Brillouin based Distributed Optical Fibre Sensors
for Strain and Temperature Monitoring
Presented By
Nages wara Lalam
(Ph.D student)
Optical Communications Research Group (OCRG),
Department of Physics and Electrical Engineering,
Northumbria University, Newcastle upon Tyne, NE1 8ST.
(E-mail: nageswara.lalam@northumbria.ac.uk)
Supervisors
Dr. Wai Pang Ng
Dr. Xuewu (Daniel) Dai
Losses in optical fibre communication
1.
2.
3.
4.
5.
Dispersion
Absorption
Scattering (Raleigh, Brillouin and Raman scattering)
Bending
Link budget, power budget
Dispersion
Scattering
Scattered light spectrum in optical Fibres
1. Raleigh Scattering (vo)
2. Brillouin scattering (vo-vb)
3. Raman scattering (vo-vr)
Input light vo
Intensity
Raleigh scattered light vo
Brillouin
Stokes
Raman
Stokes
Brillouin
Anti-stokes
T, ε
T, ε
T
•vo-vr
Raman
Ant-stokes
T
•vo-vb
•vo
Frequency
BFS ~
11 GHz
~ 13 THz
Fig: Spectrum of backscattered signal in optical fibre
Raleigh, Brillouin, Raman scattered light spectrum (cont..)
 Raleigh scattering :
Raleigh scattering occurs from the inhomogeneous microscopic particles. This
elastic scattering is related to the molecule organization degree in fibre.
 Raman scattering:
Raman scattering occurs from the interaction light with molecules vibration
modes and considered as scattering from optical phonons.
 Brillouin scattering:
Brillouin scattering arises from the interaction of light with propagating density
waves or acoustic waves.
Operating principle of OTDR
1.
Optical time domain reflectometer (OTDR) used to measure the losses in optical fibre
2.
Based on the Raleigh backscattered signal and Fresnel reflection
Brillouin optical time domain reflectometry (B-OTDR)
Fig.1: Brillouin optical time domain reflectometry (B-OTDR) sensing principle
25 km SMF
3 dB
DFB-LD
50/50
50/50
Attenuator
(Optisci-28dB)
EDFA
Sensing
Fibre
Coupler
1550 nm, 8 dBm,
(Thorlabs, 1754C)
Fibre close
end
Circulator
Pulse (Pump) Wave
(v o  v b )
(vo )
Coupler
50/50
50/50
3 dB
(D8-ir,
BW: 50GHz)
PM
Photo
Detector
Electrical spectrum
analyzer
Fig.2: Experimental setup of Brillouin optical time domain reflectometry (B-OTDR)
(DFB-LD: distributed-feedback laser diode, EDFA: erbium doped fibre amplifier, PM: power meter)
Experimental set up of BOTDR
Temperature
controller
DFB-LD
EDFA
DC Bias
Coupler
(50/50)
Attenuator
Optical
spectrum
analyzer
Circulator
Sensing fibre
(25 km)
Coupler
(50/50)
Photo
detector
Electrical
spectrum
analyzer
Temperature
oven
Fig. Experimental set up of Brillouin optical time domain reflectometry (BOTDR)
Experimental measurement of Brillouin gain spectrum (BGS)
Fig.1: Experimental Brillouin gain spectrum (BGS) of 25 km long SMF
-68
Lorentz fit of Data1_B
-70
Centre frequency (xc)= 10.867 GHz ±12964.84008)
Linewidth (FWHM) =4.362 MHz ±40026.21839)
Optical power (dBm)
-72
-74
-76
-78
-80
-82
-84
-86
-88
10.86G
10.87G
10.88G
10.89G
Brillouin Frequency Shift (BFS) in GHz
Fig.1: Lorentzian curve fitting for experimental Brillouin gain data
Temperature and strain effects on Brillouin gain spectrum (BGS)
Fig.1: Brillouin frequency shift and peak gain variations of single mode silica fibre for (a) different
temperatures (b) different strains
Brillouin frequency shift vs Temperature
Brillouin frequency shift vs applied strain
700
160
600
Frequency shift (MHz)
Frequency shift (MHz)
140
120
100
80
60
40
20
0
0
500
400
300
200
100
20
40
60
80
Temperature (oC)
100
120
140
0
0
2000
4000
6000
Strain (µ-strain)
Fig.2: Brillouin frequency shift changes linearly with temperature and strain
8000
10000
Experimental Brillouin threshold measurement
Fig.1: Backscattered spectrum for different input pump powers
Fig.2: Brillouin threshold measurement for 25-km long SMF (10.62 dBm)
Brillouin optical time domain analysis (BOTDA)
Fig 1: Operating principle of Brillouin optical time domain analysis (BOTDA)
Fig 2: Modified Brillouin optical time domain analysis (BOTDA)
Experimental setup of Brillouin optical time domain analysis
(BOTDA)
Fig: BOTDA Experimental arrangement for measuring strain and temperature
(DFB-LD=distributed feedback laser diode, PC: polarization controller, EOM=electro-optic modulator, EDFA=erbium doped fiber
amplifier, PS: polarization scrambler, PD=photo detector).
Simulation analysis of BOTDA
Strain effects on Brillouin gain spectrum:
(a)
(b)
(c)
(d)
Three-dimensional Brillouin gain spectrum (BGS) of 40m long single mode silica fibre at room temperature (a) without any applied strain
(b) 0.1% (1000 µε) applied strain (c) 0.2% (2000 µε) applied strain (d) 0.3% (3000 µε) applied strain, on 5m section of sensing fibre
Simulation analysis of BOTDA (Cont.….)
Temperature effects on Brillouin gain spectrum:
Three-dimensional Brillouin gain spectrum (BGS) of 40m long single mode silica fibre at without applied strain (a) 40oC applied
temperature (b) 60oC applied temperature
Table I: Strain effects on Brillouin frequency shift (BFS)
Strain
Strain free and room
temperature (20oC)
0.1% (1000 µε)
0.2% (2000 µε)
0.3% (3000 µε)
Brillouin frequency
shift (BFS)
11.200 GHz
Strain induced
frequency shift
----
11.260 GHz
11.320 GHz
11.380 GHz
60 MHz
120 MHz
180 MHz
Table II: Temperature effects on Brillouin frequency shift (BFS)
Temperature
Room temperature
(20oC) and strain
free
40oC
60oC
Brillouin frequency
shift (BFS)
11.200 GHz
Temperature induced
frequency shift
11.225 GHz
11.250 GHz
25 MHz
50 MHz
----
Ref: N. Lalam, W. P. Ng, X. Dai, and H. K. Al-Musawi, "Characterization of Brillouin frequency shift in Brillouin Optical Time Domain Analysis (BOTDA)," in Networks and Optical Communications (NOC), 2015 20th IEEE European Conference on, London, 2015, pp. 1-4.
Simulation analysis of BOTDA (Cont.….)
Probe light
S
ge
han
c
in
tra
re
atu
r
e
e
mp
Te chang
Pump light
Fig: Temperature (70oC ) and strain 0.2% (2000µ-strain) induced Brillouin frequency shifts
Simulation analysis of BOTDA (Cont.….)
Fig: Top view of strain and temperature induced frequency shifts at 15m and 30m, respectively, along the 60m of sensing fibre
Simulation analysis of BOTDA (Cont.….)
Table II: Measured coefficient values of BFS and peak gain for temperature and strain
Description
Change in Brillouin
frequency versus strain
Measured value
0.06 MHz/(µstrain)
Change in Brillouin
frequency versus
temperature
1.25 MHz/oC
change in Brillouin gain
versus strain
-9×10-4 %/(µstrain)
change in Brillouin gain
versus temperature
0.416 %/K
Brillouin frequency shift vs applied strain
Brillouin frequency shift vs Temperature
700
160
140
Frequency shift (MHz)
Frequency shift (MHz)
600
500
400
300
200
100
0
0
120
100
80
60
40
20
2000
4000
6000
Strain (µ-strain)
8000
10000
Fig: Brillouin frequency shift (BFS) changes with
applied strain (µ-strain)
0
0
20
40
60
80
Temperature (oC)
100
120
140
Fig: Brillouin frequency shift (BFS) changes with
applied temperature
Comparison of BOTDR and BOTDA Brillouin gain spectrums
BOTDR- three-dimensional Brillouin gain
spectrum (BGS) vs fibre distance
BOTDA- three-dimensional Brillouin gain
spectrum (BGS) vs fibre distance
Applications of Brillouin based Distributed fibre sensors
Oil and Gas pipeline Monitoring
Aeroplane monitoring
https://www.youtube.com/watch?v=x6x9BI7shVE
Bridge and Building Monitoring
Rail-track monitoring
Boarder security monitoring
Road tunnels
Source: Times of India, 2014
Causes of train delays/accidents
Source: Network rail: delays explained, 2014
Source: https://www.youtube.com/watch?v=7-ZtCFqf7UI
Current rail-track monitoring methods
Track geometry car
Video inspection
Manual inspection
Rai-track inspection through ultra sound
British rail industry investment and performance
The Passenger’s pound
British PPM performance
Investment in rail network (26p)
Track Maintenance cost (22p)
Industry Staff costs (25p)
Interest payments and Other costs (9p)
Leasing trains (11p)
Fuel for trains (4p)
Train Company profits (3p)
Source: Network rail group, 2014
Source: UK rail regulations, 2015
Rail-track monitoring using distributed fibre sensor system
Proposed solution:
The proposed research has capable of monitoring rail-track in real-time with following benefits:
1. Strain, temperature monitoring
2. Train weight, speed and acceleration
3. Axle load and axle counting
4. Train location, direction
5. Railway traffic monitoring
6. Level crossings monitoring
7. Easy maintenance
8. High sensing range (~150 km: using our proposed method)
9. High measurement accuracy (±5µε, ±0.1oC)
10. High measurement speed (< 1 min)
Advantages of Brillouin based distributed fibre
sensors

Harsh environmental capability

Low EMI

Very small size and light weight

Long distance operation (~ 150 km)

Very wide operating temperature range

Easy maintenance

Simple installation

Quick response

Distributed measurement capability (one fibre cable can have hundreds of sensors )
Thanks for your attention