Yolande Sikali 1,Yves Jaouën 2, Renaud Gabet 2, Xavier Pheron 3 Gautier Moreau 1, Frédéric Taillade 4

Transcription

1 Presented at the COMSOL Conference 2010 Paris Two-dimensional FEM Analysis of Brillouin Gain Spectra in Acoustic Guiding and Antiguiding Single Mode Optical Fibers Yolande Sikali 1,Yves Jaouën 2, Renaud Gabet 2, Xavier Pheron 3 Gautier Moreau 1, Frédéric Taillade 4 1 EDF R&D,6 Quai Watier, Chatou, France 2 Telecom ParisTech, 46 rue Barrault, Paris, France 3 ANDRA,1-7 Rue Jean Monnet, Chatenay-Malabry, France 4 LCPC, 58 Boulevard Lefebvre Paris, France Contact: yolande.sikali-mamdem@edf.fr

2 Overview Optical Fiber Sensors Optical fiber properties Distributed fiber sensors solutions Brillouin Scattering in optical fibers Brillouin Gain Spectrum computation using COMSOL Multiphysics 2D-FEM modeling Validation of the model : example of GeO 2 -doped core fiber Analysis of acoustic anti-waveguides fibers Example : Fluorine-doped cladding fibers Analysis of no-symmetrical geometry fibers Example : Stress-induced polarization-maintaining fibers 2

3 Optical fiber sensors Optical fiber properties Interrogation unit OPTICAL FIBER COATING CORE Quasi-distributed sensors Fully-distributed sensors Source Analysis CLADDING Point like sensors Application fields - Weakly intrusive - Electro-magnetic immunity - Fast information transfer/ rate Distributed fiber sensors OTDR Principle Back-scattered spectrum at λ 0 = 1550nm Power (u.a.) 3 Distance (km) 11GHz 13THz

4 Brillouin Scattering 1) Acoustic Wave Photo-elasticity 2) Propagating Bragg mirror Diffraction 3) Backscattering wave Stokes lightwave Pump wave Acoustic wave ν B = ν S -ν 0 = ±2nV a /λ 0 Dependences of the Brillouin shift ν B T ε Frequency (GHz) 4

5 Brillouin Scattering Brillouin Gain Spectrum is highly related to Doping Refractive index variation n%/wt.% Acoustic velocity variation V l %/wt.% Doping composition: GeO F P 2 O TiO Geometry and doping profiles: Frozen-in stress profiles: Need of a precise tool to predict the Brillouin Gain Spectrum! 5

6 Brillouin Scattering Optic Acoustic Monomode propagation : mode LP 01 Solutions: L 0m modes L 01 L 03 Acousto-optic overlap Brillouin Gain Spectrum 6 Y. Koyamada, Lightwave Technol., 22, (2004) L. Tartara,Optics Com., 282, (2009)

7 Simulation with COMSOL V L (x,y) and n(x,y) vary on the cross-section with doping composition, frozen-in stress and geometry E(x, y) and n eff are calculated with PDE solver Geometry Mesh Mode plot Bragg condition gives u m (x, y) andω m The gain spectrum g(ν) is calculated taking into account overlap integrals of acoustic modes with the optical mode 7

8 Validation : GeO 2 -doped core fiber A Ge0 2 -doped core fiber acts as an acoustic waveguide Input data Measured Optical index profile 1.45 Calculated acoustic velocity profile Refractive index n Cladding Core Cladding Radius (µm) Modeling results Amplitude (a.u.) 1,0 0,5 0,0 Acoustic modes Optical mode L 01 L 02 L 03 L 04-0, Radius µm) Doping concentration DSP (u.a.) V L (m/s) Cladding Core Radius (µm) Brillouin spectrum L Frequency (GHz) Modelisation Measurement L 02 L 03 L 04

9 Acoustic anti-guiding fiber A Fluorine-doped cladding fiber Applications - Pure silica core (very low attenuation transmission fibers) - High Stimulated Brillouin threshold (high power fiber lasers) - High immunity to radiations (optical sensors) Refractive index n Optical index profile Cladding Core Cladding Radius (µm) Overlap integral Overlap integrals I ao m Amplitude (u.a.) Most efficient acoustic mode and optical mode profiles Optical mode Higher order acoustic mode DSP (u.a.) Brillouin spectrum Measurement Modelisation Frequency (GHz) Radius (µm) Frequency (GHz)

10 Polarization-maintaining fiber PANDA fiber : stress-induced birefringence Frozen-in stress distributions (a) (b) 10 Modeling results Optical Birefringence profile B = nx-ny 8 x x (m) x 10-4 Brillouin spectra for polarization x and y compared to a no-stressed fiber DSP (db) No-stressed fiber PMF x PMF y MHz Frequency (GHz)

11 Summary A 2D-FEM modal analysis to investigate the Brillouin spectrum in single-mode optical fibers: no problems of convergence Model to predict effectively the Brillouin spectrum in case of acoustic anti-waveguides Model adapted for more complicated geometries and stressinduced refractive index profiles and non-axis-symmetrical fibers Useful tool to design and analyze optical fibers for optical communications and Brillouin-based fiber sensors 11

12 Thank you for your attention! 12

13 Brillouin spectrum measurement Self-heterodyne technique DFB Laser 1560nm Polarization controller EDFA Tunable attenuator Circulator Polarization scrambler Stokes wave OL wave Fiber under test Balanced photoreceiver - Electrical amplifier Spectrum Analyser Optical domain Stokes OL Electric domain ν o -ν B ν o ν B 13