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 Dispersion Absorption Scattering (Raleigh, Brillouin and Raman scattering) Bending Link budget, power budget Dispersion Scattering

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

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 Optical time domain reflectometer (OTDR) used to measure the losses in optical fibre 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 (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)

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)

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

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

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: 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) Table II: Temperature effects on Brillouin frequency shift (BFS) Strain Brillouin frequency shift (BFS) Strain induced frequency shift Strain free and room temperature (20oC) 11.200 GHz ---- 0.1% (1000 µε) 11.260 GHz 60 MHz 0.2% (2000 µε) 11.320 GHz 120 MHz 0.3% (3000 µε) 11.380 GHz 180 MHz Temperature Brillouin frequency shift (BFS) Temperature induced frequency shift Room temperature (20oC) and strain free 11.200 GHz ---- 40oC 11.225 GHz 25 MHz 60oC 11.250 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), 2015 20th IEEE European Conference on, London, 2015, pp. 1-4.

Simulation analysis of BOTDA (Cont.….) 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 Fig: Brillouin frequency shift (BFS) changes with applied strain (µ-strain) 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 Bridge and Building Monitoring Boarder security monitoring Aeroplane monitoring Rail-track monitoring Road tunnels https://www.youtube.com/watch?v=x6x9BI7shVE

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 Manual inspection Video 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: 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)

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