CN110440841A - A kind of Brillouin optical time domain analysis instrument - Google Patents
A kind of Brillouin optical time domain analysis instrument Download PDFInfo
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Abstract
The invention proposes a kind of Brillouin optical time domain analysis instrument, the transmission that light is detected in BOTDA system is regarded as the transmittance process of information in the channel, influence by excited Brillouin effect to detection light is regarded the damage to channel as and is monitored, channel response can be realized by OFDM channel estimation technique to extract, to reconstruct Brillouin spectrum, this scheme not only avoids frequency scanning operation, greatly promote measurement efficiency, be conducive to the application in dynamic scene, and brillouin gain spectrum and phase spectrum can be measured simultaneously, realize more reliable and more stable sensor-based system.
Description
Technical field
The present invention relates to Distributed Optical Fiber Sensing Techniques field more particularly to a kind of Brillouin optical time domain analysis instrument.
Background technique
Fibre optical sensor have small in size, light-weight, high sensitivity, high pressure resistant, corrosion-resistant, electrical insulating property is good, anti-electromagnetism
The advantages that interference, is widely used in the structure detections such as communications optical cable, river levee, concrete, pipeline, tunnel, bridge.Based on by
The distributed fiberoptic sensor for swashing Brillouin scattering effect is the linear relationship utilized between excited Brillouin frequency shift amount and strain,
Corresponding strain variation at the position is measured by the Brillouin shift of measurement optical fiber everywhere, to realize the distribution of strain
Measurement.There are mainly three types of types for excited Brillouin distributed fiberoptic sensor: in Brillouin optical time domain analysis (BOTDA) type, cloth
Deep optical frequency domain analysis (BOFDA) type and Brillouin scattering optical time domain reflection (BOTDR) type.And traditional BOTDA generally use by
The detection mode of spot scan reconstructs brillouin gain spectrum by scanning pump light (or detection light) frequency, and then determines in cloth
Deep frequency displacement and needs a large amount of average operations along the distribution of optical fiber to improve signal-to-noise ratio, measures very time-consuming, this is in the basic upper limit
Systematic survey efficiency has been made, and has fundamentally hindered it and further develops, has been also due to same reason, traditional is
System mentality of designing is all difficult to obtain all information of Brillouin spectrum.Therefore, to solve the above problems, the present invention provides one kind
Brillouin optical time domain analysis instrument may be implemented the measurement of all information of Brillouin's complex-specturm, while will also greatly improve measurement
Efficiency.
Summary of the invention
In view of this, the whole of Brillouin's complex-specturm may be implemented the invention proposes a kind of Brillouin optical time domain analysis instrument
The measurement of information, while will also greatly improve the efficiency of measurement.
The technical scheme of the present invention is realized as follows: the present invention provides a kind of Brillouin optical time domain analysis instrument, including
Laser, photo-coupler, the first Polarization Controller, the second Polarization Controller, the second Polarization Controller, the first electrooptic modulator,
It is second electrooptic modulator, microwave generator, random waveform transmitter, optoisolator, sensor fibre, semiconductor optical amplifier, non-
Linear Optical Amplifier, bandpass filter, photoconductivity switching, circulator, optical filter, photodetector and DSP；
Laser output light signal is divided into two through photo-coupler, is divided into and is denoted as the first branch and second branch, and first
The optical signal on road reaches the first electrooptic modulator after the first Polarization Controller, and microwave generator generates microwave signal and exports extremely
The two is carried out external modulation and exports modulated signal, modulated signal by the first electrooptic modulator, the first electrooptic modulator
The second electrooptic modulator is reached after the second Polarization Controller, arbitrary waveform generator generates random waveform and exports to the second electricity
The two is carried out OFDM Channel Modulation and obtains emphasizing the ofdm signal of system, ofdm signal by optical modulator, the second electrooptic modulator
By optoisolator isolation processing, the signal of optoisolator output is input to one end of sensor fibre as pump light signals,
The other end of sensor fibre is input to the second terminals of circulator, and the optical signal of second branch passes through third Polarization Controller
Afterwards, it is arrived by the semiconductor optical amplifier, nonlinear optics amplifier, bandpass filter and the photoconductivity switching that are sequentially electrically connected
Up to the first terminals of circulator, the optical signal into the first terminals of circulator is dissipated as excited Brillouin in sensor fibre
The pulsed light of effect is penetrated, and is output in sensor fibre from the second terminals of circulator, pulsed light and pump light signals are passing
It interacts in photosensitive fibre, excited Brillouin occurs when meeting stimulated Brillouin scattering condition between the difference on the frequency of two-way light and dissipates
Penetrate phenomenon, the pump light signals for carrying stimulated Brillouin scattering information are inputted through the second terminals of circulator, and from circulator
The output of third terminals, then after optical filter filters, detected by photodetector, DSP analysis processing photodetector detection
Ofdm signal, obtain all information of Brillouin.
On the basis of above technical scheme, it is preferred that the second electrooptic modulator carries out BPSK star using pseudo-random signal
Seat mapping, by Hermit conjugate operation, obtains the ofdm signal for intensity modulated.
It is further preferred that the frame structure of ofdm signal includes multiple cyclic prefix CPs and time slot TS1~TSn；
The first character section of the frame structure is cyclic prefix CP, and the second field is TS1, and third field is cyclic prefix
CP, and so on.
It is further preferred that the bandwidth of ofdm signal is 500MHz, number of sub carrier wave 128~512.
It is further preferred that DSP analysis processing photodetector detection ofdm signal specifically includes the following steps:
S1, synchronous reception ofdm signal, and carry out analog-to-digital conversion；
S2, serioparallel exchange is carried out to ofdm signal and removes cyclic prefix；
S3, Fast Fourier Transform (FFT) is carried out；
S4, channel estimation is carried out；
S5, transformation Brillouin's phase shift；
S6, Brillouin shift is determined.
It is further preferred that setting OFDM optical signal are as follows:S (t) is the light of transmission
Ofdm signal, f0It is optical carrier frequency, that α is indicated is the ratio of ofdm signal Yu light carrier amplitude, sBIt (t) is baseband OFDM letter
Number, it indicates are as follows:ckIndicate the symbol mapped on k-th subcarrier, fkK-th of son is respectively represented with N to carry
The frequency of wave and total sub-carrier number；
If h (t) is the shock response of system, the ofdm signal received is r (t)；Then after Fast Fourier Transform (FFT)
Ofdm signal are as follows:
It is further preferred that the complex response obtained in S4 by channel estimation are as follows:
Wherein, HSBSIt is exactly Brillouin's complex gain spectrum, indicates are as follows:
Wherein, GSBSWithFor brillouin gain and Brillouin's phase shift.
A kind of Brillouin optical time domain analysis instrument of the invention has the advantages that compared with the existing technology
(1) transmission for detecting light in BOTDA system is regarded as the transmittance process of information in the channel, excited Brillouin is made
Regard the damage to channel as with the influence to detection light and monitored, channel can be realized by OFDM channel estimation technique and ring
It should extract, to reconstruct Brillouin spectrum, this scheme not only avoids frequency scanning operation, greatly promotes measurement efficiency, favorably
In the application in dynamic scene, and brillouin gain spectrum and phase spectrum can be measured simultaneously, realize more reliable and more stable
Sensor-based system；
(2) traditional Brillouin shift (BGS) acquisition methods are as follows: after optical signal is inputted from one end of optical fiber, in the same end
After measurement to the spontaneous brillouin scattering light of return, by being closer to rear to spontaneous brillouin scattering light and a frequency
That reference light carries out difference frequency is relevant, and the lower beat signal of measurement frequency obtains Brillouin shift, and traditional BGS extraction is often
It is obtained by carrying out nonlinear fitting to BGS, computation complexity with higher；The present invention, can be with by parsing ofdm signal
Obtain the gain spectral and phase spectrum of sampled signal, and Brillouin's phase spectrum linear approximate relationship near Brillouin shift can be with
BFS can be obtained by simple linear fit, and then the complexity of calculating can be reduced.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
Some embodiments of invention for those of ordinary skill in the art without creative efforts, can be with
It obtains other drawings based on these drawings.
Fig. 1 is a kind of structure chart of Brillouin optical time domain analysis instrument of the present invention；
Fig. 2 is a kind of brillouin gain spectrum that Brillouin optical time domain analysis instrument measures of the present invention；
Fig. 3 is a kind of Brillouin's phase spectrum that Brillouin optical time domain analysis instrument measures of the present invention.
In figure, ECL- laser, Coupler- photo-coupler, PC- Polarization Controller, the first electrooptic modulator of EOM1-,
The second electrooptic modulator of EOM2-, MS- microwave generator, AWG- random waveform transmitter, ISO- optoisolator, FUT- sense light
Fibre, SOA- semiconductor optical amplifier, EDFA- nonlinear optics amplifier, BPF- bandpass filter, PS- photoconductivity switching,
Filter- optical filter, PD- photodetector, TDO- oscillograph.
Specific embodiment
Below in conjunction with embodiment of the present invention, the technical solution in embodiment of the present invention is carried out clearly and completely
Description, it is clear that described embodiment is only some embodiments of the invention, rather than whole embodiments.Base
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts all
Other embodiments shall fall within the protection scope of the present invention.
Traditional Brillouin optical time domain analysis instrument technology (Brillouin Optical Time-Domain Analysis,
BOTDA the detection mode for) generalling use point by point scanning reconstructs brillouin gain by scanning pump light or detection light frequency
Spectrum, and then determine that Brillouin shift along the distribution of optical fiber, and needs a large amount of average operations to improve signal-to-noise ratio, measurement consumes very much
When, this is fundamentally limiting systematic survey efficiency, and fundamentally hinders it and further develop, and is also due to same
The reason of, traditional thought of design is all difficult to obtain all information of Brillouin spectrum.And in a communications system, channel
Algorithm for estimating can obtain all information of channel, if this implementation and analysis means are introduced into BOTDA system,
It can be realized the measurement of all information of Brillouin's complex-specturm, while will also greatly improve the efficiency of measurement.However, on the one hand, it examines
Consider the ability that the channel estimation method in communication system does not have time-space resolution, and BOTDA system is a kind of Distributed localization
System, it is desirable that the ability with spatial discrimination；On the other hand, for the characteristics of Brillouin spectrum, needing to select in BOTDA system
Select suitable channel estimation coding mode and demodulating algorithm.Based on this two o'clock, and combine the modulation/encoding and decoding in communication forward position at present
With transmission technology, using the channel estimation technique modulated based on ofdm signal.Therefore, the present embodiment will detect in BOTDA system
The transmission of light is regarded as the transmittance process of information in the channel, and the influence by excited Brillouin effect to detection light is regarded as to channel
It damages and is monitored, channel response can be realized by OFDM channel estimation technique and extract, so that Brillouin spectrum is reconstructed, this
Scheme not only avoids frequency scanning operation, greatly promotes measurement efficiency, is conducive to the application in dynamic scene, and can
Brillouin gain spectrum and phase spectrum are measured simultaneously, realize more reliable and more stable sensor-based system, and since Brillouin's phase spectrum exists
The neighbouring linear approximate relationship of Brillouin shift (BFS), can be obtained BFS, and then can drop by simple linear fit
The complexity of low calculating.
Based on the above principles, as shown in Figure 1, a kind of Brillouin optical time domain analysis instrument of the present embodiment, including laser, light
Coupler, the first Polarization Controller, the second Polarization Controller, the second Polarization Controller, the first electrooptic modulator, the second electric light tune
Device processed, microwave generator, random waveform transmitter, optoisolator, sensor fibre, semiconductor optical amplifier, nonlinear optics are put
Big device, bandpass filter, photoconductivity switching, circulator, optical filter, photodetector and DSP；Specifically, laser output light
Signal is divided into two through photo-coupler, is divided into and is denoted as the first branch and second branch, and the optical signal of the first branch is through the first polarization
Reach the first electrooptic modulator after controller, microwave generator generates microwave signal and exports to the first electrooptic modulator, first
The two is carried out external modulation and exports modulated signal by electrooptic modulator, and modulated signal arrives after the second Polarization Controller
Up to the second electrooptic modulator, arbitrary waveform generator generates random waveform and exports to the second electrooptic modulator, the second electric light tune
The two is carried out the ofdm signal that OFDM Channel Modulation and obtaining emphasizes system by device processed, ofdm signal by optoisolator isolation at
Reason, the signal of optoisolator output are input to one end of sensor fibre as pump light signals, and the other end of sensor fibre is defeated
Enter the second terminals to circulator, the optical signal of second branch is after third Polarization Controller, by being sequentially electrically connected
Semiconductor optical amplifier, nonlinear optics amplifier, bandpass filter and photoconductivity switching reach the first wiring of circulator
End, into pulsed light of the optical signal as stimulated Brillouin scattering effect in sensor fibre of the first terminals of circulator, and
It being output in sensor fibre from the second terminals of circulator, pulsed light and pump light signals interact in sensor fibre,
Stimulated Brillouin scattering phenomenon occurs when meeting stimulated Brillouin scattering condition between the difference on the frequency of two-way light, cloth is excited in carrying
In the pump light signals of deep scattered information inputted through the second terminals of circulator, and exported from the third terminals of circulator,
It again after optical filter filters, is detected by photodetector, the ofdm signal of DSP analysis processing photodetector detection obtains cloth
In deep all information.
In the present embodiment, the frame structure of ofdm signal includes multiple cyclic prefix CPs and time slot TS1~TSn；Frame structure
First character section be cyclic prefix CP, the second field be TS1, third field be cyclic prefix CP, and so on.The work of CP
With being to eliminate symbol-interference (ISI) and interchannel interference (ICI)；TS2 is responsible for carrying out channel monitoring, in order to realize higher space
Resolution capability simultaneously facilitates demodulation, each TS2 only includes a symbol, and therefore, pulsed light is believed by the OFDM of orderly repeated arrangement
Number frame is modulated, each frame may be used to channel estimation, after excited Brillouin effect occurs with pulse pump light, letter
Number frame will carry the information of Brillouin spectrum；In order to realize spatial resolving power and accurate positionin, we added to encoded signal
For the training sequence TS1 of Timing Synchronization, so as to accurately find encoding channel initial position and with the space of optical fiber
Position is mapped.In the design of OFDM frame, BPSK constellation mapping is carried out using pseudo-random signal (PRBS), is conjugated by Hermit
Operation, can obtain the ofdm signal for intensity modulated.The low correlation of pseudo-random signal can reduce the PAPR of signal,
And the constellation mapping of BPSK can be with lifting system to the tolerance of noise, by the finally obtained real-valued signal of conjugate operation, it can
To realize intensity modulated and direct detection (IM/DD), compared with coherent system, only need a laser and detector can be real
Existing and channel estimation method is relatively simple, improves stability while reducing system complexity.It is further preferred that from frequency
It composes precision, measurement dynamic range etc. to consider, proposes meter ofdm signal bandwidth for 500MHz, number of sub carrier wave 128-512, both
The needs of Brillouin sensing are met, and do not increase requirement and algorithm complexity of the system to device.
In the present embodiment, OFDM optical signal can indicate are as follows:S (t) is transmission
Light ofdm signal, f0It is optical carrier frequency, that α is indicated is the ratio of ofdm signal Yu light carrier amplitude, sBIt (t) is base band
Ofdm signal can indicate are as follows:ckIndicate the symbol mapped on k-th subcarrier, fkWith N generation respectively
The frequency of k-th of subcarrier of table and total sub-carrier number.If h (t) is the shock response of system, the ofdm signal received is r
(t), then r (t) can be approximated to be:
Wherein, channel response function H (f) can be expressed as the Fourier transformation of system shock response:
The ofdm signal then received can simplify are as follows:
In receiving end, photodetector converts optical signals into electric signal, photodetector output current signal I (t) root
It can be expressed as follows according to square law rule:
Wherein, first item is DC component, can very easily be filtered；Section 2 contains ofdm signal phase and intensity
Response.Assuming that rkIt is the mapping signal received, then complex channel response can use formulaIt calculates, and intensity is rung
It should be then the amplitude of complex response.For Section 3, the very little that can be set due to α (be much smaller than 1), then square after can neglect
Slightly.By the complex channel receptance function for calculating each subcarrier, so that it may obtain Brillouin's complex-specturm.
In the present embodiment, r is usedk' indicate to obtain with the symbol received after pump light signals effect by channel estimation
Complex response can indicate are as follows:
Wherein, HSBSIt is exactly Brillouin's complex gain spectrum,
Wherein, GSBSWithExactly brillouin gain and Brillouin's phase shift.Thus it has turned out based on channel estimation
Brillouin gain spectrum and phase spectrum are obtained while ofdm system can be intrinsic.In traditional BOTDA system, Brillouin shift
(BFS) extraction is obtained often by BGS progress nonlinear fitting, computation complexity with higher.And Brillouin's phase
Position spectrum linear approximate relationship near BFS, this shows that BFS can be obtained by simple linear fit, and then can drop
The complexity of low calculating.
Fig. 2 and Fig. 3 be originally be result figure that embodiment is tested with 2km and 10km optical fiber respectively, near BFS, BGS
Change rate is close to zero, and BPS approximately linear changes, and has higher change rate, realizes brillouin gain spectrum and phase spectrum
While reconstruct, and have enough signal-to-noise ratio to realize that Brillouin shift accurately measures.
The foregoing is merely better embodiments of the invention, are not intended to limit the invention, all of the invention
Within spirit and principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (7)
1. a kind of Brillouin optical time domain analysis instrument, it is characterised in that: including laser, photo-coupler, the first Polarization Controller,
Two Polarization Controllers, the second Polarization Controller, the first electrooptic modulator, the second electrooptic modulator, microwave generator, random waveform
Transmitter, optoisolator, sensor fibre, semiconductor optical amplifier, nonlinear optics amplifier, bandpass filter, photoconduction are opened
Pass, circulator, optical filter, photodetector and DSP；
The laser output light signal is divided into two through photo-coupler, is divided into and is denoted as the first branch and second branch, and first
The optical signal on road reaches the first electrooptic modulator after the first Polarization Controller, and microwave generator generates microwave signal and exports extremely
The two is carried out external modulation and exports modulated signal, modulated signal by the first electrooptic modulator, the first electrooptic modulator
The second electrooptic modulator is reached after the second Polarization Controller, arbitrary waveform generator generates random waveform and exports to the second electricity
The two is carried out OFDM Channel Modulation and obtains emphasizing the ofdm signal of system, ofdm signal by optical modulator, the second electrooptic modulator
By optoisolator isolation processing, the signal of optoisolator output is input to one end of sensor fibre as pump light signals,
The other end of sensor fibre is input to the second terminals of circulator, and the optical signal of second branch passes through third Polarization Controller
Afterwards, it is arrived by the semiconductor optical amplifier, nonlinear optics amplifier, bandpass filter and the photoconductivity switching that are sequentially electrically connected
Up to the first terminals of circulator, the optical signal into the first terminals of circulator is dissipated as excited Brillouin in sensor fibre
The pulsed light of effect is penetrated, and is output in sensor fibre from the second terminals of circulator, pulsed light and pump light signals are passing
It interacts in photosensitive fibre, excited Brillouin occurs when meeting stimulated Brillouin scattering condition between the difference on the frequency of two-way light and dissipates
Penetrate phenomenon, the pump light signals for carrying stimulated Brillouin scattering information are inputted through the second terminals of circulator, and from circulator
The output of third terminals, then after optical filter filters, detected by photodetector, DSP analysis processing photodetector detection
Ofdm signal, obtain all information of Brillouin.
2. a kind of Brillouin optical time domain analysis instrument as described in claim 1, it is characterised in that: second electrooptic modulator is adopted
BPSK constellation mapping is carried out with pseudo-random signal, by Hermit conjugate operation, obtains the ofdm signal for intensity modulated.
3. a kind of Brillouin optical time domain analysis instrument as claimed in claim 2, it is characterised in that: the frame structure of the ofdm signal
Including multiple cyclic prefix CPs and time slot TS1~TSn；
The first character section of the frame structure is cyclic prefix CP, and the second field is TS1, and third field is cyclic prefix CP,
And so on.
4. a kind of Brillouin optical time domain analysis instrument as claimed in claim 3, it is characterised in that: the bandwidth of the ofdm signal is
500MHz, number of sub carrier wave 128~512.
5. a kind of Brillouin optical time domain analysis instrument as claimed in claim 4, it is characterised in that: the DSP analysis processing photoelectricity
Detector detection ofdm signal specifically includes the following steps:
S1, synchronous reception ofdm signal, and carry out analog-to-digital conversion；
S2, serioparallel exchange is carried out to ofdm signal and removes cyclic prefix；
S3, Fast Fourier Transform (FFT) is carried out；
S4, channel estimation is carried out；
S5, transformation Brillouin's phase shift；
S6, Brillouin shift is determined.
6. a kind of Brillouin optical time domain analysis instrument as claimed in claim 5, it is characterised in that: set OFDM optical signal are as follows:S (t) is the light ofdm signal of transmission, f0It is optical carrier frequency, what α was indicated is OFDM letter
Ratio number with light carrier amplitude, sB(t) it is base band OFDM signal, indicates are as follows:ckIndicate k-th
The symbol mapped on carrier wave, fkWith N respectively represent k-th of subcarrier frequency and total sub-carrier number；
If h (t) is the shock response of system, the ofdm signal received is r (t)；Then after Fast Fourier Transform (FFT)
Ofdm signal are as follows:
7. a kind of Brillouin optical time domain analysis instrument as claimed in claim 6, it is characterised in that: pass through channel estimation in the S4
Obtained complex response are as follows:
Wherein, HSBSIt is exactly Brillouin's complex gain spectrum, indicates are as follows:
Wherein, GSBSWithFor brillouin gain and Brillouin's phase shift.
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