Summary of the invention
The purpose of this invention is to provide a kind of Brillouin optical time domain analysis and mach zhender and interfere the common distribution type optical fiber sensing equipment that detects.
A kind of Brillouin optical time domain analysis and mach zhender are interfered the common distribution type optical fiber sensing equipment that detects, and it is characterized in that narrow-band light source, four photo-couplers, image intensifer, photoswitch, two optical polarization controllers, two photomodulators, two photoelectric detectors, electronic processors.Narrow-band light source is sent light and is divided into two-way through photo-coupler, and one tunnel output links to each other with the input end of photomodulator, and the output terminal of photomodulator links to each other with the input end of image intensifer; The output terminal of image intensifer links to each other with the input end of optical polarization controller; The output terminal of optical polarization controller links to each other with a of photo-coupler end, and the c end of photo-coupler links to each other with an end of optical fiber, and the d end of photo-coupler links to each other with an end of photoswitch; The other end of photoswitch links to each other with an end of optical fiber; And the other end of optical fiber is continuous respectively at a, the b end of photo-coupler, and the c of photo-coupler end links to each other with optical fiber one end, and the optical fiber other end then links to each other with the c end of photo-coupler; The a end of photo-coupler links to each other with the input end of photoelectric detector, and the b end of photo-coupler links to each other with the input end of photoelectric detector; Another road output of photo-coupler links to each other with the input end of photomodulator; The output terminal of photomodulator links to each other with the input end of optical polarization controller; The output terminal of optical polarization controller links to each other with the b of photo-coupler end, and the output terminal of photoelectric detector links to each other with the input end of electronic processors respectively.Electronic processors is controlled photomodulator.
Described photomodulator (3) can be electrooptic modulator or acousto-optic modulator, controlled by electronic processors, when device carries out Brillouin's input, carries out the light pulse modulation, makes pulsed light get into sensor fibre; And when carrying out mach zhender interference sensing, photomodulator does not carry out light amplitude modulation.
Described photomodulator (13) is the radio frequency electrooptic modulator, controlled by electronic processors, when device carries out Brillouin's input, modulates, and gets into sensor fibre after making incident light produce frequency displacement; And when carrying out mach zhender interference sensing, modulator carries out premodulation or does not carry out optical modulation.
Described photoswitch (17) is controlled by electronic processors, when device carries out Brillouin's input, breaks off, and is then closed when carrying out mach zhender interference sensing.
Utilize optical fiber Brillouin scatterometry temperature, strain principle: in optical fiber; The frequency displacement of Brillouin scattering is relevant with effective refractive index and velocity of ultrasonic sound in the optical fiber; The variation of ambient temperature and stress can both make effective refractive index and velocity of ultrasonic sound change, thereby changes Brillouin shift.So just can obtain the distribution on optical fiber of temperature or stress as long as detect the frequency displacement of Brillouin scattering.The mathematic(al) representation of Brillouin shift is:
(1)
v B Be the sharp deep frequency displacement of cloth;
nBe the fiber core refractive index;
v a Be the velocity of sound;
λBe the pumping light wavelength.When the pumping light wavelength
λDuring=1.55um, Brillouin shift is about 11GHz.
Brillouin shift and ambient temperature, strain are linear:
Wherein:
△ V B Be the Brillouin shift variable quantity;
△ε is the variable quantity of strain;
△ TBe temperature variation;
C VT Be the Brillouin shift temperature coefficient;
C τ E Be the Brillouin shift coefficient of strain;
C VT ,
C τ E Measurement can get, and when ambient temperature or strain are constant, can record extraneous strain or variation of temperature according to Brillouin shift.
Brillouin distributed optical fiber sensing mainly contains optical time domain reflection (BOTDR) and two kinds of mechanism of light time domain analysis (BOTDA), adopts light time domain analysis mode here.
Flashlight is divided into two-way after light source gets into photo-coupler (2), the one tunnel is exciting light, carries out getting into sensor fibre (7) top after the light pulse modulation through photomodulator (3); Another road is modulated the frequency displacement that produces about about 11GHz for surveying light through photomodulator (13), gets into sensor fibre (10) end.
What photoelectric detector (15) detected is to survey light, and its signal is reflected in sensor fibre stimulated Brillouin scattering size everywhere under certain frequency displacement.
When certain regional Brillouin shift equates in exciting light and the frequency difference of surveying light and the optical fiber, will produce Brillouin's enlarge-effect in this zone, the energy transfer takes place in two light beams each other.Because there are linear relationship in Brillouin shift and temperature, strain; Therefore; When the frequency of laser instrument is regulated continuously, through detecting the power of the continuous light that is coupled out from optical fiber one end, pairing difference on the frequency in the time of just can confirming that the energy transfer reaches maximum on each section of optical fiber zone; Thereby obtain temperature, strain information, realize distributed measurement.
The basic structure that mach zhender is interfered is that light source is divided into two paths of signals light through photo-coupler (2); One road flashlight is through being divided into two-way through photo-coupler (6); Inject reference arm (9) and signal arm (7) respectively; Get into through photo-coupler (8) again and return optical fiber (10), detect interference signal, be forward light by photoelectric detector (16); Another road flashlight gets into through photo-coupler (12) and returns optical fiber (10), gets into sensor fibre (comprising reference arm, signal arm) through photo-coupler (8) again, detects interference signal by photoelectric detector (15), is backlight.Positive and negative two-way light forms loop.
Flashlight transmits in the signal arm of optical fiber and reference arm, and signal arm is used for experiencing extraneous vibration, and reference arm is used for passing another road light of interferometer.As vibration or pressure signal when acting on the fiber-optic signal arm, can cause that the parameters such as physical dimension and refractive index of signal arm optical fiber change, the phase of light wave that causes transmitting therein changes.Simultaneously, similar variation does not take place in the phase of light wave that transmits in the reference arm, so produces phase differential between the two-beam of transmission in signal arm and the reference arm, when converging, will interfere, and the variation of interference light intensity is converted into the electric signal performance by photodetector.
Theoretical according to interference of light, when two-way light interfered in the arbitrfary point, this light intensity was:
(3)
,
are respectively the light intensity that interferes two-beam in the formula;
is the phase differential of two-beam; Extraneous vibration can cause the variation of
, thereby causes the variation that detects the light luminous power.
Owing to be the input of positive and negative two-beam,, just can confirm the position that vibrates according to receiving the mistiming of two-beam light intensity when changing.
Be located at signal arm
ZThe place vibrates, and then proves easily:
In the formula
LBe signal arm length,
LdFor returning fiber lengths,
nBe the fiber core refractive index,
cBe the light velocity in the vacuum,
△ TThe detection time that is two photoelectric detectors is poor.
The invention has the advantages that: in same device system, realize the Fibre Optical Sensor that Brillouin scattering and mach zhender are interfered; Can be implemented in the detection that realizes in the same device vibration and temperature (or strain); Can realize the long-distance distributed sensing of many reference amounts.
Embodiment
With reference to Fig. 1; The present invention is that a kind of Brillouin optical time domain analysis and mach zhender are interfered the common distribution type optical fiber sensing equipment that detects, and comprises narrow-band light source 1, four photo- couplers 2,6,8,12, image intensifer 4, photoswitch 17, two 3,13, two photoelectric detectors 15,16 of 5,14, two photomodulators of optical polarization controller, electronic processors 11.Narrow-band light source 1 is sent light and is divided into two-way through photo-coupler 2; One tunnel output links to each other with the input end of photomodulator 3; The output terminal of modulator 3 links to each other with the input end of image intensifer 4, and the output terminal of image intensifer 4 links to each other with the input end of optical polarization controller 5, and the output terminal of optical polarization controller 5 links to each other with a end of photo-coupler 6; The c end of photo-coupler (6) links to each other with an end of optical fiber (7); The d end of photo-coupler (6) links to each other with an end of photoswitch (17), and the other end of photoswitch (17) links to each other with an end of optical fiber (9), and the other end of optical fiber 7,9 is continuous respectively at a, the b end of photo-coupler 8; And the c of photo-coupler 8 end links to each other with optical fiber 10 1 ends; Optical fiber 10 other ends then link to each other with the c end of photo-coupler 12, and a end of photo-coupler 12 links to each other with the input end of photoelectric detector 16, and the b end of photo-coupler 6 links to each other with the input end of photoelectric detector 15; Another road output of photo-coupler 2 links to each other with the input end of photomodulator 13; The output terminal of photomodulator 13 links to each other with the input end of optical polarization controller 14; The output terminal of optical polarization controller 14 links to each other with the b end of photo-coupler 12, and the output terminal of photoelectric detector 15,16 links to each other with the input end of electronic processors 11 respectively.11 pairs of photomodulators 13 of electronic processors, modulator 3 and photoswitch 17 are controlled.
Photomodulator 3 adopts electrooptic modulator or acousto-optic modulator, and photomodulator 13 adopts the microwave electrooptical modulation, produces the frequency displacement about about 11GHz.
The work of two photomodulators of electronic processors control.When carrying out the Brillouin scattering measurement; Electronic processors 11 control photoswitches 17 break off; Produce pulsed light through photomodulator 3; Photomodulator 13 produces the light signal of about 11GHz left and right sides frequency displacement, and final Brillouin's signal exports photoelectric detector 15 to through photo-coupler 6, gets into electronic processors after the opto-electronic conversion.When carrying out the mach zhender interferometry, electronic processors 11 control photoswitches 17 closures, modulator carries out premodulation or light is not modulated, and positive and negative two-way direct current light gets into optical fiber, and forward light exports photoelectric detector 16 to through photo-coupler 12; Backlight exports photoelectric detector 15 to through photo-coupler 6, gets into electronic processors after converting electric signal to.
Through the frequency displacement
that measures Brillouin scattering; In conjunction with formula 1; Under the constant situation of ambient temperature or strain, can record extraneous strain or temperature conditions:
(5)
Measurement to mach zhender is interfered through detecting the variation of optical power signals, can reflect the extraneous vibration situation according to formula 3; According to formula 4, can calculate vibration nidus position through measuring the mistiming that two photoelectric detectors detect light signal.