CN201392205Y - A Fiber Bragg Grating Sensing Demodulation Device - Google Patents

Abstract

The utility model relates to a fiber Bragg grating sensing demodulation device which comprises a wideband light source whose center wavelength is located on an optical communication waveband, an optical fiber separator, a four-port 3-d B optical fiber coupler, a polarization controller, an adjustable optical fiber delay line, a three-port 3-d B optical fiber coupler, a sensing optical fiber grating, a linear chirped fiber grating, a photoelectric detector and an oscillograph. By utilizing the principle that the different positions of the chirped fiber grating have different reflecting wavelengths, the fiber Bragg grating sensing demodulation device can convert the variations of the sensing optical fiber grating wavelength into the variation of the system optical path difference, then detects the optical path difference by the method of low coherent demodulation, can accurately obtain the wavelength variation of the sensing optical fiber grating, and further obtains the sensing quantity. The fiber Bragg grating sensing demodulation device has strong interference resistance, simple structure and low cost, can obtain different resolution factor and parameter range, and is especially suitable for the actual use.

Description

A kind of sensing and demodulating Bragg fiber grating device

Technical field

The utility model belongs to field of sensing technologies, relates to a kind of sensing and demodulating Bragg fiber grating device.

Background technology

Bragg grating (FBG) owing to its distinctive inside of optical fibre sensitivity, Wavelength-encoding, be easy to advantage such as networking and become a kind of important devices of Fibre Optical Sensor and be used widely, as: the health monitoring of railway, bridge, dam etc., the monitoring temperature that the trunk power transmission line is along the line etc.Traditional fiber grating demodulation method often adopts the optical filter demodulation method, as tunable F-P filter method, and coupling raster method etc.These methods or higher to the performance requirement of optical filter, cost is higher; Perhaps need more optical filter, the higher and complex structure of cost has limited its popularization in actual applications.

Advantages such as coherent demodulation is a kind of new fiber grating sensing demodulation scheme that occurs in recent years, and it has simple in structure, and is cheap.But existing optical fiber grating sensing coherent demodulation scheme all is based on the intensity demodulation of the amplitude of surveying interference signal, and interference signal intensity is subjected to light source stability, fibre loss and some other environmental uncertainty influences, so the measuring accuracy of intensity demodulation scheme has been subjected to certain restriction.In addition, existing coherent demodulation scheme can only be measured the variable quantity of grating wavelength, is toward long wave or the variation of shortwave direction and can not measure it.

Summary of the invention

The purpose of this utility model is exactly at the deficiencies in the prior art, and a kind of sensing and demodulating Bragg fiber grating device is provided.

The utility model comprises wideband light source, fibre optic isolater, four port 3-dB fiber couplers, Polarization Controller, adjustable optic fibre lag line, three port 3-dB fiber couplers, sensor fibre grating, linear chirp optical fiber grating, photodetector, the oscillograph of centre wavelength at optical communicating waveband.The light output end of wideband light source is connected with the input port light of fibre optic isolater, and the output terminal of fibre optic isolater is connected with the input port light of four port 3-dB fiber couplers; Two output port homonymies of four port 3-dB fiber couplers, one of them output port is connected with the input end light of Polarization Controller, and the output terminal of Polarization Controller is connected with a port light of three port 3-dB fiber coupler dual-port ends; Another output port of four port 3-dB fiber couplers is connected with an end light of adjustable optic fibre lag line, and the other end of adjustable optic fibre lag line is connected with another port light of three port 3-dB fiber coupler dual-port ends; The port of three port 3-dB fiber coupler single port ends is connected with an end light of sensor fibre grating, the other end of sensor fibre grating is connected with linear chirp optical fiber grating light by optical fiber, and the fiber core layer effective refractive index of the optical fiber of the optical fiber at sensor fibre grating place, the optical fiber at linear chirp optical fiber grating place and connection sensor fibre grating and linear chirp optical fiber grating is identical; Four port 3-dB fiber coupler are connected with the light signal input end of photodetector with another port input port homonymy, and the electrical signal of photodetector is connected with oscillograph.

The utility model utilizes the different principle of chirped fiber grating diverse location reflection wavelength, the variation of sensor fibre grating wavelength is converted into the variation of system's optical path difference, measure this optical path difference by low coherent demodulation method then, can accurately obtain the wavelength variations of sensor fibre grating, and then obtain the sensing amount.The utility model can reach very high wavelength resolution and measuring accuracy, has strong interference immunity, simple in structure, advantage such as with low cost, and can obtain different resolution and parameter scope by selecting for use different chirped fiber gratings as a reference to reach, be highly suitable for practical application.

Description of drawings

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

Embodiment

As shown in Figure 1, a kind of sensing and demodulating Bragg fiber grating device comprises wideband light source 1, fibre optic isolater 2, four port 3-dB fiber couplers 3, Polarization Controller 4, adjustable optic fibre lag line 8, three port 3-dB fiber couplers 5, sensor fibre grating 6, linear chirp optical fiber grating 7, photodetector 10, the oscillograph 9 of centre wavelength at optical communicating waveband.The light output end of wideband light source 1 is connected with the input port light of fibre optic isolater 2, and the output terminal of fibre optic isolater 2 is connected with the input port light of four port 3-dB fiber couplers 3; Two output port homonymies of four port 3-dB fiber couplers 3, one of them output port is connected with the input end light of Polarization Controller 4, and the output terminal of Polarization Controller 4 is connected with a port light of three port 3-dB fiber couplers, 5 dual-port ends; Another output port of four port 3-dB fiber couplers 3 is connected with an end light of adjustable optic fibre lag line 8, and the other end of adjustable optic fibre lag line 8 is connected with another port light of three port 3-dB fiber couplers, 5 dual-port ends; The port of three port 3-dB fiber couplers, 5 single port ends is connected with an end light of sensor fibre grating 6, the other end of sensor fibre grating 6 is connected with linear chirp optical fiber grating 7 light by optical fiber, and the fiber core layer effective refractive index of the optical fiber of the optical fiber at sensor fibre grating place, the optical fiber at linear chirp optical fiber grating place and connection sensor fibre grating and linear chirp optical fiber grating is identical; Four port 3-dB fiber coupler 3 are connected with the light signal input end of photodetector 10 with another port input port homonymy, and the electrical signal of photodetector 10 is connected with oscillograph 9.

Concrete demodulation method may further comprise the steps:

Step (1) centre wavelength is divided into two parts light beam that intensity equates after light beam that the wideband light source of optical communicating waveband sends is by fibre optic isolater and four port 3-dB fiber couplers, part light beam is regulated its polarization state by Polarization Controller, and another part light beam postpones its light path by the adjustable optic fibre lag line; A part of light beam and another part light beam behind the optical path delay after polarization state is regulated converge by one three port 3-dB fiber coupler; Four port 3-dB fiber couplers and three port 3-dB fiber couplers and Polarization Controller, adjustable optic fibre lag line constitute the Mach-Ze Deer interferometer of a non-equiarm, have optical path difference OPD between the two-way light that converges at three port 3-dB fiber coupler places ₁, its size is by the difference decision of the brachium of Mach-Ze Deer interferometer two arms of non-equiarm;

The a part of light beam of step (2) and another part light beam merge into a branch of light beam of optical path difference that exists successively by sensor fibre grating and linear chirp optical fiber grating as a reference to be demodulated, and by these two optical grating reflections, the bragg wavelength of being answered for the sensor fibre grating pair wherein by the wavelength of sensor fibre optical grating reflection, the wavelength that is reflected by linear chirp optical fiber grating is the bragg wavelength of linear chirp optical fiber grating correspondence; The bragg wavelength that the linear chirp optical fiber grating diverse location is corresponding different, the chirp rate of linear chirp optical fiber grating is that a, length are l _c, then the bandwidth of its reflection wavelength is | λ | and=al _c, the bragg reflection wavelength λ of sensor fibre grating under free state _sIdentical with chirped fiber grating center reflection wavelength; When the sensor fibre grating since be subjected to that sensing amount (as temperature, stress etc.) waits influence reflection wavelength take place big or small when drifting about for Δ λ, on sensor fibre grating reflection light and the linear chirp optical fiber grating with the direct optical path difference OPD of the reflected light of its identical wavelength location ₂For

OPD ₂＝2n _eff(l ₀+l _c/2+Δλ/a)，(1)

The fiber core layer effective refractive index of the optical fiber of the optical fiber at sensor fibre grating place, the optical fiber at linear chirp optical fiber grating place and connection sensor fibre grating and linear chirp optical fiber grating is identical, is n _Eff, the length that connects the optical fiber of sensor fibre grating and linear chirp optical fiber grating is l ₀

Step (3) exists the light beam of optical path difference to be introduced new optical path difference after sensor fibre grating and the linear chirp optical fiber grating reflection successively, by being divided into two parts folded light beam that intensity equates behind the three port 3-dB fiber couplers, part folded light beam is regulated its polarization state by Polarization Controller, and another part folded light beam postpones its light path by the adjustable optic fibre lag line; A part of folded light beam after polarization state is regulated and another part folded light beam behind the optical path delay are received by photodetector by four port 3-dB fiber couplers coupling back, and the optical path difference OPD of two parts folded light beam after the coupling is

OPD＝OPD ₂-2OPD ₁，(2)

Step (4) is regulated the length of adjustable optic fibre lag line, thereby changes optical path difference OPD ₁, regulate Polarization Controller simultaneously interference signal is obviously shown, work as OPD=OPD ₂-2OPD ₁=0 o'clock, obtain interference signal on the photodetector, show by oscillograph; And obtain the wavelength variable quantity Δ λ of sensor fibre grating, $\mathrm{\Δ\λ}=(\frac{{\mathrm{OPD}}_1}{n_{\mathrm{eff}}}-l_0-\frac{l_c}{2})\×a.$ The direction of positive its wave length shift of negative indication of gained Δ λ value.

Claims (1)

1. A fiber Bragg grating sensing demodulation device, including a broadband light source with a central wavelength in the optical communication band, a fiber optic isolator, a four-port 3-dB fiber coupler, a polarization controller, an adjustable fiber delay line, and a three-port 3 -dB fiber optic coupler, sensing fiber grating, linear chirped fiber grating, photodetector, oscilloscope, characterized in that: the optical output end of the broadband light source is optically connected to the input port of the fiber isolator, and the output end of the fiber isolator is connected to the optical fiber isolator The input port of the four-port 3-dB fiber coupler is optically connected; the two output ports of the four-port 3-dB fiber coupler are on the same side, one of the output ports is optically connected to the input end of the polarization controller, and the output end of the polarization controller It is optically connected to one port of the dual-port end of the three-port 3-dB fiber coupler; the other output port of the four-port 3-dB fiber coupler is optically connected to one end of the adjustable fiber delay line, and the other end of the adjustable fiber delay line is connected to the The other port of the two-port end of the three-port 3-dB fiber coupler is optically connected; the port at the single-port end of the three-port 3-dB fiber coupler is optically connected to one end of the sensing fiber grating, and the other end of the sensing fiber grating is connected to the linear through the optical fiber. Chirped fiber grating optical connection, the effective refractive index of the fiber core layer of the optical fiber where the sensing fiber grating is located, the optical fiber where the linear chirped fiber grating is located, and the fiber connecting the sensing fiber grating and the linear chirped fiber grating are the same; four ports 3 The other port of the -dB fiber optic coupler on the same side as the input port is connected to the optical signal input end of the photodetector, and the electrical signal output end of the photodetector is connected to an oscilloscope.

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