CN103604446A - Multi-channel fiber bragg grating absolute wavelength demodulation system based on single detector and method thereof - Google Patents

Multi-channel fiber bragg grating absolute wavelength demodulation system based on single detector and method thereof Download PDF

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Publication number
CN103604446A
CN103604446A CN201310538011.0A CN201310538011A CN103604446A CN 103604446 A CN103604446 A CN 103604446A CN 201310538011 A CN201310538011 A CN 201310538011A CN 103604446 A CN103604446 A CN 103604446A
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grating
light
demodulation
fiber bragg
circulator
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CN103604446B (en
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杨昌喜
梅佳伟
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Tsinghua University
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Tsinghua University
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Abstract

A multi-channel fiber bragg grating absolute wavelength demodulation system based on a single detector comprises a broadband light source, a circulator, reference fiber bragg gratings, a 1*N optical switch, N-path sensing fiber bragg grating arrays, a tunable filter, a photoelectric detector and a data acquisition card. The invention simultaneously provides a demodulation method based on the system. The method is characterized in that the broadband light source generates light; the light passes through the circulator, then passes through the two reference fiber Bragg gratings and then is divided into transmission light and reflected light; the transmission light enters into the 1*N optical switch; a gating signal generated by the data acquisition card makes the light enter into a corresponding sensing fiber bragg grating channel; the reflected light enters into the tunable filter via the circulator; reflected light of a sensing fiber bragg grating also enters into the tunable filter via the circulator; frequency sweeping light is received by the photoelectric detector; a spectrum signal is converted into a time domain signal; then demodulation is performed so that a relative position of the reference fiber bragg gratings and the sensing fiber bragg grating is acquired. By using the system and the method of the invention, the system structure can be simplified and a wavelength measurement error caused by optical fiber transmission is eliminated.

Description

A kind of multi-channel fiber Bragg grating absolute wavelength demodulating system and method based on simple detector
Technical field
The invention belongs to technical field of optical fiber sensing, particularly a kind of multi-channel fiber Bragg grating absolute wavelength demodulating system and method based on simple detector.
Background technology
Along with developing rapidly of Fibre Optical Communication Technology, fiber Bragg grating sensor is more and more paid close attention to as a kind of novel senser element of realizing strain and temperature sensing.Than traditional electricity, optical strain sensor, fiber grating has distinct advantages, as highly sensitive, because transducing signal is that Wavelength-encoding is not subject to electromagnetic interference (EMI), is easy to multiplexing and can realizes quasi-distributed sensing, in fields such as civilian structure, Aero-Space, boats and ships shipping, petrochemical complex and medical science, be widely used at present.Wavelength variations for demodulating fiber bragg grating, people have proposed a lot of demodulation schemes, such as: coupling grating filter method, CCD demodulation method and Fabry Perot demodulation scheme etc., recently sweeping laser device is also applied in fiber grating demodulation, by being that time domain changes by the change transitions of the centre wavelength of fiber grating, can realizing fast demodulation and meet the multiplexing requirement of many fiber optics.
In traditional frequency sweep demodulation method, frequency sweep light has all been divided into reference path and sensing light path, in reference path, placed the spectrum positioning devices such as fiber grating, FP chamber etalon, acetylene absorption line and be used for calibrating the wavelength shake of swept light source, reference signal is converted to by photodetector that electric signal enters demodulation module and transducing signal is compared.Sensing light path can form ,Mei road a plurality of fiber gratings of having connected by multi-channel parallel.Minute being arranged of reference path and sensing light path increased the complexity of system, and each passage sensing light path all needs to configure a detector, and detector quantity is too much.In addition often far away apart from swept light source for remote recording sensor fibre grating, so Transmission Fibers is longer, and the long like this transmission time can be added in last demodulation result, causes the measuring error of wavelength.When frequency sweep light transmits in long-distance optical fiber, can introduce non-linear and dispersion simultaneously, reduce demodulation accuracy.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, the object of the present invention is to provide a kind of multi-channel fiber Bragg grating absolute wavelength demodulating system and method based on simple detector, can also eliminate the wavelength measurement error of introducing because of Optical Fiber Transmission by simplied system structure.
To achieve these goals, the technical solution used in the present invention is:
A multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector, comprising:
Wideband light source 1;
Circulator 2, its first port connects the light source that wideband light source 1 is launched;
Reference optical fiber grating 3, is positioned on the light source route of circulator 2 second ports;
1 * N photoswitch 4, its input end picks out the light source of reference optical fiber grating 3;
N sensor fibre grating 5, lays respectively in the output terminal light path of 1 * N photoswitch 4N road;
Tunable optic filter 6, its input end connects circulator 2 the 3rd port;
Photodetector 7, its input termination tunable optic filter 6 output terminals;
Data collecting card 8, its input termination photodetector 7 output terminals produce for the gating signal of gating 1 * N photoswitch 4 and the scanning voltage signal that drives tunable optic filter 6 simultaneously.
Wherein, using described reference optical fiber grating 3 is two, and as wavelength reference, series connection is arranged on light source route.。
Preferably, the centre wavelength of reference optical fiber grating 3 is positioned at the two ends of scanning optical spectrum.
Preferably, the centre wavelength of described sensor fibre grating 5 is between the centre wavelength of two reference optical fiber gratings 3.
The present invention provides the demodulation method based on described demodulating system simultaneously, comprises the steps:
Wideband light source 1 produces light, after circulator 2, through two reference optical fiber gratings 3, be divided into transmitted light and reflected light two parts again, wherein transmitted light enters 1 * N photoswitch 4, the gating signal being produced by data collecting card 8 is controlled light and is entered corresponding sensor fibre grating passage 5, reflected light returns through circulator 2 and enters tunable optic filter 6, the reflected light of sensor fibre grating 5 returns also and enters tunable optic filter 6 through circulator 2, frequency sweep transmitted light is received by photodetector 7, convert spectral signal to time-domain signal, then carry out demodulation, obtain the relative position of reference optical fiber grating 3 and sensor fibre grating 5.
Preferably, the scanning voltage of described swept filter 6 is triangular wave or sawtooth wave.
Preferably, first according to scanning electric signal, determine the reflection peak time-domain position of reference optical fiber grating 3, then determine the reflection peak time-domain position of sensor fibre grating 5, according to go out the relative variation of the time-domain position of sensor fibre grating 5 by interpolation calculation with reference to reflection peak time-domain position, realize optic fiber grating wavelength demodulation.
Preferably, in order to realize the continuous while demodulation of N passage fiber grating, produced the gating signal of circulation by data collecting card, this cycle period is synchronizeed with scanning voltage, i.e. in each scan period, make a-road-through road gating, successively circulation.
Compared with prior art, the invention has the beneficial effects as follows:
1. by adopting fiber grating as with reference to standard of wavelength, can realize the series connection of reference path and sensing light path, can share a detector, simplify light channel structure and circuit structure, improve collection and demodulation speed.
2. by adopting photoswitch light splitting scheme to substitute traditional coupling mechanism light splitting scheme, improved the reflective light intensity of each sensing passage, improved the signal to noise ratio (S/N ratio) of restituted signal, and reduced detector array, use just detectable N road sensor array of a detector, simplified light channel structure and circuit structure.
3. adopt wideband light source first after sensing grating through the scheme of tunable optic filter, can eliminate while transmitting in optical fiber because of transducing signal the measuring error that transducing signal absolute wavelength that the transmission time stack that produces causes is measured, can realize absolute wavelength and measure, improve demodulation accuracy.
By tunable optic filter as for after fiber grating, shortened the light path of swept filter and detector, dispersion and non-linear the caused time demodulation error that can avoid frequency sweep light to introduce because of long optical fibers, improve the precision of demodulation.
Accompanying drawing explanation
Fig. 1 is the structural representation of this demodulation method.
Fig. 2 is this demodulation method schematic diagram.
Fig. 3 is the signal schematic representation of this demodulation method, wherein Fig. 3 (a) be sensing with reference to reflectance spectrum signal graph (the c port outgoing spectrum of circulator), Fig. 3 (b) is transducing signal and the time-domain signal figure of reference signal after wave filter.
Embodiment
Below in conjunction with drawings and Examples, describe embodiments of the present invention in detail.
As shown in Figure 1, wideband light source 1 be one with output tail optical fiber light source, its output light is through circulator 2 by the reference optical fiber grating 3 antireflection part light of two series connection, and reflected light consists of two narrow band light, and the centre wavelength of narrow band light corresponds respectively to the central wavelength lambda of two reference optical fiber gratings 3 ref1and λ ref2, reflected light incides tunable optic filter 6 through the b of circulator 2 port, c port successively.Wideband light source 1 arrives corresponding sensor fibre grating 5 place passages through the transmitted light of reference optical fiber grating 3 through 1 * N photoswitch 4 (N=4), wherein data collecting card 8 produces the corresponding passage of gating signal gating (00 → 1 passage, 01 → 2 passage, 10 → 3 passages, 11 → 4 passages).After broadband light is reflected by the sensor fibre grating 5 in passage, its reflected signal is via the c port of 1 * N photoswitch 4 (N=4) and circulator 2, merge with reflection reference signal, its spectrogram is as shown in Fig. 3 (a), then incident tunable optic filter 6 in the lump, tunable optic filter 6 is realized linear frequency sweep under triangular voltage sweep driving effect, in this process, spectral signal can be converted into time domain light intensity signal, wavelength signals changes into time-domain signal, as shown in Figure 3 (b), by photodetector 7, received, convert analog electrical signal to and enter the demodulation module based on data collecting card 8, now can carry out by measuring the relative position of crest the variation of measuring optical fiber raster center wavelength, realize fiber grating demodulation.The concrete grammar of demodulation of the present invention as shown in Figure 2, first analog electrical signal is carried out to digital-to-analog conversion, then carry out digital filtering, utilize peak-seeking algorithm to find all peak dots in one-period, then take triangular signal minimum point as starting point, the peak dot of finding the two ends in half period, this is reference signal, determines the position t at reference optical fiber optical grating reflection peak by suitable peak-seeking threshold value and peak width are set ref1and t ref2, being then positioned at two peak-to-peak all peak dots of sensing, these peak dots are the position at sensor fibre optical grating reflection peak, and wherein certain the sensor fibre grating of take is example, and establishing its time location is t sensor, by method of interpolation, just can calculate sensor fibre raster center wavelength like this there is corresponding relation in the variation of centre wavelength and extraneous sensing amount, therefore can realize the sensing of physical quantity.

Claims (8)

1. the multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector, is characterized in that, comprising:
Wideband light source (1);
Circulator (2), its first port connects the light source that wideband light source (1) is launched;
Reference optical fiber grating (3), is positioned on the light source route of circulator (2) second ports;
1 * N photoswitch (4), its input end picks out the light source of reference optical fiber grating (3);
N sensor fibre grating (5), lays respectively in the output terminal light path of 1 * N photoswitch (4) N road;
Tunable optic filter (6), its input end connects circulator (2) the 3rd port;
Photodetector (7), its input termination tunable optic filter (6) output terminal;
Data collecting card (8), its input termination photodetector (7) output terminal produces for the gating signal of gating 1 * N photoswitch (4) and the scanning voltage signal that drives tunable optic filter (6) simultaneously.
2. the multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector according to claim 1, it is characterized in that, use described reference optical fiber grating (3) as wavelength reference, and the centre wavelength of reference optical fiber grating (3) is positioned at the two ends of scanning optical spectrum.
3. according to the multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector described in claim 1 or 2, it is characterized in that, described reference optical fiber grating (3) is two, and series connection is arranged on light source route.
4. the multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector according to claim 3, is characterized in that, the centre wavelength of described sensor fibre grating (5) is positioned between the centre wavelength of two reference optical fiber gratings (3).
5. the demodulation method based on system described in claim 1, is characterized in that, comprises the steps:
Wideband light source (1) produces light, after circulator (2), through two reference optical fiber gratings (3), be divided into transmitted light and reflected light two parts again, wherein transmitted light enters 1 * N photoswitch (4), the gating signal being produced by data collecting card (8) is controlled light and is entered corresponding sensor fibre grating passage (5), reflected light returns through circulator (2) and enters tunable optic filter (6), the reflected light of sensor fibre grating (5) returns also and enters tunable optic filter (6) through circulator (2), frequency sweep light is received by photodetector (7), convert spectral signal to time-domain signal, then carry out demodulation, obtain the relative position of reference optical fiber grating (3) and sensor fibre grating (5).
6. demodulation method according to claim 5, is characterized in that, the scanning voltage of described swept filter (6) is triangular wave or sawtooth wave.
7. demodulation method according to claim 5, it is characterized in that, the described method that time-domain signal is carried out to demodulation is: the reflection peak time-domain position of first determining reference optical fiber grating (3) according to scanning electric signal, then determine the reflection peak time-domain position of sensor fibre grating (5), the relative variation that goes out the time-domain position of sensor fibre grating (5) by interpolation calculation, realizes fiber grating demodulation.
8. demodulation method according to claim 5, is characterized in that, in order to realize the continuous while demodulation of N passage fiber grating, by data collecting card, produced the gating signal of circulation, this cycle period is synchronizeed with scanning voltage, i.e. in each scan period, make a-road-through road gating, successively circulation.
CN201310538011.0A 2013-11-04 2013-11-04 A kind of demodulation method of the multi-channel fiber Bragg grating absolute wavelength demodulating system based on simple detector Expired - Fee Related CN103604446B (en)

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CN104297852A (en) * 2014-10-13 2015-01-21 武汉邮电科学研究院 Multi-input multi-output optical node based on single wavelength selection switch and implementation method thereof
CN105783948A (en) * 2016-03-25 2016-07-20 北京信息科技大学 FBG sensor system based on cooperation of multiple sensing modules
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CN111006600A (en) * 2019-10-31 2020-04-14 中国空间技术研究院 System for measuring satellite temperature and deformation quantity by using fiber bragg grating

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CN108387251B (en) * 2018-01-22 2020-07-14 大连理工大学 Fiber grating demodulation instrument and method

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CN105783948A (en) * 2016-03-25 2016-07-20 北京信息科技大学 FBG sensor system based on cooperation of multiple sensing modules
CN105783948B (en) * 2016-03-25 2018-02-06 北京信息科技大学 A kind of FBG sensor system based on the cooperation of more sensing modules
CN107655503A (en) * 2017-08-29 2018-02-02 北京航空航天大学 A kind of multi-channel optical fibre grating sensor demodulation method based on optical switch stack
CN110806234A (en) * 2019-10-28 2020-02-18 中广核核电运营有限公司 Optical fiber grating sensing equipment
CN111006600A (en) * 2019-10-31 2020-04-14 中国空间技术研究院 System for measuring satellite temperature and deformation quantity by using fiber bragg grating

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