CN101907495A - Fiber bragg grating wavelength demodulation system with long-period fiber bragg grating Sagnac loop - Google Patents
Fiber bragg grating wavelength demodulation system with long-period fiber bragg grating Sagnac loop Download PDFInfo
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- CN101907495A CN101907495A CN 201010231143 CN201010231143A CN101907495A CN 101907495 A CN101907495 A CN 101907495A CN 201010231143 CN201010231143 CN 201010231143 CN 201010231143 A CN201010231143 A CN 201010231143A CN 101907495 A CN101907495 A CN 101907495A
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Abstract
The invention relates to a fiber bragg grating wavelength demodulation system with a long-period fiber bragg grating Sagnac loop, belonging to the optical fiber sensor field. In the system, the light source of the demodulation system is a line cavity type fiber laser formed by using a fiber Bragg grating (4) and the Sagnac loop (8) with a long-period fiber bragg grating as the endoscopy; one end of the long-period fiber bragg grating (7) is connected with the third port (63) of a 2*2 coupler, the other end of the long-period fiber bragg grating is connected with the fourth port (64) of the 2*2 coupler, thus forming the Sagnac loop with the long-period fiber bragg grating; one end of the fiber Bragg grating is connected with the first port (61) of the 2*2 coupler through an Er-doped fiber (5), the other end is connected with the third port (63) of a wavelength division multiplexer; the second port (32) of the wavelength division multiplexer is connected with a pump light source (2), and the first port (31) of the wavelength division multiplexer is connected with a signal processing system (1). By using the demodulation system of the invention, the defects that signal-to-noise ratio and measurement precision are low and the system is subject to environmental disturbance.
Description
Technical field
The present invention relates to a kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac loop, belong to the fiber optic sensor technology field.
Background technology
Fiber-optic grating sensor has that antijamming capability is strong, good reliability, corrosion-resistant, advantage such as volume is little, in light weight and Wavelength-encoding mode is reliable, is more and more paid attention to by people.How simply, fast, accurately small wavelength shift demodulation is come out this sensor is converted to the variation of grating operation wavelength to the variation of measured parameter,, be vital problem in the fiber-optic grating sensor system.
At present, the Wavelength demodulation technology of fiber grating practicability mainly contains and interferes demodulation techniques, tunable F-P demodulation by filter technology and adopt light spectrum image-forming technology that dispersion element combines with ccd array etc.The Fiber Bragg Grating FBG SI/SM series wavelength demodulation device of U.S. MICRONOPICS company is the representative of optic fiber grating wavelength demodulation field advanced technology.The researcher of various countries has also proposed other demodulation scheme in succession, as matched filtering demodulation technology, linear chirp optical fiber grating demodulation techniques and long period fiber grating edge filter linear demodulation technology etc.
The D.A.Jackson of Britain kent university in 1993 and the people such as L.Reekie of southampton university have reported and have utilized coupling grating filter method that optic fiber grating wavelength is carried out demodulation (simple multiplexingscheme for a fiber optic grating sesnor network, optics letters, Vl.18, No.14 1993:1192-1194), this method is used simple, but the demodulation scope is little.
Propositions such as Zhao D in 2002 and Shu X utilization is contained linear chirp optical fiber grating Sagnac loop demodulation sensor fibre grating wavelength (Sensor Interrogation technique Using Chirped FiberGrating-Based Sagnac Loop, Electron.Lett.Vol.38, No.72002:312-313).
Optics journal 2004 the 24th volume the 2nd phase 199-202 page or leaf has reported that contemporary optics research institute of Nankai University studies long period fiber grating edge filter linear demodulation system.This demodulating system comprises: signal processing system, long period fiber grating, Fiber Bragg Grating FBG, wideband light source.Owing to adopted the lower wideband light source of power, detected signal a little less than, cause making an uproar than low, measuring accuracy is restricted.
The Zhan Yage of Donghua University etc. has proposed the high temperature fiber grating sensing system (CN 201034747Y) of long period fiber grating demodulation.Cardinal principle is to utilize long period fiber grating that wideband light source is modulated, produce one in particular range of wavelengths intensity be the light source of linear change.Again this light source is incided the sensor fibre grating, the luminous power after its reflection is detected, reach the purpose of Wavelength demodulation.
Comprehensive above-mentioned several wavelength demodulation schemes adopt the light source of wideband light source as sensor-based system more, by detecting the narrow-band spectrum through the fiber grating reflection, realize Wavelength demodulation.But the wide spectrum light source power that this wavelength demodulation scheme adopts is low, and has only the light in the fiber grating reflection bandwidth to be detected, and causes the Signal-to-Noise that detects lower, reduced the measuring accuracy of wavelength, and stability is subject to environmental interference.
Summary of the invention
Technical matters to be solved by this invention is that the signal to noise ratio (S/N ratio) of existing demodulating system is lower, and measuring accuracy is low, is subject to the defective of environmental interference.A kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac-ring is proposed.
Technical scheme of the present invention:
A kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac loop.The light source of this Wavelength demodulation system is that Fiber Bragg Grating FBG constitutes line chamber type fiber laser with the Sagnac loop that contains long period fiber grating as the chamber mirror.
The Sagnac loop that contains long period fiber grating comprises: 2 * 2 coupling mechanisms and long period fiber grating; One end of long period fiber grating is connected with the 3rd port of 2 * 2 coupling mechanisms, and the 4th port of the other end of long period fiber grating and 2 * 2 coupling mechanisms is connected, and forms the Sagnac loop that contains long period fiber grating.
One end of Fiber Bragg Grating FBG is connected with first port of 2 * 2 coupling mechanisms by Er-doped fiber.
The other end of Fiber Bragg Grating FBG is connected with the 3rd port of wavelength division multiplexer, and second port of wavelength division multiplexer is connected with pump light source, and first port of wavelength division multiplexer is connected with signal processing system.
Beneficial effect of the present invention:
1) the present invention does not need special wavelength measurement equipment, only needs the exploring laser light output power value, according to the linear relationship of wavelength and laser power value, just can demodulate the skew of Fiber Bragg Grating FBG operation wavelength, greatly reduces the cost of system.
2) the present invention can realize high s/n ratio, high-acruracy survey.Adopt wideband light source to compare with the traditional fiber Bragg grating sensing system, the present invention adopts and contains long period fiber grating Sagnac loop and fiber grating formation laser structure, and output power is very high.Under same environmental conditions, improve measuring-signal signal to noise ratio (S/N ratio) and measuring accuracy greatly.
3) measurement dynamic range of the present invention and measurement sensitivity are all adjustable.The measurement dynamic range of the big more system of the range of linearity of the long period fiber grating master's loss peak both sides transmission spectrum that adopts is big more, and the precipitous degree of linear transmission spectrum is high more, and it is high more that sensitivity is measured in the measurement of system.So, can be according to selecting different long period fiber grating to regulate the measurement dynamic range of Fiber Bragg Grating FBG Wavelength demodulation system involved in the present invention and measuring sensitivity.
Description of drawings
A kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac-ring of Fig. 1.
Fig. 2 contains the Sagnac loop reflectance spectrum of long period fiber grating.
One of transmission spectrum of the Fiber Bragg Grating FBG that Fig. 3 adopts.
Two of the transmission spectrum of the Fiber Bragg Grating FBG that Fig. 4 adopts.
Among the figure: signal processing system 1, pump light source 2, wavelength division multiplexer 3, Fiber Bragg Grating FBG 4, Er-doped fiber 5,2 * 2 coupling mechanisms 6, long period fiber grating 7, contain the Sagnac loop 8 of long period fiber grating.
Embodiment
The invention will be further described in conjunction with the accompanying drawings.
A kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac loop, the light source of this Wavelength demodulation system are that Fiber Bragg Grating FBG 4 constitutes line chamber type fiber laser with the Sagnac loop 8 that contains long period fiber grating as the chamber mirror.
The Sagnac loop 8 that contains long period fiber grating comprises: 2 * 2 coupling mechanisms 6 and long period fiber grating 7; One end of long period fiber grating 7 is connected with the 3rd port 63 of 2 * 2 coupling mechanisms, and the 4th port 64 of the other end of long period fiber grating 7 and 2 * 2 coupling mechanisms is connected, and forms the Sagnac loop 8 that contains long period fiber grating.
One end of Fiber Bragg Grating FBG 4 is connected with first port 61 of 2 * 2 coupling mechanisms by Er-doped fiber 5.
The other end of Fiber Bragg Grating FBG 4 is connected with the 3rd port 33 of wavelength division multiplexer, and second port 32 of wavelength division multiplexer is connected with pump light source 2, and first port 31 of wavelength division multiplexer is connected with signal processing system 1.
Described long period fiber grating 7 is to make according to the long period fiber grating research and development proposal of 2000 the 20th the 5th phases of volume of optics journal Beijing Jiaotong University's lightwave technology research institute report.This long period fiber grating adopts the amplitude mask plate to be made by the high frequency excimer laser, and behind annealing experiment, at normal temperatures, the transmission spectrum shape has long stability.The main loss peak wavelength of long period fiber grating 7 is 1548.431nm, and main loss peak both sides transmissivity is linear change with wavelength.
The described Sagnac loop 8 that contains long period fiber grating is consistent with the transmission spectrum shape of long period fiber grating 7 at the reflectance spectrum of first port 61 of 2 * 2 coupling mechanisms.Its reflectance spectrum as shown in Figure 2, its main loss peak is 1548.431nm, main loss peak left side is the linear trailing edge of the reflectance spectrum of the Sagnac loop that contains long period fiber grating, and its right side is to contain under the linearity of reflectance spectrum of Sagnac loop of long period fiber grating to rise the limit.
Described pump light source 2 adopts 980nm, 1380nm all can.
Described wavelength division multiplexer 3 adopts 980nm/1550nm or 1380nm/1550nm.When pump light source 2 adopted 980nm, 3 of wavelength division multiplexers adopted 980nm/1550nm; When pump light source 2 adopted 980nm, 3 of wavelength division multiplexers adopted 1380nm/1550nm.
Described Er-doped fiber 5, doping content scope are 700ppm～1000ppm, and length range is 1m～2m.
The peak wavelength of described Fiber Bragg Grating FBG 4 is 1544.394nm or 1550.243nm.When selecting Fiber Bragg Grating FBG 4 shown in Figure 3 for use, its peak wavelength and peak reflectivity are respectively 1544.394nm and 89.53% (transmission depth of 9.8dB), are positioned at the linear trailing edge that contains long period fiber grating Sagnac loop reflectance spectrum.External parameter causes Fiber Bragg Grating FBG 4 operation wavelengths when the long wavelength drifts about, and the sensor output intensity is along with wavelength linear reduces.When selecting Fiber Bragg Grating FBG 4 shown in Figure 4 for use, its peak wavelength and peak reflectivity are respectively 1550.243nm and 96.84% (transmission depth of 15dB), are positioned at the linear rising edge of the Sagnac loop reflectance spectrum that contains long period fiber grating.External parameter causes the Fiber Bragg Grating FBG operation wavelength when the long wavelength drifts about, and the sensor output intensity is along with wavelength linear increases.
Introduce the principle of utilizing the Sagnac loop demodulation Fiber Bragg Grating FBG wavelength that contains long period fiber grating below.When first port 61 incidents of light, can detect reflectance spectrum at this port 61 from 2 * 2 coupling mechanisms of the Sagnac loop 8 that contains long period fiber grating.This reflectance spectrum is consistent with long period fiber grating 7 transmission spectrum shapes.Comprise a main absorption loss peak in the reflectance spectrum, its reflectivity is reduce (or the increase) of linear (the linear fit error is in the 10-4 magnitude) in the wavelength coverage that the strength degradation limit (or rising edge) of main loss peak is comprised.It has constituted two chamber mirrors of line chamber type laser instrument with the Fiber Bragg Grating FBG 4 of using sensing head, when drift takes place the Fiber Bragg Grating FBG operation wavelength, will produce a LASER Light Source with Wavelength strength generation linear change (descend or rise).By the detection laser output intensity, just can realize demodulation to the Fiber Bragg Grating FBG operation wavelength.
Claims (3)
1. optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac loop, this Wavelength demodulation system comprises: signal processing system, long period fiber grating, Fiber Bragg Grating FBG, light source;
It is characterized in that: light source is that Fiber Bragg Grating FBG (4) constitutes line chamber type fiber laser with the Sagnac loop (8) that contains long period fiber grating as the chamber mirror;
The Sagnac loop (8) that contains long period fiber grating comprising: 2 * 2 coupling mechanisms (6) and long period fiber grating (7); One end of long period fiber grating (7) is connected with the 3rd port (63) of 2 * 2 coupling mechanisms, and the 4th port (64) of the other end of long period fiber grating (7) and 2 * 2 coupling mechanisms is connected, and forms the Sagnac loop (8) that contains long period fiber grating;
One end of Fiber Bragg Grating FBG (4) is connected with first port (61) of 2 * 2 coupling mechanisms by Er-doped fiber (5);
The other end of Fiber Bragg Grating FBG (4) is connected with the 3rd port (33) of wavelength division multiplexer, and second port (32) of wavelength division multiplexer is connected with pump light source (2), and first port (31) of wavelength division multiplexer is connected with signal processing system (1).
2. a kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac-ring according to claim 1 is characterized in that:
Described long period fiber grating (7) is that employing amplitude mask plate is made by the high frequency excimer laser, and behind annealing experiment, at normal temperatures, the transmission spectrum shape has long stability, and main loss peak both sides transmissivity is linear change with wavelength.
3. a kind of optic fiber grating wavelength demodulating system that contains the long period fiber grating Sagnac-ring according to claim 1 and 2 is characterized in that:
The described Sagnac loop (8) that contains long period fiber grating is consistent with the transmission spectrum shape of long period fiber grating (7) at the reflectance spectrum of first port (61) of 2 * 2 coupling mechanisms.
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103166094A (en) * | 2013-02-20 | 2013-06-19 | 广东汉唐量子光电科技有限公司 | High-pulse-contrast-ratio nanosecond fiber laser |
| CN103368045A (en) * | 2013-07-04 | 2013-10-23 | 中国科学院上海光学精密机械研究所 | Narrow-linewidth single-frequency fiber laser based on all-fiber slow-light element |
| CN104019760A (en) * | 2014-06-23 | 2014-09-03 | 上海交通大学 | Sensitivity enhancement demodulation method and device of fiber optical Bragg grating strain sensor |
| CN108534811A (en) * | 2018-04-13 | 2018-09-14 | 西安工业大学 | A kind of cavity length demodulating algorithm of short cavity optical fiber Fabry-Perot sensor |
| CN109494555A (en) * | 2018-12-29 | 2019-03-19 | 北京信息科技大学 | Adjustable optic fibre laser based on cascaded fiber grating combination Sagnac ring |
| CN112432724A (en) * | 2020-12-01 | 2021-03-02 | 东北林业大学 | Stress sensor based on vernier effect of optical fiber resonant cavity and stress measurement method |
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| CN101013792A (en) * | 2007-02-05 | 2007-08-08 | 北京交通大学 | Linear tunable single-frequency single-polarization fiber laser |
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| CN201213194Y (en) * | 2008-06-03 | 2009-03-25 | 北京交通大学 | Linear cavity multiple wavelength dual path outputting optical fiber laser |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103166094A (en) * | 2013-02-20 | 2013-06-19 | 广东汉唐量子光电科技有限公司 | High-pulse-contrast-ratio nanosecond fiber laser |
| CN103368045A (en) * | 2013-07-04 | 2013-10-23 | 中国科学院上海光学精密机械研究所 | Narrow-linewidth single-frequency fiber laser based on all-fiber slow-light element |
| CN104019760A (en) * | 2014-06-23 | 2014-09-03 | 上海交通大学 | Sensitivity enhancement demodulation method and device of fiber optical Bragg grating strain sensor |
| CN108534811A (en) * | 2018-04-13 | 2018-09-14 | 西安工业大学 | A kind of cavity length demodulating algorithm of short cavity optical fiber Fabry-Perot sensor |
| CN108534811B (en) * | 2018-04-13 | 2020-11-27 | 西安工业大学 | Cavity length demodulation algorithm of short-cavity optical fiber Fabry-Perot sensor |
| CN109494555A (en) * | 2018-12-29 | 2019-03-19 | 北京信息科技大学 | Adjustable optic fibre laser based on cascaded fiber grating combination Sagnac ring |
| CN112432724A (en) * | 2020-12-01 | 2021-03-02 | 东北林业大学 | Stress sensor based on vernier effect of optical fiber resonant cavity and stress measurement method |
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