Adrien GODET:"Brillouin Spectroscopy of Micro and Optical Silicon Nanowires"

PhD Work of Adrien Gaudet: "Brillouin Spectroscopy of Micro and Optical Silicon Nanowires" 

Résumé : This thesis reports the design and fabrication of subwavelength-diameter silica optical fibers, also known as optical micro and nanowires. These hair-like slivers of glass, manufactured by tapering optical fibers down to a size hundred times smaller than a strand of human hair, have a number of optical and mechanical properties that make them very attractive for both fundamental physics and technological applications. In addition to providing strong light confinement and enhanced nonlinear optical effects, they exhibit a large evanescent field, enabling applications not currently possible with comparatively bulky optical fibers. We here explore their elastic properties through Brillouin spectroscopy. We specifically provide a complete description, both theoretically and experimentally, of the backward Brillouin spectra including the observation of both bulk hybrid and surface acoustic waves with many anti-crossings. A very good agreement is found between numerical simulations of the elastodynamics equation and the experimental Brillouin spectra for a wide range of wire diameters. From this study, we demonstrate a simple and non-destructive in-situ technique for measuring the diameter of these ultra-thin fibers and their uniformity with a high sensitivity of only a few nanometers. A distributed measurement of both the surface and hybrid acoustic waves along an optical microwire was then performed using Brillouin optical correlation technique. We further investigate the tensile strain dependence of Brillouin scattering in optical microwires and report, for the first time to our knowledge, evidence of a strong elasticity and nonlinearity of the elastic constants of silica. This thesis therefore demonstrates that optical microwires can find various potential applications for strain optical sensing.

Evaluation committee: :

Mme Maria-Pilar Bernal, Directrice de recherche CNRS , FEMTO-ST, Présidente
Mr Pascal Besnard,  Professeur, ENSSAT, Lannion, Rapporteur
Mr Yves Jaouen, Professeur, Télécom Paris Tech, Paris, Rapporteur
Mr Yves Quiquempois, Professeur, Université de Lille 1, Examinateur
Mme Sylvie Lebrun, Maître de conférences, HDR, Institut d'Optique, Paris, invitée
Kien Phan Huy, Maître de conférences, HDR, Université de Franche Comté, Directeur de thèse
Jean-Charles Beugnot, Chargé de recherche CNRS, FEMTO-ST, Codirecteur de thèse
Thibaut sylvestre, Directeur de recherche CNRS, FEMTO-ST, Codirecteur de thèse

Location : Amphithéâtre JJ Gagnepain, 15B, Avenue des Montboucons à Besançon