CN104677398B - A kind of Φ OTDR photosensitivity-enhancing methods and device based on frequency drift dynamic compensation - Google Patents
A kind of Φ OTDR photosensitivity-enhancing methods and device based on frequency drift dynamic compensation Download PDFInfo
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- CN104677398B CN104677398B CN201510111885.7A CN201510111885A CN104677398B CN 104677398 B CN104677398 B CN 104677398B CN 201510111885 A CN201510111885 A CN 201510111885A CN 104677398 B CN104677398 B CN 104677398B
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Abstract
The invention discloses a kind of Φ OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation, carry out the scanning of active using the method for internal modulation or external modulation to the source output frequency of Φ OTDR, the Φ OTDR curve groups under different light frequency points are obtained；By computing cross-correlation is carried out to the Φ OTDR curves under each Frequency point, confirm size and the direction of light source frequency drift, and the output frequency of feedback control light source accordingly；In data handling procedure, choose cross correlation value highest Φ OTDR curves between different curve groups and, as valid data, abandon the relatively low curve of other cross correlation values, with the curvilinear distortion that this compensatory light frequency drift is brought.The invention also discloses a kind of Φ OTDR enhanced sensitivity devices based on frequency drift dynamic compensation, the present invention carries out correlation computations using to the Φ OTDR curves under each Frequency point, determine frequency drift size and Orientation, accordingly the driving of feedback phase manipulator, light source frequency drift is compensated；The solution of the present invention reduces Φ OTDR sensor-based systems for the demand of light source stability, and the ability of system acquisition low-frequency excitation is greatly improved.
Description
Technical field
The present invention relates to technical field of optical fiber, particularly a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation and
Device.
Background technology
Strengthen border take precautions against, improve energy security, improve social security etc. be social stability, rapid economic development basic
Require.The perimeter security monitoring of some important base facilities of the multiple fields such as military and national defense, large-scale industrial and mineral, civilian security protection, be
Avoid causing heavy economic lossess, the effective means of development of maintaining social stability.With the continuous development of society, the security protection of people
Consciousness is improved constantly, and various safety monitoring technologies are also evolving.Fiber optic intrusion based on optical time domain reflectometer OTDR is sensed
Device system, with distributed, high sensitivity, monitoring range wide, can hidden, the advantage such as do not limited by topography and geomorphology, in circumference peace
Great potential in terms of anti-intrusion monitoring, it has also become the study hotspot of people.
Phase sensitivity optical time domain reflectometer (Phase-sensitive Optical Time Domain Reflectometry,
Φ-OTDR) grow up on the basis of original OTDR distributed sensors, it is a kind of typical distributed optical fiber sensing skill
Art, sensitivity are high, whole passive, can continuously perceive the spatial distribution of dynamic parameter and the times such as strain in transmission path, vibration
Change information.
Φ-OTDR are exactly to employ coherent source from the different of traditional OTDR maximums, and require that light source has narrow line
Wide and low frequency drift characteristic.According to sensor fibre disturbed when, the phase place of backward Rayleigh scattering light can change, through optical fiber pass
Defeated, the interference strength for reaching photoelectric detector changes so as to be detected, as detection information is the phase place that is modulated at light
On, the sensitivity of system is greatly improved compared to traditional approach.
Common commercial light source is constantly present obvious frequency drift phenomenon, even the narrow line with high degree of coherence
Wide light source.Therefore carrying out effective compensation to light source frequency drift just becomes pass of the raising Φ-OTDR systems to low-frequency excitation sensitivity
Key.
Content of the invention
The technical problem to be solved is to overcome the deficiencies in the prior art and provide a kind of based on frequency drift dynamic benefit
Φ-OTDR the photosensitivity-enhancing methods that repays and device, the method on the basis of existing Φ-OTDR sensor-based systems, the frequency of dynamic compensation light source
The brought rayleigh backscattering interference of light characteristic distortion of rate drift, to lift power of test of the Φ-OTDR to low frequency perturbation.
The present invention is employed the following technical solutions for solving above-mentioned technical problem：
According to a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation proposed by the present invention, comprise the following steps：
Step one, using the continuous light of light source output, continuous light is divided into two-way：Detection light and local oscillator light；
Step 2, modulation detection light, are input to sensor fibre, obtain back rayleigh scattering optical signal after obtaining pulsed light；
Step 3, local oscillator light is coupled with the back rayleigh scattering optical signal after, obtain the signal of telecommunication through opto-electronic conversion, should
The signal of telecommunication obtains initial light frequency f of light source after process0Under Φ-OTDR curves, as reference curve Wref(i-1),
Initialization iterationses i=1；
Step 4, the frequency of tuning source, carry out linear scanning to the frequency of light source, at the same by continuous light modulation into
Φ-OTDR direct impulses, obtain one group of optical frequency continually varying Φ-OTDR direct impulse sequence；
Step 5, using in step 4 obtain direct impulse sequence carry out respectively Φ-OTDR measurement, obtain one group of Φ-
OTDR curve Ai, and store；Wherein,
Ai=[Wf-NΔf(t),Wf-(N-1)Δf(t),…Wf+(N-1)Δf(t),Wf+NΔf(t)]；
Wherein, Wf-NΔfT () is by the Φ-OTDR curves that light frequency is f-N Δ f direct impulses acquisition, numbers of the N for pulse
Amount, t are the initial time of i ＆ lt scanning, and f is the light source frequency after the i-th -1 time compensation, and Δ f is the optical frequency of direct impulse sequence
Scanning stepping；
Step 6, calculating WrefAnd A (i-1)iIn all Φ-OTDR curves between cross correlation value, obtain 2N+1 mutually
The cross correlation value is simultaneously stored in array R by correlation in orderiIn, wherein：
Ri=[Cov [Wref(i-1),Wf-NΔf(t)],Cov[Wref(i-1),Wf-(N-1)Δf(t)],…Cov[Wref(i-1),
Wf+NΔf(t)]]
Wherein, Cov [i] is related operation；
Search array RiIn maximum, determine its index value in array, calculate accordingly light source frequency drift
Size delta ν and direction, and using corresponding for maximum Φ-OTDR curves as new reference curve Wref(i)；
Step 7, size delta ν according to the light source frequency drift that tries to achieve in step 6 and direction, the output light of tuning source
Frequency, compensates its frequency drift so as to come back to initial light frequency f of light source0；
Step 8, i=i+1 is made, jump to step 4.
As a kind of further prioritization scheme of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation of the present invention,
It is internal modulation method or the niobium using semiconductor light source itself to carry out linear scanning in the step 4 to the frequency of light source
The external modulation method of sour lithium I/Q modulator, or acousto-optic modulator directly produces optical frequency com, divides in data processing
The method that the signal on each light frequency is managed in other places.
As a kind of further prioritization scheme of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation of the present invention,
The N determines that frequency drift compensation range, Δ f determine compensation precision.
As a kind of further prioritization scheme of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation of the present invention,
The N=20, Δ f=200kHz.
Based on a kind of device of above-mentioned Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation, including narrow linewidth light source,
First fiber coupler, phase-modulator, erbium-doped fiber amplifier, acousto-optic modulator, optical fiber circulator, random waveform occur
Device, FPGA impulse generators, the second fiber coupler, balanced detector, data acquisition module, data processing module and sense light
Fine；Wherein：
The light that narrow linewidth light source sends is divided into two-way through the first fiber coupler：It is flashlight all the way, another road is local
Reference light；The flashlight produces multiple sideband optical signals after standing the phase modulator modulation that AWG (Arbitrary Waveform Generator) is controlled,
The optical signal is exported to the acousto-optic modulator driven by FPGA impulse generators after erbium-doped fiber amplifier amplification, modulated into
The first port of pulsed light injection fibre circulator, pulsed light are incident in sensor fibre by the second port of optical fiber circulator,
Pulsed light produces the second port that backscatter signals return to optical fiber circulator in sensor fibre, and by optical fiber circulator
Three ports are exported to the second fiber coupler；The local reference light is input into the second fiber coupler and backscatter signals coupling
The signal of telecommunication is converted into through balanced detector after conjunction, the signal of telecommunication is converted into exporting to data after digital signal through digital collection module
Processing module, is processed to the Φ-OTDR curves for collecting, and obtains light source frequency drift, according to the light source frequency drift for obtaining
Move, control the control signal of AWG (Arbitrary Waveform Generator) and the pulse-modulated signal of acousto-optic modulator, realize dynamic compensation light source frequency
Rate is drifted about.
The present invention adopts above technical scheme compared with prior art, with following technique effect：
(1) present invention carries out correlation computations using to the fluctuating pattern that must be concerned with each Frequency point, determines frequency drift size and side
To the driving of feedback phase manipulator accordingly is compensated to light source frequency drift；
(2) the solution of the present invention reduces Φ-OTDR sensor-based systems for the demand of light source stability, and system is greatly improved
The ability of capture low-frequency excitation.
Description of the drawings
Fig. 1 is the schematic flow sheet of the inventive method.
Fig. 2 is one group of optical frequency continually varying Φ-OTDR direct impulses sequence and Φ-OTDR curve synoptic diagrams.
Fig. 3 is the computational methods schematic diagram of light source frequency drift value size and Orientation.
Fig. 4 is the structural representation of apparatus of the present invention.
Fig. 5 is drift situation schematic diagram in calculating gained cross correlation measure peak during 100 active sweep-frequencies.
Fig. 6 a are the Φ-OTDR curve charts before compensation.
Fig. 6 b are the Φ-OTDR curve charts after compensation.
Reference in figure is construed to：1- narrow linewidth light sources, the first fiber couplers of 2-, 3- phase-modulators, 4- are mixed
Doped fiber amplifier, 5- acousto-optic modulators, 6- optical fiber circulators, 7- AWG (Arbitrary Waveform Generator), 8-FPGA impulse generators, 9-
Two fiber couplers, 10- balanced detectors, 11- data acquisition modules, 12- data processing modules, 13- sensor fibres.
Specific embodiment
Below in conjunction with the accompanying drawings technical scheme is described in further detail：
It is the schematic flow sheet of the inventive method as shown in Figure 1, a kind of Φ-OTDR enhanced sensitivity sides based on frequency drift dynamic compensation
Method, comprises the following steps：
Step one, using the continuous light of light source output, continuous light is divided into two-way：Detection light and local oscillator light；
Step 2, modulation detection light, are input to sensor fibre, obtain back rayleigh scattering optical signal after obtaining pulsed light；
Step 3, local oscillator light is coupled with the back rayleigh scattering optical signal after, obtain the signal of telecommunication through opto-electronic conversion, should
The signal of telecommunication obtains initial light frequency f of light source after process0Under Φ-OTDR curves, as reference curve Wref(i-1),
Initialization iterationses i=1；
Step 4, the frequency of tuning source, carry out linear scanning to the frequency of light source, at the same by continuous light modulation into
Φ-OTDR direct impulses, obtain one group of optical frequency continually varying Φ-OTDR direct impulse sequence；
Step 5, using in step 4 obtain direct impulse sequence carry out respectively Φ-OTDR measurement, obtain one group of Φ-
OTDR curve Ai, and store；Wherein,
Ai=[Wf-NΔf(t),Wf-(N-1)Δf(t),…Wf+(N-1)Δf(t),Wf+NΔf(t)]；
Wherein, Wf-NΔfT () is by the Φ-OTDR curves that light frequency is f-N Δ f direct impulses acquisition, numbers of the N for pulse
Amount, t are the initial time of i ＆ lt scanning, and f is the light source frequency after the i-th -1 time compensation, and Δ f is the optical frequency of direct impulse sequence
Scanning stepping；
Step 6, calculating WrefAnd A (i-1)iIn all Φ-OTDR curves between cross correlation value, obtain 2N+1 mutually
The cross correlation value is simultaneously stored in array R by correlation in orderiIn, wherein：
Ri=[Cov [Wref(i-1),Wf-NΔf(t)],Cov[Wref(i-1),Wf-(N-1)Δf(t)],…Cov[Wref(i-1),
Wf+NΔf(t)]]
Wherein, Cov [i] be related operation, Cov [Wref(i-1),Wf-NΔf(t)] represent Φ-OTDR curve Wf-NΔf(t) with
The related operation of reference curve；
Search array RiIn maximum, determine its index value in array, calculate accordingly light source frequency drift
Size delta ν and direction, and using corresponding for maximum Φ-OTDR curves as new reference curve Wref(i)；
Step 7, size delta ν according to the light source frequency drift that tries to achieve in step 6 and direction, the output light of tuning source
Frequency, compensates its frequency drift so as to come back to initial light frequency f of light source0；
Step 8, i=i+1 is made, jump to step 4.
It is one group of optical frequency continually varying Φ-OTDR direct impulses sequence and Φ-OTDR curve synoptic diagrams as shown in Figure 2,
In described step two, the different Φ-OTDR direct impulse sequences of optical frequency are obtained.As light source frequency that may be present drifts about,
The original output optical frequency of light source is possible to have occurred that change, it is assumed which is f.Due to light source frequency drift direction unknown, institute
By the frequency scanning of light source centered on original output optical frequency f, scan to f+N Δ f from f-N Δ f, in the process, modulate altogether
2N+1 direct impulse.Due to pulse width minimum compared with pulse interval, it is possible to think same pulse width with
Interior optical frequency keeps constant.Different Φ-OTDR direct impulse the sequences of one group of optical frequency can be obtained by above method, comprising arteries and veins
Quantity is rushed for 2N+1, frequency is changed to f+N Δ f from f-N Δ f, the optical frequency stepping between adjacent pulse is Δ f.
Described optical frequency sweep stepping Δ f determines that frequency compensated precision, N Δ f determine the maximum frequency that can compensate for
Drift value.The N determines that frequency drift compensation range, Δ f determine compensation precision；If N is constant, the less compensation precisions of Δ f are more in theory
Height, but in real system, Δ f is more little, and the maximum frequency drift value that can compensate for is less；If Δ f is constant, N is more big then can be most
Big frequency drift value is bigger, but frequency scan time will be caused to greatly increase.In this programme, conventional N values are 20, and Δ f is
200kHz.The frequency scanning method of described light source has several alternatives as follows：
1) using the scheme of the internal modulation of semiconductor light source itself；
2) Lithium metaniobate (LiNbO is utilized3) I/Q modulator external modulation scheme；
3) optical frequency com is directly produced using acousto-optic modulator, process each light frequency in data processing respectively
On signal scheme；
What described Φ-OTDR curves were obtained using analog-digital converter (ADC) in systems in practice is series of discrete
Point, might as well assume Φ-OTDR curve Wa(t) and WbT () is by M groups of samples into M is the integer more than 0：Wa(tm) and Wb
(tm), wherein m ∈ [1, M], tmThe time of m-th sampled point is represented, m is the integer more than 0.So two Φ-OTDR curve Wa
(t) and WbT the computational methods of () cross correlation value are defined as
Wherein<*>Represent that asking for for expected value, Var [*] represent asking for for variance.Cross correlation value is used for assessing two curves
Similarity degree：If two curve waveform is more similar, then its cross correlation value is bigger, identical duration is 1；If conversely, two
The shape differences of bar curve are bigger, then its cross correlation value is less, and entirely different duration is 0.
It is the computational methods schematic diagram of light source frequency drift value size and Orientation as shown in Figure 3, described frequency drift value calculating method
As follows：In the case that light source does not have disturbance, then graphically array RiThe size of middle element, as shown in phantom in Figure 3,
The peak of dotted line is located at frequency f, represents Wref(t) and WfThe cross correlation value highest of (t).Because in the feelings without frequency drift
Under condition, direct impulse of this two curves from same optical frequency.If the frequency of light source there occurs certain drift, then cross-correlation is bent
The peak of line will shift.For example, when the peak of cross-correlation curve is offset to f-i Δ f, then W is describedref(t) with
Wf-iΔfT () is derived from the direct impulse of identical optical frequency, so there is f=f0+ i Δ f, show that light source frequency has drifted about+i Δ f.
It is the structural representation of apparatus of the present invention as shown in Figure 4, is increased based on a kind of Φ-OTDR based on frequency drift dynamic compensation
The device of quick method, including narrow linewidth light source 1, the first fiber coupler 2, phase-modulator 3, erbium-doped fiber amplifier (EDFA)
4th, acousto-optic modulator (AOM) 5, optical fiber circulator 6, AWG (Arbitrary Waveform Generator) (AWG) 7, FPGA impulse generators 8, the second optical fiber
Bonder 9, balanced detector 10, data acquisition module 11, data processing module 12 and sensor fibre 13；Wherein,
The light that narrow linewidth light source sends is divided into two-way through the first fiber coupler：It is flashlight all the way, another road is local
Reference light；The flashlight produces multiple sideband optical signals after standing the phase modulator modulation that AWG (Arbitrary Waveform Generator) is controlled,
The optical signal is exported to the acousto-optic modulator driven by FPGA impulse generators after erbium-doped fiber amplifier amplification, modulated into
The first port of pulsed light injection fibre circulator, pulsed light are incident in sensor fibre by the second port of optical fiber circulator,
Pulsed light produces the second port that backscatter signals return to optical fiber circulator in sensor fibre, and by optical fiber circulator
Three ports are exported to the second fiber coupler；The local reference light is input into the second fiber coupler and backscatter signals coupling
The signal of telecommunication is converted into through balanced detector after conjunction, the signal of telecommunication is converted into exporting to data after digital signal through digital collection module
Processing module, is processed to the Φ-OTDR curves for collecting, and obtains light source frequency drift, according to the light source frequency drift for obtaining
Move, control the control signal of AWG (Arbitrary Waveform Generator) and the pulse-modulated signal of acousto-optic modulator, realize dynamic compensation light source frequency
Rate is drifted about.
First fiber coupler is 90/10 fiber coupler, and the second fiber coupler is 50/50 fiber coupler.
It is in 100 active sweep-frequencies, to calculate gained cross correlation measure peak drift situation schematic diagram, white blocks in figure as shown in Figure 5
High relevance degree is represented, grey block represents low relevance degree.As can be seen that cross correlation measure curve was there occurs significantly partially with the time
Move, correspondingly, the frequency of light source was drifted about with the time.As shown in figure 5, the light source frequency of the 100th frequency sweep is compared to initial
State drifts away 6.4MHz.If do not compensated to which, Φ-OTDR waveforms at C points by by mistake as corresponding with A points
Effective waveform, the frequency drift of laser brings the distortion of scattered light interference pattern.Result of calculation analysis in by figure is obtained,
Waveform at B points is the precision waveform corresponding with A points.In this way, so that it is determined that the size of light source frequency drift and side
To carrying out real-Time Compensation to system.
Φ-OTDR waveforms at above-mentioned cross correlation measure peak value may be considered and be produced by same detection light frequency, therefore,
Φ-OTDR waveforms are taken as effective Φ-OTDR data along cross correlation measure peak, can effectively be compensated and be drawn due to light source frequency drift
The curvilinear distortion for rising.
Fig. 6 a are the Φ-OTDR curve charts before compensation, and Fig. 6 b are the Φ-OTDR curve charts after compensation, it can be seen that this
Bright scheme restrained effectively the curvilinear distortion problem caused due to light source frequency drift, improve Φ-OTDR systems to low frequency
The capture ability of disturbance.
Above content is further description made for the present invention with reference to specific preferred implementation, it is impossible to assert
The present invention be embodied as be confined to these explanations.For general technical staff of the technical field of the invention,
On the premise of without departing from present inventive concept, some simple deductions or replacement can also be made, should all be considered as belonging to the present invention's
Protection domain.
Claims (5)
1. a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation, it is characterised in that comprise the following steps：
Step one, using the continuous light of light source output, continuous light is divided into two-way：Detection light and local oscillator light；
Step 2, modulation detection light, are input to sensor fibre, obtain back rayleigh scattering optical signal after obtaining pulsed light；
Step 3, local oscillator light is coupled with the back rayleigh scattering optical signal after, obtain the signal of telecommunication through opto-electronic conversion, the telecommunications
After process, number obtain initial light frequency f of light source0Under Φ-OTDR curves, as reference curve Wref(i-1), initially
Change iterationses i=1；
Step 4, the frequency of tuning source, carry out linear scanning to the frequency of light source, at the same by continuous light modulation into Φ-
OTDR direct impulses, obtain one group of optical frequency continually varying Φ-OTDR direct impulse sequence；
Step 5, using in step 4 obtain direct impulse sequence carry out respectively Φ-OTDR measurement, obtain one group of Φ-OTDR
Curve Ai, and store；Wherein,
Ai=[Wf-NΔf(t),Wf-(N-1)Δf(t),…Wf+(N-1)Δf(t),Wf+NΔf(t)]；
Wherein, Wf-NΔfT it is Φ-OTDR curves that f-N Δ f direct impulses are obtained by light frequency that () is, quantity of the N for pulse, and t is
The initial time of i ＆ lt scanning, f are the light source frequency after the i-th -1 time compensation, and Δ f is that the optical frequency sweep of direct impulse sequence is walked
Enter；
Step 6, calculating WrefAnd A (i-1)iIn all Φ-OTDR curves between cross correlation value, obtain 2N+1 cross-correlation
The cross correlation value is simultaneously stored in array R by value in orderiIn, wherein：
Ri=[Cov [Wref(i-1),Wf-NΔf(t)],Cov[Wref(i-1),Wf-(N-1)Δf(t)],…Cov[Wref(i-1),Wf+NΔf
(t)]]
Wherein, Cov [] is related operation；
Search array RiIn maximum, determine its index value in array, calculate accordingly light source frequency drift size delta
ν and direction, and using corresponding for maximum Φ-OTDR curves as new reference curve Wref(i)；
Step 7, size delta ν according to the light source frequency drift that tries to achieve in step 6 and direction, the output optical frequency of tuning source
Rate, compensates its frequency drift so as to come back to initial light frequency f of light source0；
Step 8, i=i+1 is made, jump to step 4.
2. a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation according to claim 1, it is characterised in that institute
It is internal modulation method or the niobic acid using semiconductor light source itself to state
The external modulation method of lithium I/Q modulator, or acousto-optic modulator directly produces optical frequency com, distinguishes in data processing
The method for processing the signal on each light frequency.
3. a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation according to claim 1, it is characterised in that institute
State N and determine that frequency drift compensation range, Δ f determine compensation precision.
4. a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation according to claim 1, it is characterised in that institute
State N=20, Δ f=200kHz.
5. the device based on a kind of Φ-OTDR photosensitivity-enhancing methods based on frequency drift dynamic compensation described in claim 1, its feature exist
In including narrow linewidth light source, the first fiber coupler, phase-modulator, erbium-doped fiber amplifier, acousto-optic modulator, fiber optic loop
Shape device, AWG (Arbitrary Waveform Generator), FPGA impulse generators, the second fiber coupler, balanced detector, data acquisition module, number
According to processing module and sensor fibre；Wherein：
The light that narrow linewidth light source sends is divided into two-way through the first fiber coupler：It is detection light all the way, another road is local oscillator light；Institute
State after detection light stands the phase modulator modulation that AWG (Arbitrary Waveform Generator) is controlled and produce multiple sideband optical signals, optical signal warp
Erbium-doped fiber amplifier is exported after amplifying to the acousto-optic modulator driven by FPGA impulse generators, modulated into pulsed light injection
The first port of optical fiber circulator, pulsed light are incident in sensor fibre by the second port of optical fiber circulator, and pulsed light is being passed
The second port that backscatter signals return to optical fiber circulator is produced in photosensitive fibre, and is exported by the 3rd port of optical fiber circulator
To the second fiber coupler；The local oscillator light is input into after being coupled to the second fiber coupler with backscatter signals through balance detection
Device is converted into the signal of telecommunication, and the signal of telecommunication is converted into exporting to data processing module after digital signal through data acquisition module, to adopting
Φ-OTDR the curves for collecting are processed, and obtain light source frequency drift, according to the light source frequency drift for obtaining, control any ripple
The control signal of shape generator and the pulse-modulated signal of acousto-optic modulator, realize that dynamic compensation light source frequency drifts about.
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