1. 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. (
Supervisors
Dr. Wai Pang Ng
Dr. Xuewu (Daniel) Dai

2. Losses in optical fibre communication
Dispersion
Absorption
Scattering (Raleigh, Brillouin and Raman scattering)
Bending
Link budget, power budget
Dispersion
Scattering

3. Scattered light spectrum in optical Fibres
Raleigh Scattering (vo)
Brillouin scattering (vo-vb)
Raman scattering (vo-vr)
Intensity
Brillouin Stokes
Brillouin
Anti-stokes
T, ε
T, ε
Raman
Stokes
Raman
Ant-stokes T T
vo-vr
vo-vb vo
Frequency
BFS ~
11 GHz
~ 13 THz
Fig: Spectrum of backscattered signal in optical fibre

4. 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.

5. Operating principle of OTDR
Optical time domain reflectometer (OTDR) used to measure the losses in optical fibre
Based on the Raleigh backscattered signal and Fresnel reflection

6. Brillouin optical time domain reflectometry (B-OTDR)
Fig.1: Brillouin optical time domain reflectometry (B-OTDR) sensing principle
25 km SMF
3 dB
(Optisci-28dB)
1550 nm, 8 dBm, (Thorlabs, 1754C)
3 dB
(D8-ir,
BW: 50GHz)
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)

7. Experimental set up of BOTDR
Temperature controller
EDFA
Optical spectrum analyzer
Sensing fibre (25 km)
DC Bias
Electrical spectrum analyzer
DFB-LD
Circulator
Photo detector
Coupler (50/50)
Attenuator
Coupler (50/50)
Temperature oven
Fig. Experimental set up of Brillouin optical time domain reflectometry (BOTDR)

8. Experimental measurement of Brillouin gain spectrum (BGS)
Fig.1: Experimental Brillouin gain spectrum (BGS) of 25 km long SMF
Fig.1: Lorentzian curve fitting for experimental Brillouin gain data

9. 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
Fig.2: Brillouin frequency shift changes linearly with temperature and strain

10. 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)

11. 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)

12. 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).

13. Simulation analysis of BOTDA
Strain effects on Brillouin gain spectrum:
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

14. 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) Table II: Temperature effects on Brillouin frequency shift (BFS)
Strain
Brillouin frequency shift (BFS)
Strain induced frequency shift
Strain free and room temperature (20oC)
GHz
----
0.1% (1000 µε)
GHz
60 MHz
0.2% (2000 µε)
GHz
120 MHz
0.3% (3000 µε)
GHz
180 MHz
Temperature
Brillouin frequency shift (BFS)
Temperature induced frequency shift
Room temperature (20oC) and strain free
GHz
----
40oC
GHz
25 MHz
60oC
GHz
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), th IEEE European Conference on, London, 2015, pp. 1-4.

15. Simulation analysis of BOTDA (Cont.….)
Fig: Temperature (70oC ) and strain 0.2% (2000µ-strain) induced Brillouin frequency shifts

16. 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

17. Simulation analysis of BOTDA (Cont.….)
Table II: Measured coefficient values of BFS and peak gain for temperature and strain
Fig: Brillouin frequency shift (BFS) changes with applied strain (µ-strain)
Fig: Brillouin frequency shift (BFS) changes with applied temperature

18. 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

19. Applications of Brillouin based Distributed fibre sensors
Oil and Gas pipeline Monitoring
Bridge and Building Monitoring
Boarder security monitoring
Aeroplane monitoring
Rail-track monitoring
Road tunnels

20. Source: Times of India, 2014

21. Causes of train delays/accidents
Source: Network rail: delays explained, 2014
Source:

22. Current rail-track monitoring methods
Track geometry car
Manual inspection
Video inspection
Rai-track inspection through ultra sound

23. 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

24. 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:
Strain, temperature monitoring
Train weight, speed and acceleration
Axle load and axle counting
Train location, direction
Railway traffic monitoring
Level crossings monitoring
Easy maintenance
High sensing range (~150 km: using our proposed method)
High measurement accuracy (±5µε, ±0.1oC)
High measurement speed (< 1 min)

25. 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 )

26. Thanks for your attention