CN104729750A - Distributed optical fiber temperature sensor based on Brillouin scattering - Google Patents

Distributed optical fiber temperature sensor based on Brillouin scattering Download PDF

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Publication number
CN104729750A
CN104729750A CN201310697476.0A CN201310697476A CN104729750A CN 104729750 A CN104729750 A CN 104729750A CN 201310697476 A CN201310697476 A CN 201310697476A CN 104729750 A CN104729750 A CN 104729750A
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brillouin
optical fiber
frequency
brillouin scattering
sensing optical
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熊思亚东
张振荣
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Guangxi University
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Guangxi University
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Abstract

The invention design a distributed optical fiber temperature sensor based on Brillouin scattering, comprising a narrow-line-width light source, a coupler, a pulse modulator, an erbium-doped fiber amplifier, a sensing optical fiber 1, a sensing optical fiber 2, and a detection unit. Laser light emitted by the narrow-line-width light source is used as incident light after pulse modulation and power amplification, and the incident light is split by the coupler and then goes into the sensing optical fiber 1 and the sensing optical fiber 2. Backward Brillouin scattered light in the two sensing optical fibers laid together is combined at the coupler, and a beat-frequency Brillouin signal is generated through photoelectric conversion. By detecting the frequency shift of the beat-frequency Brillouin signal, the temperature information of an environment where the sensing optical fibers are arranged can be detected. On the premise of not introducing a local-oscillation light frequency shifting device, the photoelectric detection bandwidth required by the detection unit is reduced, and the cost and system complexity are reduced through the beat frequency of the two sensing optical fibers.

Description

A kind of based on Brillouin scattering distributed optical fiber temperature sensor
Technical field
The present invention relates to sensory field of optic fibre, specifically, relate to a kind of based on Brillouin scattering distributed optical fiber temperature sensor.
Background technology
Temperature sensor is for measuring the temperature of environment residing for it.Fibre optic temperature sensor utilizes sensor fibre as carrier, adopts the information such as the frequency of the light signal of transmission in optical fiber, phase place, amplitude and polarization to measure environment temperature.Relatively and other temperature sensors, to distributed optical fiber temperature sensor the remarkable advantage possessed can carry out distributed measurement to residing environment, namely can measure optical fiber Temperature Distribution along the line.Therefore, it is possible to be widely used in the monitoring of large scale structure, such as pipeline, bridge etc.
All be better than other Distributed Optical Fiber Sensing Techniques based on the measuring accuracy of the distributed optical fiber temperature sensor of Brillouin scattering, measurement range and spatial resolution, thus obtain research widely and pay close attention to.Incident light and sound wave interaction in optical fiber is utilized and the Brillouin scattering produced carrys out measuring tempeature based on Brillouin scattering distributed optical fiber temperature sensor.Specifically, by detecting the frequency shift (FS) of Brillouin scattering relative to incident light, the temperature that position occurs scattered light can just be measured.Said frequencies skew is referred to as Brillouin shift v b, it can be expressed as
V b=2nv a/ λ formula (1)
Wherein n is sensor fibre effective refractive index, v athe velocity of sound and lambda1-wavelength in sensor fibre respectively with λ.Brillouin shift is at about 11GHz.
When the temperature in environment somewhere residing for sensor fibre or stress change, Brillouin's frequency shift (FS) can correspondingly linear change, and it can be expressed as
Δ v b(T, ε)=C tΔ T+C εΔ ε formula (2)
Wherein C tand C cbrillouin shift respectively about the response coefficient of temperature and STRESS VARIATION.
At present, the distributed optical fiber temperature sensor based on Brillouin scattering mainly concentrates on two aspects:
1) based on the time domain reflection technology distributed fiberoptic sensor of Brillouin scattering;
2) based on the time-domain analysis technical point cloth Fibre Optical Sensor of Brillouin scattering.
Fig. 1 shows the time domain reflection technology distributed fiberoptic sensor structure based on Brillouin scattering.As shown in Figure 1, this structure comprises light source, pulse-modulator, coupling mechanism, sensor fibre and detecting unit.Light source can be narrow linewidth light source.Coupling mechanism can be X-coupler (i.e. four port coupler) or Y type coupling mechanism (i.e. three port coupler), to realize the beam splitting of light beam and again to converge.
Based in the time domain reflection technology distributed fiberoptic sensor of Brillouin scattering, when transmitting in sensor fibre through pulse modulated incident light, Brillouin scattering dorsad can be detected in the incidence end of sensor fibre.Because the frequency shift (FS) of the relative incident light of Brillouin scattering is by the impact of temperature, therefore temperature information can be obtained by mensuration.
Fig. 2 shows the time-domain analysis technical point cloth Fibre Optical Sensor based on Brillouin scattering.As shown in Figure 3, this structure comprises pump light source, probe source, pulse-modulator, coupling mechanism, sensor fibre and detecting unit.Light source can be Wavelength tunable laser.
Based in the time-domain analysis technical point cloth Fibre Optical Sensor of Brillouin scattering, when pump light with detection light difference on the frequency with when in sensor fibre, the Brillouin shift in certain region is consistent, stimulated Brillouin scattering effect can be there is at this place, make, between two-way light beam, energy trasfer occurs.Therefore, by regulating continuously the frequency of two light sources, by detecting the luminous power that sensor fibre end is coupled out, sensor fibre Brillouin shift everywhere can be determined, thus obtain temperature information.
In the detecting unit of above-mentioned two kinds of structures, there are two kinds of detection meanss at present, is direct Detection Method and relevant detection method respectively.Direct-detection carries out filtering to the scattered light of end of probe, takes out useful Brillouin scattering.Preferably, filtering device can be fiber grating, Fabry-Perot interferometer or Mach-Zehnder interferometer.Relevant detection method introduces local oscillations light in the structure, detective bandwidth is down to Brillouin shift magnitude, namely 11GHz. also have method using incident light after shift frequency as local oscillations light.Shift frequency method has by acousto-optic modulator, electrooptic modulator, Brillouin optical fiber laser etc.The detective bandwidth of these methods can be down to hundreds of about MHz.
But above-described detecting unit all has complex structure, the shortcoming such as with high costs, adds application difficulty.
Summary of the invention
The problem to be solved in the present invention is, for existing based on the complex structure in Brillouin scattering distributed optical fiber temperature sensor existing for detecting unit, problem that cost is higher, the low cost Brillouin scattering distributed optical fiber temperature sensor that a kind of detective bandwidth reduces is proposed.
To achieve these goals, the invention provides a kind of Brillouin scattering distributed optical fiber temperature sensor, it comprises narrow linewidth light source, pulse-modulator, Erbium-Doped Fiber Amplifier (EDFA), coupling mechanism, is laid on sensor fibre 1 together and sensor fibre 2, and detecting unit.
The laser that narrow linewidth light source sends, after pulsed modulation and Erbium-Doped Fiber Amplifier (EDFA) are amplified, is divided into two-way by coupling mechanism and detects light.First via detection light enters sensor fibre 1, and the second tunnel detection light enters sensor fibre 2.Two-way sensor fibre all can produce the Brillouin scattering dorsad comprising temperature information.Two-way back-scattering light closes at coupling mechanism place and restraints and be coupled to detecting unit, thus we can extract the beat frequency Brillouin signal containing temperature information on sensor fibre link.
Due to the doping in fiber core and fibre core diameter difference, different sensor fibres has different Brillouin shifts.The Brillouin back scattering luminous of multichannel sensor fibre is closed Shu Houjing and is crossed detecting unit, can be created on beat frequency Brillouin signal frequency domain with multimodal characteristic.The beat frequency Brillouin signal frequency displacement of sensor fibre 1 and sensor fibre 2 is:
δ v B 12 = ( v B 1 , ref - v B 2 , ref ) + ( C T 1 - C T 2 ) ( T - T ref ) + ( C ϵ 1 - C ϵ 2 ) ( ϵ - ϵ ref ) Formula (3)
Because different sensor fibres has different temperature, stress coefficient, when ambient temperature and stress change, the frequency displacement of beat frequency Brillouin signal also produces linear change.Variation value is:
Δδ v B ij = ( C T i - C T j ) ΔT + ( C ϵ i - C ϵ j ) Δϵ Formula (4)
Therefore, by the frequency displacement of detection beat frequency Brillouin signal, temperature information can be obtained.
Preferably, described coupling mechanism is three-dB coupler, and splitting ratio is 50:50.The output of Erbium-Doped Fiber Amplifier is coupled with 1 port of coupling mechanism; Sensor fibre 1 and sensor fibre 2 are coupled with 3 and 4 ports of coupling mechanism respectively; Detecting unit is coupled with 2 ports of coupling mechanism.
Preferably, the detecting unit in this structure comprises photoelectric commutator and electric spectrum analyzer.Light signal is converted to electric signal by photoelectric commutator, thus obtains beat frequency Brillouin signal.Electricity spectrum analyzer can detect beat frequency Brillouin signal.
Preferably, the pulse-modulator in this structure can be acousto-optic modulator or electrooptic modulator.The incident beam modulated is the rectangular pulse signal having certain intervals by pulse-modulator.The repetition frequency of modulated pulse signal determines sensing scope, and the pulsewidth of pulse signal determines sensing resolution.
Preferably, what the photoelectric commutator in detecting unit only needed lower bandwidth just can complete measurement, because the bandwidth of beat frequency Brillouin signal is roughly about 1GHz.
The advantage that hinge structure of the present invention has is, two-way sensor fibre Brillouin scattering is utilized to carry out beat frequency, high-frequency detection is made to be converted to low-frequency acquisition, thus the high bandwidth photoelectric commutator not needing cost higher, do not need to carry out frequency modulation (PFM) thus lift structure complexity to local oscillator light in advance yet.
In order to realize above-mentioned and relevant object, will describe in detail and the feature particularly pointed out in the claims after one or more aspect of the present invention comprises.Explanation below and accompanying drawing describe some illustrative aspects of the present invention in detail.But what these aspects indicated is only some modes that can use in the various modes of principle of the present invention.In addition, the present invention is intended to comprise all these aspects and their equivalent.
Accompanying drawing explanation
By reference to the content below in conjunction with the description of the drawings and claims, and understand more comprehensively along with to of the present invention, other object of the present invention and result will be understood and easy to understand more.In the accompanying drawings:
Fig. 1 is the schematic diagram of the time domain reflection technology distributed fiberoptic sensor structure based on Brillouin scattering;
Fig. 2 is the schematic diagram of the time-domain analysis technical point cloth optical fibre sensor structure based on Brillouin scattering;
Fig. 3 is general structure schematic diagram of the present invention;
Fig. 4 is the spectrogram measuring the beat frequency Brillouin signal obtained;
Fig. 5 is measured beat frequency Brillouin signal frequency displacement and linear fit result under different design temperature.
Embodiment
In the following description, for purposes of illustration, in order to provide the complete understanding to one or more embodiment, many details have been set forth.But, clearly, also these embodiments can be realized when there is no these details.In other example, one or more embodiment for convenience of description, known structure and equipment illustrate in block form an.
Below with reference to accompanying drawings each embodiment of the present invention is described in detail.
With reference to shown in Fig. 3, of the present invention based on Brillouin scattering distributed optical fiber temperature sensor, comprise light source, pulse-modulator, Erbium-Doped Fiber Amplifier (EDFA), coupling mechanism, be laid on sensor fibre 1 together and sensor fibre 2, photoelectric commutator and electric spectrum analyzer.Preferably, light source can be narrow linewidth laser, and its centre wavelength is 1550nm, and live width is MHz magnitude.The output of narrow linewidth light source as incident light, is then coupled with 1 port of coupling mechanism after pulse-modulator modulation carries out power amplification with Erbium-Doped Fiber Amplifier (EDFA).Preferably, the coupling mechanism that splitting ratio is 50:50 is used, i.e. three-dB coupler.
Incident light, after coupling mechanism beam splitting, to be coupled with sensor fibre 1 and sensor fibre 2 by 3 ports of coupling mechanism and 4 ports respectively as detection light.The sensor fibre that two-way is laid on together all can produce the Brillouin scattering dorsad comprising temperature information.Two-way back-scattering light returns in coupling mechanism place conjunction bundle and is converted into beat frequency Brillouin electric signal by detecting unit, thus we can extract containing the temperature information on sensor fibre link.
In electric frequency spectrograph end of probe, beat frequency Brillouin signal is roughly near 1GHz.Compare the 11GHz of traditional scheme, obtain larger optimization, thus reduce detection cost.
Fig. 4 show the frequency spectrum of the beat frequency Brillouin signal that measurement obtains when 20 DEG C, 50 DEG C and 80 DEG C respectively and raw data to amplitude carry out 50 times average after carry out the result of Lorentz fit (degree of fitting be respectively R 2=0.948,0.977,0.975).When ambient temperature raises, the power of beat frequency Brillouin signal becomes large; Meanwhile, the full width at half maximum of its frequency spectrum reduces.This phenomenon is consistent with the characteristic of the Brillouin signal gain spectral of traditional structure.We are still using the centre frequency of Lorentz fit as the beat frequency Brillouin signal frequency displacement under current design temperature.Visible in figure, the frequency displacement of beat frequency Brillouin signal is at about 1.1GHz, and the variation range within the scope of the temperature change of setting is 25MHz, and therefore detective bandwidth is all lower than traditional structure.
The result of Fig. 5 measured beat frequency Brillouin signal frequency displacement under showing different design temperatures, straight line representative adopts least square method to carry out the result of linear fit.The slope of linear fit is the temperature coefficient of beat frequency Brillouin shift.The linear relationship of beat frequency Brillouin shift and design temperature is
δ v b(MHz)=0.34166T+1116.5 formula (5)
The temperature of T environment setting residing for sensor fibre in formula.In traditional structure, the temperature coefficient of Brillouin shift is about 1MHz/ DEG C. and the temperature coefficient of beat frequency Brillouin signal frequency displacement diminishes and thermometric error may be made to increase, and the metering system of multiple averaging can be revised to some extent to this error.
Therefore, the beat frequency Brillouin signal that the Brillouin scattering of the sensor fibre that the present invention utilizes two-way to be laid on together produces, can use the photoelectric detection equipment of lower bandwidth, thus reduces the cost of structure.
Although disclosed content shows exemplary embodiment of the present invention above, it should be noted that under the prerequisite not deviating from the scope of the present invention that claim limits, can multiple change and amendment be carried out.According to the structure of inventive embodiments described herein, the element of claim can substitute with the element of any function equivalent.Therefore, protection scope of the present invention should be determined by the content of appending claims.

Claims (4)

1., based on a Brillouin scattering distributed optical fiber temperature sensor, comprise narrow linewidth laser, pulse-modulator, Erbium-Doped Fiber Amplifier (EDFA), coupling mechanism, sensor fibre 1, sensor fibre 2 and detecting unit.Wherein, the laser that narrow linewidth laser sends is after pulsed modulation and power amplification, entered Brillouin scattering dorsad in sensor fibre 1 and sensor fibre 2. two-way sensor fibre and closed bundle by coupling mechanism beam splitting at coupling mechanism, and be converted to electric signal via the photoelectric commutator in detecting unit, i.e. beat frequency Brillouin signal.
2. according to claim 1 based on Brillouin scattering distributed optical fiber temperature sensor, wherein, two-way sensor fibre has different Brillouin shift.
3. according to claim 1 based on Brillouin scattering distributed optical fiber temperature sensor, wherein, detecting unit comprises photoelectric commutator and electric spectrum analyzer.
4. according to claim 3 based on Brillouin scattering distributed optical fiber temperature sensor, wherein, photoelectric commutator bandwidth is 1.5GHz, and electric spectrum analyzer is for showing beat frequency Brillouin signal frequency spectrum.
CN201310697476.0A 2013-12-18 2013-12-18 Distributed optical fiber temperature sensor based on Brillouin scattering Pending CN104729750A (en)

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CN106225816A (en) * 2016-07-01 2016-12-14 南京大学 A kind of grating sensing apparatus and method based on Brillouin's wave filter
CN108645500A (en) * 2018-06-11 2018-10-12 桂林电子科技大学 Method and device for vehicle vibration sensing sensitivity enhancement
WO2018207214A1 (en) * 2017-05-12 2018-11-15 INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT Madras) System for simultaneous multi-point dynamic parameter measurement in distributed optical sensing, and methods thereof
CN111628408A (en) * 2020-05-19 2020-09-04 电子科技大学 Frequency stabilization system of semiconductor laser
JPWO2021234887A1 (en) * 2020-05-21 2021-11-25

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Application publication date: 20150624