CN105806380A - Multiplexing demodulation equipment based on long-cycle fiber grating reflective sensor - Google Patents
Multiplexing demodulation equipment based on long-cycle fiber grating reflective sensor Download PDFInfo
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- CN105806380A CN105806380A CN201610210919.2A CN201610210919A CN105806380A CN 105806380 A CN105806380 A CN 105806380A CN 201610210919 A CN201610210919 A CN 201610210919A CN 105806380 A CN105806380 A CN 105806380A
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
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Abstract
The invention relates to multiplexing demodulation equipment based on long-cycle fiber grating reflective sensors.The multiple long-cycle fiber grating reflective sensors are provided with different optical path differences; a broadband light source is connected with the first port of a three-port circulator, the second port of the three-port circulator is connected with an optical fiber connected with the multiple long-cycle fiber grating reflective sensors in series, and the third port is connected with the input end of a first optical fiber coupler; an output end of the first optical fiber coupler is connected with the input end of a polarization controller, and the other output end of the first optical fiber coupler is connected with the input end of an electric adjustable delay line; the output end of the polarization controller and the output end of the electric adjustable delay line are connected with two input ends of a second optical fiber coupler; the output end of the second optical fiber coupler is connected with the input end of a photoelectric detector, and the output end of the photoelectric detector is connected with a data acquisition card.By means of the multiplexing demodulation equipment, system spatial resolution is high, the reusable number is large, and cost is low.
Description
Technical field
The present invention relates to technical field of optical fiber sensing, particularly relate to a kind of multiplexing demodulation equipment based on LPFG reflection sensor.
Background technology
At sensory field of optic fibre, LPFG is due to its high susceptibility that temperature, stress and strain, ambient refractive index etc. are changed, and becomes a kind of highly important senser element.Compared with Bragg grating, long-period grating pair temperature, stress etc. have higher susceptiveness, and its cladding mode ambient refractive index to external world is sensitive, it is possible to suitable in the high-acruracy survey of liquid refractivity.Although having outstanding one point sensing performance, LPFG lags far behind Bragg grating in the practicalization of application.Bragg grating is very narrow owing to its frequency domain reflects frequency range, is generally less than 1nm, it is possible to be built into distributed sensor-based system very easily and demodulate with wavelength-division multiplex or time-division multiplex technology.The spectrum signature of LPFG is that multiple transmission loss peak coexists, and the spectral bandwidth of each loss peak is very big, and the bandwidth of the higher high-order mode of ambient refractive index sensitivity is had at least tens nanometers, and therefore its frequency domain cannot adopt wavelength-division multiplex system to demodulate.LPFG is sandwich layer mould and the cladding mode coupling of symport, and almost without reflecting spectrum, therefore it cannot adopt the time division multiplex system of current technology maturation to demodulate.The research of multiplexing and demodulation method owing to lacking of LPFG distributed sensing, the practicalization of the LPFG with excellent sensing characteristics is greatly affected.
Low coherence interference technology is to use wide spectrum optical as light source, according to the relevant principle of white light, utilizes zero order interference fringe as reference position, thus obtaining a kind of interference system accurately measuring absolute location information in the larger context.Low coherence interference system is interferometer for obtaining the sensor construction of detectable signal, and demodulation part is the interferometer of sweep type, and different sensors adopts different optical path difference designs, it is possible to achieve multichannel sensing multiplexing.Owing to Low coherence system adopting interferometer mode demodulate each sensor information amount, it is possible to the environment noise that the factor such as avoid flashing fixed introduces, there is higher anti-interference；Make full use of all data of interferogram to evaluate measured signal, there is the effect of the average effect that accurate measurement theory is favored, it is thus achieved that higher certainty of measurement；Build optical fiber low coherence interference system, do not need the tunable laser source that high coherent interference system uses, signal analysis and processing is also without valuable precision equipments such as spectrogrph, Network Analyzer, vector analysis instrument, and system cost is well below systems such as now widely used wavelength-division multiplex, time division multiplexes.Multiplexing demodulation system based on Low coherence principle is a function admirable and multiplex system with low cost, but this systematic difference research at present also lags far behind time division multiplex system, wavelength-division multiplex system etc..
Summary of the invention
The technical problem to be solved is to provide a kind of multiplexing demodulation equipment based on LPFG reflection sensor so that System spatial resolution is high, reusable number is big, with low cost.
The technical solution adopted for the present invention to solve the technical problems is: provide a kind of multiplexing demodulation equipment based on LPFG reflection sensor, including wideband light source and multiple LPFG reflection sensor, the plurality of LPFG reflection sensor has different optical path differences；First port of described wideband light source and three port circulators is connected, and the second port of described three port circulators is connected with the optical fiber being in series with the plurality of LPFG reflection sensor, and the input of the 3rd port and the first fiber coupler is connected；One outfan of described first fiber coupler is connected with the input of Polarization Controller, and another outfan is connected with the input of electronic variable delay line；The outfan of described Polarization Controller and the outfan of electronic variable delay line connect two inputs of the second fiber coupler respectively；The described outfan of the second fiber coupler is connected with the input of photodetector, and the outfan of described photodetector is connected with data collecting card.
Described LPFG reflection sensor is prepared from by the LPFG that stiffness of coupling is 3dB, one end optical fiber of described LPFG retains to access system, and the optical fiber cutter of the other end cut off and adopt sputtering method to plate metallic reflective coating.
The plurality of LPFG reflection sensor is linked in same optical fiber by the 3rd fiber coupler series connection.
The light source range of described wideband light source covers the bandwidth at the resonance loss peak of described long-period fiber grating sensor.
The single-mode fiber sandwich layer of described LPFG reflection sensor and cladding-effective-index difference are 10-2。
In adjacent LPFG reflection sensor raster center to the range difference of end face more than or equal to 2.7mm.
The spectral region of described wideband light source is 60nm.
The centre wavelength of described LPFG reflection sensor is 1550nm, and loss peak bandwidth is 20nm.Beneficial effect
Owing to have employed above-mentioned technical scheme, the present invention is compared with prior art, have the following advantages that and good effect: the present invention utilizes Data collection and precessing system that interference signal carries out Fourier transformation extraction frequency can obtain the centre wavelength of interference light, thus obtaining the demodulation of the temperature information of sensor.Utilize electronic variable delay line shuttle-scanning, it is achieved that the multiplexing of LPFG reflection sensor.The present invention has the advantage that System spatial resolution height, reusable number are big, with low cost.
Accompanying drawing explanation
Fig. 1 is the structural representation of the present invention.
Detailed description of the invention
Below in conjunction with specific embodiment, the present invention is expanded on further.Should be understood that these embodiments are merely to illustrate the present invention rather than restriction the scope of the present invention.In addition, it is to be understood that after having read the content that the present invention lectures, the present invention can be made various changes or modifications by those skilled in the art, and these equivalent form of values fall within the application appended claims limited range equally.
As shown in Figure 1, wideband light source 1 is connected with first port optical signal of three port circulators 2, LPFG reflection sensor 4 is connected in series on same optical fiber by a fiber coupler 3, the individual different optical fiber of optical path difference sensor of the n (n >=2) that connected are connected with second port optical signal of circulator, and the 3rd port of circulator is connected with the input light of fiber coupler 5.One outfan of fiber coupler 5 is connected with the input light of Polarization Controller 6, another outfan of fiber coupler 5 is connected with the input light of electronic variable delay line 7, the outfan of Polarization Controller 6 and the input light of fiber coupler 8 connect, and the outfan of electronic variable delay line 7 and another input light of fiber coupler 8 connect.The outfan of fiber coupler 8 is connected with photodiode 9 input optical signal.Photodiode 9 is connected with data storage and process equipment 10 signal of telecommunication.Above-mentioned multiple LPFG reflection sensors 4 are preset in monitored environment as temperature sensor, wideband light source 1, circulator 2 and signal demodulation part are all in monitoring center, broadband light enters multiple sensor 4 by circulator 2, then is passed flashlight back monitoring center by single-mode fiber and carry out signal demodulation and process.
Described LPFG reflection sensor is prepared from by the LPFG that stiffness of coupling is 3dB, one end optical fiber of LPFG retains to access system, the optical fiber cutter of the other end cut off and adopt sputtering method to plate metallic reflective coating, form LPFG reflection sensor.In different LPFG reflection sensors, raster center is different to the distance between reflection end.
Selecting spectral region in present embodiment is the wideband light source of 60nm, light source range to cover the bandwidth at LPFG resonance loss peak, and light energy is incorporated in the sensor being connected on an optical fiber by the light of light source output by the circulator of three ports.In sensor LPFG 50% light energy be coupled in fibre cladding high-order mode, remaining light energy is transmitted at fiber core layer, after one section of optical fiber, transmit the light at sandwich layer and covering all to be reflected by the reflectance coating of fiber end face, when the light being reflected back again passes by LPFG, transmit the part light at covering and can be again coupled back into sandwich layer, converge with the light energy transmitted at sandwich layer.The effective refractive index of fiber core layer is different with the effective refractive index of fibre cladding high-order mode, can introduce optical path difference be always in sensor between the light of sandwich layer transmission and the light being coupled back into again sandwich layer after being coupled to covering
δ=2 (nco-ncl)·d(1)
Wherein ncoAnd nclRepresenting the effective refractive index of fiber core layer and covering high-order mode respectively, d represents in sensor that long-period gratings center is to the distance reflecting end face.Preset raster center in different sensors different to reflection end distance, then the optical path difference that in each sensor, optical signal introduces is just different.
The transducing signal that sensor is reflected back enters in an interferometer demodulating system through the 3rd port of circulator after returning then through optical fiber collection transmission.Optical signal is divided into aplanatic two bundles by fiber coupler, light beam therein passes through an electronic variable delay line, making to introduce between two-way light variable optical path difference, along with the scanning of variable delay line, the optical path difference of introducing can compensate the optical path difference that different sensors introduces.Another bundle optical fiber light path is constant, and the effect accessing a Polarization Controller is to allow system obtain best interference signal.Two-way light after compensation produces to interfere after another fiber coupler converges.Interference signal is converted to the signal of telecommunication by photodiode detection, then is gathered by data collecting card and store, and the data handling equipment interference signal to collecting carries out data analysis and information demodulation.
The optical path difference introduced due to different sensors is different, so when variable delay line scans a certain position, the optical path difference that certain sensor introduces is compensated for as zero, then the low-coherent light interference signal that this sensor is corresponding occurs, its interference fringe is:
Wherein, A (z) is the amplitude external envelope of interference fringe, and P is the cycle of interference fringe,Being the initial phase of interference fringe, z is the position of variable delay line scanning.The centre wavelength of interference light and the relation of interference fringe are
λ=2P (3)
After interference fringe is carried out the frequency that Fourier transformation tries to achieve interference fringe, according to formula (3), it is possible to obtain participate in the centre wavelength of the light interfered.Namely interference light centre wavelength be the centre wavelength at LPFG transmission loss peak.The coupling loss peak center wavelength of LPFG can drift about along with variations in temperature, and wavelength drift is changing into proportional relation with temperature, and its proportionality coefficient can calibrate acquisition by experiment.Native system calculates the resonance loss peak wavelength location of sensor by meter, and then demodulates the information that ambient temperature is to be measured.In system, the sensitivity of sensor and the sensitivity of LPFG are consistent.The spatial resolution of demodulation scheme depends on the coherence length of LPFG loss peak.By the sensor of a series of different optical path differences of arranged in series, and by controlling an electronic variable delay line scanning demodulated interferential instrument wherein arm, it may be achieved the multiplexing of multiple sensor.
In present embodiment, LPFG centre wavelength all takes optic communication typical case wave band 1550nm, and general LPFG loss peak bandwidth is 20nm, then the interference length of LPFG loss peak is 53 μm.If the sweep limits using electronic variable delay line is 10cm, native system can demodulate at most 1886 sensors.In order to aliasing does not occur different sensor interferometer signals, it is about 10 according to single-mode fiber sandwich layer and cladding-effective-index difference-2, in adjacent sensors, raster center is to the range difference at least 2.7mm of end face.
Owing to variations in temperature can cause the drift of LPFG resonance loss spike length in sensor, thus the centre wavelength of interference light can change, utilize Data collection and precessing system that interference signal carries out Fourier transformation extraction frequency and can obtain the centre wavelength of interference light, thus obtaining the demodulation of the temperature information of sensor.Electronic variable delay line shuttle-scanning, it is achieved that the multiplexing of LPFG reflection sensor.The present invention has the advantage that System spatial resolution height, reusable number are big, with low cost.
Claims (8)
1. based on a multiplexing demodulation equipment for LPFG reflection sensor, including wideband light source and multiple LPFG reflection sensor, it is characterised in that the plurality of LPFG reflection sensor has different optical path differences；First port of described wideband light source and three port circulators is connected, and the second port of described three port circulators is connected with the optical fiber being in series with the plurality of LPFG reflection sensor, and the input of the 3rd port and the first fiber coupler is connected；One outfan of described first fiber coupler is connected with the input of Polarization Controller, and another outfan is connected with the input of electronic variable delay line；The outfan of described Polarization Controller and the outfan of electronic variable delay line connect two inputs of the second fiber coupler respectively；The described outfan of the second fiber coupler is connected with the input of photodetector, and the outfan of described photodetector is connected with data collecting card.
2. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterized in that, described LPFG reflection sensor is prepared from by the LPFG that stiffness of coupling is 3dB, one end optical fiber of described LPFG retains to access system, and the optical fiber cutter of the other end cut off and adopt sputtering method to plate metallic reflective coating.
3. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that the plurality of LPFG reflection sensor is linked in same optical fiber by the 3rd fiber coupler series connection.
4. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that the light source range of described wideband light source covers the bandwidth at the resonance loss peak of described long-period fiber grating sensor.
5. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that single-mode fiber sandwich layer and the cladding-effective-index difference of described LPFG reflection sensor are 10-2。
6. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that in adjacent LPFG reflection sensor raster center to the range difference of end face more than or equal to 2.7mm.
7. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that the spectral region of described wideband light source is 60nm.
8. the multiplexing demodulation equipment based on LPFG reflection sensor according to claim 1, it is characterised in that the centre wavelength of described LPFG reflection sensor is 1550nm, and loss peak bandwidth is 20nm.
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Cited By (5)
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| CN106442340A (en) * | 2016-09-27 | 2017-02-22 | 山东省科学院生物研究所 | Device and method for detecting seawater salinity based on long period fiber grating |
| CN106643841A (en) * | 2016-12-30 | 2017-05-10 | 中国科学院深圳先进技术研究院 | Weak reflection-FIZEAU sensing device |
| CN107631814A (en) * | 2017-09-14 | 2018-01-26 | 电子科技大学 | Light senses light channel structure, frequency displacement change detecting method and sensing device from relevant |
| GB2568305A (en) * | 2017-11-13 | 2019-05-15 | Univ Cranfield | A fibre optic sensing device |
| CN110207849A (en) * | 2019-07-02 | 2019-09-06 | 浙江科技学院 | A kind of temperature sensor and measurement method based on reflective long-period fiber grating |
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| GB2568305B (en) * | 2017-11-13 | 2022-06-15 | Univ Cranfield | A fibre optic sensing device |
| CN110207849A (en) * | 2019-07-02 | 2019-09-06 | 浙江科技学院 | A kind of temperature sensor and measurement method based on reflective long-period fiber grating |
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