Experimental observation of surface acoustic wave Brillouin scattering in a small core photonic crystal fiber
Résumé
Brillouin scattering is a nonlinear phenomen on due to interaction between light and elastic waves. Nowadays, the dynamic of Brillouin scattering in conventional fibers are well known, with many applications ranging from optical telecommunications to sensors. Brillouin scattering has recently been the subject of a renewed interest in tiny optical waveguides [1,2]. This has been recently shown in small-core PCF, where multiple hybrid shear and longitudinal modes have been observed, giving rise to multimode broadband Brillouin spectra with high onset threshold [1]. It has been also shown that light propagating in a subwavelength-diameter silica tapered fiber can generate surface acoustic waves (SAWs), because the strongly confined light senses the vibrations of the boundaries, leading to surface-localized light-sound interaction [2]. Such a phenomenon is not observed in conventional telecom fibers because their core is much larger than the optical wavelength and the optical mode does not extend to the boundaries. In this work, we report on the experimental observation of surface acoustic wave Brillouin scattering (SAWBS) in a small-core PCFs. We show that the surface acoustic wave frequency can be widely tuned in the range of 5-6 GHz by changing the air-hole microstructure surrounding the core. Very good agreement is observed between experiments and simulations based on the elastodynamics equation. These new intriguing dynamics of SAWBS in small-core optical fibers open interesting opportunities for various sensor applications but also in other area such as telecommunications, microwave photonics and plasmonics. [1] P. Dainese et al., “Stimulated Brillouin scattering from multi-GHz-guided acoustic phonons in nanostructured photonic crystal fibres,” Nature Physics 2, 388-392 (2006). [2] J.-C. Beugnot et al., “Brillouin light scattering from surface acoustic waves in a subwavelength-diameter optical fibre,” Nature Communication 5, 5242 (2014).