CN102879022B - Method and device for demodulating fiber bragg grating (FBG) sensor - Google Patents

Method and device for demodulating fiber bragg grating (FBG) sensor Download PDF

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CN102879022B
CN102879022B CN201210362260.4A CN201210362260A CN102879022B CN 102879022 B CN102879022 B CN 102879022B CN 201210362260 A CN201210362260 A CN 201210362260A CN 102879022 B CN102879022 B CN 102879022B
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fbg
comb filter
wavelength
reflective
sensor
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CN102879022A (en
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高少锐
张小平
柴伊琦
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HANGZHOU UNIONOPT Ltd
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HANGZHOU UNIONOPT Ltd
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Abstract

The invention discloses a method and a device for demodulating a fiber bragg grating (FBG) sensor. The method comprises the following steps of: controlling a wavelength scanning laser device to generate narrow-band scanning laser rays with continuously changed wavelengths by using a computer; splitting beams of the narrow-band scanning laser rays generated by the wavelength scanning laser device; enabling a generated reflection spectrum to enter a photoelectric detector again via an optical fiber coupler to be converted into electric signals after the beam-split narrow-band scanning laser rays respectively enter the FBG sensor to be measured and a reflecting FBG comb filter with a temperature compensation package function via the optical fiber coupler, and acquiring the electric signals by the computer after the electric signals are amplified; obtaining wavelengths of peaks of the reflecting FBG comb filter with the temperature compensation package function by the computer through a peak-detection algorithm; calibrating the reflection spectrum of the FBG sensor by the wavelengths; and calculating an absolute wavelength value of the FBG sensor.

Description

A kind of demodulation method of FBG sensor and device
Technical field
The present invention relates to a kind of demodulation method and device of FBG sensor, belong to technical field of optical fiber sensing.
Background technology
Fiber-optic grating sensor reliability is high, anti-electromagnetic interference capability is strong, corrosion-resistant.Especially, the quasi-distributed measurement advantage on its Wavelength-encoding characteristic and single fiber is that other sensor institute is incomparable, has broad application prospects.But one of main obstacle of current limit fibre grating sensor large-scale practical application is the demodulation to fiber grating sensor wavelength signal.
Experiencing the development of two more than ten years, there is multiple fiber grating demodulation technology in optical fiber grating sensing field.Classic demodulation techniques comprises spectrometer detection method, matched FBG demodulation method, non-equilibrium Mach-Zeng Deer interferometric method, tunable F-P demodulation by filter method and tunable narrow-band laser demodulation method etc.In numerous demodulation techniques, system architecture is different, and performance differs, but from aspect Integrated comparative such as signal to noise ratio (S/N ratio), resolution, spectral range, demodulation speed and capacity, only tunable narrow-band laser demodulation method possesses significant advantage, and engineering practicability is strong.
The existing laser instrument of tunable narrow-band on a large scale comprises core component tunable TEA CO2 laser.Tunable TEA CO2 laser is due to the restriction of the manufacturing process of device own, and when repeatedly scanning, by the impact of electromagnetic induction and electric charge sluggishness etc., can not scan all inregisters, consequent systematic error seriously reduces the accuracy of detection of whole demodulating system at every turn.In addition, the piezoelectric ceramics of tunable TEA CO2 laser is easily subject to the impact of ambient temperature and service time and offsets, and this also can cause adverse effect to the accuracy of detection of system.In order to avoid this situation, need one to calibrate the scanning wavelength of tunable TEA CO2 laser not by the exact references grating that the external condition such as environment temperature, stress affects, ensure that demodulating system is to the accuracy of detection of sensing grating to be measured.
By wavelength calibration, demodulation accuracy and the measurement range of demodulating system accurately can be determined.Immobilize with reference to the position of grating within the scan period, by sensing grating to be measured in the position of scan period in contrast than, namely by calculating the centre wavelength of the reflecting light obtaining this sensing grating to be measured, realize accurately detecting.
Ideally, the reference grating that demodulating system uses is two.According to the Wavelength distribution situation of sensing grating to be measured, choose the centre wavelength that its spectral range two ends are reference grating, and make to keep constant environment temperature with reference to grating and without strain, guarantee that the centre wavelength with reference to grating is not drifted about.Carry out with reference to the centre wavelength of grating and the scanning voltage of system position and the scanning voltage one_to_one corresponding that linear fit makes centre wavelength, the centre wavelength of the sensing grating to be measured now recorded can be calculated according to magnitude of voltage.
But in fact, the position of centre wavelength and scanning voltage are not simple linear relationship, adopt two errors with reference to grating approach still larger.In order to improve the accuracy of detection of demodulating system further, five, nine and even more reference grating, i.e. comb filter can be increased to reference to the number of grating from two.
Although the number from theory with reference to grating is more, the interval divided by scanning voltage is more, and the fit correlation formula of reference grating wavelength and scanning voltage is close to reality, and accuracy of detection is higher.But use in practical operation more multiple reference light grid time, with reference to grating need connected and carry out constant temperature and without strain encapsulation, considerably increase complexity.Therefore, the number of reference grating unrestrictedly can not be increased in order to improve measuring accuracy.A feasible solution adopts the fiber comb filter based on F-P wave filter, avoid the complicacy of multiple independent reference gratings in series and encapsulation, as described in document " research of high-speed high capacity fiber Bragg grating (FBG) demodulator " (Acta Optica, the 32nd volume the 3rd phase in 2012).
Comb filter, the i.e. wave filter of spectral shape as comb, its kind is a lot of.Common comb filter mainly contains Mach-Zeng Deer interferometer comb filter, F-P interferometer comb filter and Comb-filter With Fiber Gratings.Although Mach-Zeng Deer interferometer comb filter structure is simple, with low cost, its temperature drift coefficient is comparatively large, and insertion loss is large, generally not as the wavelength reference device of fiber Bragg grating (FBG) demodulator.Due to the comb filter technology maturation of F-P interferometer, commercial degree is high, is used widely in fiber Bragg grating (FBG) demodulator.F-P wave filter is made up of two pieces of dull and stereotyped P1, P2 of parallel placement, and two dull and stereotyped relative faces are coated with the film of high reflectance.Usually the F-P wave filter that two dull and stereotyped spacings are fixing is called F-P etalon.But the measure of precision of the comb filter of F-P interferometer is high, manufacturing process is comparatively complicated, needs equally to use constant-temperature circuit to make it keep constant temperature, otherwise will seriously reduce the measuring accuracy of (FBG) demodulator as during wavelength reference device.
Fiber Bragg Grating technology is developed so far existing 30 years, and technology maturation, reliability is high.Adopt Fiber Bragg Grating technology can produce multiple comb filter equally, and have compact conformation, spectrum shape is customizable, and dirigibility is large, makes the advantages such as relatively simple.A kind of comb filter based on fiber grating reported by document " Comb-filter With Fiber Gratings and the application in novel wavelength selectable laser thereof " (Acta Optica, the 24th volume the 6th phase in 2004), and have eight reflectance spectrums, reflectivity consistance is good.Therefore, by improving the manufacture craft based on the comb filter of Fiber Bragg Grating technology, can be fiber Bragg grating (FBG) demodulator and the High Performance Fiber Gratings comb filter possessing good wavelength reference ability is provided.
Summary of the invention
The object of the invention is to, a kind of demodulation method and device of FBG sensor is provided.It can improve the demodulation accuracy of FBG sensor, and can reduce the manufacture difficulty of the demodulating equipment of FBG sensor.
Technical scheme of the present invention: a kind of demodulation method of FBG sensor, be characterized in, comprise: make the Wavelength-swept laser generation wavelength continually varying narrow band scanning laser that computerizeds control, narrow band scanning laser again by producing Wavelength-swept laser carries out beam splitting, narrow band scanning laser after beam splitting is respectively after the reflective FBG comb filter that fiber coupler enters FBG sensor to be measured and band temperature compensation packaging (including but not limited to that bimetallic material physical construction compensates and thermostat compensates), produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength at reflective each peak of FBG comb filter reflectance spectrum of band temperature compensation packaging by peak-seeking algorithm, and demarcate with the reflectance spectrum of this wavelength to FBG sensor, calculate the absolute wavelength values of FBG sensor.
The demodulation method of above-mentioned FBG sensor, also comprise: the narrow band scanning laser of Duo Fen mono-road Wavelength-swept laser generation again, this road narrow band scanning laser enters with reference to FBG through fiber coupler, or directly connect with reflective FBG comb filter with reference to FBG, with reference to FBG produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength with reference to each peak of FBG reflectance spectrum by peak-seeking algorithm, according to different from reference to FBG temperature control after reflective FBG comb filter band temperature compensation packaging, choose a certain reflection peak of reflective FBG comb filter as benchmark, when Wavelength-swept laser continuous sweep, calculate wavelength difference Δ λ between this reflection peak benchmark and reference FBG reflection peak, namely laser scanning is recorded to the wavelength location be scanned with reference to FBG reflection peak moment reflective FBG comb filter, and laser scanning is to the wavelength location in reflective FBG comb filter a certain baseline reflectance peak moment, both differences are Δ λ (because reflective FBG comb filter is different from the temperature control with reference to FBG, gap is obvious, therefore, under different temperatures, both Δ λ are different, as the Δ λ of Fig. 4 t1with Δ λ t2shown in), by the scale function of FBG comb filter, measure a certain baseline reflectance peak of reflective FBG comb filter under different temperatures and the Δ λ with reference to FBG, draw the once linear function of Δ λ and Current Temperatures, in actual demodulation process, according to the current Δ λ value obtained, instead can release current temperature, then the accurate wavelength of reflective FBG comb filter under drawing this temperature current according to the temperature response curve of reflective FBG comb filter, thus realize the real-time accurate temperature compensation to reflective FBG comb filter.
In the demodulation method of aforesaid FBG sensor, described reflective FBG comb filter is in same optical fiber, arrange different FBG of multiple cycle by Fiber Bragg Grating technology, and its reflectance spectrum is comb δ function formula.The method for making of reflective FBG comb filter can be overlapping write raster method, amplitude samples raster method and phase sample raster method etc.Overlapping write raster method is the grating utilizing universal optical fibre preparing grating technology (mask plate method, double beam interferometry) to write multiple different cycles in same section of region of optical fiber, to obtain the fiber bragg grating device that reflectance spectrum has the comb δ function formula of multiple wavelength, namely this device can be used as reflective FBG comb filter.Amplitude samples raster method and phase sample raster method utilize universal optical fibre preparing grating technology, the amplitude of grating or phase place is made alongst to produce periodic index distribution when making grating, its reflectance spectrum profile can regard the Fourier transform of refractive index distribution function as, reflectance spectrum presents comb δ function formula, then this grating can be used as reflective FBG comb filter.
In the demodulation method of aforesaid FBG sensor, described reflective FBG comb filter is replaced with transmission-type LPG (long period fiber grating) comb filter, the transmission spectrum that transmission-type LPG comb filter produces directly enters photodetector; Or replace with tandem FBG comb filter, and temperature compensation packaging is transferred to reference on FBG.Principle carries out temperature compensation packaging to reflective FBG comb filter or with reference to FBG, but due to tandem FBG comb filter, is difficult to after series connection realize temperature compensation packaging, so temperature compensation packaging can only be carried out to reference to FBG.
In the demodulation method of aforesaid FBG sensor, described transmission-type LPG comb filter is in same optical fiber, arrange two LPG at a distance of the transmissivity about 50% of several millimeters to several centimetres by Fiber Bragg Grating technology, and its transmission spectrum is comb δ function formula.
In the demodulation method of aforesaid FBG sensor, it is characterized in that: described tandem FBG comb filter is expanded by the series connection of plural reflective FBG comb filter and formed.
Realize the demodulating equipment of a kind of FBG sensor of preceding method, be characterized in: comprise Wavelength-swept laser, the laser emitting end of Wavelength-swept laser is connected with power splitter, the multiplexer channel that power splitter separates is respectively through the reflective FBG comb filter of 50:50 fiber coupler with band temperature compensation, be connected with FBG sensor to be measured with reference to FBG, or reflective FBG comb filter and reference FBG series connection, the a-road-through road that shared power splitter separates, reflective FBG comb filter, be connected with data collecting card with amplifying circuit by photodetector with the reflection end of FBG sensor to be measured with reference to FBG, data collecting card is connected with computing machine, and data collecting card is connected with the input end of Wavelength-swept laser.
In the demodulating equipment of aforesaid FBG sensor, described reflective FBG comb filter replaces with transmission-type LPG comb filter, and the projection end of transmission-type LPG comb filter is connected with photodetector.When using transmission-type LPG comb filter, do not adopt transmission-type LPG comb filter and the method with reference to FBG series connection.
In the demodulating equipment of aforesaid FBG sensor, described reflective FBG comb filter expands to the tandem FBG comb filter of plural reflective FBG comb filter series connection, and the not temperature compensated encapsulation of tandem FBG comb filter, be with temperature compensation packaging with reference to FBG.
Compared with prior art, the comb filter (bag expands reflective FBG comb filter, transmission-type LPG comb filter and tandem FBG comb filter) that the present invention makes by adopting fiber grating, the insertion loss of comb filter can be reduced, improve the signal to noise ratio (S/N ratio) of reference wavelength; And adopt fiber grating to make comb filter, technology maturation, process, reduce the manufacture difficulty of comb filter, improve the spectrum shape customization capability of comb filter; Based on the spectrum lock-in techniques of fiber grating, can improve the measuring accuracy of FBG sensor (FBG) demodulator, make demodulating equipment in different wavelength range, realize high precision becomes possibility simultaneously.The present invention also utilize band temperature compensation packaging reflective FBG comb filter and with reference to FBG to the method for the absolute reference wavelength of reflective FBG comb filter under calculating different temperatures, namely accurate temperature compensation is realized to shape wave filter, improve the measuring accuracy of the demodulating equipment of FBG sensor further.
Accompanying drawing explanation
Fig. 1 is the demodulating equipment structural representation of the embodiment of the present invention 1 based on the FBG sensor of reflective FBG comb filter;
Fig. 2 is the structural representation of the reflective FBG comb filter of embodiment 1;
Fig. 3 is the reflectance spectrum simulation drawing of the reflective FBG comb filter of embodiment 1;
Fig. 4 is reflective FBG comb filter and the temperature-responsive schematic diagram with reference to FBG in embodiment 1;
Fig. 5 is the demodulating equipment structural representation of embodiment 2 based on the FBG sensor of transmission-type LPG comb filter;
Fig. 6 is the structural representation of the transmission-type LPG comb filter of embodiment 2;
Fig. 7 is the transmitted spectrum simulation drawing of the transmission-type LPG comb filter of embodiment 2;
Fig. 8 is the demodulating equipment structural representation of embodiment 3 based on the FBG sensor of tandem FBG comb filter.
Embodiment
Below in conjunction with drawings and Examples, the present invention is further illustrated, but not as the foundation limited the present invention.
Embodiment.A kind of demodulation method of FBG sensor comprises: make the Wavelength-swept laser generation wavelength continually varying narrow band scanning laser that computerizeds control, narrow band scanning laser again by producing Wavelength-swept laser carries out beam splitting, narrow band scanning laser after beam splitting is respectively after the reflective FBG comb filter that fiber coupler enters FBG sensor to be measured and band temperature compensation packaging, produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength at reflective each peak of FBG comb filter reflectance spectrum of band temperature compensation packaging by peak-seeking algorithm, and demarcate with the reflectance spectrum of this wavelength to FBG sensor, calculate the absolute wavelength values of FBG sensor.Also comprise: the narrow band scanning laser of Duo Fen mono-road Wavelength-swept laser generation again, this road narrow band scanning laser enters with reference to FBG through fiber coupler, produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength with reference to each peak of FBG reflectance spectrum by peak-seeking algorithm, according to different from reference to FBG temperature control after reflective FBG comb filter band temperature compensation packaging, choose a certain reflection peak of reflective FBG comb filter as benchmark, when Wavelength-swept laser continuous sweep, calculate wavelength difference Δ λ between this reflection peak benchmark and reference FBG reflection peak, namely laser scanning is recorded to the wavelength location be scanned with reference to FBG reflection peak moment reflective FBG comb filter, and laser scanning is to the wavelength location in reflective FBG comb filter a certain baseline reflectance peak moment, both differences are Δ λ, by the scale function of FBG comb filter, measure a certain baseline reflectance peak of reflective FBG comb filter under different temperatures and the Δ λ with reference to FBG, draw the once linear function of Δ λ and Current Temperatures, in actual demodulation process, according to the current Δ λ value obtained, instead can release current temperature, then the accurate wavelength of reflective FBG comb filter under drawing this temperature current according to the temperature response curve of reflective FBG comb filter, thus realize the real-time accurate temperature compensation to reflective FBG comb filter.Described reflective FBG comb filter is in same optical fiber, arrange different FBG of multiple cycle by Fiber Bragg Grating technology, and its reflectance spectrum is comb δ function formula.Described reflective FBG comb filter can be replaced with transmission-type LPG comb filter, the transmission spectrum that transmission-type LPG comb filter produces directly enters photodetector; Or replace with tandem FBG comb filter, and temperature compensation packaging is transferred to reference on FBG.Described transmission-type LPG comb filter is in same optical fiber, arrange two at a distance of the LPG of several millimeters to several centimetres by Fiber Bragg Grating technology, and its transmission spectrum is comb δ function formula.Described tandem FBG comb filter is expanded by the series connection of plural reflective FBG comb filter and is formed.
Realize the demodulating equipment of a kind of FBG sensor of said method, comprise Wavelength-swept laser, the laser emitting end of Wavelength-swept laser is connected with power splitter, the multiplexer channel that power splitter separates is respectively through the reflective FBG comb filter of 50:50 fiber coupler with band temperature compensation, be connected with FBG sensor to be measured with reference to FBG, reflective FBG comb filter, be connected with data collecting card with amplifying circuit by photodetector with the reflection end of FBG sensor to be measured with reference to FBG, data collecting card is connected with computing machine, and data collecting card is connected with the input end of Wavelength-swept laser.Described reflective FBG comb filter can replace with transmission-type LPG comb filter, and the projection end of transmission-type LPG comb filter is connected with photodetector.Described reflective FBG comb filter can expand to the tandem FBG comb filter of plural reflective FBG comb filter series connection, and the not temperature compensated encapsulation of tandem FBG comb filter, be with temperature compensation packaging with reference to FBG.
Embodiment 1.As shown in Figure 1, for the demodulating equipment structural representation of the FBG sensor based on reflective FBG comb filter that the present invention proposes, comprise Wavelength-swept laser 1-1,1 × N power splitter 1-2, N road 50:50 fiber coupler 1-3, the reflective FBG comb filter 1-4 of band temperature compensation packaging, with reference to FBG 1-5, (N-1) the FBG sensor 1-6 on the sensing passage of road, N road photodetector (PD) 1-7, amplification appliance 1-8, data collecting card 1-9 and computing machine 1-10.The principle of work of the principal character of each device and the demodulating equipment of FBG sensor is as follows:
Described Wavelength-swept laser 1-1 is fiber laser, adopts ring cavity structure, produces laser of narrowband signal.Preferably, the gain device of fiber laser selects Erbium-Doped Fiber Amplifier (EDFA) (EDFA) or semiconductor optical amplifier (SOA), F-P tunable optic filter selected by length scanning device, the external electric signal provided by the D/A passage of data collecting card 1-9 drives, realize wide range of wavelengths scanning, maximum magnitude can cover C+L wave band.The inside of Wavelength-swept laser fills optoisolator before output terminal, prevents laser instrument from being damaged by external optical signal.
Described 1 × N power splitter 1-2 adopts optical fiber power beam splitter, after the luminous power N decile input, exports N road 50:50 fiber coupler 1-3 respectively to by Wavelength-swept laser 1-1.According to real work needs, the output way N of optical fiber power beam splitter generally can select 4,8,16 grades (selection of N is determined by product requirement and general-purpose device parameter).
The input end of described every road 50:50 fiber coupler 1-3 connects every road output terminal of corresponding 1 × N power splitter.The output terminal of fiber coupler 1-3 connects the reflective FBG comb filter 1-4 of connecting band temperature compensation packaging respectively, with reference to FBG 1-5 and multichannel FBG sensor 1-6.The reflected signal of each FBG device enters in the PD 1-7 of N road respectively through each 50:50 fiber coupler 1-3.
The reflective FBG comb filter 1-4 of described band temperature compensation packaging refers to that to adopt Fiber Bragg Grating technology on optical fiber, make a feature be reflectance spectrum and is the optical fibre device of comb δ function formula, and by temperature compensation packaging method, the sensitivity of the wavelength of reflective FBG comb filter temperature variation is to external world reduced greatly, and as standard of wavelength device, for FBG demodulating equipment provides Wavelength calibration function.Fig. 2 provides the structural representation of a reflective FBG comb filter made based on amplitude samples or overlapping raster method, and as shown in Figure 3, centre wavelength 1536nm ~ 1562nm, has 16 reflection peaks to its reflectance spectrum simulation drawing, spacing 1.6 nm.But the reflectance spectrum of reflective FBG comb filter is not limited to the example shown in Fig. 3, reflected spectral range can be determined according to the feature of the operating wavelength range of required demodulating equipment and Fabrication Methods of Fiber Gratings.The described Fiber Bragg Grating technology being used for making reflective FBG comb filter, includes but not limited to overlapping write raster method, amplitude samples raster method and phase sample raster method etc.Overlapping write raster method is the grating utilizing universal optical fibre preparing grating technology (mask plate method, double beam interferometry) to write multiple different cycles in same section of region of optical fiber, to obtain the fiber bragg grating device that reflectance spectrum has the comb δ function formula of multiple wavelength, namely this device can be used as reflective FBG comb filter.Amplitude samples raster method and phase sample raster method utilize universal optical fibre preparing grating technology, the amplitude of grating or phase place is made alongst to produce periodic index distribution when making grating, its reflectance spectrum profile can regard the Fourier transform of refractive index distribution function as, reflectance spectrum presents comb δ function formula, then this grating can be used as reflective FBG comb filter.Described temperature compensation packaging method, includes but not limited to that bimetallic material physical construction compensates and thermostat compensates.
Described is for monitoring demodulating equipment environment temperature with reference to FBG 1-5, and the accurate wavelength getting rid of temperature impact calculating FBG sensor for demodulating equipment provides reference.Not overlapping with the spectrum of the reflective FBG comb filter 1-4 of band temperature compensation packaging with reference to FBG 1-5, there is certain wavelength interval.
Described PD 1-7 and amplifying circuit 1-8 is by the reflective FBG comb filter 1-4 of band temperature compensation packaging, and the light signal be reflected back with reference to FBG 1-5 and multichannel FBG sensor 1-6 is transformed into electric signal, delivers to the input end of data collecting card 1-9 after amplifying.
Described data collecting card 1-9 has N road A/D ALT-CH alternate channel, by the reflective FBG comb filter 1-4 of band temperature compensation packaging.Computing machine 1-10 is sent to after converting digital signal to reference to the signal of FBG 1-5 and multichannel FBG sensor 1-6.
Under the control of computing machine 1-10, in each cycle, the drive singal of the Wavelength-swept laser that computing machine 1-10 produces is sent to data collecting card 1-9, D/A passage through data collecting card 1-9 delivers to Wavelength-swept laser 1-1, produces wavelength continually varying narrow band scanning laser.Scanning laser enters the reflective FBG comb filter 1-4 of band temperature compensation packaging respectively after power splitter 1-2 and fiber coupler 1-3, with reference to FBG 1-5 and multichannel FBG sensor 1-6, the reflectance spectrum of generation again enters PD 1-7 through fiber coupler 1-3 and converts electric signal to and be exaggerated circuit 1-8 and amplify.Spectrum computing machine 1-10 generating each device is sent to after data collecting card 1-9 gathers.By peak-seeking algorithm, calculate the wavelength value at the pectination reflectance spectrum of the reflective FBG comb filter 1-4 of band temperature compensation packaging and each peak of reflectance spectrum with reference to FBG 1-5, and utilize pectination reflectance spectrum and demarcate with reference to the reflectance spectrum of FBG reflectance spectrum to multichannel FBG sensor 1-6, calculate the absolute wavelength values of FBG sensor.
The reflective FBG comb filter that the present invention proposes, based on fiber optic materials, equally to responsive to temperature, has the temperature control the same with common FBG.In the present embodiment, although the reflective FBG comb filter 1-4 of band temperature compensation packaging possesses very low temperature control, be in fact difficult to ensure that its temperature control is zero by temperature compensation packaging, namely completely insensitive to temperature.Therefore in the computation process of (FBG) demodulator Wavelength calibration, error can be introduced unavoidably.
In order to improve the precision of (FBG) demodulator Wavelength calibration, propose a kind of utilize band temperature compensation packaging reflective FBG comb filter and with reference to FBG to the method for the absolute reference wavelength of reflective FBG comb filter under calculating different temperatures, namely accurate temperature compensation is realized to reflective FBG comb filter.As shown in Figure 4, be reflective FBG comb filter and the temperature-responsive schematic diagram with reference to FBG, the temperature control of the reflective FBG comb filter wherein with temperature compensation packaging is N/mono-of the reference FBG without temperature compensation packaging.Because the peak-to-peak interval of reflection of reflective FBG comb filter does not vary with temperature, as shown in Figure 3, there is scale function.Choose a certain reflection peak of reflective FBG comb filter as benchmark, when Wavelength-swept laser continuous sweep, calculate wavelength difference Δ λ between this reflection peak benchmark and reference FBG reflection peak, namely laser scanning is recorded to the wavelength location be scanned with reference to FBG reflection peak moment reflective FBG comb filter, and laser scanning is to the wavelength location in reflective FBG comb filter a certain baseline reflectance peak moment, both differences are Δ λ.Because reflective FBG comb filter is different from the temperature control with reference to FBG, gap is obvious, and therefore, under different temperatures, both Δ λ are different, as the Δ λ of Fig. 4 t1with Δ λ t2shown in.By the scale function of FBG comb filter, measure a certain baseline reflectance peak of reflective FBG comb filter under different temperatures and the Δ λ with reference to FBG.Due to the once linear function that Δ λ is Current Temperatures, instead can release current temperature, then the accurate wavelength of reflective FBG comb filter under calculating this temperature current according to the temperature response curve of reflective FBG comb filter, thus realize the real-time accurate temperature compensation to reflective FBG comb filter.
Embodiment 2.As shown in Figure 5, for the demodulating equipment structural representation of the FBG sensor based on transmission-type LPG comb filter that the present invention proposes, comprise Wavelength-swept laser 5-1,1 × N power splitter 5-2, (N-1) road 50:50 fiber coupler 5-3, transmission-type LPG comb filter 5-4, with the reference FBG 5-5 of temperature compensation packaging, (N-2) the FBG sensor 5-6 on the sensing passage of road, N road photodetector (PD) 5-7, data collecting card 5-8, amplification appliance 5-9 and computing machine 5-10.The principle of work of the principal character of each device and the demodulating equipment of FBG sensor is as follows:
Described Wavelength-swept laser 5-1 is fiber laser, adopts ring cavity structure, produces laser of narrowband signal.Preferably, the gain device of fiber laser selects Erbium-Doped Fiber Amplifier (EDFA) (EDFA) or semiconductor optical amplifier (SOA), F-P tunable optic filter selected by length scanning device, the external electric signal provided by the D/A passage of data collecting card 5-8 drives, realize wide range of wavelengths scanning, maximum magnitude can cover C+L wave band.The inside of Wavelength-swept laser fills optoisolator before output terminal, prevents laser instrument from being damaged by external optical signal.
Described 1 × N power splitter 5-2 adopts optical fiber power beam splitter, after the luminous power N decile input, exports (N-1) road 50:50 fiber coupler 5-3 and transmission-type LPG comb filter 5-4 respectively to by Wavelength-swept laser 5-1.The output terminal of transmission-type LPG comb filter 5-4 directly connects PD 5-7.According to real work needs, the output way N of optical fiber power beam splitter generally can select 4,8,16 etc.
The input end of described every road 50:50 fiber coupler 5-3 connects every road output terminal of corresponding 1 × N power splitter.The reference FBG 5-5 of the output terminal difference connecting band temperature compensation packaging of fiber coupler 5-3 and multichannel FBG sensor 5-6.The reflected signal of FBG device enters in the PD 5-7 of (N-1) road respectively through each 50:50 fiber coupler 5-3 again.
Described transmission-type LPG comb filter 5-4 refers to that adopting Fiber Bragg Grating technology on optical fiber, make a feature be transmitted spectrum is the optical fibre device of comb δ function formula, for FBG demodulating equipment provides Wavelength calibration function.Fig. 6 provides the structural representation of a transmission-type LPG comb filter done based on pointwise write grating legal system, two LPG are cascaded formation Mach-Zeng Deer interferometer, its transmitted spectrum simulation drawing as shown in Figure 7, centre wavelength covers 1510nm ~ 1590nm, there are 32 transmission peaks, spacing 2.8 nm.But the transmitted spectrum of transmission-type LPG comb filter is not limited to the example shown in Fig. 7, transmitted spectrum scope can be determined according to the feature of the operating wavelength range of required demodulating equipment and Fabrication Methods of Fiber Gratings.The described Fiber Bragg Grating technology being used for making transmission-type LPG comb filter, includes but not limited to pointwise write raster method and vibration amplitude mask plate method etc.Pointwise write raster method be exciamer laser UV is focused to be of a size of tens to hundreds of micron hot spot after shine directly on optical fiber and expose, and control time shutter and the exposure cycle of every bit by High Precision Linear Motor, form LPG.Utilize pointwise to write raster method at the LPG of same optical fiber fabrication two at a distance of several millimeters to several centimetres, then the device that this two LPG is formed is Mach-Zeng Deer interferometer, and its transmitted spectrum is comb δ function formula, and namely this device can be used as transmission-type LPG comb filter.Pointwise write raster method usually increases a slit and limits hot spot after hot spot, improves optical quality, to improve long period fiber grating quality.Vibration amplitude mask plate method refers to and utilizes vibration amplitude mask plate directly to carry out uv-exposure to optical fiber, forms LPG.Compare pointwise write raster method, the vibration amplitude mask plate method cycle is fixed, and arbitrarily can not regulate the cycle of long period fiber grating.Utilize vibration amplitude mask plate method at the LPG of same optical fiber fabrication two at a distance of several millimeters to several centimetres, then the device that this two LPG is formed is Mach-Zeng Deer interferometer, and its transmitted spectrum is comb δ function formula, and namely this device also can be used as transmission-type LPG comb filter.
The reference FBG 5-5 of described band temperature compensation packaging refers to and by physical construction or thermostat, the sensitivity of the centre wavelength of FBG temperature variation is to external world reduced greatly, and as standard of wavelength device, the wavelength calculating FBG sensor for FBG demodulating equipment provides absolute wavelength reference.Described temperature compensation packaging method, includes but not limited to that bimetallic material physical construction compensates and thermostat compensates.
Described PD 5-7 and amplifying circuit 5-8 is by transmission-type LPG comb filter 5-4, and the band reference FBG 5-5 of temperature compensation packaging and the light signal of multichannel FBG sensor 5-6 are transformed into electric signal, delivers to the input end of data collecting card 5-9 after amplifying.
Described data collecting card 5-9 has N road A/D ALT-CH alternate channel, just transmission-type LPG comb filter 5-4, is sent to computing machine 5-10 after the band reference FBG 5-5 of temperature compensation packaging and the signal of multichannel FBG sensor 5-6 convert digital signal to.
Under the control of computing machine 5-10, in each cycle, the drive singal of the Wavelength-swept laser that computing machine 5-10 produces is sent to data collecting card 5-9, D/A passage through data collecting card 5-9 delivers to Wavelength-swept laser 5-1, produces wavelength continually varying narrow band scanning laser.Scanning laser enters transmission-type LPG comb filter 5-4 respectively after power splitter 5-2 and fiber coupler 5-3, the reference FBG 5-5 of band temperature compensation packaging and multichannel FBG sensor 5-6.Transmission-type LPG comb filter 5-4 produce transmission spectrum directly enter PD 5-7 convert to electric signal and be exaggerated circuit 5-8 amplify, the reflectance spectrum that reference FBG 5-5 with temperature compensation packaging and multichannel FBG sensor 5-6 produce again enters PD 5-7 through fiber coupler 5-3 and converts electric signal to and be exaggerated circuit 5-8 and amplifies, is sent to the spectrum of each device of generation on computing machine 5-10 after data collecting card 5-9 gathers.By peak-seeking algorithm, calculate the wavelength value at the pectination transmitted spectrum of transmission-type LPG comb filter 5-4 and each peak of reflectance spectrum with reference to FBG 5-5, and utilize pectination transmitted spectrum and demarcate with reference to the reflectance spectrum of FBG reflectance spectrum to multichannel FBG sensor 5-6, calculate the absolute wavelength values of FBG sensor.
Embodiment 3.As shown in Figure 8, for the demodulating equipment structural representation of the FBG sensor based on tandem FBG comb filter that the present invention proposes, comprise Wavelength-swept laser 8-1,1 × N power splitter 8-2, N road 50:50 fiber coupler 8-3, tandem FBG comb filter 8-4, with the reference FBG 8-5 of temperature compensation packaging, (N-1) the FBG sensor 8-6 on the sensing passage of road, N road photodetector (PD) 8-7, data collecting card 8-8, amplification appliance 8-9 and computing machine 8-10.The main devices characteristic sum principle of work of the demodulating equipment of the FBG sensor of tandem FBG comb filter is identical with the demodulating equipment of the FBG sensor of FBG comb filter reflective in embodiment 1.The key distinction is that tandem FBG comb filter 8-4 is expanded by the series connection of two or more reflective FBG comb filter 1-4 to form, deficiency when needing larger wavelength scanning range and single reflective FBG comb filter can not provide enough wide Wavelength calibration scope with the demodulating equipment making up FBG sensor.Such as, but the demodulating equipment of FBG sensor needs to scan the FBG sensor within the scope of 1510nm ~ 1590nm, and due to the restriction of preparing grating technology, as grating length restriction, photosensitivity restriction etc., the single reflective FBG comb filter of 16 passage 32nm bandwidth can only be made, then now need the reflective FBG comb filter series connection of 3 different-wavebands could meet the requirement of the demodulating equipment 80nm wavelength scanning range of FBG sensor.
Foregoing description of the present invention is only exemplary attribute, and the various distortion that so there is no depart from main idea of the present invention ought to be within the scope of the present invention.These distortion should not be regarded as departing from the spirit and scope of the present invention.

Claims (8)

1. the demodulation method of a FBG sensor, it is characterized in that, comprise: make the Wavelength-swept laser generation wavelength continually varying narrow band scanning laser that computerizeds control, narrow band scanning laser again by producing Wavelength-swept laser carries out beam splitting, narrow band scanning laser after beam splitting is respectively after the reflective FBG comb filter that fiber coupler enters FBG sensor to be measured and band temperature compensation packaging, produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength at reflective each peak of FBG comb filter reflectance spectrum of band temperature compensation packaging by peak-seeking algorithm, and demarcate with the reflectance spectrum of this wavelength to FBG sensor, calculate the absolute wavelength values of FBG sensor, the narrow band scanning laser of Duo Fen mono-road Wavelength-swept laser generation again, this road narrow band scanning laser enters with reference to FBG through fiber coupler, or directly connect with reflective FBG comb filter with reference to FBG, with reference to FBG produce reflectance spectrum again through fiber coupler enter photodetector convert to electric signal and be exaggerated after have computing machine collection, computing machine draws the wavelength with reference to each peak of FBG reflectance spectrum by peak-seeking algorithm, according to different from reference to FBG temperature control after reflective FBG comb filter band temperature compensation packaging, choose a certain reflection peak of reflective FBG comb filter as benchmark, when Wavelength-swept laser continuous sweep, calculate wavelength difference Δ λ between this reflection peak benchmark and reference FBG reflection peak, namely laser scanning is recorded to the wavelength location be scanned with reference to FBG reflection peak moment reflective FBG comb filter, and laser scanning is to the wavelength location in reflective FBG comb filter a certain baseline reflectance peak moment, both differences are Δ λ, by the scale function of FBG comb filter, measure a certain baseline reflectance peak of reflective FBG comb filter under different temperatures and the Δ λ with reference to FBG, draw the once linear function of Δ λ and Current Temperatures, in actual demodulation process, according to the current Δ λ value obtained, instead can release current temperature, then the accurate wavelength of reflective FBG comb filter under drawing this temperature current according to the temperature response curve of reflective FBG comb filter, thus realize the real-time accurate temperature compensation to reflective FBG comb filter.
2. the demodulation method of FBG sensor according to claim 1, is characterized in that: described reflective FBG comb filter is in same optical fiber, arrange different FBG of multiple cycle by Fiber Bragg Grating technology, and its reflectance spectrum is comb δ function formula.
3. the demodulation method of FBG sensor according to claim 1, is characterized in that: described reflective FBG comb filter is replaced with transmission-type LPG comb filter, and the transmission spectrum that transmission-type LPG comb filter produces directly enters photodetector; Or replace with tandem FBG comb filter, and temperature compensation packaging is transferred to reference on FBG.
4. the demodulation method of FBG sensor according to claim 3, is characterized in that: described transmission-type LPG comb filter for arrange two LPG by Fiber Bragg Grating technology in same optical fiber, and its transmission spectrum is comb δ function formula.
5. the demodulation method of FBG sensor according to claim 3, is characterized in that: described tandem FBG comb filter is expanded by the series connection of plural reflective FBG comb filter and formed.
6. realize the demodulating equipment of a kind of FBG sensor of method described in the arbitrary claim of claim 1 to 5, it is characterized in that: comprise Wavelength-swept laser, the laser emitting end of Wavelength-swept laser is connected with power splitter, the multiplexer channel that power splitter separates is respectively through the reflective FBG comb filter of 50:50 fiber coupler with band temperature compensation, be connected with FBG sensor to be measured with reference to FBG, or reflective FBG comb filter and reference FBG series connection, the a-road-through road that shared power splitter separates, reflective FBG comb filter, be connected with data collecting card with amplifying circuit by photodetector with the reflection end of FBG sensor to be measured with reference to FBG, data collecting card is connected with computing machine, and data collecting card is connected with the input end of Wavelength-swept laser.
7. the demodulating equipment of FBG sensor according to claim 6, is characterized in that: described reflective FBG comb filter replaces with transmission-type LPG comb filter, and the projection end of transmission-type LPG comb filter is connected with photodetector.
8. the demodulating equipment of FBG sensor according to claim 6, it is characterized in that: described reflective FBG comb filter expands to the tandem FBG comb filter of plural reflective FBG comb filter series connection, and the not temperature compensated encapsulation of tandem FBG comb filter, be with temperature compensation packaging with reference to FBG.
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