CN105973277A - Realization apparatus and method for distributed optical fiber sensing system based on single photon detection - Google Patents
Realization apparatus and method for distributed optical fiber sensing system based on single photon detection Download PDFInfo
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Abstract
The invention discloses a realization apparatus and method for a width dynamic scope distributed optical fiber sensing system based on single photon detection. A single-photon detector is employed to replace a conventional photo-detector, so that the detection sensitivity of the system is improved. The real-time shaping of the return signal amplitude of sensing fibers using an optical intensity modulator is realized, which solves the problem of small dynamic range due to the fact that the saturation light intensity of the single-photon detector is too low and improves the sensing distance of the optical fiber. The structural principle lies in that a laser injects laser pulses in the sensing fiber via a circulator, backscattered light carrying the sensing information is re-introduced through the circulator into the light intensity modulator, and a waveform generator outputs a drive signal synchronized with the backscattered optical signal to control the attenuation value of the optical intensity modulator. The attenuated light signal is detected by the single-photon detector. A signal processing unit restores the intensity of the original signal light according to the attenuation value of the optical intensity modulator and the output value of the single-photon detector, thereby realizing the wide dynamic range distributed optical fiber sensing.
Description
Technical field
The present invention relates to technical field of optical fiber sensing, realize device and method more particularly, to a kind of wide dynamic range distribution formula optical fiber sensing system based on single photon detection.
Background technology
Distributed Optical Fiber Sensing Techniques is to utilize one-dimensional in fiber geometries to measure, sensing element both made by optical fiber, make again transfer element, it using tested parameter as the function of fiber position length, external physical parameter along fiber geometries path profile is measured continuously, it is provided that obtain the means of the information that tested physical parameter changes with room and time simultaneously.It most significant advantage is that stress, the temperature that can measure exactly on optical fiber arbitrfary point along the line, vibrate and the information such as damage, it is not necessary to constitute loop.The one-dimensional distribution that one-shot measurement is measured in just can obtaining whole fiber area, optical fiber is laid to network structure and just can measure measured two dimension or distributed in three dimensions situation, simultaneously because fiber transmission attenuation is little, so the full distributed measurement of dozens or even hundreds of kilometer can be realized.Parameters variation can be detected in real time, this is conducive to networking on a large scale and intelligentized development, realize the all-around intelligent monitoring to monitoring object, thus overcome the drawback of conventional port monitoring missing inspection, sensor fibre in distributed optical fiber sensing system is owing to possessing the ability of the segment information extracting large-range measuring field, can solve the problem that numerous difficult problems for current fields of measurement, therefore there is huge application potential.It is allowed to occupy critical role in defense and commercial industry.
nullSuch as，For measuring certain physical quantity (temperature、Stress etc.) distributed fiberoptic sensor，It is typically to be distributed sensor fibre along Physical Quantity Field，Laser Measurement is produced scattered light when transmitting in sensor fibre，According to the physical message to be measured entrained by scattered light，Use optical time domain reflection technology simultaneously，Spatial distribution and time dependent heat transfer agent along optical fiber transmission path is measured and monitor: laser instrument injects laser through circulator to sensor fibre under certain control，And sensor fibre is laid in field to be measured，Nonlinear effect is there is in light pulse during fiber-optic transfer，Produce scattered light，The physical quantity of tested point is characterized again by the size of coherent signal in theory analysis back-scattering light，Its correspondence position on optical fiber was determined later according to receiving this signal elder generation in time in measuring terminals，Thus the distributed measurement of measured physical quantity field is realized with sensor fibre.
But the most technically there are two problems:
(1) decay can be produced when light pulse signal transmits in a fiber, transmit the most remote, decay the biggest, the distance sensing of sensor fibre is the longest, the scattered light signal that far-end returns is the most weak, even can be submerged in noise, can not this signal extraction being buried in noise out with common detection method, so just requiring that detector has the highest sensitivity.And single-photon detector uses a kind of atomic weak light detection method, and the faint optical signal of single photon energy level can be detected, high 5～7 orders of magnitude of detector that remolding sensitivity is common.Single-photon detecting survey technology is applied in distributed optical fiber sensing system, the sensitivity along with optical fiber sensing system and the signal to noise ratio of measurement result can be greatly improved.
(2) dynamic range of distributing optical fiber sensing is defined as initial backscattering luminous power and noise peak power ratio.The maximum distance sensing that the system of which determining can record, typically uses log unit (dB).For increasing the maximum distance sensing measured, it is necessary for improving Dynamic Range, after detector is determined, namely needs to increase the initial backscattering luminous power of system and device.The incident backscattering luminous power of single-photon detector is necessarily less than the maximum saturation luminous power of detector, and pile up effect otherwise occurs, and causes counting saturated.The maximum count frequency of ultrared single-photon detector is restricted by afterpulse problem at present, is far smaller than the repetition rate of detector circuit.The counting saturation effect caused by pile up effect is affected, and the saturated light power of single-photon detector is much smaller than conventional detectors, so the scope increasing scattered light power is the most restricted, this is difficult point and the problem that current single-photon detector is badly in need of solving.
Summary of the invention
In order to overcome above-mentioned the deficiencies in the prior art, present invention firstly provides a kind of wide dynamic range distribution formula optical fiber sensing system based on single photon detection realizes device.The method uses single-photon detector to replace traditional photo-detector, improves the detectivity of system；Use light intensity modulator that the return signal amplitude of sensor fibre is carried out real-time shaping, overcome the too low problem causing dynamic range little of the saturated light intensity of single-photon detector, improve Fibre Optical Sensor distance.
The present invention also provides for the implementation method of a kind of wide dynamic range distribution formula optical fiber sensing system based on single photon detection.
To achieve these goals, the technical solution adopted in the present invention is:
A kind of distributed optical fiber sensing system based on single photon detection width dynamic range realize device, mainly comprise pulse laser (light source), circulator, (sensor fibre refers to the optical fiber being placed in physical environment to be measured to sensor fibre；When incident illumination is acted on by physical environment in transmitting procedure in sensor fibre, scattering effect can occur, and the back-scattering light along backtracking wherein produced seeks to the flashlight carrying heat transfer agent of detection), waveform generator, light intensity modulator, single-photon detector and signal processing unit.Described pulse laser injects laser pulse through circulator to sensor fibre under the triggering of clock generator, the back-scattering light carrying heat transfer agent incides light intensity modulator through circulator, waveform generator exports the pad value that drive signal control light intensity modulator Tong Bu with backscattering optical signal, make the backscattering optical signal of sensor fibre, make the backscattering optical signal originally presenting certain exponential decay form big to the decay of its near-end at light intensity modulator, after the adjustment that far-end decay is little, the signal intensity entering into single-photon detector will tend to the most steady, the last intensity being recovered raw scattered flashlight by signal processing unit, thus realize the distributing optical fiber sensing (dynamic range of distributing optical fiber sensing represents initial backscattering luminous power and the difference of noise peak power) of wide dynamic range.
The function of light intensity modulator: the mainly intensity amplitude value of Returning scattering light on modulation whole piece sensor fibre so that the backscattering optical signal near-end decay of sensor fibre is big, far-end decay is little, makes the output intensity of light intensity modulator tend towards stability.When increasing incident intensity, it is excessive and cause single-photon detector saturated that back-scattering light after light intensity modulation shaping not only avoid near-end light intensity, and make the scattered light intensity of sensor fibre can increase with incident optical power and strengthen, thus avoid remote signaling and be submerged in noise because crossing weak, last re-demodulation recovers signal, such that it is able to increase dynamic range, improve distance sensing.
The cardinal principle of apparatus of the present invention is as follows:
Optical fiber itself, as sensing element, utilizes its material scattering properties to light wave itself, can be built into distributed Fibre Optical Sensor.In distributed optical fiber sensing system, inject the high-power light pulse in sensor fibre (sensing element), can be owing to absorbing in transmitting procedure, the mechanism such as scattering and waveguide imperfection produce power attenuation, thus cause light intensity attenuation, distributed fiberoptic sensor is exactly the intensity utilizing the backscattering optical signal returned, present a curve tilted over the display, the attenuation quotient of optical fiber can be measured according to this curve, uneven point according to any lump, such as junction, fusing point, spike that breakpoint etc. occur in the echo-signal curve of back-scattering light or depression；And external environment condition, including temperature and the change of adaptability to changes, the most also can be reflected on the intensity curve of echo-signal, thus analyze, according to curve characteristic, physical event and the position that place to be measured occurs very much.
Distributed fiberoptic sensor is as the sign of optical fiber attenuation characteristic and the detection means of breakpoint, disturbance, temperature, pressure etc., dynamic range is one of its main performance index, the dynamic range of distributing optical fiber sensing represents initial backscattering luminous power and noise peak power ratio, and the maximum which determining sensor fibre effectively measures length.When dynamic range is less, when sensor fibre has higher loss, the signal that far-end returns may disappear in noise；And when dynamic range is bigger, curve linear is the best, then can find range from the longest.
Increase dynamic range and mainly have two approach:
1) noise peak power is reduced: noise peak power is minimum measurable effective backscattering luminous power.
2) initial backscattering luminous power is increased: i.e. increase the incident optical power of sensor fibre.
Single-photon detector is a kind of ultra-low noise device, use a kind of atomic weak light detection method, and the faint optical signal of single photon energy level can be detected, high 5～7 orders of magnitude of detector that remolding sensitivity is common, the weak scattering optical signal that far-end is returned is unlikely to be submerged in noise, so replacing traditional photodetector with single-photon detector can improve detectivity, reduce noise peak.But single-photon detector dynamic range is limited and is easily saturated: the maximum count frequency of single-photon detector is restricted by afterpulse problem, it is far smaller than the repetition rate of detector circuit, when the backscattering luminous power maximum saturation luminous power more than detector entering single-photon detector, pile up effect will occur, cause counting saturated, the i.e. saturated light power of single-photon detector is much smaller than conventional detectors, incident intensity is limited, so, while reducing system noise peak value by single-photon detector, maximum back-scattering light power limited can be made, the real purpose increasing Dynamic Range cannot be arrived.
So, light intensity modulator is introduced in the system that distribution is Fibre Optical Sensor by the present invention, can be while increasing the incident optical power of sensor fibre, can guarantee that again the back-scattering light of return, after light intensity modulator is modulated, saturated conditions occurs not over the maximum response of single-photon detector.So, single-photon detector and light intensity modulator are placed in system, have both reduced the noise peak power of system, increase initial backscattering luminous power, be that the Dynamic Range of distributed fiberoptic sensor is significantly improved.
In summary, it is in fiber optic sensor system, to be simultaneously introduced single-photon detector and light intensity modulator in general distribution, system can be increased and allows the maximum input light intensity of sensor fibre while reducing noise peak power, it is achieved thereby that the distributing optical fiber sensing of wide dynamic range.
The implementation method of a kind of based on single photon detection width dynamic range the distributed optical fiber sensing system of the present invention, comprises the following steps:
1) pulse laser described in sets the size of input optical pulse power by the actual measurement range demand of sensor fibre, and provides light pulse signal for whole system under the triggering of clock generator；
2) pulse laser signal is P by being connected power with described circulator0Light pulse inject sensor fibre, when light pulse is transmitted in sensor fibre, can be due to the character of optical fiber itself, temperature, pressure, abutment, bending or other similar event and produce scattering, reflect, decay, in addition, light pulse can occur nonlinear effect during fiber-optic transfer, sensing reason information and back-scattering light that luminous power is P (L) are carried in generation, and when back-scattering light returns to light intensity modulator in reverse direction, its luminous power becomes PS(L), the optical fiber now obtained is along the curve that backscattering luminous power is an exponential damping on road, and this curve table shows the optical fiber loss situation along road, now, dynamic range D1By initial back-scattering light power P1With noise peak power P2(noise peak power is minimum measurable effective backscattering luminous power) determines, thus obtaining the most measurable distance sensing is L1。
3) by described light intensity modulator and waveform generator, the back-scattering light returned being carried out synchronous modulation, the backscattering optical attenuation decay big, far-end making near-end is little.The luminous power of the back-scattering light before entering to inject light intensity modulator exponentially decays, then, interim level trend can be presented through the true curve of output of backscattering luminous power of light intensity device modulation.
Compared with prior art, the invention has the beneficial effects as follows:
(1) single-photon detector is a kind of ultra-low noise device, use a kind of atomic weak light detection method, and the faint optical signal of single photon energy level can be detected, high 5～7 orders of magnitude of detector that remolding sensitivity is common, the weak scattering optical signal that far-end is returned is unlikely to be submerged in noise, so replacing traditional photodetector with single-photon detector can improve detectivity, reduce the noise peak of system and device.
(2) by using light intensity modulator that the return signal amplitude of sensor fibre is carried out real-time shaping, the backscattering optical signal near-end entering the sensor fibre of manipulator is decayed greatly, far-end is decayed little, thus increases the maximum incident optical power that sensor fibre allows.Overcome the too low problem causing dynamic range to increase of the saturated light intensity of single-photon detector, improve system maximum distance sensing.
(3) define according to the dynamic range of distributed fiberoptic sensor, the present invention increases, by light intensity modulator, the maximum initial backscattering luminous power that system allows, the noise peak power of system is reduced, so that the wide dynamic range of system and device is better achieved by single-photon detector.
Accompanying drawing explanation
Fig. 1 be wide dynamic range distribution formula optical fiber sensing system based on single photon detection realize schematic diagram.
Fig. 2 be incident intensity be P0Time the relevant curve comparison figure of distributed optical fiber sensing system luminous power I (L).
Fig. 3 be incident intensity be P0′(P0′>P0) time the relevant curve comparison figure of distributed optical fiber sensing system luminous power I ' (L).
Detailed description of the invention
Accompanying drawing being merely cited for property explanation, it is impossible to be interpreted as the restriction to this patent；In order to the present embodiment is more preferably described, some parts of accompanying drawing have omission, zoom in or out, and do not represent the size of actual product；
To those skilled in the art, in accompanying drawing, some known features and explanation thereof may will be understood by omission.With embodiment, technical scheme is described further below in conjunction with the accompanying drawings.
A kind of distributed optical fiber sensing system based on single photon detection width dynamic range realize device, mainly comprise light source (pulse laser), circulator, sensor fibre, waveform generator, light intensity modulator, single-photon detector and signal processing unit.nullDescribed pulse laser injects laser pulse through circulator to sensor fibre under the triggering of clock generator，The back-scattering light carrying heat transfer agent incides light intensity modulator through circulator，Waveform generator exports the pad value that drive signal control light intensity modulator Tong Bu with backscattering optical signal，Make the backscattering optical signal of sensor fibre，Make the backscattering optical signal originally presenting certain exponential decay form big to the decay of its near-end at light intensity modulator、After the adjustment that far-end decay is little，The signal intensity entering into single-photon detector will tend to the most steady，The last intensity being recovered raw scattered flashlight by signal processing unit，Thus realize the distributing optical fiber sensing (dynamic range of distributing optical fiber sensing represents initial backscattering luminous power and the difference of noise peak power) of wide dynamic range，As shown in Figure 1.
The function of light intensity modulator: the mainly intensity amplitude value of Returning scattering light on modulation whole piece sensor fibre so that the backscattering optical signal near-end decay of sensor fibre is big, far-end decay is little, makes the output intensity of light intensity modulator tend towards stability.When increasing incident intensity, it is excessive and cause single-photon detector saturated that back-scattering light after light intensity modulation shaping not only avoid near-end light intensity, and make the scattered light intensity of sensor fibre can increase with incident optical power and strengthen, thus avoid remote signaling and be submerged in noise because crossing weak, last re-demodulation recovers signal, such that it is able to increase dynamic range, improve distance sensing.
The cardinal principle of the present invention is as follows:
Optical fiber itself, as sensing element, utilizes its material scattering properties to light wave itself, can be built into distributed Fibre Optical Sensor.In distributed optical fiber sensing system, inject the high-power light pulse in sensor fibre (sensing element), can be owing to absorbing in transmitting procedure, the mechanism such as scattering and waveguide imperfection produce power attenuation, thus cause light intensity attenuation, distributed fiberoptic sensor is exactly the intensity utilizing the backscattering optical signal returned, present a curve tilted over the display, the attenuation quotient of optical fiber can be measured according to this curve, uneven point according to any lump, such as junction, fusing point, spike that breakpoint etc. occur in the echo-signal curve of back-scattering light or depression；And external environment condition, including temperature and the change of adaptability to changes, the most also can be reflected on the intensity curve of echo-signal, thus analyze, according to curve characteristic, physical event and the position that place to be measured occurs very much.
Distributed fiberoptic sensor is as the sign of optical fiber attenuation characteristic and the detection means of breakpoint, disturbance, temperature, pressure etc., dynamic range is one of its main performance index, the dynamic range of distributing optical fiber sensing represents initial backscattering luminous power and noise peak power ratio, and the maximum which determining sensor fibre effectively measures length.When dynamic range is less, when sensor fibre has higher loss, the signal that far-end returns may disappear in noise；And when dynamic range is bigger, curve linear is the best, then can find range from the longest.
Increase dynamic range and mainly have two approach:
1) noise peak power is reduced: noise peak power is minimum measurable effective backscattering luminous power.
2) initial backscattering luminous power is increased: i.e. increase the incident optical power of sensor fibre.
Single-photon detector is a kind of ultra-low noise device, use a kind of atomic weak light detection method, and the faint optical signal of single photon energy level can be detected, high 5～7 orders of magnitude of detector that remolding sensitivity is common, the weak scattering optical signal that far-end is returned is unlikely to be submerged in noise, so replacing traditional photodetector with single-photon detector can improve detectivity, reduce noise peak.But single-photon detector dynamic range is limited and is easily saturated: the maximum count frequency of single-photon detector is restricted by afterpulse problem, it is far smaller than the repetition rate of detector circuit, when the backscattering luminous power maximum saturation luminous power more than detector entering single-photon detector, pile up effect will occur, cause counting saturated, the i.e. saturated light power of single-photon detector is much smaller than conventional detectors, incident intensity is limited, so, while reducing system noise peak value by single-photon detector, maximum back-scattering light power limited can be made, the real purpose increasing Dynamic Range cannot be arrived.
So, light intensity modulator is introduced in the system that distribution is Fibre Optical Sensor by the present invention, can be while increasing the incident optical power of sensor fibre, can guarantee that again the back-scattering light of return, after light intensity modulator is modulated, saturated conditions occurs not over the maximum response of single-photon detector.So, single-photon detector and light intensity modulator are placed in system, have both reduced the noise peak power of system, increase initial backscattering luminous power, be that the Dynamic Range of distributed fiberoptic sensor is significantly improved.
The function of light intensity modulator: the mainly intensity amplitude value of Returning scattering light on modulation whole piece sensor fibre so that the backscattering optical signal near-end decay of sensor fibre is big, and far-end decay is little, makes the output intensity of light intensity modulator tend towards stability.When increasing incident intensity, back-scattering light after light intensity modulation shaping not only will cause single-photon detector saturated because near-end light intensity is excessive, thus avoid remote signaling and be submerged in noise because crossing weak, last re-demodulation recovers signal, such that it is able to increase dynamic range, improve distance sensing.
Note:
1) when only substituting the detector in traditional distributed Fibre Optical Sensor with single-photon detector, and when not adding light intensity modulator, it is known that the dynamic range of single-photon detector is d1[p2,p1] (wherein p2For the minimum detectable light intensity of single-photon detector, p1For maximum response) time, the Dynamic Range of distributed fiberoptic sensor is D1[P2,P1]；According to photodetection principle, Dynamic Range now is determined by the dynamic range of single-photon detector, it may be assumed that
D1[P2,P1]∝d1[p2,p1]
Owing to entering to inject sensor fibre through circulator from laser pulse, producing back-scattering light to distance L at a distance, again return in this period of time of light intensity modulator t, the distance of optical transport is 2L.Therefore according to the propagation principle of light:
L=vt/2 (2) wherein v is light spread speed in a fiber.
From optical fiber transmission property, an Important Parameters of optical fiber is optical signal power attenuation when transmitting in a fiber.When the attenuation quotient that sensor fibre is total is α, if the power entering to inject sensor fibre is P0, then light pulse propagation is to luminous power during optical fiber L position:
Pa(L)=P0·e- α L (3)
Additionally, pulsed light can occur nonlinear effect during fiber-optic transfer, produce the back-scattering light carrying heat transfer agent.When the pulsed light that width is w is transferred at L with v ray velocity in sensor fibre, convolution (3), the scattered light power produced in this place:
Wherein αsIt it is scattering coefficient.
When back-scattering light returns to single-photon detector in reverse direction, transmitting procedure is affected by optical fiber transmission attenuation characteristic equally, and its luminous power becomes:
Now PS(L) it is the input optical power of single-photon detector, again because the peak response luminous power of single-photon detector is p1, so:
From the foregoing, it will be observed that the incident optical power that system allows sensor fibre maximum is:
So, now dynamic range D of system1[P2,P1]=D1[P2,Pomax], such as Fig. 2.
2) such as Fig. 1, before above-mentioned single-photon detector, a light intensity modulator is added, it is known that the dynamic range of single-photon detector is d1[p2,p1], now the Dynamic Range of distributed fiberoptic sensor is D2[P′2,P′1]；Owing to the maximum noise peak value (minimum detectable light intensity) of system is determined by single-photon detector, so P2=P '2。
According to formula (5), when back-scattering light returns to intensity modulator input in reverse direction, its luminous power is similarly:
That is, PS(L) being the input optical power of light intensity modulator, according to the operation principle of photoelectricity intensity modulator, now, its Output optical power is:
Wherein, V represents that the input offset voltage of light intensity modulator, V π represent the half-wave voltage of manipulator, it may be assumed that output intensity is from changing to greatly the minimum magnitude of voltage needing and changing.
Now, PC(L) it is the input optical power of single-photon detector.In like manner, again because the peak response luminous power of single-photon detector is p1, so:
From the foregoing, it will be observed that the incident optical power that now system allows sensor fibre maximum is:
So, the now dynamic range of system:
D2[P′2,P′1]=D2[P′2,P′omax]=D2[P2,P′omax]
In conjunction with note: 1) and 2) can obtain:
So:
D2[P′2,P′1] ＞ D1[P2,P1] (13)
In summary, it is in fiber optic sensor system, to be simultaneously introduced single-photon detector and light intensity modulator in general distribution, system can be increased and allows the maximum input light intensity of sensor fibre while reducing noise peak power, it is achieved thereby that the distributing optical fiber sensing of wide dynamic range.
The implementation method of a kind of based on single photon detection the wide dynamic range distribution formula optical fiber sensing system of the present invention, comprises the following steps:
1) pulse laser described in sets the size of input optical pulse power by the actual measurement range demand of sensor fibre, and provides light pulse signal for whole system under the triggering of clock generator；
2) pulse laser number is P by being connected power with described circulator0Light pulse inject sensor fibre, when light pulse is transmitted in sensor fibre, can be due to the character of optical fiber itself, temperature, pressure, abutment, bending or other similar event and produce scattering, reflect, decay, in addition, light pulse can occur nonlinear effect during fiber-optic transfer, sensing reason information and back-scattering light that luminous power is P (L) are carried in generation, and when back-scattering light returns to light intensity modulator in reverse direction, its luminous power becomes PS(L), the optical fiber now obtained is along the curve that backscattering luminous power is an exponential damping on road, and this curve table shows the optical fiber loss situation along road, as shown in the curve a in Fig. 2, now, dynamic range D1By initial back-scattering light power P1With noise peak P2Determine, thus obtaining the most measurable distance sensing is L1。
3) by described light intensity modulator and waveform generator, the back-scattering light returned being carried out synchronous modulation, the backscattering optical attenuation decay big, far-end making near-end is little.The luminous power of the back-scattering light before entering to inject light intensity modulator exponentially decays, then, interim level trend can be presented, as shown in the curve b in Fig. 2 through the true curve of output of backscattering luminous power of light intensity device modulation.
Note: as it is shown on figure 3, be P when increasing incident intensity0' (＞ P0) time, understand according to formula (4), the scattered light power produced at L:
Understanding further according to formula (5), now scattered light returns to the luminous power of light intensity modulator:
When not considering the physical event that sensor fibre is gone up on the way, the backscattering optical signal near-end making sensor fibre is decayed greatly, far-end decay is little, reach maximum transmission distance, the Output optical power of light intensity modulator should convergence constant k, i.e. power output level of approximation curve, needs modulation function F (t) arranging light intensity modulator to meet the most before this:
Again according to formula (9), the Output optical power of light intensity modulator is also P 'C(L), so:
That is: the Output optical power k after intensity modulator is modulated is by the bias voltage V of manipulator and half-wave voltage VπDetermine.
Clock generator can arrive the time t of the light inlet mouth of light intensity modulator according to the scattered light returned, and controls light intensity modulator to one synchronizing clock signals of waveform generator and the backscattering optical signal returned is carried out synchronous modulation.
Now, the Output optical power after modulation is as shown in the curve b ' in Fig. 3, on the premise of only increasing incident intensity, and PC' (L) should be at [PC,P1(the P in corresponding diagram 2 in the range of]1、PC), i.e. PC' maximum can get P1, obtaining now maximum distance sensing is L2。
4) after, from described single-photon detector to modulation after luminous power be PC' the optical signal of (L) carries out photon counting, record enters the number of photons of detector the most in the same time, within the unit interval, relatively steady state it is in owing to entering the number of photons of single photon detection after being modulated, when physical change events such as occurrence temperature, pressure, abutment, bendings, corresponding scattered light intensity can change on the basis of modulation, and the number of photons of now single-photon detector detection is affected by respective physical event also can occur respective change；
5) then by described signal processing unit according to driving signal (bias voltage V and half-wave voltage V with manipulator set by intensity modulatorπIt is associated), by the output intensity P of single-photon detectord(L) (=P 'c(L)=k) revert to the size before back-scattering light entrance light intensity modulatorI.e. PCCurve after ' (L) recovers is as shown in the curve a ' in Fig. 3, and dynamic range now is D2, PC' value [P2′,P1'] in the range of.
By step 3) know, PC' value also should be at [PC, P1Within], again because of at identical distance L,
PC' ＞ PC (18)
Thus draw, P1' ＞ P1, P2'=P2(being determined by the noise peak of single-photon detector).In summary, dynamic range D2＞ D1, maximum distance sensing L2＞ L1。
6) information after demodulation being recovered again carries out later stage process, there is the positional information of physical event on the way in the change actual response sensor fibre making luminous power, the optical information returned is detected by single-photon detector after light intensity modulator, from formula (1), with from optical signal launch to the time t used by returning, and the speed v that light is in a fiber, it is possible to calculate distance L, thus obtain last fibre circuit condition information curve chart, as shown in the curve a ' in Fig. 3；
7) from step 3) and step 5), the implementation method of this kind of based on single photon detection the wide dynamic range distribution formula optical fiber sensing system adding light intensity modulator in post-processing stages and device, after increasing incident intensity, the back-scattering light modulated through light intensity modulator not only will cause single-photon detector saturated because near-end light intensity is excessive, the scattered light intensity making sensor fibre on the contrary can increase with incident optical power and strengthen, thus avoids far-end and carry the backscattering optical signal of information and be submerged in noise because crossing the most weak.Finally demodulation recovers the information such as the true luminous power in light path, it is achieved the distributed sensing of wide dynamic range, expands distance sensing.
As shown in Figure 1, in the implementation method of a kind of distributed optical fiber sensing system based on single photon detection width dynamic range, mainly comprise direct impulse generation unit (pulse laser), circulator, sensor fibre, waveform generator, light intensity modulator, single-photon detector and signal processing unit.Described pulse laser is connected with circulator by Transmission Fibers, then the other end of circulator is connected with sensor fibre, make light pulse after circulator enters sensor fibre, the scattered light axially returned along optical fiber with one end detection intensity information after light intensity modulator enters back into single-photon detector, detection optical information is carried out recovering to solve reconciliation process by last signal processing unit.
Above-mentioned pulse laser uses the bench pulse laser instrument of Ming Xin laser company MTFLP-series, and wavelength is tunable in the range of 1539nm 1562nm；1 50ns level pulse output；Live width is 20MHz (mm)；Pulsewidth, frequency, power are the most adjustable；Light source as distributed optical fiber sensing system device, it is achieved the transmission of pulsed optical signals.
Above-mentioned waveform generator uses the function/arbitrary waveform generator of spectrum source RIGOL DG4162, and sample rate is 500MSa/s, and vertical resolution reaches 14bits, and standard configuration bandwidth reaches 160MHz, 2ppm high frequency stability, the Low Phase Noise Signal output of-115dBc/Hz.
Company 2.5G Mach-Zehnder electro-optic intensity modulator (M-ZEOIM) when above-mentioned light intensity modulator uses Sheng Ming, its extinction ratio is more than 27dB, modulation bandwidth 3GHz, and insertion loss is 4dB, and half-wave voltage is about 3.8V.
Above-mentioned single-photon detector uses the ID200 single-photon detector of idQuantique, this detector is single-photon detector based on InGaAs/InP APD (InGaAs/InP SPAD), possess detection performance height, reliability high, InGaAs/InP SPAD operates mainly in 0.9-1.6 μm near infrared band, its detection principle is based on avalanche photodiode structure (p-ti or p-i-n junction), detection efficient η ≈ 10% (about-60 DEG C), dark counting pdc=2000s-1, noise equivalent power
The above embodiment of the present invention is only for clearly demonstrating example of the present invention, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here without also cannot all of embodiment be given exhaustive.All any amendment, equivalent and improvement etc. made within the spirit and principles in the present invention, within should be included in the protection domain of the claims in the present invention.
Claims (4)
1. a wide dynamic range distribution formula optical fiber sensing system based on single photon detection realize device, it is characterised in that should
Device includes pulse laser, circulator, clock generator, waveform generator, sensor fibre, light intensity modulator, monochromatic light
Sub-detector and signal processing unit, described pulse laser is noted to sensor fibre through circulator under the triggering of clock generator
Entering laser pulse, generation is carried the back-scattering light of heat transfer agent and is incided light intensity modulator, waveform generator through circulator
Export the driving signal Tong Bu with backscattering optical signal, control the pad value of light intensity modulator, decay through light intensity modulator
After signal detected by single-photon detector again, finally by signal processing unit according to the signal intensity detected, and recover original
The intensity of scattered signal light, thus realize the distributing optical fiber sensing of wide dynamic range.
Device the most according to claim 1, it is characterised in that use the light intensity modulator return signal to sensor fibre
Amplitude carries out real-time shaping so that the backscattering optical signal near-end decay of the sensor fibre entering light intensity modulator is big, far-end
Decay little.
Device the most according to claim 1, it is characterised in that it is characterized in that: above-mentioned dynamic range is defined as initial
Backscattering luminous power and noise peak power ratio, light intensity modulator can increase distributed optical fiber sensing system and allow
Big initial backscattering luminous power, single-photon detector can reduce distributed optical fiber sensing system noise peak power, so that
The wide dynamic range of device is better achieved.
4. applying the method realizing device of wide dynamic range distribution formula optical fiber sensing system based on single photon detection, it is special
Levy and be, comprise the following steps:
1) pulse laser sets the size of input optical pulse power by the actual measurement range demand of sensor fibre, and time
Light pulse signal is provided under the triggering of clock generator；
2) light pulse signal is by being connected with circulator, is P by power0Light pulse inject sensor fibre, when light pulse pass
In photosensitive fibre during transmission, scattering can be produced due to the character of optical fiber itself, reflect or decay, additionally, light pulse is passing
Photosensitive fine transmitting procedure can occur nonlinear effect, produce and carry heat transfer agent and back-scattering light that luminous power is P (L), when
When back-scattering light returns to light intensity modulator in reverse direction, its luminous power becomes PS(L) sensor fibre, now obtained is along road
The curve that backscattering luminous power is an exponential damping, this curve table shows the sensor fibre loss situation along road, now,
Dynamic range D1By initial back-scattering light power P1With noise peak power P2Determine, thus obtain the most measurable biography
Sense distance is L1；
3) by light intensity modulator and waveform generator, the back-scattering light returned is carried out synchronous modulation, makes near-end dorsad
Scattered light decay decay big, far-end is little, and the luminous power of the back-scattering light before entering to inject light intensity modulator exponentially decays,
So, the true curve of output through the backscattering luminous power of light intensity device modulation can present interim level trend.
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