CN103604446A

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

Info

Publication number: CN103604446A
Application number: CN201310538011.0A
Authority: CN
Inventors: 杨昌喜; 梅佳伟
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2013-11-04
Filing date: 2013-11-04
Publication date: 2014-02-26
Anticipated expiration: 2033-11-04
Also published as: CN103604446B

Abstract

A multi-channel fiber grating absolute wavelength demodulation system based on a single detector, including a broadband light source, a circulator, a reference fiber grating, a 1×N optical switch, an N-way sensing fiber grating array, a tunable filter, and a photodetector and a data acquisition card; the present invention provides a demodulation method based on the system at the same time. The broadband light source generates light, which is divided into transmitted light and reflected light by two reference fiber gratings after passing through the circulator, wherein the transmitted light enters 1× N optical switch, the strobe signal generated by the data acquisition card controls the light to enter the corresponding sensing fiber grating channel, the reflected light returns to the tunable filter through the circulator, and the reflected light of the sensing fiber grating also enters the tunable filter through the circulator. tuned filter, the sweeping light is received by the photodetector, the spectral signal is converted into a time-domain signal, and then demodulated to obtain the relative position of the reference fiber grating and the sensing fiber grating. The present invention can simplify the system structure and eliminate the Wavelength measurement error introduced by transmission.

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

1. A multi-channel fiber grating absolute wavelength demodulation system based on single detector, is characterized in that, comprises:

broadband light source (1);

A circulator (2), the first port of which is connected to the light source emitted by the broadband light source (1);

The reference fiber grating (3) is located on the light source route out of the second port of the circulator (2);

1×N optical switch (4), the input end of which is connected to the light source of the reference fiber grating (3);

N sensing fiber gratings (5), respectively located on the optical paths of the N output ends of the 1×N optical switch (4);

A tunable filter (6), the input terminal of which is connected to the third port of the circulator (2);

A photodetector (7), the input terminal of which is connected to the output terminal of the tunable filter (6);

The data acquisition card (8), the input end of which is connected to the output end of the photodetector (7), simultaneously generates the gating signal for gating the 1×N optical switch (4) and the scanning voltage for driving the tunable filter (6) Signal.

2. The multi-channel fiber Bragg grating absolute wavelength demodulation system based on a single detector according to claim 1, characterized in that the reference fiber Bragg grating (3) is used as a wavelength reference, and the center wavelength of the reference fiber Bragg grating (3) at both ends of the scanning spectrum.

3. The single-detector-based multi-channel fiber grating absolute wavelength demodulation system according to claim 1 or 2, characterized in that there are two reference fiber gratings (3), which are arranged in series on the light source route.

4. The single-detector-based multi-channel FBG absolute wavelength demodulation system according to claim 3, characterized in that the central wavelength of the sensing FBG (5) is located at the center of the two reference FBGs (3) between wavelengths.

5. The demodulation method based on the described system of claim 1, is characterized in that, comprises the steps:

The broadband light source (1) generates light, which is divided into transmitted light and reflected light by two reference fiber gratings (3) after passing through the circulator (2), and the transmitted light enters the 1×N optical switch (4) The gating signal generated by the acquisition card (8) controls the light to enter the corresponding sensing fiber grating channel (5), the reflected light returns to the tunable filter (6) through the circulator (2), and the sensing fiber grating (5) The reflected light also enters the tunable filter (6) through the circulator (2), and the swept light is received by the photodetector (7), and the spectral signal is converted into a time domain signal, and then demodulated to obtain a reference fiber grating ( 3) and the relative position of the sensing fiber grating (5).

6. The demodulation method according to claim 5, characterized in that, the scanning voltage of the frequency scanning filter (6) is a triangular wave or a sawtooth wave.

7. The demodulation method according to claim 5, characterized in that the method of demodulating the time-domain signal is: first determine the time-domain position of the reflection peak of the reference fiber grating (3) according to the scanning electrical signal, and then determine The time-domain position of the reflection peak of the sensing optical fiber grating (5) is calculated, and the relative change of the time-domain position of the sensing optical fiber grating (5) is calculated by an interpolation method, so as to realize the demodulation of the optical fiber grating.

8. according to the described demodulation method of claim 5, it is characterized in that, in order to realize the continuous simultaneous demodulation of N channel fiber gratings, the strobe signal of cycle is produced by data acquisition card, this cycle is synchronous with scanning voltage, promptly every Make one channel strobe in one scan cycle, and cycle in turn.