Interação Brillouin em microesferas de sílica

Author(s)

Letícia de Sousa Magalhães

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2022-07-28

Examining board members

Gustavo Silva Wiederhecker; Hugo Enrique Hernández Figueroa; Pierre Louis de Assis

• Advisor: Gustavo Silva Wiederhecker

Abstract

Stimulated Brillouin Scattering (SBS) is a type of inelastic scattering concerning two optical and one acoustic wave. In this dissertation, SBS is seen as a common ground for phononic and photonic co-design in spherically symmetric systems. Firstly, we developed a suitable numerical methodology to solve the vibrational modes of onion-like systems, i.e., with radially piece-wise uniform material properties. This framework is suitable for our object of interest: optical resonators coated with layers of different materials. We focused on glass microspheres coated with alumina thin films because of their higher refractive index and higher acoustic velocities. We investigate the effect on the acoustic response when adding a stiffer-material film on an otherwise free surface. We demonstrate that surface-acoustic waves are importantly affected and enter a pseudo-bulk regime for increasing alumina layers. We use these results to calculate the Brillouin optomechanical coupling rates for the surface mode. We find a 12-fold enhancement of the Brillouin gain (compared to an uncoated sphere), the possibility of self-cancellation, and independent cancellation of photoelastic and moving boundary contributions for different alumina thicknesses. This strategy, therefore, provides remarkable tunability of Brillouin interaction parameters. Next, we experimentally observed SBS in uncoated silica microspheres from longitudinal (bulk) acoustic waves. We propose an experimental technique, here coined "gated measurements," to dynamically excite cavity resonances while avoiding thermal nonlinearities. Circumventing thermal drifts enable us to identify the resonances involved in an SBS event and perform a dispersion characterization. Finally, we take advantage of the thermal effects and demonstrate enhancement and suppression of the Brillouin signal by controlling the sample temperature (AU)

• FAPESP's process: 19/14370-0 - Brillouin interaction in optical waveguides and microcavities
• Grantee: Letícia de Sousa Magalhães
• Support Opportunities: Scholarships in Brazil - Master