Espalhamento Brillouin estimulado em guias de onda de niobato de lítio

Author(s)

Caique Conde Rodrigues

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2025-02-27

Examining board members

Gustavo Silva Wiederhecker; Newton Cesário Frateschi; Felippe Alexandre Silva Barbosa; Paulo Clóvis Dainese Júnior; Alexandre de Almeida Prado Pohl

• Advisor: Gustavo Silva Wiederhecker; Thiago Pedro Mayer Alegre

Abstract

In this thesis, two particular works of mine will be discussed in more depth, those involving lithium niobate on insulator (LNOI), which are precisely the works I chose to present for my defense. In these works, we demonstrate through numerical simulations that LNOI waveguides can support confined, short-wavelength surface acoustic waves that strongly interact with optical fields via backward stimulated Brillouin scattering (BSBS) in both $Z$ and $X$-cut orientations. Our fully anisotropic simulations account for not only the moving boundary and photoelastic effects but also roto-optic forces involved in the Brillouin interaction. Following these simulations, we conducted an experimental demonstration of cross-polarization backward stimulated Brillouin scattering in LNOI waveguides. Using polarization-sensitive pump and probe measurements, we observed both intra- and intermodal scattering between counterpropagating fundamental TE and TM optical modes. Remarkably, cross-polarization scattering achieved SBS gains exceeding $G_{B}=\SI{80}{\m^{-1}\W^{-1}}$, a result that not only expands the role of polarization in SBS, but also opens up possibilities for high-performance devices, including ultra-narrowband lasers, robust broadband nonreciprocal devices, RF filters, and microwave-to-optical converters. We will also discuss my first Ph.D. project, where we experimentally demonstrate entrainment of a silicon-nitride optomechanical oscillator driven up to the fourth harmonic of its $\SI{32}{\mega\hertz}$ fundamental frequency. Exploring this effect, we also experimentally demonstrate a purely optomechanical RF frequency divider, where we performed frequency division up to a 4:1 ratio, i.e., from $\SI{128}{\mega\hertz}$ to $\SI{32}{\mega\hertz}$. Further developments could harness these effects towards frequency synthesizers, phase-sensitive amplification and nonlinear sensing (AU)

• FAPESP's process: 19/14377-5 - Lithium niobate opto-electro-mechanics
• Grantee: Caique Conde Rodrigues
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)