CN105806465B - A kind of novel Φ-OTDR detection device and its detection method based on fixation reflex point - Google Patents

A kind of novel Φ-OTDR detection device and its detection method based on fixation reflex point Download PDF

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CN105806465B
CN105806465B CN201610141340.5A CN201610141340A CN105806465B CN 105806465 B CN105806465 B CN 105806465B CN 201610141340 A CN201610141340 A CN 201610141340A CN 105806465 B CN105806465 B CN 105806465B
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light
fiber
detection
coupler
pulse
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CN201610141340.5A
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CN105806465A (en
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张益昕
孙振鉷
张旭苹
单媛媛
李研亭
傅思怡
蔡银森
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南京大学
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01HMEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors

Abstract

The invention discloses a kind of novel Φ-OTDR detection devices based on fixation reflex point, including delay time generator, laser, pulse-modulator, erbium-doped fiber amplifier, optical circulator, fiber-optic probe unit, the first coupler, time delay optical fiber, Polarization Controller, the second coupler, avalanche photodetector and data acquisition card;The fiber-optic probe unit includes several sequentially connected optical fiber, and the both ends junction of optical fiber is respectively formed fixed reflection point.The invention also discloses a kind of detection methods of novel Φ-OTDR detection device based on fixation reflex point, the present invention measures the vibration of surrounding by using fiber-optic probe unit, and carrying out the demodulation of three port phases by look-up table may be implemented the real-time monitoring of the position to vibration, frequency and amplitude;Optical fiber is divided into several segments using fiber-optic probe unit, avoids a position vibration event interfering on whole section of optical fiber, while the system of this structure is easy dismounting maintenance.

Description

A kind of novel Φ-OTDR detection device and its detection method based on fixation reflex point
Technical field
The present invention relates to technical field of optical fiber sensing, especially a kind of novel Φ-OTDR detection based on fixation reflex point Device and its detection method.
Background technique
Phase sensitive optical time domain reflectometer (Φ-OTDR) vibration measuring is quickly grown in past more than ten years, in important field There is important application value in institute's security monitor and civil infrastructure health monitoring.Such as the peace of prison fence or national boundary Anti- monitoring and bridge, highway and building will inevitably be damaged with the increase of the service life, can will divide Cloth vibration measuring system is mounted in security protection region or building surface is for monitoring the vibration as caused by special event, in order to reality When monitor or have found that it is likely that the hidden danger for causing building accident early.
Φ-OTDR can be detected additional on sensor fibre by the interference fading phenomenon of the backward Rayleigh scattering light in optical fiber The position of disturbance and the information of frequency domain.As other optical time domain reflectometers, Φ-OTDR is also the sensor-based system of single-ended measurement, But available backward Rayleigh scattering light time-domain curve in order to obtain, need the laser using narrow linewidth, frequency stabilization.Narrowband Short pulse be launched into sensor fibre, the relevant effect quilt of the waveform of the Rayleigh scattering of return due to different scattering centers It is modulated into zigzag.By the variation for analyzing this zigzag Rayleigh waveform, so that it may monitor in sensor fibre since the external world is disturbed Dynamic bring variations in refractive index, weak variations in refractive index can be strengthened by the coherent effect between scattering member.
Φ-OTDR has two clear advantages of fast response time and high sensitivity.Compared to Brillouin scattering and drawing Graceful scattering light measurement vibration, Rayleigh scattering light has stronger scattering optical power, therefore the signal that photodetector detects is also relatively strong, Without multiple cumulative mean, thus the fast response time of Φ-OTDR, it can be used for detecting fast-changing dynamic disturbances, example Such as vibration signal, then it can be obtained by by suitable data processing method the time domain and frequency domain information of vibration signal.In Φ- In OTDR, extraneous disturbance information is obtained by the Rayleigh interference fading phenomenon of Rayleigh scattering light backward in sensor fibre, And influence Rayleigh interference fading is the phase of light in optical fiber, as long as so detecting the phase of light in extraneous disturbing influence optical fiber Position, then Φ-OTDR just has the ability to detect extraneous disturbance event, so Φ-OTDR high sensitivity, is capable of detecting when small External disturbance.
But there is also obvious disadvantages by currently used Φ-OTDR, are merely able to detect the generation position of strain mostly Its frequency domain information is set and extracts, no standard measure measures strain value.Main cause is the optical signal that receiving end obtains Relationship do not determined with the strain value loaded on optical fiber, one-to-one, so light can not be calculated by demodulating algorithm The strain value loaded on fibre.A Masoudi, M Belal of the University of Southampton of Britain etc. are in " A distributed Optical fibre dynamic strain sensor based on phase-OTDR " use 3 × 3 couplers and delay Detection to amplitude may be implemented to carry out phase demodulating in optical fiber, but a position vibration event is easy on whole section of optical fiber It interferes, if optical fiber is damaged, optical fiber dismounting is repaired complicated;The Zhu Fan in Nanjing University's fiber-optic communication project research center, Zhang Yixin etc. is in " Improved Φ-OTDR Sensing System for Distributed Strain Variation Measurement based on Ultra-weak Fiber Bragg Grating Array " use Bragg grating reflection Signal carries out phase demodulating, but needs to carry out laser frequency sweep control, and solution phase algorithm is relative complex, while needing to adopt Cause spatial resolution lower with broad pulse;And Zhang Yixin, Zhang Xuping etc. are in " the phase sensitivity light based on bragg grating array Time Domain Reflectometry device and method " in (patent No.: CN201510389252.2) this patent to the side in Zhu Fan, Zhang Yixin paper Method is improved, and high spatial resolution can be realized on the basis of quantitative analysis, but in order to realize high space Resolution ratio, the grating used is more intensive, can to detect cost raising, reparation complex process is complicated after installation and damage, right Operator requires high, it is difficult to promote and apply in engineering.
Summary of the invention
It is provided the technical problem to be solved by the present invention is to overcome the deficiencies in the prior art a kind of based on fixation reflex point Novel Φ-OTDR detection device and its detection method, the present invention be to pass through on the basis of existing Φ-OTDR sensor-based system Fiber-optic probe unit is introduced to measure the vibration of surrounding, three port phases demodulation realization is carried out to the position of vibration by look-up table It sets, the real-time monitoring of frequency and amplitude.
The present invention uses following technical scheme to solve above-mentioned technical problem:
A kind of novel Φ-OTDR detection device based on fixation reflex point proposed according to the present invention, including delay occur Device, laser, pulse-modulator, erbium-doped fiber amplifier, optical circulator, fiber-optic probe unit, the first coupler, delay light Fibre, Polarization Controller, the second coupler, avalanche photodetector and data acquisition card;The fiber-optic probe unit includes several The both ends junction of a sequentially connected optical fiber, optical fiber is respectively formed fixed reflection point;Wherein,
Delay time generator, for generating modulation pulse, trigger pulse;Pulse input is modulated to pulse-modulator, triggers arteries and veins Punching is input to data acquisition card;
Laser for generating continuous mode narrow-linewidth laser, and outputs this to pulse-modulator;
It is defeated to be converted to pulsed light for modulating pulse based on the received by pulse-modulator for continuous mode narrow-linewidth laser Out to erbium-doped fiber amplifier;
Erbium-doped fiber amplifier, for exporting after pulsed light is zoomed into detection light to optical circulator;
Optical circulator is inputted by its 1st port for that will detect light, and is injected into fiber-optic probe unit by its 2nd port;
Fiber-optic probe unit, back rayleigh scattering light and reflection light output to the 2nd end of optical circulator for that will generate Mouthful, and exported by the 3rd port of optical circulator to the first coupler;
First coupler, for reflected light and back rayleigh scattering light to be divided into two-way: first via light output to the light that is delayed Fibre, the second tunnel light output to Polarization Controller;
Time delay optical fiber, for being delayed to first via light, the first via light after exporting delay to the second coupler;
Polarization Controller, for controlling the polarization state of the second road light, so that the polarization phase of its polarization state and first via light Match, the second tunnel light output to the second coupler after polarization;
Second coupler, for the second road light after the first via light and polarization after delay to be carried out relevant beat frequency, so that Phase difference, three tunnel light outputs to avalanche photodetector are generated between three road light of output;
Avalanche photodetector, for exporting after three road light are converted into electric signal to data acquisition card;
Data acquisition card, for converting electrical signals to digital signal and carrying out subsequent processing according to trigger pulse.
As a kind of novel Φ-OTDR detection device side of advanced optimizing based on fixation reflex point of the present invention Cycle synchronisation of the period of case, the modulation pulse and trigger pulse with detection light.
As a kind of novel Φ-OTDR detection device side of advanced optimizing based on fixation reflex point of the present invention Case, fiber-optic probe unit are several sequentially connected optical patchcords.
As a kind of novel Φ-OTDR detection device side of advanced optimizing based on fixation reflex point of the present invention Case, first via light differ the time of a reflection interval length with the first via light after delay.
As a kind of novel Φ-OTDR detection device side of advanced optimizing based on fixation reflex point of the present invention Case, first coupler are 50:50 coupler.
As a kind of novel Φ-OTDR detection device side of advanced optimizing based on fixation reflex point of the present invention Case, second coupler are 3 × 3 couplers, 120 ° of the phase phase difference of three road light.
Based on a kind of detection method of novel Φ-OTDR detection device based on fixation reflex point, include the following steps,
Step 1: generating continuous mode narrow-linewidth laser using laser, continuous mode narrow-linewidth laser is converted into arteries and veins It washes off, and exports after its pulsed light is zoomed into detection light into several sequentially connected optical fiber, the both ends of the optical fiber connect The place of connecing is respectively formed fixed reflection point;
Step 2: detection light generates back rayleigh scattering light in a fiber, the reflection point in the both ends junction of optical fiber produces Raw reflected light;The back rayleigh scattering light is for detecting vibration position, and reflected light is for detecting vibration frequency and amplitude;
Step 3: reflected light and back rayleigh scattering light are divided into two-way: first via light and the second road light;
Step 4: first via light is delayed, the first via light after delay differs a reflection interval with first via light The time of length;
Step 5: the polarization state of the second road light of control, so that its polarization state and the polarization of first via light match;
Step 6: the second road light after the first via light and polarization after delay is carried out relevant beat frequency, three road light are exported, this Phase difference is generated between three road light;
Step 7: phase information is demodulated according to the intensity of three road light, to realize to the position of vibration, frequency and vibration The real-time monitoring of width;The method of demodulation is using look-up table, and look-up table precalculates to obtain, so that phase is in (- π, π) Change at certain intervals, the intensity value of corresponding three road light is calculated and the table that is formed, according to tri- tunnel actual detection Chu The intensity of light obtains corresponding phase information by searching for table to search.
The invention adopts the above technical scheme compared with prior art, has following technical effect that
(1) present invention measures the vibration of surrounding by using fiber-optic probe unit, carries out three port phases by look-up table The real-time monitoring of the position to vibration, frequency and amplitude may be implemented in position demodulation;
(2) optical fiber is divided into several segments using fiber-optic probe unit, avoids a position vibration event on whole section of optical fiber Interfere, while this structure system be easy dismounting maintenance.
Detailed description of the invention
Fig. 1 is system construction drawing of the invention.
Fig. 2 is coherent signal measuring principle figure.
Fig. 3 is to look for table method demodulation schematic diagram.
Specific embodiment
Technical solution of the present invention is described in further detail with reference to the accompanying drawing:
It is system construction drawing of the invention as shown in Figure 1, a kind of novel Φ-OTDR detection dress based on fixation reflex point It sets, including delay time generator, laser, pulse-modulator, erbium-doped fiber amplifier, optical circulator, fiber-optic probe unit, first Coupler, time delay optical fiber, Polarization Controller, the second coupler, avalanche photodetector and data acquisition card;The fiber-optic probe Unit includes several sequentially connected optical fiber, and the both ends junction of optical fiber is respectively formed fixed reflection point;Wherein,
Delay time generator, for generating modulation pulse, trigger pulse;Pulse input is modulated to pulse-modulator, triggers arteries and veins Punching is input to data acquisition card;
Laser for generating continuous mode narrow-linewidth laser, and outputs this to pulse-modulator;
It is defeated to be converted to pulsed light for modulating pulse based on the received by pulse-modulator for continuous mode narrow-linewidth laser Out to erbium-doped fiber amplifier;
Erbium-doped fiber amplifier, for exporting after pulsed light is zoomed into detection light to optical circulator;
Optical circulator is inputted by its 1st port for that will detect light, and is injected into fiber-optic probe unit by its 2nd port;
Fiber-optic probe unit, back rayleigh scattering light and reflection light output to the 2nd end of optical circulator for that will generate Mouthful, and exported by the 3rd port of optical circulator to the first coupler;
First coupler, for reflected light and back rayleigh scattering light to be divided into two-way: first via light output to the light that is delayed Fibre, the second tunnel light output to Polarization Controller;
Time delay optical fiber, for being delayed to first via light, the first via light after exporting delay to the second coupler;
Polarization Controller, for controlling the polarization state of the second road light, so that the polarization phase of its polarization state and first via light Match, the second tunnel light output to the second coupler after polarization;
Second coupler, for the second road light after the first via light and polarization after delay to be carried out relevant beat frequency, so that Phase difference, three tunnel light outputs to avalanche photodetector are generated between three road light of output;
Avalanche photodetector, for exporting after three road light are converted into electric signal to data acquisition card;
Data acquisition card, for converting electrical signals to digital signal and carrying out subsequent processing according to trigger pulse.
Cycle synchronisation of the period of the modulation pulse and trigger pulse with detection light.
Laboratory uses device performance: the model RIO laser of laser, which is 1550nm, line width For 10kHz, Output optical power 13dBm;Pulse-modulator selects electrooptic modulator, can produce the light pulse of minimum 20ns; The amplifier of emerging BA series, centre frequency can achieve in 1550nm, operation wavelength 20nm, invariable power gain in EDFA selection 17dBm.First coupler is 50:50 coupler, and the second coupler is 3 × 3 couplers.
Specific experiment condition: using optical patchcord as detection optical fiber in this programme, the end face of connector generates reflection.Installation With will be on flange to most tight when tie jumper, when measurement, does not need to manually adjust its tightness to control fiber end face reflection, And if wherein one section of optical fiber is influenced to change length by extraneous vibration, will not affect that the transmission of light in adjacent wire jumper. By the comparative analysis to fibre-optical splice assembled scheme not of the same race, this system selects the connection type of FC/PC-FC/PC.The company It connects under mode, the reflection substantially -50dBm that fiber end face generates, and the Rayleigh scattering light in optical fiber is that -70dBm arrives -60dBm Between, enable reflective light intensity to be significantly stronger than Rayleigh scattering signal.The sensor fibre length used in experiment is L=5km, then The required pulse period should be greater than 50 μ s.5 sections of optical patchcords are accessed in the end of 5km optical fiber, each section of optical patchcord length is d =20m, time delay optical fiber length are 40m.
Specific step is as follows for Binding experiment parameter:
Step 1: laser generates continuous mode narrow-linewidth laser, and continuous mode narrow-linewidth laser is converted to pulsed light, Pulse width is in 20ns -1us;Then it is detection light after EDFA amplifies, fiber-optic probe list is entered after optical circulator Member.
Step 2: it as shown in Fig. 2, detection light is transmitted in fiber-optic probe unit, encounters reflection point and reflects, obtain To the original signal of reflection, original signal is divided by the first coupler, and the light of first part 50% obtains after time delay optical fiber Signal after to delay, the signal differ the time of a reflection interval length with original signal;Another part 50% is by inclined Vibration controller inhibits polarization noise to keep its polarization state to match with time delayed signal, and then this two paths of signals passes through the second coupler Occur to be concerned with, and is output to three APD and is converted into electric signal by capture card acquisition process.It is original in case of vibration event The phase of signal and time delayed signal can change, and the signal light intensity after being concerned with can occur significantly to change.
Step 3: the principle of three ports demodulation is the signal that signal to be demodulated is divided into three 2 π/3 of phase phase difference, is carried out The phase term in original signal is restored after the operations such as summation, differential, integral, i.e., by formulaIt obtainsProcess.Here is the quantitative interpretation to three port demodulation principles:
Due to device property, the three road light phase difference that the reflected light of system obtains after three port couplers are not differed 2 π/3 can state are as follows:
Wherein, D is the average value of reflected signal strength, and E is the peak power compared with this average value,It is to need to solve The light phase of tune, k=1,2,3.
Above-mentioned three road signal is summed, then the result for exchanging item addition is zero, thus obtains the DC terms D in signal.Often All the way signal subtract summed result 1/3 after obtain only comprising exchange item signal:
Differential is carried out to the signal to obtainCarry out lower column operations:And Resulting result is summed to obtain
Pass throughBe easy to get toIt is obtained finally by integral operationNamely the phase of signal.
So directly carrying out the mode of three port demodulation, complexity is calculated, it is time-consuming more, it is unable to satisfy the need calculated in real time It asks.So light phase value corresponding to the intensity that three detectors measure is precomputed, in practical survey using lookup table mode Amount intermediate value needs the intensity value measured carrying out matching with existing value to find corresponding phase value.As shown in figure 3, generating one Three-dimensional space table, reference axis are the light intensity I that three detectors obtain, and can be obtained using the value that detector obtains as coordinated indexing To phase
The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be said that Specific implementation of the invention is only limited to these instructions.For those of ordinary skill in the art to which the present invention belongs, exist Under the premise of not departing from present inventive concept, several simple deductions or substitution can also be made, all shall be regarded as belonging to of the invention Protection scope.

Claims (5)

1. a kind of novel Φ-OTDR detection device based on fixation reflex point, including delay time generator, laser, impulse modulation Device, erbium-doped fiber amplifier, optical circulator, fiber-optic probe unit, the first coupler, time delay optical fiber, Polarization Controller, the second coupling Clutch, avalanche photodetector and data acquisition card;It is characterized in that, the fiber-optic probe unit is that several are sequentially connected The both ends junction of optical patchcord, optical patchcord is respectively formed fixed reflection point;The length of each optical patchcord is identical and optical fiber The reflectivity of the tie point of wire jumper is consistent;Wherein,
Delay time generator, for generating modulation pulse, trigger pulse;Pulse input is modulated to pulse-modulator, trigger pulse is defeated Enter to data acquisition card;
Laser for generating continuous mode narrow-linewidth laser, and outputs this to pulse-modulator;
Continuous mode narrow-linewidth laser is converted to pulse light output extremely for modulating pulse based on the received by pulse-modulator Erbium-doped fiber amplifier;
Erbium-doped fiber amplifier, for exporting after pulsed light is zoomed into detection light to optical circulator;
Optical circulator is inputted by its 1st port for that will detect light, and is injected into fiber-optic probe unit by its 2nd port;
Fiber-optic probe unit, back rayleigh scattering light and reflection light output to the 2nd port of optical circulator for that will generate, and It is exported by the 3rd port of optical circulator to the first coupler;
First coupler, for reflected light and back rayleigh scattering light to be divided into two-way: first via light output to time delay optical fiber, the Two tunnel light outputs are to Polarization Controller;
Time delay optical fiber, for being delayed to first via light, the first via light after exporting delay to the second coupler;First via light The time of a reflection interval length is differed with the first via light after delay;
Polarization Controller, for controlling the polarization state of the second road light, so that its polarization state and the polarization of first via light match, partially The second tunnel light output to the second coupler after vibration;
Second coupler, for the second road light after the first via light and polarization after delay to be carried out relevant beat frequency, so that output Three road light between generate phase difference, three tunnel light outputs to avalanche photodetector;
Avalanche photodetector, for exporting after three road light are converted into electric signal to data acquisition card;
Data acquisition card, for converting electrical signals to digital signal and carrying out subsequent processing according to trigger pulse.
2. a kind of novel Φ-OTDR detection device based on fixation reflex point according to claim 1, which is characterized in that Cycle synchronisation of the period of the modulation pulse and trigger pulse with detection light.
3. a kind of novel Φ-OTDR detection device based on fixation reflex point according to claim 1, which is characterized in that First coupler is 50:50 coupler.
4. a kind of novel Φ-OTDR detection device based on fixation reflex point according to claim 1, which is characterized in that Second coupler is 3 × 3 couplers, 120 ° of the phase phase difference of three road light.
5. based on a kind of novel Φ-OTDR detection device based on fixation reflex point of any of claims 1-4 Detection method, which is characterized in that include the following steps,
Step 1: generating continuous mode narrow-linewidth laser using laser, continuous mode narrow-linewidth laser is converted into pulsed light, And by its pulsed light zoom into detection light after output into several sequentially connected optical fiber, the both ends junction of the optical fiber is equal Form fixed reflection point;
Step 2: detection light generates back rayleigh scattering light in a fiber, the reflection point in the both ends junction of optical fiber generates instead Penetrate light;The back rayleigh scattering light is for detecting vibration position, and reflected light is for detecting vibration frequency and amplitude;
Step 3: reflected light and back rayleigh scattering light are divided into two-way: first via light and the second road light;
Step 4: first via light is delayed, the first via light after delay differs a reflection interval length with first via light Time;
Step 5: the polarization state of the second road light of control, so that its polarization state and the polarization of first via light match;
Step 6: the second road light after the first via light and polarization after delay is carried out relevant beat frequency, three road light, this three tunnel are exported Phase difference is generated between light;
Step 7: phase information is demodulated according to the intensity of three road light, to realize to the position of vibration, frequency and amplitude Real-time monitoring;The method of demodulation is using look-up table, and look-up table precalculates to obtain, so that phase is in (- π, π) with one Fixed interval variation calculates the intensity value of corresponding three road light and the table that is formed, according to tri- road light of actual detection Chu Intensity obtains corresponding phase information by searching for table to search.
CN201610141340.5A 2016-03-11 2016-03-11 A kind of novel Φ-OTDR detection device and its detection method based on fixation reflex point CN105806465B (en)

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