CN105910546A - BOTDR system based on dual-channel Mach-Zehnder interferometer - Google Patents

Abstract

The invention provides a BOTDR system based on a dual-channel Mach-Zehnder interferometer. The BOTDR system comprises a laser device, an acousto-optic modulator, a pulse signal generator, an erbium-doped fiber amplifier, a first optical circulator, a fiber bragg grating, a second optical circulator, a sensing fiber, a first optical isolator, the dual-channel Mach-Zehnder interferometer, a photoelectric detector, an amplification circuit and an oscilloscope. The laser device, the acousto-optic modulator, the erbium-doped fiber amplifier, the first optical circulator, the second optical circulator, the sensing fiber and the first optical isolator are connected in turn. The pulse signal generator is connected with the acousto-optic modulator. The fiber bragg grating is connected with the first optical circulator. The input end of the dual-channel Mach-Zehnder interferometer is connected with the second optical circulator, and the output end is connected with the photoelectric detector, the amplification circuit and the oscilloscope in turn.

Description

A kind of BOTDR system based on dual pathways Mach-Zehnder interferometer

Technical field

The present invention relates to technical field of optical fiber communication, be specifically related to a kind of based on the interference of dual pathways Mach-Zehnder The BOTDR system of instrument.

Background technology

Relative to traditional quasi-distributed sensing technology of fiber grating, long-distance distributed optical fiber sensing technology Ambient parameter can be measured continuously.Advantage based on Brillouin scattering distributed sensing technology is Temperature and strain can be measured simultaneously, there are again spatial resolution height, precision height and far measuring distance etc. excellent Gesture, therefore application prospect is the most extensive.

Brillouin light Time Domain Reflectometry is mainly had based on optical fiber Brillouin scatter distributions formula sensing technology And two kinds of structures of Brillouin optical time domain analysis (BOTDA) (BOTDR).BOTDA sensing technology It is pulse pump light and the continuous probe flashlight being injected separately into counterpropagate at the two ends of sensor fibre, comes Strengthen Brillouin scattering.Set up the BOTDA on the basis of stimulated Brillouin scattering, there is signal intensity The feature of high and good spatial resolution, but owing to needs are at sensor fibre two ends input relative transport Light, causes its structure complicated, adds engineer applied difficulty and fault rate；And due to BOTDA system System exists non-local effect, limits the raising of its certainty of measurement and distance sensing.

Distributing optical fiber sensing measuring technology based on BOTDR is capable of high spatial resolution, length Distance detection and single-ended measurement.One of key technology as BOTDR system, to faint Brillouin Scattered signal carries out detecting mainly Direct Inspection Technology and two kinds of methods of relevant detection.Wherein relevant detection Technology includes the relevant inspection of coherent detection technology based on acousto-optic frequency translation, BOTDR based on electrooptic modulator Survey technology and BOTDR microwave heterodyne detection technology.

Direct Inspection Technology is to extract Brillouin scattering optical signal by various optically filtering methods, conventional Method has F-P interferometer and M-Z interferometer (Mach-Zehnder Interferometer, MZI). Owing to the Free Spectral Range of F-P interferometer is narrow, therefore range of accommodation is limited and certainty of measurement is the highest； And Mach-Zehnder interferometer has, and insertion loss is little, simple in construction, cost performance high, can be effective Suppression ground separates and extracts spontaneous Brillouin scattered light signal.And due to the delustring of single channel M-Z interferometer Ratio is relatively low, is difficult to the spontaneous brillouin scattering light in back-scattering light and Rayleigh scattering light desired separated. Remaining Rayleigh scattering light will make the measurement to spontaneous brillouin scattering light produce error, thus affects The performance of whole optical fiber sensing system.

Can dissipate by the spontaneous Brillouin in the back-scattering light of separation and Extraction sensor fibre accordingly, it would be desirable to a kind of Penetrate the device of light.

Summary of the invention

It is an object of the invention to provide a kind of BOTDR system based on dual pathways Mach-Zehnder interferometer System, including: laser instrument, acousto-optic modulator, pulse signal generator, erbium-doped fiber amplifier, first Optical circulator, Fiber Bragg Grating FBG, the second optical circulator, sensor fibre, the first optoisolator, double Passage Mach-Zehnder interferometer, photodetector, amplifying circuit and oscillograph, wherein, described laser instrument, Acousto-optic modulator, erbium-doped fiber amplifier, the first optical circulator, the second optical circulator, sensor fibre, First optoisolator is sequentially connected with, and pulse signal generator connects acousto-optic modulator, Fiber Bragg Grating FBG Connecting the first optical circulator, the input of dual pathways Mach-Zehnder interferometer connects the second optical circulator, defeated Go out end and be sequentially connected with photodetector, amplifying circuit and oscillograph.

Preferably, described dual pathways Mach-Zehnder interferometer includes: the first fiber coupler, the second optical fiber Bonder, connect the first bonder and the first single-mode fiber of the second bonder and the second single-mode fiber, light Isolator, described first single-mode fiber and the second single-mode fiber constitute two interference arms of described interferometer, institute State optoisolator and connect the second fiber coupler.

Preferably, described first single-mode fiber is provided with electronic fibre delay line.

Preferably, described second single-mode fiber is provided with Polarization Controller.

Preferably, described laser instrument is the Distributed Feedback Laser of wavelength 1550nm.

Preferably, described sensor fibre is the general single mode fiber of a length of 4.8km.

Preferably, the range of accommodation of described electronic fibre delay line is 0-330ps, and minimum step is spaced apart 0.05ps。

Preferably, described first fiber coupler, the second fiber coupler are three-dB coupler.

Preferably, the method utilizing the system as claimed in claim 1 separation Brillouin scattering: bag Include following steps:

1) continuous light that laser instrument sends；

2) continuous light that laser instrument is sent by acousto-optic modulator is modulated into the pulse of corresponding pulsewidth and repetition rate Light；

3) pulsed light is amplified by erbium-doped fiber amplifier；

4) pulse signal after amplifying is by a filter being made up of first annular device and Fiber Bragg Grating FBG Ripple device carries out optical noise and filters；

5) port by the second optical circulator of the pulsed optical signals after filtered, is injected into sense light Fibre, pulse light transmission in sensor fibre can produce back-scattering light, and these back-scattering lights are through One port of two optical circulators enters the input of dual pathways Mach-Zehnder interferometer；

6) back-scattering light enters photodetector, amplification after dual pathways Mach-Zehnder interferometer exports Circuit and oscillograph.

Preferably, described step 5) also include: back-scattering light enters dual pathways Mach-Zehnder interferometer After, by regulating the time delay of electronic fibre delay line, change between Mach-Zehnder interferometer two-arm Optical path difference, make spontaneous brillouin scattering light separate from Rayleigh scattering light and extract.

Should be appreciated that aforementioned description substantially is exemplary illustration and explanation with follow-up detailed description, The restriction of content claimed to the present invention should not be used as.

Accompanying drawing explanation

With reference to the accompanying drawing enclosed, the more purpose of the present invention, function and advantage will be implemented by the present invention The described below of mode is illustrated, wherein:

Fig. 1 is the structural representation of single channel Mach-Zehnder interferometer.

Fig. 2 is the structural representation of the adjustable Mach-Zehnder interferometer of the dual pathways according to the present invention.

Fig. 3 is the dual pathways adjustable Mach-Zehnder interferometer output spectrum of different delayed time time.

Fig. 4 is BOTDR system structure chart based on dual pathways Mach-Zehnder interferometer.

Fig. 5 is sensor fibre back-scattering light spectrogram.

Fig. 6 is that back-scattering light is through the filtered spectrogram of dual pathways M-Z interferometer.

Detailed description of the invention

Fig. 1 is the structural representation of single channel Mach-Zehnder interferometer.Single channel all-fiber Mach-Zehnder The structure of interferometer 100 is as it is shown in figure 1, include: the first fiber coupler C₁, the second fiber coupler C₂, And connect the first bonder and the first single-mode fiber of the second bonder and the second single-mode fiber, Qi Zhong One single-mode fiber and the second single-mode fiber constitute two interference arms of interferometer 100, and commonly referred to as one of them is Reference arm, another is signal arm.Light field is E₁、E₂Incident illumination respectively from the first bonder C₁Port 1,2 it is injected in Mach-Zehnder interferometer 100, through C₁At a length of L after light splitting₁And L₂First single Transmitting in mode fiber and the second single-mode fiber, due to two optical lengths interfering arm, two-beam transmits To the second bonder C₂Place is the formation of certain phase contrastProduce and interfere and through the second bonder C₂Port 3,4 output, forming light field is E₃And E₄Interference light.Interfere and just have regular comb Shape transmission spectrum, therefore it is also called Mach-Zehnder interferometer comb filter.

The overall transfer matrix M of whole single channel M-Z interferometer_MZFor:

M_MZ=M (C₁)*J_F*M(C₂) (1)

Wherein M (C₁)、M(C₂) it is respectively bonder C₁、C₂Transmission matrix, J_FFor interfering the transmission of arm Matrix.

As two fiber coupler C₁、C₂When being all standard three-dB coupler, its transmission matrix such as formula:

$\begin{array}{c}M\left(C_1\right)=M\left(C_2\right)\\ =2^{-1/2}\left[\begin{array}{cc}1& \exp (-i\mathrm{\π}/2)\\ \exp (-i\mathrm{\π}/2)& 1\end{array}\right]\end{array}---\left(2\right)$

When input light field E_inOnly E₁Time, i.e. E₂=0 and composition interferometer two-arm optical fiber be same material During optical fiber, the transfer function that can obtain interferometer output port is:

Representing the transmission phase contrast of two interference arms, λ is the wavelength of input light.Can be further The wavelength interval Δ λ derived in Mach-Zehnder interferometer output transmission spectrum between adjacent two peak wavelengths is:

$\mathrm{\Δ}\mathrm{\λ}=\frac{{\mathrm{\λ}}^2}{n\mathrm{\Δ}L}=\frac{{\mathrm{\λ}}^2}{n\left|L_1-L_2\right|}---\left(4\right)$

The extinction ratio of single channel M-Z interferometer is relatively low, is difficult to dissipate the spontaneous Brillouin in back-scattering light Penetrate light and Rayleigh scattering light desired separated.Remaining Rayleigh scattering light will make spontaneous brillouin scattering The measurement of light produces error, thus affects the performance of whole optical fiber sensing system.

Fig. 2 is the adjustable Mach-Zehnder interferometer of the dual pathways according to the present invention, the described dual pathways is adjustable Mach -Zehnder interferometer 200 includes: first fiber coupler the 201, second fiber coupler 202, connects the One bonder 201 and the first single-mode fiber 203 of the second bonder 202 and the second single-mode fiber 204 with And optoisolator 205, wherein the first single-mode fiber and the second single-mode fiber constitute the two dry of interferometer 200 Relate to arm, be wherein provided with electronic fibre delay line 206, the second single-mode fiber on the first single-mode fiber 203 Polarization Controller 207 it is provided with, as shown in Figure 2 on 204.Electronic fibre delay line 206 time delay Range of accommodation is big, has the function being fine-tuned.Electronic fibre delay line is replaced traditional piezoelectric ceramics Signal arm in structure dual pathways M-Z interferometer, for changing the delay of a M-Z interferometer wherein arm Time t, thus cause creating between M-Z interferometer two-arm delay-time difference Δ t, it is equivalent to two brachiums Degree difference Δ L there occurs change.And traditional dual pathways M-Z interferometer needs wherein to make pottery at piezoelectricity by an arm It is wound around multi-turn on porcelain or is affixed directly on piezoelectric ceramics, and needing tension optical fiber.Polarization Controller 207 (polarization controller, PC) is for regulating the polarization state of an interferometer wherein arm so that M-Z interferometer obtains higher extinction ratio and improves its stability.

When the length difference Δ L of Mach-Zehnder interferometer two-arm meets following relation

Δ L=c/ (2n υ_B) (5)

C is the light velocity in vacuum, and n is the refractive index of medium, υ_BIt it is Brillouin shift.Can be from by light-metering In fine back-scattering light, spontaneous brillouin scattering is separated with Rayleigh scattering.And the two-arm of interferometer is prolonged Time t is as follows with the relation of two-arm length difference Δ L late:

$\frac{tc}{n}=\mathrm{\Δ}L---\left(6\right)$

Can be obtained by formula (5) and (6):

$t=\frac{1}{2{\mathrm{\υ}}_B}---\left(7\right)$

By change an interferometer wherein arm time delay so that between interferometer two-arm time delay t with Brillouin shift υ_BWhen meeting the relation of formula (7), it is possible to realize spontaneous brillouin scattering light and Rayleigh The separation of scattered light signal.

By C-band wideband light source (ASE) the access dual pathways adjustable M-Z interferometer as shown in Figure 2 Input.Regulation fibre delay line 206 time delay, and record its output spectrum figure (spectrogrph Minimum resolution is 0.02nm).In Fig. 3 from top to bottom be respectively delay time be arranged on 150ps, When 160ps, 170ps, 180ps and 190ps, the spectrum of interferometer output.From the figure 3, it may be seen that along with The time delay of an interferometer wherein arm is continuously increased, and is i.e. equivalent to two-arm length difference Δ L when constantly increasing, Output spectrum adjacent peak wavelength interval is gradually reduced, 0.62nm change to 0.15nm, and interferometer Extinction ratio be gradually lowered, 24dB be reduced to 16dB.Due to the adjustable electric used in interferometer The range of accommodation of fibre delay line is 0～330ps, and minimum step is spaced apart 0.05ps, therefore can realize On a large scale and high-precision filtering regulatory function.

According to the present invention based on dual pathways Mach-Zehnder interferometer for BOTDR system by following tool Body embodiment is described in detail.

First building the light channel structure such as Fig. 4, Fig. 4 is based on dual pathways Mach-Zehnder interferometer BOTDR system structure chart.BOTDR system 400 based on dual pathways Mach-Zehnder interferometer is wrapped Include: laser instrument 401, acousto-optic modulator 402, pulse signal generator 403, erbium-doped fiber amplifier 404, the first optical circulator 405, Fiber Bragg Grating FBG the 406, second optical circulator 407, sense light Fine 408, first optoisolator 409, dual pathways Mach-Zehnder interferometer 200, photodetector 410, Amplifying circuit 411 and oscillograph 412.Wherein, laser instrument 401, acousto-optic modulator 402, er-doped light Fiber amplifier the 404, first optical circulator the 405, second optical circulator 407, sensor fibre 408, first Optoisolator 409 is sequentially connected with, and pulse signal generator 403 connects acousto-optic modulator 402, optical fiber cloth Glug grating 406 connects the first optical circulator 405.The input of dual pathways Mach-Zehnder interferometer 200 Connecting the second optical circulator 407, outfan is sequentially connected with photodetector 410, amplifying circuit 411 and Oscillograph 412.

First, the continuous light that wavelength 1550nm Distributed Feedback Laser 401 sends, acousto-optic modulator (AOM) The continuous light that wavelength 1550nmDFB laser instrument sends is modulated into corresponding pulsewidth and repetition rate by 402 Pulsed light, such as width be 100ns (corresponding spatial resolution be 10m) repetition rate be 20kHz Pulsed light, pulse signal generator 403 is configured with specific pulse width and repetition rate electricity arteries and veins Rush signal, act on acousto-optic modulator high frequency driver 402.Pulsed light passes through erbium-doped fiber amplifier (EDFA) 404 it is amplified.Pulse signal after amplification passes through one by first annular device 405 He Reflection wavelength is the wave filter of Fiber Bragg Grating FBG (FBG) 406 composition of 1550nm, this filtering Device can filter amplifying, through EDFA, the most of natural emission optical noise produced, thus suppression is to cloth In deep pool scattered signal interference.Filter major part spontaneous emission noise after, filtered after pulsed optical signals By the port 2 of the second optical circulator 407, it is injected into sensor fibre.Sensor fibre is a length of 4.8km General single mode fiber.The interference of reflection light is produced, at sensor fibre in order to get rid of sensor fibre end End is connected to the first optoisolator 409.Second optical circulator 407 connects dual pathways Mach-Zehnder and interferes First fiber coupler 201 (as shown in Figure 2) of instrument 200.Pulse light passes in sensor fibre Defeated can produce back-scattering light, these back-scattering lights enter double through the port 3 of the second optical circulator 407 Passage Mach-Zehnder interferometer.After back-scattering light enters dual pathways Mach-Zehnder interferometer, by adjusting The time delay of section electric fibre delay line, it is equivalent to change the optical path difference between M-Z interferometer two-arm, Spontaneous brillouin scattering light is made to separate from Rayleigh scattering light and extract.Again through photodetector 410 convert thereof into the signal of telecommunication.The signal of telecommunication of its output is more weak, after amplified circuit 411 amplifies, logical Cross oscillograph 413 to carry out signal and show, obtain the time domain signal waveform of Brillouin scattering power.

In order to eliminate the interference of Rayleigh astigmatism, by back-scattering light through the port 3 of the second optical circulator 407 Incide bilateral Mach-Zehnder interferometer 200.The delay of electronic fibre delay line in regulation M-Z interferometer Time, observe the output spectrum of spectrogrph.As shown in Figure 6, after M-Z interferometer filters, background of cloth The wavelength of deep pool scattered light is 1550.16nm, and light intensity is-48.24dBm；Rayleigh scattering optical wavelength is 1550.03nm, light intensity is-58.36dBm.After after filtering, the beam intensity ratio of Brillouin scattering is auspicious The profit high about 10dB of scattered light intensity.Contrast is by the spectrogram 5 and Fig. 6 before and after M-Z interferometer, Rayleigh The light intensity of scattering is reduced to filtered-58.36dBm, M-Z interferometer by the-34.5dBm before filtering Suppression to Rayleigh scattering light is 23.86dB, restrained effectively the Rayleigh scattering light in back-scattering light, Brillouin scattering is separated from back-scattering light, for follow-up signal processing.

When the pumping current of EDFA is 240mA, the port 3 output back of the body of the second optical circulator 407 To scattered light spectrum as shown in Figure 5, it is seen that middle Rayleigh astigmatism peak wavelength is 1550.03nm, light It is by force-34.5dBm；Brillouin's Stokes peak wavelength on the right side of it is 1550.16nm, and light intensity is -45.3dBm, both wavelength difference are 0.09nm, and Rayleigh scattering light intensity is relative to Brillouin's Stokes The high about 11dB of light intensity.

The present invention devises the adjustable Mach-Zehnder interferometer of the dual pathways based on electronic fibre delay line, passes through The time delay of the adjustable electric fibre delay line in change interferometer, the cycle of tuning filtering spectrum, for dividing Spontaneous brillouin scattering light in the back-scattering light extracting sensor fibre.Due to traditional dual pathways M-Z interferometer needs wherein to be wound around multi-turn on piezoelectric ceramics or be affixed directly to piezoelectric ceramics by an arm On, and need tension optical fiber.Electronic fibre delay line is used to replace traditional piezoelectric ceramics structure dual pathways Signal arm in M-Z interferometer, has time delay range of accommodation big, the function such as is fine-tuned.

Relative to BOTDR coherent detection technology, this Mach-Zehnder interferometer has simple in construction, low The features such as cost.Present invention C-band wideband light source has carried out the test of delustring when adjustability to it, real Test result and show that this interferometer is capable of large scale and high accuracy scalable filter function.Use it to 5km General single mode fiber in back-scattering light filtered, it is thus achieved that Rayleigh scattering light is suppressed over The effect of 20dB.Result shows, this structure M-Z interferometer is possible not only to realize dissipating spontaneous Brillouin Penetrate the extraction of optical signal, and process for follow-up detection and be capable of large scale and high accuracy scalable Filter function, is suppressed over 20dB to Rayleigh scattering light, can be effectively by the cloth in back-scattering light In deep pool scattered light signal separation and Extraction out.

In conjunction with explanation and the practice of the present invention disclosed here, other embodiments of the present invention are for ability Field technique personnel are easy to expect and understand.Illustrate and embodiment be to be considered only as exemplary, True scope and the purport of the present invention are all defined in the claims.

Claims (10)

1. a BOTDR system based on dual pathways Mach-Zehnder interferometer, including: laser instrument, Acousto-optic modulator, pulse signal generator, erbium-doped fiber amplifier, the first optical circulator, optical fiber Bradley Lattice grating, the second optical circulator, sensor fibre, the first optoisolator, dual pathways Mach-Zehnder interferometer, Photodetector, amplifying circuit and oscillograph,

Wherein, described laser instrument, acousto-optic modulator, erbium-doped fiber amplifier, the first optical circulator, Two optical circulators, sensor fibre, the first optoisolator are sequentially connected with, and pulse signal generator connects acousto-optic Manipulator, Fiber Bragg Grating FBG connects the first optical circulator, the input of dual pathways Mach-Zehnder interferometer End connects the second optical circulator, and outfan is sequentially connected with photodetector, amplifying circuit and oscillograph.

2. the system as claimed in claim 1, wherein said dual pathways Mach-Zehnder interferometer includes: the One fiber coupler, the second fiber coupler, connect the first single mode of the first bonder and the second bonder Optical fiber and the second single-mode fiber, optoisolator, described first single-mode fiber and the second single-mode fiber constitute institute Stating two interference arms of interferometer, described optoisolator connects the second fiber coupler.

3. system as claimed in claim 2, wherein said first single-mode fiber is provided with electronic optical fiber Delay line.

4. system as claimed in claim 2, wherein said second single-mode fiber is provided with Polarization Control Device.

5. the system as claimed in claim 1, wherein said laser instrument is the DFB of wavelength 1550nm Laser instrument.

6. the system as claimed in claim 1, wherein said sensor fibre is the common of a length of 4.8km Single-mode fiber.

7. system as claimed in claim 3, the range of accommodation of wherein said electronic fibre delay line is 0-330ps, minimum step is spaced apart 0.05ps.

8. system as claimed in claim 2, wherein said first fiber coupler, the second optical fiber coupling Device is three-dB coupler.

9. the method utilizing the system as claimed in claim 1 separation Brillouin scattering: include Following steps:

1) continuous light that laser instrument sends；

2) continuous light that laser instrument is sent by acousto-optic modulator is modulated into the pulse of corresponding pulsewidth and repetition rate Light；

3) pulsed light is amplified by erbium-doped fiber amplifier；

4) pulse signal after amplifying is by a filter being made up of first annular device and Fiber Bragg Grating FBG Ripple device carries out optical noise and filters；

5) port by the second optical circulator of the pulsed optical signals after filtered, is injected into sense light Fibre, pulse light transmission in sensor fibre can produce back-scattering light, and these back-scattering lights are through One port of two optical circulators enters the input of dual pathways Mach-Zehnder interferometer；

6) back-scattering light enters photodetector, amplification after dual pathways Mach-Zehnder interferometer exports Circuit and oscillograph.

10. system as claimed in claim 9, wherein step 5) also include: back-scattering light enters double After passage Mach-Zehnder interferometer, by regulating the time delay of electronic fibre delay line, change Mach Optical path difference between-Zehnder interferometer two-arm, makes spontaneous brillouin scattering light separate also from Rayleigh scattering light Extract.