CN101975626B - Brillouin scattering based distributive fiber sensing system - Google Patents

Brillouin scattering based distributive fiber sensing system Download PDF

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CN101975626B
CN101975626B CN2010105053825A CN201010505382A CN101975626B CN 101975626 B CN101975626 B CN 101975626B CN 2010105053825 A CN2010105053825 A CN 2010105053825A CN 201010505382 A CN201010505382 A CN 201010505382A CN 101975626 B CN101975626 B CN 101975626B
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brillouin
light
fiber
laser
distributed
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CN2010105053825A
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CN101975626A (en
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孙军强
唐健冠
吴奇
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华中科技大学
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Abstract

The invention relates to a Brillouin scattering based distributive fiber sensing system which comprises a Brillouin fiber annular laser A and a distributive Brillouin fiber sensor B, wherein surplus pump light output by the Brillouin fiber annular laser A is used as detection light input into the distributive Brillouin fiber sensor B; laser output by the Brillouin fiber annular laser A is used as local oscillation light of the distributive Brillouin fiber sensor B; the detection light is input into the distributive Brillouin fiber sensor B to obtain back Brillouin scattered light containing temperature and stain information; and the back Brillouin scattered light is mixed with the local oscillation light to obtain the required temperature and stain information. The Brillouin scattering based distributive fiber sensing system has simple and stable structure and can be used for simultaneously measuring the temperature and the stain with a longer distance.

Description

A kind of distributed optical fiber sensing system based on Brillouin scattering
Technical field
The invention belongs to fiber laser and sensory field of optic fibre, be specifically related to a kind of distributed optical fiber sensing system.
Background technology
Brillouin fiber ring laser is that optical fiber is placed in the resonator cavity, utilizes brillouin gain in the optical fiber and lasing.Brillouin fiber ring laser has advantages such as width, frequency stabilization, gain direction sensitivity, is the focus that people study therefore always.And it is widely used in following many aspects: distributed temperature, pressure transducer; Narrow-band amplifier; The microwave frequency generator; Frequency shifter.
At present aspect the fiber laser of stimulated Brillouin scattering, carrying out many very significant work both at home and abroad; A lot of schemes have been proposed; Such as conventional brillouin fiber ring laser; With the chamber brillouin fiber ring laser, nonequilibrium brillouin fiber ring laser, brillouin fiber ring laser is amplified in er-doped.At this, we have proposed a kind of brillouin fiber ring laser of novelty, and it is simple in structure, and is low to light source requirements.
Fibre Optical Sensor is compared with conventional sensors as the novel sensing technology that the seventies grows up, and has many good qualities: anti-electromagnetic interference (EMI), and electrical isolation, corrosion-resistant, essential safety; Highly sensitive; In light weight, volume is little, and external form is variable; Cost is low.
Along with using the development of optical time domain reflection (OTDR) technology very widely in the engineering, produced the distributing optical fiber sensing technology.Compare with the quasi-distributed optical fiber sensing technology, the distributing optical fiber sensing technology has the ability of in the sensor fibre zone, obtaining simultaneously in time with spatial variations continuous distribution information.Since distributed fiberoptic sensor have other sensing technology incomparable advantage, therefore become the focus of present Research on Sensing area research.
At present based on the main theory of the research of the distributed fiberoptic sensor of scattering mechanism according to mainly containing Rayleigh scattering, these three kinds of Raman scattering and Brillouin scatterings.Wherein later relatively based on the starting of the profile optical fiber sensing technology of Brillouin scattering, but it measure when can realize temperature, strain, and the precision that can reach, measurement range and spatial resolution all are superior to other optical fiber sensing technology.Research based on the temperature sensor technology of Brillouin scattering mainly contains: 1. based on the profile optical fiber temperature sensor technology (BOTDR) of Brillouin light Time Domain Reflectometry; 2. based on the profile optical fiber temperature sensor technology (BOTDA) of Brillouin optical time domain analysis; 3. based on the profile optical fiber temperature sensor technology (BOFDA) of Brillouin light frequency-domain analysis.
Wherein the structure of BOTDR is comparatively simple, does not need two light sources, support breakpoint to measure, so lot of domestic and international research concentrates on this scheme.People such as Kurashima at first utilized the method for Coherent Detection to realize the temperature strain distributed measurement of spontaneous brillouin scattering signal in 1993.This method implements comparatively simple, but light source stability is had relatively high expectations.People such as T.P.Newson of Britain had realized the experimental study of direct detection brillouin scattering signal respectively with methods such as F-P interferometer and Mach-Zehnde interferometers afterwards; And, temperature and strain information have been realized obtaining simultaneously through Brillouin shift and intensity are measured simultaneously.People such as H.H.Kee and T.P.Newson adopted the measurement Rayleigh signal and the method for the ratio (Landau-Placzek Ratio) of Brillouin's signal that spatial resolution has been brought up in tens centimetres the scope in recent years, but the measuring accuracy that is realized is poor.
Summary of the invention
The present invention is based on the deficiency of prior art and makes; Its objective is provides a kind of optical fiber sensing system based on Brillouin scattering; This sensor-based system comprises Brillouin optical fiber laser and distributed Brillouin light fiber sensor, and this laser instrument can provide the output of a kind of width, frequency stabilization; This distributed Brillouin light fiber sensor can be measured temperature and strain signal simultaneously.
The concrete technical scheme that adopts is following:
A kind of distributed optical fiber sensing system based on Brillouin scattering; Comprise brillouin fiber ring laser A and distributed Brillouin light fiber sensor B; The residual pump light of said brillouin fiber ring laser A output is input among the said distributed Brillouin light fiber sensor B as surveying light; The laser of said brillouin fiber ring laser A output is as the local oscillator light of distributed Brillouin light fiber sensor B; Said detection light is imported in the sensor fibre of distributed Brillouin light fiber sensor B; Obtain containing the Brillouin scattering dorsad of temperature and strain information, this dorsad Brillouin scattering and said local oscillator light carry out mixing, can obtain required temperature and strain information.
As further improvement of the present invention; Described brillouin fiber ring laser A comprises pump laser; Polarization Controller, first optical circulator, single-mode fiber and photo-coupler; The pump light of said pump laser output is input to 1 port of first optical circulator again through its polarization state of Polarization Controller adjustment; Said single-mode fiber one end is connected with 2 ports of first optical circulator, and the other end is connected to photo-coupler; 3 ports of said first optical circulator also are connected to photo-coupler through Polarization Controller, and said brillouin fiber ring laser A exports described laser and residual pump light through photo-coupler.
As further improvement of the present invention; Said distributed Brillouin light fiber sensor B comprises modulator; Second optical circulator, sensor fibre and photodetector, said detection light is through being input to 1 port of second optical circulator after the modulators modulate; 2 ports of said second optical circulator connect one section sensor fibre; This sensor fibre is surveyed 3 ports that the sense light that obtains is passed through this second optical circulator, and injects photodetector with said local oscillator light, can obtain required temperature and strain information.
As further improvement of the present invention, said distributed Brillouin light fiber sensor B also comprises electric spectrum analyzer, and said photodetector is connected to this electricity spectrum analyzer, is used to show resulting temperature and strain information.
As further improvement of the present invention, said pump laser is a Distributed Feedback Laser, as the pump light source of brillouin fiber ring laser A.
As further improvement of the present invention, said modulator is used for continuous residual pump light is modulated into the pulse signal of the rectangle of certain intervals.
The invention provides a kind of Brillouin optical fiber laser, lower to the linewidth requirements of pump light source, adopt common single mode optical fibres can produce laser output, the device of use is simple, the laser rays width of output, stable.
In the laser instrument provided by the invention, comprise the Distributed Feedback Laser of a narrow linewidth, the optical circulator of one three port, a photo-coupler, the general single mode fiber of two Polarization Controllers and certain-length.
The present invention adopts one section common single mode optical fibres as gain media, the nonlinear effect in the utilization optical fiber---excited Brillouin gain amplifying optical signals, and need not media such as Er-doped fiber or semiconductor optical amplifier.Because the excited Brillouin gain only can appear at dorsad, so when 2 port input pumping lights, can obtain brillouin scattering signal dorsad at 2 ports.Brillouin's signal of 2 ports output re-enters single-mode fiber from 3 ports, as seed light, causes the excited Brillouin gain in the optical fiber, is further amplified, and exports from 2 ports once more.Above process repeats, and can produce light signal stable, narrow linewidth.
The present invention adopts a photo-coupler output laser.This coupling mechanism can adopt different splitting ratios, under the prerequisite that guarantees the Brillouin optical fiber laser steady operation, to regulate the output power of laser instrument.And remaining pump light also can be from another port output of coupling mechanism.
The invention provides a kind of distributed Brillouin light fiber sensor, it is characterized in that the Brillouin optical fiber laser that provides based on first aspect, make designs simplification, good stability.It comprises a modulator, an optical circulator, one section common single mode optical fibres, a photodetector and some analytical equipments.
The present invention is the detection light of the remaining pump light of the laser instrument that provides as sensor, and the output signal of the Brillouin optical fiber laser that above-mentioned laser instrument is provided is as local oscillator light.
The detection light that modulators modulate of the present invention is continuous becomes it and is suitable for pulsed optical signals of the present invention.
Pulsed light of the present invention from the output of 2 ports, gets into detection optical fiber from the 1 port input of optical fiber circulator.Because spontaneous Brillouin scattering only occurs in the back side, so transducing signal is imported from 2 ports, exports from 3 ports.Its transducing signal with respect to detectable signal the frequency displacement relevant with temperature and strain has taken place and intensity changes.
The present invention imports photodetector simultaneously with the continuous laser output that sense light signal and first of the present invention provide.Because two signals all pass through Brillouin shift, can produce the signal of low frequency through beat frequency, thereby only need the low-frequency acquisition device just can well detect transducing signal.Pass through certain signal Processing again, just can analyze the temperature and the strain information that wherein comprise.And confirm the positional information of occurrence temperature and STRESS VARIATION according to the time that pulsed light is input to detector.
The present invention is based on existing brillouin fiber ring laser and distributed Brillouin light fiber sensor provides a kind of new solution.This laser instrument is lower to the requirement of pump light source on the one hand, and general Distributed Feedback Laser just can meet the demands preferably.And common single mode optical fibres just can be used as gain media, does not need expensive Er-doped fiber.And the output of this laser instrument is not only stable but also width.On the other hand; The characteristic of the frequency displacement of this Fibre Optical Sensor utilization Brillouin optical fiber laser; High frequency is surveyed converted into low-frequency acquisition; Thereby do not need the but optics frequency-shift equipment of less stable of expensive high-frequency rate photodetector or complex structure, practiced thrift cost greatly, and reduced the complexity of system.The Brillouin laser of narrow linewidth has also increased the precision of sensing simultaneously as local oscillator light.Because what extrapolation received is usefulness, be achieved along the temperature and the high-resolution while sensor measuring of strain of the long range distribution of optical fiber.
Description of drawings
Fig. 1 is the structural representation that the present invention is based on the optical fiber sensing system of Brillouin scattering, comprises brillouin fiber ring laser A and distributed Brillouin light fiber sensor B.
Embodiment
Hereinafter combines accompanying drawing and specific embodiment that the present invention is done further explain.
Fig. 1 is the structural representation of the optical fiber sensing system based on Brillouin scattering of the present invention.This optical fiber sensing system comprises brillouin fiber ring laser A and distributed Brillouin light fiber sensor B.The residual pump light of said brillouin fiber ring laser output is input in the distributed Brillouin light fiber sensor as surveying light, and the laser of output is as the local oscillator light of this distributed Brillouin light fiber sensor.Survey in the sensor fibre of this distributed Brillouin light fiber sensor of light input, obtain containing the Brillouin scattering dorsad of temperature and strain information, itself and said local oscillator light carry out mixing, can obtain required temperature and strain information.
Said brillouin fiber ring laser A comprises pump laser 11 (like Distributed Feedback Laser), Polarization Controller 12 and 14, optical circulator 13, single-mode fiber 15, photo-coupler 16.The pump light of pump laser 11 outputs is input to 1 port of optical circulator 13 through Polarization Controller 12 its polarization states of adjustment.Single-mode fiber 15 1 ends are connected with 2 ports of optical circulator 13, and the other end is connected to photo-coupler 16, and 3 ports of optical circulator 13 also are connected to photo-coupler 16 through Polarization Controller 14.Brillouin laser and remaining pump light that said brillouin fiber ring laser produces through photo-coupler 16 outputs.
Said distributed Brillouin light fiber sensor B comprises modulator 17, optical circulator 18, sensor fibre 19, photodetector 20 and electric spectrum analyzer 21.Survey light and modulate 1 port that is input to optical circulator 18 through modulator 17.2 ports of optical circulator 18 connect one section sensor fibre 19, and this sensor fibre is surveyed 3 ports that the sense light that obtains is passed through optical circulator 18, and inject photodetector 20 with said local oscillator light.Sensor fibre 20 is connected electric spectrum analyzer 21, can see required temperature and strain information.
Pump laser 11 wherein is a Distributed Feedback Laser, is used for the pump light source as brillouin fiber ring laser.Regulate the output power of pump laser 11, make the threshold value of the luminous power of its injection fibre ring greater than the excited Brillouin amplification.The threshold value of excited Brillouin laser device is lower, and the excited Brillouin that therefore is readily embodied in the general single mode fiber amplifies.
Polarization Controller 12 and 14 can be for regulating the device of optical polarization arbitrarily.Because the polarization sensitivity of stimulated Brillouin scattering so need connect a Polarization Controller 12 its polarization states of control at the back at light source, is imported pump light 1 port of optical circulator 13 again.
The length of single-mode fiber is shorter in the present invention, and this will make entire equipment more or less freely integrated.Principle according to the excited Brillouin gain; Its amplification only occurs in dorsad, so the excited Brillouin gain signal that has amplified from the 2 ports input of optical fiber circulator 13, and is exported from 3 ports; Again get in the optical fiber ring laser, as the seed light of amplifying next time.When brillouin fiber ring laser concussion at first, flashlight whenever turns around and all is exaggerated.When through the regular hour, gain when equaling loss, laser instrument reaches a stable status.In ring laser, add a Polarization Controller 14, control its polarization state, make the more stable work of laser instrument.
Because therefore the folk prescription of optical circulator 13 has also just limited the generation of second order excited Brillouin gain to through characteristic in the brillouin fiber ring laser.And because the live width compression of stimulated Brillouin scattering, the live width that makes laser instrument can satisfy the application of a lot of aspects much smaller than original pump laser live width.
Brillouin fiber ring laser is through a coupling mechanism 16 output laser in this invention.This coupling mechanism is the ordinary optic fibre coupling mechanism, and the coupling ratio of coupling mechanism can swash the needs of penetrating condition and output power according to practical laser and select.Remaining pump light is also exported from another port of coupling mechanism 16, for sensor provides light source.
Modulator 17 is modulated into continuous remaining pump light the pulse signal of the rectangle of certain intervals.Modulator has very big influence to this system.Division is following: the length of the recurrent interval of modulation by sensor fibre decides; The pulse width size of modulation has then determined the size of sensor spatial resolution; The extinction ratio of modulator then has very big influence to the performance of system.In sum, the choose reasonable modulator, and it is great to set the rational modulation parameter meaning.
Light signal through ovennodulation is imported from 1 port of optical circulator 18, and gets into sensor fibre 19 from the output of 2 ports.Because brillouin scattering signal occurs in dorsad, therefore contain in the sensor fibre transducing signal light of temperature and strain information and just import from 2 ports of optical circulator, export from 3 ports.
From the flashlight that contains temperature and strain of 3 ports of circulator 18 output and the laser entering photodetector of from brillouin fiber ring laser, exporting 20.Two signals interfere, and produce and frequency and difference frequency.Owing to surpassed the responsive bandwidth of photodetector with frequency frequently, so in photodetector, can only receive difference frequency signal.Following expression is exactly the signal that we obtain in photodetector:
I ac ( t ) = 2 ρ P s ( t ) P L cos [ ( ω s - ω L ) t + ( φ s - φ L ) ]
Therefrom we can see I AcIn comprised all information such as amplitude, frequency and phase place.Simultaneously high-frequency signal is changed for a low frequency signal down, be convenient to receive and handle.Because detector can be selected the detector of low frequency for use, and the low-frequency acquisition utensil has very high sensitivity, the sensitivity that has therefore improved total system.
Final system is imported electric spectrum analyzer 20 with the low frequency signal that obtains and is observed.Frequency displacement and Strength Changes formula according to the formula Brillouin scattering:
v B=2nV aOsin(θ/2)
P B=P OBWv/2
And temperature and the strain stress relation corresponding according to parameter wherein, can handle the temperature and the strain information that obtain comprising in the optical fiber.
After above-mentioned device connects into the structure of Fig. 1 as requested, open Distributed Feedback Laser, and regulate Polarization Controller, just can obtain the output of stable single longitudinal mode laser.Open photodetector then, obtain temperature and strain signal along fiber distribution.

Claims (4)

1. distributed optical fiber sensing system based on Brillouin scattering; Comprise brillouin fiber ring laser A and distributed Brillouin light fiber sensor B; The residual pump light of said brillouin fiber ring laser A output is input among the said distributed Brillouin light fiber sensor B as surveying light; The laser of said brillouin fiber ring laser A output is as the local oscillator light of distributed Brillouin light fiber sensor B; Said detection light is imported in the sensor fibre of distributed Brillouin light fiber sensor B; Obtain containing the Brillouin scattering dorsad of temperature and strain information, this dorsad Brillouin scattering and said local oscillator light carry out mixing, can obtain required temperature and strain information;
Described brillouin fiber ring laser A comprises pump laser (11); Polarization Controller (12; 14), first optical circulator (13), single-mode fiber (15) and photo-coupler (16); The pump light of said pump laser (11) output is adjusted its polarization state through first Polarization Controller (12), is input to 1 port of first optical circulator (13) again; Said single-mode fiber (15) one ends are connected with 2 ports of first optical circulator (13), and the other end is connected to photo-coupler (16); 3 ports of said first optical circulator (13) also are connected to photo-coupler (16) through second Polarization Controller (14), and said brillouin fiber ring laser A is through photo-coupler (16) described laser of output and residual pump light;
Said distributed Brillouin light fiber sensor B comprises modulator (17); Second optical circulator (18); Sensor fibre (19) and photodetector (20); Be input to 1 port of second optical circulator (18) after said detection light is modulated through modulator (17), 2 ports of said second optical circulator (18) connect one section sensor fibre (19), and this sensor fibre (19) is surveyed 3 ports that the sense light that obtains is passed through this second optical circulator (18); And inject photodetector (20) with said local oscillator light, can obtain required temperature and strain information.
2. a kind of distributed optical fiber sensing system according to claim 1 based on Brillouin scattering; It is characterized in that; Said distributed Brillouin light fiber sensor B also comprises electric spectrum analyzer (21); Said photodetector (20) is connected to this electricity spectrum analyzer (21), is used to show resulting temperature and strain information.
3. a kind of distributed optical fiber sensing system based on Brillouin scattering according to claim 1 and 2 is characterized in that said pump laser (11) is a Distributed Feedback Laser, as the pump light source of brillouin fiber ring laser A.
4. a kind of distributed optical fiber sensing system based on Brillouin scattering according to claim 1 and 2 is characterized in that said modulator (17) is used for continuous residual pump light is modulated into the pulse signal of the rectangle of certain intervals.
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