CN101532850B - Method and device for sensing and demodulating Bragg fiber grating - Google Patents
Method and device for sensing and demodulating Bragg fiber grating Download PDFInfo
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- CN101532850B CN101532850B CN2009100978691A CN200910097869A CN101532850B CN 101532850 B CN101532850 B CN 101532850B CN 2009100978691 A CN2009100978691 A CN 2009100978691A CN 200910097869 A CN200910097869 A CN 200910097869A CN 101532850 B CN101532850 B CN 101532850B
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Abstract
The invention relates to a method and device for sensing and demodulating Bragg fiber grating. The method in the invention uses the principle that chatter fiber grating has different reflective wavelengths at different positions to convert the change of sensed fiber grating wavelength into the change of system optical path difference, and then the optical path difference is measured by low coherent demodulating method, thereby being capable of accurately obtaining wavelength change of sensed fiber grating so as to obtain sensing amount. The device realizing the method comprises a broadband light source at the optical communication band of center wavelength, a fiber optic isolator, a four-port 3-dB optical fiber coupler, a polarization controller, a tunable fiber delay line, a three-port 3-dB optical fiber coupler, a sensing fiber grating, a linear chatter fiber grating, a photodetector and an oscillograph. The invention has higher measurement precision of wavelength resolution, has the advantages of strong anti-interference, simple structure, low cost, and the like, and can obtain different resolutions and parameter ranges, thereby being much applied to practical application.
Description
Technical field
The invention belongs to field of sensing technologies, related to and a kind ofly utilized a linear chirp optical fiber grating as a reference to realize the method for high precision optical fiber grating sensing and demodulating in conjunction with low coherent demodulation technology, and the equipment of realizing this method.
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
Purpose of the present invention is exactly at the deficiencies in the prior art, has proposed the sensing and demodulating Bragg fiber grating scheme of a kind of utilization linear chirp optical fiber grating as a reference in conjunction with low coherent demodulation technology, and the equipment of realizing this method is provided simultaneously.
The inventive 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, wherein a part of 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,
The device of realizing said method 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 present invention 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 inventive method 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 invention.
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,
The direction of positive its wave length shift of negative indication of gained Δ λ value.
Claims (2)
1. the method for a sensing and demodulating Bragg fiber grating is characterized in that this 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, wherein a part of 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; There is optical path difference OPD between the two-way light that converges at three port 3-dB fiber coupler places
1
The a part of light beam of step (2) and another part light beam merge into a branch of light beam that has optical path difference, 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 linear chirp optical fiber grating center reflection wavelength; When the sensor fibre grating since be subjected to the sensing amount 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)
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
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,
2. realize the sensing and demodulating Bragg fiber grating device of method according to claim 1, comprise 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 and the oscillograph of centre wavelength at optical communicating waveband, it is characterized in that: 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.
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| CN101769762B (en) * | 2010-01-29 | 2011-10-19 | 武汉理工大学 | Sensing demodulating system for optical chirped-grating |
| CN101915595B (en) * | 2010-08-11 | 2011-08-31 | 武汉理工大学 | Wavelength division multiplexing network construction method and system based on frequency domain reflection fiber grating sensing technique |
| CN105606039B (en) * | 2015-12-22 | 2018-10-16 | 中国科学院长春光学精密机械与物理研究所 | A kind of method and device of precise measuring source collimation |
| CN105806380B (en) * | 2016-04-06 | 2018-10-02 | 东华大学 | A kind of multiplexing demodulation equipment based on long-period fiber grating reflection sensor |
| JP6989703B2 (en) * | 2017-07-26 | 2022-01-05 | テッラ１５ プロプライエタリー リミテッド | Distributed optical sensing system and method |
| CN108106533A (en) * | 2017-12-21 | 2018-06-01 | 北京信息科技大学 | Realize the long chirped fiber grating sensor-based system of distributed location identification |
| CN108332947B (en) * | 2018-01-16 | 2019-07-19 | 西安交通大学 | A kind of fiber grating refractive index sensing demodulation method based on cutoff wavelength |
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