Stimulated Brillouin scattering from surface acoustic waves in sub-wavelength photonic microwires

摘要

Brillouin scattering in optical fibres is a fundamental interaction betweenlight and sound with important implications ranging from optical sensors toslow and fast light. In usual optical fibres, light both excites and feelsshear and longitudinal bulk elastic waves, giving rise to forward guidedacoustic wave Brillouin scattering and backward stimulated Brillouinscattering. In a subwavelength-diameter optical fibre, the situation changesdramatically, as we here report with the first experimental observation ofstimulated Brillouin scattering from surface acoustic waves. TheseRayleigh-type hypersound waves travel the wire surface at a specific velocityof 3400 m.s$^{\mathrm{-1}}$ and backscatter the light with a Doppler shift ofabout 6 GHz. As these acoustic resonances are highly sensitive to surfacedefects or features, surface acoustic wave Brillouin scattering opens newopportunities for various sensing applications, but also in other domains suchas microwave photonics and nonlinear plasmonics.