CN106482822A - A kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne - Google Patents
A kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne Download PDFInfo
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- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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Abstract
The invention discloses a kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne, the system is made up of laser instrument, coupler, acousto-optic modulator, electrooptic modulator, erbium-doped fiber amplifier, wave filter, circulator, balanced detector, power-sharing device, data collecting card etc.；The modulation light for receiving and the beat signal of local oscillator light are converted into AC signal by balanced detector 1, beat signal of the balanced detector 2 by the Reyleith scanttering light for receiving with local oscillator light is converted into AC signal, two parts AC signal passes through power-sharing device 1,2 respectively, it is mixed two-by-two, the AC signal of output is converted into data signal by data collecting card, carries out Digital Signal Processing in a computer；Present system tracks the drift of feeler arm medium frequency and the change of phase place with the beat signal not comprising vibration information for interfering reference arm to produce, measured signal distortion phenomenon can effectively be overcome, so as to stable vibration signal intensity and frequency information is obtained, the discrimination of vibration source is improved.
Description
Technical field
The present invention relates to a kind of distributed optical fiber vibration sensing system, more particularly to a kind of based on double homologous heterodyne phase
The phase sensitive optical time domain reflection system of dry detection.
Background technology
At present, phase sensitive optical time domain reflection technology quickly grows, and it can realize the real-time monitoring of multipoint disturbance, have
Sensitivity is high, wide dynamic range, the advantages of electromagnetism interference characteristic is strong, therefore circumference can invade, pipe safety, building knot
Structure health, the multiple fields such as train running state carry out safety monitoring and real-time early warning.Research for the technology is by many
Accurately identifying for precise positioning turn signal is put, to reduce system rate of false alarm.
The realization of phase sensitive optical time domain reflection technology depends on two kinds of system architectures：Direct-detecting mode and relevant inspection
Survey formula.The structure of direct-detecting mode and demodulation method are simple, but can only detection signal Strength Changes, it is impossible to meet vibration thing
The needs of part identification, then propose a kind of phase sensitive optical time domain reflection system based on coherence detection.For-
For OTDR system, the signal demodulating method based on relevant detection mainly has two kinds, including the relevant detection of heterodyne and digital coherent
Detection.Heterodyne detection method is made reference signal using local oscillator light and is concerned with the detectable signal comprising vibration information, using complicated reality
When synchronous circuit and FLL come reduce system fluctuation caused by the frequency drift brought by laser instrument and acousto-optic modulator (
First technology [1]:“Qin,Z.；Chen,L.；Bao,X.Continuous wavelet transform for non-
stationary vibration detection with phase-OTDR.”Opt.Express 2012,20,20459–
20465).AC signal is converted to data signal by another kind of method first, then carries out digital mixing in a computer, numeral
Filtering, therefore digital coherent detection need the data collecting card of a superelevation frequency acquisition, simultaneously need to more memory spaces
Data process time, causes the real-time of digital coherent detection method poor.(first technology [2]:“Pan,Z.；Liang,
K.；Zhou,J.；Ye,Q.；Cai,H.；Qu,R.Interference-fading-free phase-demodulated OTDR
System. ", In Proceedings of the 22nd International Conference on Optical Fiber
Sensor,Beijing,China,15–19October 2012.).The accurate intensity for obtaining disturbing signal, frequency, phase information
The key for realizing disturbing signal pattern-recognition, it is desirable between reference signal and measured signal with strict clock synchronous and
Metastable phase difference.
Content of the invention
In this patent, it is proposed that a kind of phase sensitive optical time domain reflection system of the detection method that is concerned with based on double homologous heterodyne
System.The system tracks the drift of feeler arm medium frequency using the beat signal not comprising vibration information for interfering reference arm to produce
With the change of phase place, effectively can overcome due to system real time synchronization poor, laser frequency drift and acousto-optic modulator temperature
The measured signal distortion phenomenon that degree bad adaptability causes.
The technical solution of the present invention is as follows：
A kind of phase sensitive optical time domain reflection system of the detection method that is concerned with based on double homologous heterodyne, feature are its composition
Structure includes：Narrow linewidth, low frequency float, the ECLD 1 of low phase noise, low relative intensity noise, the first optical fiber
Coupler 2, the second fiber coupler 3, acousto-optic modulator 4, Acousto-Optic Modulator Driver 5, the 3rd fiber coupler the 6, the 4th
The balance of fiber coupler 7, first amplifies detector 8, the first bandpass filter 9, the first power-sharing device 10, electrooptic modulator
11st, erbium-doped fiber amplifier 12, the second bandpass filter 13, circulator 14, sensor fibre 15, the 5th fiber coupler 16,
Two balance amplifiers 17, the 3rd bandpass filter 18, the second power-sharing device 19, the first frequency mixer 20, the first low pass filter
21st, the second frequency mixer 22, the second low pass filter 23, capture card 24, interprocess communication 25, data processing, the position of above-mentioned part
Put relation as follows：
The output end of described ECLD is connected with the input of the first fiber coupler by optical fiber,
Second output port of the first fiber coupler is connected with the second fiber coupler first input end, and the first output end is adjusted with acousto-optic
The input connection of device processed, the output end of the acousto-optic modulator are connected with the first input port of the 3rd fiber coupler, institute
First output port of the second fiber coupler that states is connected with the first input port of the 4th fiber coupler, the 3rd optical fiber
Second output port of coupler is connected with the 4th the second input port of fiber coupler, described the 4th fiber coupler
First output port, the second output port connect the first balance respectively and amplify the first input port of detector, the second input
Mouthful, the output port of the detector is connected with the first bandpass filter input, the output end of the bandpass filter and first
The input of power-sharing device is connected, the first output end of described the 3rd fiber coupler and the input of electrooptic modulator
It is connected, the output end of the electrooptic modulator is connected with the input of erbium-doped fiber amplifier, the erbium-doped fiber amplifier
Output end is connected with the input port of the second bandpass filter, and the output port of the wave filter is connected with the first port of circulator
Connect, the second port of the circulator is connected with sensor fibre, the 3rd output port of the circulator and the 5th fiber coupler
First input port be connected, the second output end of the second described fiber coupler is defeated with the second of the 5th fiber coupler
Enter end to be connected, the first of the first output end of the 5th fiber coupler and respectively with the second balance amplifier of the second output end is defeated
Enter end, the second input to be connected, the output port of the detector is connected with the 3rd bandpass filter input, the band logical filter
The output end of ripple device is connected with the input of the second power-sharing device, the first output end of described the first power-sharing device and
First output end of the second power-sharing device connects first port and the second port of the first frequency mixer respectively.The frequency mixer defeated
Exit port connects the input port of the first low pass filter, the described end of the first power-sharing device and the end of the second power-sharing device
First port, the second port of second frequency mixer are connect respectively, and the output port of the frequency mixer connects the input of the second low pass filter
Port, the output port of first, second described low pass filter connect the first input port of capture card, the second input respectively
Mouthful.The output port of the capture card connects electrooptic modulator, and the output port of capture card is connected with computer.Described acousto-optic modulation
The modulated terminal of device is connected with direct current standard TTL power supply.
Be concerned with the phase sensitive optical time domain reflection system of detection based on double homologous heterodyne, it is characterised in that the system is adopted
The beat signal not comprising vibration information for interfering reference arm to produce tracking the drift of feeler arm medium frequency and the change of phase place,
Effectively can overcome as between capture card and frequency modulator, real time synchronization is poor, laser frequency is drifted about, acousto-optic modulator temperature
The measured signal distortion phenomenon that degree bad adaptability causes.
For the system, interfere the formation of beat signal in reference arm：
The continuous light sent by ECLD 12 after the first fiber coupler, the local oscillator light of 10% part
Field intensity is EL(t)=ELexpj[wLt+ΦL(t)], with the output of the 3rd fiber coupler 6 by sound after the second fiber coupler 3
10% of continuous light after the modulation of optical modulator 4 is interfered in the 4th fiber coupler 7, and the light field intensity of output can be expressed as
Here EL、wL, ΦLT (), is the amplitude of local oscillator light, angular frequency, initial phase respectively.EL,AT () is the dry of output
Relate to amplitude, IL,AT () is the interference light intensity of output, EA、wAThe amplitude of the light that has respectively been modulated by acousto-optic modulator 4, angular frequency,
Δ w and Φ (t) are that laser frequency is drifted about as between capture card and frequency modulator, real time synchronization is poor, 4 temperature of acousto-optic modulator
The angular frequency transfer of the light that degree bad adaptability causes and phase place change.
Interference reference arm in the system, local oscillator light is with the continuous probe light that has been modulated by acousto-optic modulator 4 by relevant
Beat signal is obtained, is obtained and eliminates local oscillator light angular frequency wLWith initial phase ΦLThe signal of (t).
For the system, the formation of the beat signal comprising vibration information in feeler arm：
The continuous light sent by ECLD 1 after 2 light splitting of the first fiber coupler, 90% detection light
Acousto-optic modulator 4 is entered, and by the continuous light after shift frequency, pulsed light is chopped into through electrooptic modulator 11, then is put through Er-doped fiber
Big device 12, the first bandpass filter 13, light pulse are injected into sensor fibre 15 through circulator 14, carry vibration signal dorsad
Rayleigh scattering light is interfered in the 5th fiber coupler 16 with the local oscillator light exported from the second fiber coupler 3, the containing of output
The beat signal of vibration information can be expressed as
EL,ST () is the interference amplitude of output, IL,sT () is the interference light intensity of output, r is the amplitude of Rayleigh scattering, ESFor
Probe optical pulse, comprising pulse shape function, γ is the coherence factor determined by Light source line width, and α is fibre loss, and z is optical fiber
In location point, θ is the polarization angle for deviateing local oscillator light wave, and φ (t) is to detect the phase shift transmission of light and scattering phase shift sum.
For the feeler arm in system, it is characterised in that local oscillator light passes through relevant with the Rayleigh scattering light for carrying vibration information
Beat signal is obtained, is obtained and eliminates local oscillator light angular frequency wLWith initial phase ΦL(t) and the signal comprising vibration information.
For the system, it is characterised in that four kinds of signals are mixed in frequency mixer：
The beat signal that 4th fiber coupler 7 is exported amplifies detector 8, the first low pass filter 9 by the through photo-equilibrium
One power divider 10 is divided into two parts I1(t) and I2T (), wherein the second tunnel are madePhase shift, second balance amplify photoelectricity
Detector 17 export AC signal, two parts I is divided into by the second power divider 19 by the 3rd low pass filter 183(t)
And I4(t).Then I3(t) and I1T () is mixed in the first frequency mixer 20, I2(t) and I4T () is mixed in the second frequency mixer 21,
The beat signal that frequency mixer 20,21 is exported is represented by
I1(t)·I3(t)=A B [cos (2 (wAt+Φ(t)+φ(t))+cos(φ(t)))]
I2(t)·I4(t)=A B [sin (2 (wAt+Φ(t)+φ(t))+sin(φ(t)))]
A=2ELEA, B=r γ ELESe-αzcos(θ)
Then LPF, the HFS in isolation signals, obtain intensity and the phase information of vibration signal, Jing Guoji
Intensity and the phase information for obtaining vibration signal is calculated, then frequency is obtained by phase demodulating process.
Compared with homogeneous system, the invention has the advantages that：
1. using the phase sensitive optical time domain reflection system of the structure, stable vibration signal intensity, frequency can be obtained, increase
Adding system frequency response range, supports so as to the reliable data of offer that accurately identify for vibration source.
2. the system tracks feeler arm intermediate frequency using the beat signal not comprising vibration information for interfering reference arm to produce
The drift of rate and the change of phase place, effectively can overcome as between capture card and frequency modulator, real time synchronization is poor, laser instrument
Frequency drift, the measured signal distortion phenomenon that acousto-optic modulator thermal adaptability difference causes.
3. the system can also simplify and shorten the reaction time of system, improve data-handling efficiency, and committed memory is few,
High-speed data acquisition equipment is not needed, reduces system cost.
Description of the drawings
Fig. 1 be the present invention based on double homologous heterodyne be concerned with detection phase sensitive optical time domain reflection system structural representation
Figure.
Fig. 2 is the Digital Signal Processing flow chart to vibration signal demodulation.
Specific embodiment
The present invention is further described with reference to example and accompanying drawing, but the protection model of the present invention should not be limited with this
Enclose.
Fig. 1 be based on double homologous heterodyne be concerned with detection phase sensitive optical time domain reflection system structural representation.Its
It is characterised by that system architecture includes：ECLD 1, the first fiber coupler 2, the second fiber coupler 3, acousto-optic are adjusted
Device processed 4, Acousto-Optic Modulator Driver 5, the 3rd fiber coupler 6, the 4th fiber coupler 7, first are balanced and amplify detector
8th, the first bandpass filter 9, the first power-sharing device 10, electrooptic modulator 11, erbium-doped fiber amplifier 12, the second bandpass filtering
Device 13, circulator 14, sensor fibre 15, the 5th fiber coupler 16, second are balanced and amplify detector 17, the 3rd bandpass filter
18th, the second power-sharing device 19, the first frequency mixer 20, the first low pass filter 21, the second frequency mixer 22, the second low pass filter
23rd, capture card 24.
By optical fiber by the input 201 of the output end of described ECLD 1 and the first fiber coupler 2
Connection, the second output port 203 of the first fiber coupler 2 are connected with 3 first input end 301 of the second fiber coupler, and first
Output end 202 is connected with the input of acousto-optic modulator 4, and the of the output end of the acousto-optic modulator 4 and the 3rd fiber coupler 6
One input port 601 is connected, the first output port 502 of described the second fiber coupler 5 and the 4th fiber coupler 7
First input port 701 is connected, and the second output port 603 of the 3rd fiber coupler 6 is defeated with the 4th fiber coupler 7 second
Inbound port 702 is connected, and the first output port 703 of described the 4th fiber coupler 7, the second output port 704 connect respectively
Connect the first balance and amplify the first input port 801 of detector 8, the second input port 802, the output port 803 of the detector 8
It is connected with 9 input of the first bandpass filter, the input of the output end of the bandpass filter 9 and the first power-sharing device 10
1001 are connected, and the first output end 602 of the 3rd described fiber coupler 6 is connected with the input of electrooptic modulator 11,
The output end of the electrooptic modulator 11 is connected with the input of erbium-doped fiber amplifier 12, the erbium-doped fiber amplifier 12 defeated
Go out end to be connected with the input port of the second bandpass filter 13, the first port of the output port of the wave filter 13 and circulator 14
1401 are connected, and the second port 1402 of the circulator is connected with sensor fibre 15, the 3rd output port of the circulator
1403 are connected with the first input port 1601 of the 5th fiber coupler 16, the second of the second described fiber coupler 3 is defeated
Go out end 303 to be connected with the second input 1602 of the 5th fiber coupler 16, the first output end of the 5th fiber coupler 16
1603 are connected with the first input end 1701 of 1604 respectively with the second balance amplifier 17 of the second output end, the second input 1702
Connect, the output port 1703 of the detector 17 is connected with 18 input of the 3rd bandpass filter, the bandpass filter 18 defeated
Go out end to be connected with the input 1901 of the second power-sharing device 19,1002 ends of described the first power-sharing device and the second work(
1902 ends of rate divider connect the first port 2001 of the first frequency mixer 20 and second port 2002 respectively.The frequency mixer 20
Output port 2003 connects the input port of the first low pass filter 21,1003 ends of described the first power-sharing device and the second work(
1903 ends of rate divider connect the first port 2201 of the second frequency mixer 22, second port 2202, the output of the frequency mixer respectively
Port 2203 connects the input port of the second low pass filter 23, the output port of described first, second low pass filter 21,23
The first input port 2401 of capture card 24, second input port 2402 are connect respectively.The output port 2403 of the capture card connects electricity
Optical modulator, the output port of capture card 24 are connected with computer.The modulated terminal of described acousto-optic modulator and direct current standard TTL
Power supply is connected.
The first described fiber coupler 2 is 90：10 fiber coupler, the coupler play a part of light splitting, by light
The continuous light that source sends is divided into two-way, and, used as detection light, 10% light is used as local oscillator light for 90% light.
Embodiment:
Light source 1 is centre wavelength 1550.12nm, low live width, low frequency float, low phase noise, low relative intensity noise outer
Cavity semiconductor laser 1, the effect of light source are to provide detection light and local oscillator light, by the method for 2 light splitting of the first fiber coupler
The light that light source 1 is exported is divided into two-way, i.e. a road as detection light, enters sensor fibre and causes backward Rayleigh scattering.Another road
As local oscillator light, the Reyleith scanttering light that returns with scattering is coherent to form the beat signal with vibration information, serves relevant amplification
Effect.
First fiber coupler 2 is one 90：10 fiber coupler, the coupler play a part of light splitting, that is,
The continuous light that light source 1 is sent is entered after the first fiber coupler 2 from 201 ports and is divided into two-way, and a road is used as detection light from 202
Port exports, and as local oscillator light from 203 outputs, the power ratio for detecting light and local oscillator light is 90 on another road：10..
Second fiber coupler 3 is one 50：50 fiber coupler, the coupler play light splitting effect, that is, will
The local oscillator light that first fiber coupler 2 is exported, is divided into the equal two parts of power.
Acousto-optic modulator 4 carries Acousto-Optic Modulator Driver module 5, makees acousto-optic modulator with the bias voltage of 3.3V
Terminal radio frequency drives, the frequency of the continuous light that the first output port 202 of the first fiber coupler 2 is exported by acousto-optic modulator 4
A 80M frequency shift amount is generated with respect to the continuous light of input, that is, the light that light source 1 is exported is through the first fiber coupler 2
After being divided into two-way, the light wherein as detection mono- tunnel of Guang is by shift frequency.
3rd fiber coupler 6 has 601,602,603 totally three ports, and the 3rd fiber coupler 6 is one 90：10
Fiber coupler, the coupler play a part of light splitting, and the continuous modulation light sent from acousto-optic modulator 3 is entered from 601 ports
Enter the 3rd light coupler 6, a road continues to serve as detection light and exports from port 602, and another road is used as and the local oscillator interference of light, from end
Mouth 603 is exported, and it is 90 to detect light and the power ratio as the light that interferes:10.
Claims (7)
1. a kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne, it is characterised in that：Its structure
Including ECLD (1), the first fiber coupler (2), the second fiber coupler (3) acousto-optic modulator (4), acousto-optic
Modulator driving power supply (5), the 3rd fiber coupler (6), the 4th fiber coupler (7), first balance amplify detector (8),
First bandpass filter (9), the first power-sharing device (10), electrooptic modulator (11), erbium-doped fiber amplifier (12), the second band
Bandpass filter (13), circulator (14), sensor fibre (15), the 5th fiber coupler (16), the second balance amplifier (17),
Three bandpass filters (18), the second power-sharing device (19), the first frequency mixer (20), low pass filter (21), the second frequency mixer
(22), the second low pass filter (23), the above-mentioned part of capture card (24) position relationship as follows：
By optical fiber by the input of the output end of described ECLD (1) and the first fiber coupler (2)
(201) connection, second output port (203) of the first fiber coupler (2) and the second fiber coupler (3) first input end
(301) connection the first output end of j (202) is connected with the input of acousto-optic modulator (4), the output end of the acousto-optic modulator (4)
It is connected with the first input port (601) of the 3rd fiber coupler (6), the first of described the second fiber coupler (3) is defeated
Exit port (302) is connected with the first input port (701) of the 4th fiber coupler (7), and the of the 3rd fiber coupler (6)
Two output ports (603) are connected with (7) second input port (702) of the 4th fiber coupler, and the 4th described optical fiber is coupled
First output port (703) of device (7), the second output port (704) connect the first balance respectively and amplify the first of detector (8)
Input port (801), the second input port (802), the output port (803) of the detector (8) and the first bandpass filter (9)
Input is connected, and the output end of the bandpass filter (9) is connected with the input (1001) of the first power-sharing device (10),
First output end (602) of the 3rd described fiber coupler (6) is connected with the input of electrooptic modulator (11), the electric light
The output end of modulator (11) is connected with the input of erbium-doped fiber amplifier (12), the erbium-doped fiber amplifier (12) defeated
Go out end to be connected with the input port of the second bandpass filter (13), the of the output port of the wave filter (13) and circulator (14)
Single port (1401) is connected, and the second port (1402) of the circulator is connected with sensor fibre (15), and the of the circulator
Three output ports (1403) are connected with the first input port (1601) of the 5th fiber coupler (16), described the second light
Second output end (303) of fine coupler (3) is connected with second input (1602) of the 5th fiber coupler (16), and the 5th
First output end (1603) of fiber coupler (16) and respectively with the second balance amplifier (17) of the second output end (1604)
First input end (1701), the second input (1702) are connected, and the output port (1703) of the detector (17) is carried with the 3rd
Bandpass filter (18) input is connected, the input of the output end of the bandpass filter (18) and the second power-sharing device (19)
(1901) it is connected, described (1002) end of the first power-sharing device and (1902) end of the second power-sharing device connect respectively
The first port (2001) and second port (2002) of the first frequency mixer (20)；The output port (2003) of the frequency mixer (20) connects
The input port of the first low pass filter (21), (1003) of the first described power-sharing device are held and the second power-sharing device
(1903) end connects first port (2201), the second port (2202) of the second frequency mixer (22), the output end of the frequency mixer respectively
Mouthful (2203) connect the input port of the second low pass filter (23), described first, second low pass filter (21), (23) defeated
Exit port connects the first input port (2401) of capture card (24), the second input port (2402) respectively；The output of the capture card
Port (2403) connects electrooptic modulator, and the output port of capture card (24) is connected with computer；The tune of described acousto-optic modulator
End processed is connected with direct current standard TTL power supply.
2. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：The system tracks feeler arm medium frequency using the beat signal not comprising vibration information for interfering reference arm to produce
Drift and phase place change, effectively can overcome due to capture card (24) real time synchronization and between frequency modulator poor, laser
Device (1) frequency drift, the measured signal distortion phenomenon that acousto-optic modulator (4) thermal adaptability difference causes.
3. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：Interfere the formation of beat signal in reference arm, the continuous light sent by ECLD (1) is through the first light
After fine coupler (2), the local oscillator light (E of 10% partL(t)=ELexpj[wLt+ΦL(t)]), through the second fiber coupler
(3) export with the 3rd fiber coupler (6) afterwards by AOM (4) modulate after 10% continuous light in the 4th fiber coupler (7)
Interfere, can be expressed as
Here EL、wL, ΦLT (), is the field intensity of local oscillator light, angular frequency, initial phase respectively；EL,AT () is the interference field of output
By force, IL,AT () is the interference light intensity of output, EA、wAThe amplitude of the light that has respectively been modulated by acousto-optic modulator (4), angular frequency, Δ
W and Φ (t) are that laser frequency is drifted about, acousto-optic modulator temperature as between capture card and frequency modulator, real time synchronization is poor
The angular frequency transfer of the light that bad adaptability causes and phase place change.
4. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：Reference arm is interfered to be characterised by that local oscillator light is clapped by relevant with the continuous probe light that has been modulated by AOM (4)
Frequency signal, obtains and eliminates local oscillator light angular frequency wLWith initial phase ΦLThe signal of (t).
5. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：The formation of the beat signal comprising vibration information in feeler arm：Sent by ECLD (1) is continuous
After the first fiber coupler (2) light splitting, 90% detection light enters acousto-optic modulator (4) to light, by the continuous light after shift frequency,
Light pulse is chopped into through electrooptic modulator (11), then through erbium-doped fiber amplifier (12), the second bandpass filter (13), light arteries and veins
Punching is injected into sensor fibre (15) through circulator (14), carries the back rayleigh scattering light of vibration signal and from the second optical fiber coupling
The local oscillator light that clutch (3) is exported is interfered in the 5th fiber coupler (16), and the beat signal with vibration information of output can
To be expressed as
EL,ST () is the interference light field intensity of output, IL,sT () is the interference light intensity of output, r is the amplitude of Rayleigh scattering, ESFor probe
Light field intensity, γ are the coherence factor determined by Light source line width, and α is fibre loss, and z is the location point in optical fiber, and θ is for deviateing local oscillator
The polarization angle of light wave, φ (t) are phase shift transmission and the scattering phase shift sum for detecting light.
6. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：Local oscillator light obtains beat signal with the Rayleigh scattering light for carrying vibration information by relevant, obtains and eliminates local oscillator light
Angular frequency wLWith initial phase ΦL(t) and the signal comprising vibration information.
7. the phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne according to claim 1, its
It is characterised by：Four kinds of signals are mixed in frequency mixer.
The beat signal that 4th fiber coupler (7) is exported amplifies detector BAPD1 (8), the first LPF through the first balance
Device (9) is divided into two parts I by the first power divider (10)1(t) and I2T (), wherein the second tunnel are madePhase shift, second
Balance amplify detector BAPD2 (17) export AC signal, by the second low pass filter (18) by the second power divider
(19) it is divided into two parts I3(t) and I4(t)；Then I3(t) and I1(t) mixing, I in the first frequency mixer (20)2(t) and I4(t)
Mixing in the second frequency mixer (22), the beat signal that frequency mixer (20), (22) export are represented by
I1(t)·I3(t)=A B [cos (2 (wAt+Φ(t)+φ(t))+cos(φ(t)))]
I2(t)·I4(t)=A B [sin (2 (wAt+Φ(t)+φ(t))+sin(φ(t)))]
A=2ELEA, B=r γ ELESe-αzCos (θ), then LPF, the HFS in isolation signals, are received by capture card
The intensity and phase information of vibration signal, through being calculated intensity and the phase place of vibration signal, then is obtained by phase calculation
Frequency.
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