CN103630229B - A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method and system - Google Patents
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method and system Download PDFInfo
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Abstract
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method and system, comprise: 1 × 2 optical branching device, the conjunction beam port of 1 × 2 optical branching device is connected with laser instrument, a point of beam port connects No. 1 port that postpones optical fiber and the one 3 port circulator successively, this 3 port circulator No. 2 ports connect an optical fiber in sensing optic cable, and No. 3 ports are connected with a point of beam port of Polarization Controller and 2 × 1 optical combiners in turn; Another point of beam port is connected directly to No. 1 port of the 23 port circulator, this 3 port circulator No. 2 ports connect another root optical fiber in sensing optic cable, and No. 3 ports connect another another point of beam port postponing optical fiber, phase-modulator and 2 × 1 optical combiners successively.The conjunction beam port of 2 × 1 optical combiners is connected with photodetector.The backscattering light signal that the pulsed light that laser instrument sends is formed in two optical fiber of sensing optic cable, is concerned with at the conjunction beam port of 2 × 1 optical combiners.
Description
Technical field
The present invention is a kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method and system, relates to Distributed Optical Fiber Sensing Techniques field and optical coherence detection field.
Background technology
Optical fiber sensing technology is the technology developed rapidly with the development of Fibre Optical Communication Technology the seventies and eighties in last century, and it take laser as communications carrier, and optical fiber is communication media, the New Sensing Technology of perception and the extraneous measured signal of transmission.Fibre Optical Sensor has that measurement sensistivity is high, electromagnetism interference, radioresistance, high pressure resistant, corrosion-resistant, volume is little, lightweight, adapt to the plurality of advantages such as rugged surroundings, and fiber optic component itself is detecting element and transfer element, many Fibre Optical Sensor unit can be connected form large-scale remote sensing system on fiber optic backbone, carry out distributed monitoring and measurement.
Distributed Optical Fiber Sensing Techniques can continuous coverage along the physical quantity of fiber distribution, and the space distribution state of this tittle can be obtained.Most of distributed sensing technology is mainly used to measure some static amount or gradual amount, closely achieves very high index at present.But in application scenarios such as Air-liquid pipeline monitoring, fire alarm and circumference security protections, need sensor to detect and become disturbance with when location sound, vibration etc.At present, distributed optical fiber vibration sensing technology mainly contains long distance interference technique, coherent light time domain reflection technology.
Based on the long distributed vibration sensing system apart from interference technique mainly through the frequency response distributed measurement that realize vibrate relevant to disturbance location of interferometer, be difficult to the detection and positioning realizing multiple spot vibration event.The phase place change of the back-scattering light that relevant time domain scatter-type distributed optical fiber vibration sensing system is produced in sensor fibre by coherent measurement light pulse comes perception extraneous vibration and location, there is location algorithm simple, detection and positioning while multiple spot vibration event can be realized.Coherent measurement technology mainly contains two kinds: common relevant and differential coherence.Adopting the method for common coherent measurement, there is larger impact to the detection of vibration in environment temperature, pressure etc. slowly change.The method that employing differential coherence is measured, to environment temperature, pressure etc., slowly change is insensitive, responsive to accident, is more suitable for the monitoring for the detection of circumference intrusion event and Air-liquid pipeline.
It is large to there is power attenuation in current differential coherence time domain scatter-type distributed optical fiber vibration sensing system, there is multiple blind area, the shortcoming that distance sensing is short.In engineering construction, need in sensing optic cable, add fiber reel and avoid blind area, difficulty of construction is large, and the stability of simultaneity factor is also subject to larger impact.These shortcomings all limit the market application of the differential coherence time domain scatter-type distributed optical fiber vibration sensing system with features such as low environment noise height vibration event, perceptual sensitivity.
Summary of the invention
The invention provides a kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method and system, the present invention postpones optical fiber by two, 3 port circulators, the combination of two Fibre Optical Sensor optical cable, define dipulse light---back-scattering light orthoscopic differential interference structure, the differential coherence achieving the backscattering light wave modulated by extraneous vibration signal phase in sensing optic cable detects, to vibration bursts event, there is high sensitivity, insensitive to gradual environment parameter, signal to noise ratio (S/N ratio) is high, compared with traditional differential coherence time domain scatter-type distributed optical fiber vibration sensing system, there is optical path loss little, highly sensitive, without sensing blind area, the advantages such as continuous large sensing is dynamic.
The present invention adopts following technical scheme:
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method, the pulsed light that laser instrument exports also is divided into two pulsed lights by 1 × 2 optical branching device,
A pulsed light postpones optical fiber through one, be transferred to No. 1 port of the one 3 port circulator, through No. 2 ports of the one 3 port circulator, be transferred in a sensor fibre in sensing optic cable, and scattering is there is in described sensor fibre, the back-scattering light produced, described back-scattering light is transferred to No. 2 ports of the one 3 described port circulator with the direction contrary with a pulsed light transmission direction in described sensor fibre, 2 × 1 optical combiners are transferred to successively through No. 3 ports of the one 3 described port circulator and Polarization Controller,
Another pulsed light is through being directly transferred to No. 1 port of the 23 port circulator, through No. 2 ports of the 23 port circulator, be transferred in another root sensor fibre in described sensing optic cable, and scattering is there is in another described root sensor fibre, the back-scattering light produced, described back-scattering light is transferred to No. 2 ports of the 23 described port circulator with the direction contrary with another pulsed light transmission direction in another described root sensor fibre, pass through No. 3 ports of the 23 described port circulator successively, another postpones optical fiber and phase-modulator, be transferred to 2 × 1 optical combiners,
Two bundle back-scattering lights, after the conjunction beam port of 2 × 1 optical combiners is interfered, are transferred to photodetector.Described delay optical fiber (31) is identical with the fiber core refractive index that another postpones optical fiber (32), and the live width Δ f of length difference Δ L and described laser instrument (1) meets following relation:
N is described delay optical fiber (31) and the fiber core refractive index of another delay optical fiber (32), and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing system, comprising: 1 × 2 optical branching device, sensing optic cable and 2 × 1 optical combiners, the conjunction beam port of 1 × 2 optical branching device is connected with laser instrument,
A point of beam port of 1 × 2 optical branching device is connected with one and postpones optical fiber, and a point of beam port of 1 × 2 described optical branching device postpones optical fiber one end be connected with described one, described one other end postponing optical fiber is connected with the one 3 port circulator, and described delay other end for optical fiber is connected with No. 1 port of the one 3 port circulator, No. 2 ports of the one 3 described port circulator are connected with the sensor fibre one end of in sensing optic cable, No. 3 ports of the one 3 described port circulator are connected with Polarization Controller and are connected with one end of Polarization Controller, the other end of described Polarization Controller is connected with a point of beam port of 2 × 1 optical combiners,
Another point of beam port of 1 × 2 optical branching device is connected with the 23 port circulator and is connected with No. 1 port of the 23 port circulator, No. 2 ports of the 23 described port circulator are connected with another root sensor fibre one end in sensing optic cable, No. 3 ports of the 23 described port circulator are connected with another to postpone optical fiber and is connected with another described port postponing optical fiber, another described another port postponing optical fiber is connected with phase-modulator and is connected with a port of phase-modulator, another port of described phase-modulator is connected with another point of beam port of 2 × 1 optical combiners,
The conjunction beam port of 2 × 1 described optical combiners is connected with photodetector.A described delay optical fiber is identical with the fiber core refractive index that another postpones optical fiber, and the live width Δ f of length difference Δ L and described laser instrument meets following relation:
N is a described fiber core refractive index postponing optical fiber and postpone optical fiber with another, and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
Compared with prior art, tool of the present invention has the following advantages:
The present invention, by two sensing optic cable conbined usage postponing optical fiber, 3 port circulators, twin-core fiber, achieves dipulse light---backscattering light beam orthoscopic differential interference.Pulsed light is divided into two pulses light by 1 × 2 optical branching device, a branch of pulsed light first postpones optical fiber through one, then be coupled in sensing optic cable in a sensor fibre by No. 1, the one 3 port circulator, No. 2 ports, the back-scattering light produced in sensor fibre more thus circulator be coupled to 2 × 1 optical combiners from its No. 3 ports through Polarization Controller; Another beam pulse light to be directly coupled in sensing optic cable in another root sensor fibre by No. 1, the 23 port circulator, No. 2 ports, the back-scattering light produced in sensor fibre more thus circulator be coupled to another from its No. 3 ports and postpone optical fiber, be transferred to 2 × 1 optical combiners through phase-modulator.Because two postpone the length approximately equal of optical fiber, its length difference is less than the coherent length of laser instrument, and two-beam interferes.Two sensor fibres are in same optical cable, and the optical-fiber deformation that extraneous vibration causes is similar to identical, and the phase place occurred by the same vibration modulation change of two bundle back-scattering lights is consistent.Because a branch of backscattering only first postpones to modulate again, another bundle is that backscattering is only first modulated and postponed, there is the phase-modulation mistiming in two bundle back-scattering lights, formula (1) give photoelectric detector of the present invention to backscatter signals power be scattered in the relational expression of the position occurred in sensor fibre:
In formula (1), S represents backscattering capture coefficient, and a represents fibre loss coefficient (unit is Km-1), a
srepresent fibre scattering coefficient (unit is Km-1), w represents light impulse length (unit is Km), L
1represent the length postponing optical fiber, P
0represent light source output power, v
grepresent the velocity of propagation of light in fibre core,
represent the phase place change of the light wave propagated in a fiber that extraneous vibration causes,
represent due to two constant light path differences postponing the two bundle back-scattering lights that the different and phase-modulator of fiber lengths is introduced.
As can be seen from formula (1), interfering in this is differential interference, for the environment parameter of slowly change, in formula (1-1)
the luminous power that the conjunction road port of optical combiner exports can not change along with the change of these physical quantitys, thus eliminates the restriction of these physical quantitys to system performance and stability.
Contrast adopts the relevant time domain scatter-type distributed optical fiber vibration sensing system of super-narrow line width laser instrument, external modulation and plain interference, the performance of system can not be subject to the restriction of gradual environment parameter, stability and reliability are all improved, and do not need to use super-narrow line width laser instrument, cost is low.
Contrast adopts closes the loop structure conventional differential of Wave coupling based on coupling mechanism and to be concerned with time domain scatter-type distributed optical fiber vibration sensing system, due to the double-sensing optical fiber of the present invention's employing, dipulse light---the back-scattering light orthoscopic differential interference of individual delays, light beam does not need to be coupled in same sensor fibre by coupling mechanism, can not there is conventional differential to be concerned with the sensing blind zone problem of time domain scatter-type distributed optical fiber vibration sensing system, optical path loss is 1/4 of legacy system optical path loss.So the sensing scope of differential coherence time domain scatter-type distributed optical fiber vibration sensing system that the present invention proposes and sensitivity are all better than traditional conventional differential and are concerned with time domain scatter-type distributed optical fiber vibration sensing system.Owing to there is not sensing blind area, do not need the blind area using fiber reel to avoid on sensing scope, the stability problem do not introduced because of the use of these fiber reels, engineering construction is simple, and native system is reliable and stable.
Accompanying drawing explanation
Fig. 1 is the DC-OTDR type distributed optical fiber vibration sensing system structural drawing that the present invention proposes;
Fig. 2 is extraneous friction signal, in the DC-OTDR type distributed optical fiber vibration sensing system that the present invention proposes photoelectric detector to backscattering light signal and the relation of its position produced in sensor fibre;
Fig. 3 is that the external world has vibration signal, the frequency response characteristic of the DC-OTDR type distributed optical fiber vibration sensing system vibration signal to external world that the present invention proposes.
Embodiment
Embodiment 1
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method, the pulsed light that laser instrument 1 exports also is divided into two pulsed lights by 1 × 2 optical branching device 21,
A pulsed light postpones optical fiber 31 through one, be transferred to No. 1 port 4101 of the one 3 port circulator 41, through No. 2 ports 4102 of the one 3 port circulator 41, be transferred in a sensor fibre 81 in sensing optic cable 8, and scattering is there is in described sensor fibre 81, the back-scattering light produced, described back-scattering light is transferred to No. 2 ports 4102 of the one 3 described port circulator 41 with the direction contrary with a pulsed light transmission direction in described sensor fibre 81, 2 × 1 optical combiners 22 are transferred to successively through No. 3 ports 4103 of the one 3 described port circulator 41 and Polarization Controller 5,
Another pulsed light is through being directly transferred to No. 1 port of the 23 port circulator 42, through No. 2 ports 4202 of the 23 port circulator 42, be transferred in another root sensor fibre 82 in described sensing optic cable 8, and scattering is there is in another described root sensor fibre 82, the back-scattering light produced, described back-scattering light is transferred to No. 2 ports 4202 of the 23 described port circulator 42 with the direction contrary with another pulsed light transmission direction in another described root sensor fibre 82, pass through No. 3 ports 4203 of the 23 described port circulator 42 successively, another postpones optical fiber 32 and phase-modulator 6, be transferred to 2 × 1 optical combiners 22,
Two bundle back-scattering lights, after the conjunction beam port of 2 × 1 optical combiners 22 is interfered, are transferred to photodetector 7.A described delay optical fiber 31 is identical with the fiber core refractive index that another postpones optical fiber 32, and the live width Δ f of length difference Δ L and described laser instrument 1 meets following relation:
N is a described fiber core refractive index postponing optical fiber 31 and postpone optical fiber 32 with another, and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
Embodiment 2
A kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing system, comprising: 1 × 2 optical branching device 21, sensing optic cable 8 and 2 × 1 optical combiner 22, the conjunction beam port of 1 × 2 optical branching device 21 is connected with laser instrument 1,
A point of beam port of 1 × 2 optical branching device 21 is connected with one and postpones optical fiber 31, and a point of beam port of 1 × 2 described optical branching device 21 postpones optical fiber 31 one end be connected with described one, described one other end postponing optical fiber 31 is connected with the one 3 port circulator 41, and described delay other end for optical fiber 31 is connected with No. 1 port 4101 of the one 3 port circulator 41, No. 2 ports 4102 of the one 3 described port circulator 41 are connected with the sensor fibre 81 of in sensing optic cable 8 one end, No. 3 ports 4103 of the one 3 described port circulator 41 are connected with Polarization Controller 5 and are connected with one end of Polarization Controller 5, the other end of described Polarization Controller 5 is connected with a point of beam port of 2 × 1 optical combiners 22,
Another point of beam port of 1 × 2 optical branching device 21 is connected with the 23 port circulator 42 and is connected with No. 1 port 4201 of the 23 port circulator 42, No. 2 ports 4202 of the 23 described port circulator 42 are connected with another root sensor fibre 82 one end in sensing optic cable 8, No. 3 ports 4203 of the 23 described port circulator 42 are connected with another to postpone optical fiber 32 and is connected with another described port postponing optical fiber 32, another described another port postponing optical fiber 32 is connected with phase-modulator 6 and is connected with a port of phase-modulator 6, another port of described phase-modulator 6 is connected with another point of beam port of 2 × 1 optical combiners 22,
The conjunction beam port of 2 × 1 described optical combiners 22 is connected with photodetector 7.A described delay optical fiber 31 is identical with the fiber core refractive index that another postpones optical fiber 32, and the live width Δ f of length difference Δ L and described laser instrument 1 meets following relation:
N is a described fiber core refractive index postponing optical fiber 31 and postpone optical fiber 32 with another, and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
In the implementation case, the length postponing optical fiber 31 is 20145m, and another length postponing optical fiber 32 is 20146m, and the live width of laser instrument 1 is 2MHz, and sensing optic cable length is 15Km, has built system.After tested, the loss of light path is 3.3dB, and closing the loop structure conventional differential of the Wave coupling time domain scatter-type distributed optical fiber vibration sensing system that is concerned with based on coupling mechanism is 9.7dB.The optical path loss of differential coherence time domain scatter-type distributed optical fiber vibration sensing system that the present invention proposes be about conventional differential be concerned with time domain scatter-type distributed optical fiber vibration sensing system optical path loss 1/4.Fig. 2 gives and adopts the DC-OTDR type distributed optical fiber vibration sensing system of the present invention's proposition when extraneous friction, the backscattering light signal that photoelectric detector arrives.As can be seen from the figure, during extraneous friction, backscattering light signal is continuous print, characterizes sensing optic cable and can measure extraneous vibration signal in non-blind area continuously.Fig. 3 gives when the applying mechanical vibration of sensing optic cable 5Km, 10Km and 12.5Km place, the backscattering light signal that the photoelectric detector in the DC-OTDR type distributed optical fiber vibration sensing system that the present invention proposes arrives.Can obviously find out from Fig. 3, at 5Km, 10Km and 12.5Km place, photoelectric detector to backscattering optical signal power there occurs sudden change, based on this, detection and the location of vibration event can be realized.
Claims (4)
1. a differential coherence time domain scatter-type distributed optical fiber vibration sensing method, is characterized in that, the pulsed light that laser instrument (1) exports is divided into two pulsed lights by 1 × 2 optical branching device (21),
A pulsed light postpones optical fiber (31) through one, be transferred to No. 1 port (4101) of the one 3 port circulator (41), through No. 2 ports (4102) of the one 3 port circulator (41), be transferred in a sensor fibre (81) in sensing optic cable (8), and scattering is there is in described sensor fibre (81), produce back-scattering light, described back-scattering light is transferred to No. 2 ports (4102) of the one 3 described port circulator (41) with the direction contrary with a pulsed light transmission direction in described sensor fibre (81), No. 3 ports (4103) and the Polarization Controller (5) that pass through the one 3 described port circulator (41) are successively transferred to 2 × 1 optical combiners (22),
Another pulsed light is through being directly transferred to No. 1 port of the 23 port circulator (42), through No. 2 ports (4202) of the 23 port circulator (42), be transferred in another root sensor fibre (82) in described sensing optic cable (8), and scattering is there is in another described root sensor fibre (82), produce back-scattering light, described back-scattering light is transferred to No. 2 ports (4202) of the 23 described port circulator (42) with the direction contrary with another pulsed light transmission direction in another described root sensor fibre (82), pass through No. 3 ports (4203) of the 23 described port circulator (42) successively, another postpones optical fiber (32) and phase-modulator (6), be transferred to 2 × 1 optical combiners (22),
Two bundle back-scattering lights, after the conjunction beam port of 2 × 1 optical combiners (22) is interfered, are transferred to photodetector (7).
2. a kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing method according to claim 1, it is characterized in that, described delay optical fiber (31) is identical with the fiber core refractive index that another postpones optical fiber (32), and described one postpones optical fiber (31) and meets following relation with the live width Δ f of another length difference Δ L and described laser instrument (1) postponing optical fiber (32):
N is described delay optical fiber (31) and the fiber core refractive index of another delay optical fiber (32), and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
3. a differential coherence time domain scatter-type distributed optical fiber vibration sensing system, it is characterized in that, comprise: 1 × 2 optical branching device (21), sensing optic cable (8) and 2 × 1 optical combiners (22), the conjunction beam port of 1 × 2 optical branching device (21) is connected with laser instrument (1)
A point of beam port of 1 × 2 optical branching device (21) is connected with one and postpones optical fiber (31), and a point of beam port of described 1 × 2 optical branching device (21) postpones optical fiber (31) one end be connected with described one, described one other end postponing optical fiber (31) is connected with the one 3 port circulator (41), and described other end postponing optical fiber (31) is connected with No. 1 port (4101) of the one 3 port circulator (41), No. 2 ports (4102) of the one 3 described port circulator (41) are connected with sensor fibre (81) one end in sensing optic cable (8), No. 3 ports (4103) of the one 3 described port circulator (41) are connected with Polarization Controller (5) and are connected with one end of Polarization Controller (5), the other end of described Polarization Controller (5) is connected with a point of beam port of 2 × 1 optical combiners (22),
Another point of beam port of 1 × 2 optical branching device (21) is connected with the 23 port circulator (42) and is connected with No. 1 port (4201) of the 23 port circulator (42), No. 2 ports (4202) of the 23 described port circulator (42) are connected with another root sensor fibre (82) one end in sensing optic cable (8), No. 3 ports (4203) of the 23 described port circulator (42) are connected with another and postpone optical fiber (32) and be connected with another described port postponing optical fiber (32), another described another port postponing optical fiber (32) is connected with phase-modulator (6) and is connected with a port of phase-modulator (6), another port of described phase-modulator (6) is connected with another point of beam port of 2 × 1 optical combiners (22),
The conjunction beam port of described 2 × 1 optical combiners (22) is connected with photodetector (7).
4. a kind of differential coherence time domain scatter-type distributed optical fiber vibration sensing system according to claim 3, it is characterized in that, described delay optical fiber (31) is identical with the fiber core refractive index that another postpones optical fiber (32), and described one postpones optical fiber (31) and meets following relation with the live width Δ f of another length difference Δ L and described laser instrument (1) postponing optical fiber (32):
N is described delay optical fiber (31) and the fiber core refractive index of another delay optical fiber (32), and C is the speed that in vacuum, light is propagated, and meanwhile, length difference Δ L is less than 10m.
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| CN103954348B (en) * | 2014-05-12 | 2016-04-13 | 重庆大学 | Based on the distributed optical fiber vibration sensing system of differential pulse sequence |
| CN104567957B (en) * | 2014-12-30 | 2017-02-22 | 东南大学 | Method and device for leveling scattering path line of distributed fiber-optic sensing system |
| CN105675080A (en) * | 2016-04-14 | 2016-06-15 | 长安益阳发电有限公司 | Liquid level measurement device outside thermal power plant desulfurizing absorption tower |
| CN106197649A (en) * | 2016-07-25 | 2016-12-07 | 北京众成探知信息技术有限公司 | A kind of optical fiber distributed type pipe vibration signal detecting method based on multifiber cable |
| CN110617874B (en) * | 2019-10-16 | 2021-11-23 | 南京理工大学 | phi-OTDR system based on double-pulse phase-shifting interference and phase demodulation method |
| CN110987038B (en) * | 2019-12-17 | 2021-12-07 | 南京曦光信息科技有限公司 | Distributed optical fiber disturbance detection device |
| CN114234818B (en) * | 2021-12-17 | 2023-09-22 | 中国计量科学研究院 | Laser interferometry displacement measurement system and method |
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| CN101893475B (en) * | 2010-03-11 | 2015-11-25 | 上海华魏光纤传感技术有限公司 | A kind of distributed optical fiber vibration sensing system based on fiber delay line |
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