so cost is relatively low; Because sensor array is connected in the Sarnia gram ring, anti-ambient temperature fluctuation of equipment and mechanical disturbance performance are strong in addition.

Description of drawings

Fig. 1 is a structural representation of the present utility model.

Embodiment

As shown in Figure 1, semiconductor laser 1 is connected with an input port light of four port 3-dB fiber couplers 3 by fibre optic isolater 2; Another input port of four port 3-dB fiber couplers 3 is connected with the input end light of photodiode 4, and the output terminal of photodiode 4 is electrically connected with the input end of data collecting card 5, and the output terminal of data collecting card 5 is electrically connected with fft analysis instrument 6.Two output ports of four port 3-dB fiber couplers 3 connect by single-mode fiber, and single-mode fiber is divided into two sections by electrooptic modulator 8, are respectively measuring section single-mode fiber 11 and linkage section single-mode fiber 7, and length is respectively L _aAnd L _b, L _aL _bThe electric drive signal mouth of electrooptic modulator 8 is electrically connected with sinusoidal signal generator 9.The two-port of inserting the input end of three port 3-dB fiber couplers, 10, three port 3-dB fiber couplers 10 in the measuring section single-mode fiber 11 is connected with measuring section single-mode fiber 11 respectively, and another output port is connected with sensor array single-mode fiber 13.A plurality of sensing FBG12 are connected on the sensor array single-mode fiber 13 successively.

In concrete the detection, the laser that semiconductor laser light resource sends by fibre optic isolater and four port 3-dB fiber couplers after, enter in the Sarnia gram ring.

Laser is divided into two-way after entering Sarnia gram ring, wherein one the tunnel enter the known measuring section single-mode fiber of length, incide the optical fiber Bragg grating sensing array that is connected into by a plurality of Fiber Bragg Grating FBGs consistent with LASER Light Source centre wavelength by the three port 3-dB fiber couplers that insert in the measuring section single-mode fiber again, laser is by each Fiber Bragg Grating FBG reflection on the sensor array; Laser after the reflection is got back to the measuring section single-mode fiber through three port 3-dB fiber couplers, produces frequency conversion by electrooptic modulator, and the sinusoidal signal generator that described electrooptic modulator is modulated by frequency drives; Laser after the frequency conversion is got back to four port 3-dB fiber couplers through the known linkage section single-mode fiber of length; Got back to four port 3-dB fiber couplers, its electric field strength E by i Fiber Bragg Grating FBG beam reflected on the sensor array _1-iFor:

$E_{1-i}=-J_1\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)E_i\left\{\begin{array}{c}\exp (i(\mathrm{\ω}-\mathrm{\Ω})t+\mathrm{ni}[\frac{L_a+2L_i}{C}\mathrm{\ω}+\frac{L_b}{C}(\mathrm{\ω}-\mathrm{\Ω})])\\ +\exp (i(\mathrm{\ω}+\mathrm{\Ω})t+\mathrm{ni}[\frac{L_a+2L_i}{C}\mathrm{\ω}+\frac{L_b}{C}(\mathrm{\ω}+\mathrm{\Ω})])\end{array}\right\}---\left(1\right)$

J wherein ₁Be first-order bessel function, α is the normalized amplitude of electrooptic modulator drive signal, E _iBe the electric field intensity of i Fiber Bragg Grating FBG laser light reflected, ω is the angular frequency of laser, and Ω is the angular frequency of electrooptic modulator drive signal.N is the refractive index of single-mode fiber, and C is the light velocity, L _iBe the fiber lengths between i Fiber Bragg Grating FBG and the three port 3-dB fiber couplers, L _aBe the length of measuring section single-mode fiber, L _bBe the length of linkage section single-mode fiber, L _aL _b

Another road laser at first passes through the known linkage section single-mode fiber of length, produces frequency conversion by electrooptic modulator then, and the laser after the frequency conversion enters the known measuring section single-mode fiber of length; Laser incides the optical fiber Bragg grating sensing array by the three port 3-dB fiber couplers that insert in the measuring section single-mode fiber, laser is by each Fiber Bragg Grating FBG reflection on the optical fiber Bragg grating sensing array, laser after the reflection is got back to the measuring section single-mode fiber through three port 3-dB fiber couplers, returns four port 3-dB fiber couplers; Electric field strength E when i Fiber Bragg Grating FBG laser light reflected got back to four port 3-dB fiber couplers on the sensor array _2-iFor:

$E_{2-i}=-J_1\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)E_i\left\{\begin{array}{c}\exp (i(\mathrm{\ω}-\mathrm{\Ω})t+\mathrm{ni}[\frac{L_b}{C}\mathrm{\ω}+\frac{L_a+2L_i}{C}(\mathrm{\ω}-\mathrm{\Ω})])\\ +\exp (i(\mathrm{\ω}+\mathrm{\Ω})t+\mathrm{ni}[\frac{L_b}{C}\mathrm{\ω}+\frac{L_a+2L_i}{C}(\mathrm{\ω}+\mathrm{\Ω})])\end{array}\right\}---\left(2\right)$

Two bundle laser of i Fiber Bragg Grating FBG correspondence interfere the intensity I of the laser of transmission in four port 3-dB fiber couplers _T-iFor:

$I_{T-i}={J_1}^2\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right){\left|E_i\right|}^2\left[\begin{array}{c}4+2\cos \left[2(\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}{L}_b)\right]+2\cos \left[2(\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}(L_a+2L_i))\right]\\ +4\cos \left[(2\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}(L_a+L_b+2L_i))\right]+4\cos \left[\frac{\mathrm{n\Ω}}{C}(L_a+2L_i-L_b)\right]\end{array}\right]---\left(3\right)$

Photodiode is surveyed the intensity of the laser that sees through Sarnia gram ring of i Fiber Bragg Grating FBG correspondence, and light intensity signal is converted into electric signal simultaneously, photodiode be f by frequency _b, f _b＜＜Ω, the light intensity I that receives by photodiode _TFor:

$I_T={J_1}^2\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)\{4+4\cos \left[\frac{\mathrm{n\Ω}}{C}(L_a+2L_i+L_b)\right]\}---\left(4\right)$

The driving frequency Ω of electrooptic modulator makes linear change according to 2 π wt, and by linear sweep, the transmitted light intensity of each sensing FBG laser light reflected is pressed cos (f respectively _iT) change

$f_{i}t=2\mathrm{\πn}\frac{L_a+2L_i-L_b}{C}\mathrm{wt}---\left(5\right)$

F wherein _iFrequency for the light intensity variation.

Electric signal carries out fast Fourier transform (FFT) through data collecting card, obtains each corresponding peak of formula (5) on frequency spectrum.By measuring the frequency f at each peak _iObtain the corresponding position L of sensor fibre Bragg grating on the optical fiber Bragg grating sensing network _i:

$L_i=(\frac{{\mathrm{Cf}}_i}{2\mathrm{\πn\ω}}-L_a+L_b)/2---\left(6\right)$

The intensity at each peak is by the position extent decision of the centre wavelength of each sensing Bragg grating centre wavelength of correspondence and light source on the frequency spectrum.Stress application on each sensor fibre Bragg grating successively makes centre wavelength to the drift of long wave direction, and the change of the intensity at each corresponding peak concerns on the amount of movement of records center wavelength and the frequency spectrum.

Each Fiber Bragg Grating FBG is installed in the environment that needs sensing, and when measured physical quantity changed in the environment, the centre wavelength of each sensor fibre Bragg grating was moved, and caused that the intensity of peak value corresponding on the frequency spectrum changes; The relation of the intensity change at each corresponding peak on amount of movement and the frequency spectrum according to the centre wavelength of record obtains the amount of movement of each Fiber Bragg Grating FBG centre wavelength, finally obtains the environmental physics amount of each Fiber Bragg Grating FBG institute sensing.

The wavelength shift of the centre wavelength of Fiber Bragg Grating FBG and be prior art to the pass between the environmental physics quantitative changeization of inductive sensing (variations such as little curved, temperature, stress).

Claims (1)

1, a kind of optical fibre optical grating sensing array demodulation device, it is characterized in that: semiconductor laser is connected by the input port light of fibre optic isolater with four port 3-dB fiber couplers, the output port of four port 3-dB fiber couplers is connected with the input end light of photodiode, photodiode output is electrically connected with the input end of data collecting card, and the output terminal of data collecting card is electrically connected with the fast fourier transform analyser;

Two other port of four port 3-dB fiber couplers connects by single-mode fiber, and single-mode fiber is divided into two sections by electrooptic modulator, is respectively measuring section single-mode fiber and linkage section single-mode fiber, and length is respectively L _aAnd L _b, L _aL _b, the electric drive signal mouth of electrooptic modulator is electrically connected with sinusoidal signal generator; Insert three port 3-dB fiber couplers in the measuring section single-mode fiber, the two-port of the input end of three port 3-dB fiber couplers is connected with the measuring section single-mode fiber respectively, and another port is connected with optical fiber Bragg grating sensing array light;

The centre wavelength of described LASER Light Source is at communication band, and its 3dB live width is smaller or equal to 0.1nm; Described optical fiber Bragg grating sensing array is in series by a plurality of Fiber Bragg Grating FBGs consistent with LASER Light Source centre wavelength, and the reflectivity of Fiber Bragg Grating FBG is less than 3%.