The acousto-optic interaction in aluminosilicate-based optical fibres

• Main Author: Mountfort, Francesca
• Other Authors: Sahu, Jayanta
• Published: University of Southampton 2015
• Subjects: 621.36
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694504

In fibre optic technology there is a drive to innovate more sophisticated telecommunications and narrow linewidth laser application systems. Brillouin scattering, with its low threshold powers - the lowest of all nonlinear processes - presents a fundamental barrier, in many cases, to achieving desired efficiencies. Aluminosilicate fibres have presented the possibility of thwarting this effect. The incorporation of aluminium oxide into silica fibre is not new. Historically its been used in applications requiring the deposition of rare-earth ions in the fibre core; mostly broad bandwidth fibre amplifier applications. However, with its unique acoustic properties - optically waveguiding and acoustically anti-waveguiding - it possesses the promise of minimising the interplay between optical and acoustic modes, thereby mitigating Brillouin scattering. The work presented in this thesis is an investigation of the acousto-optic interaction in a variety of different aluminosilicate single-mode optical fibres. These fibres include aluminosilicate, ytterbium-doped aluminosilicate, aluminophosphosilicate, ytterbium-doped aluminophosphosilicate as well as an aluminosilicate PANDA-type optical fibre wherein the position of the two stress rods changes longitudinally. A heterodyne coherent detection technique was used to measure the spontaneous Brillouin spectrum of these fibres. The characterisation of this work is distinctive in that, rather than using the Brillouin Stokes signal to measure the Brillouin spectrum, the Brillouin anti-Stokes signal was used. The Stokes Brillouin signal experiences gain with an increase in power, and hence the Brillouin spectrum experiences exhibits gain narrowing effects. However, characterising the Brillouin spectra with an increase in power using the Brillouin anti-Stokes signal reveals a spectral broadening. The Brillouin spectrum of these fibres were exhaustively characterised according to the Brillouin frequency shift and linewidth with changes in temperature, strain and input power.