Distributed On-chip Brillouin Sensing: Toward Sub-mm Spatial Resolution

Abstract

Stimulated Brillouin scattering (SBS) involves nonlinear interaction of an optical wave with material, which under the phase-matching condition results in generation of an acoustic wave. In turns, part of the optical wave is scattered by the acoustic wave through an inelastic scattering process. SBS enables unique applications in optical fibers and more recently in on-chip photonic waveguides, ranging from RF-signal processing to lasing, frequency combs, RF sources, and light storage. Harnessing on-chip SBS paves the way to photonic integration by enabling powerful functionalities in an integrated, scalable, energy-efficient and potentially CMOS-compatible platform. In this thesis, we explore the possibility of enabling SBS in a silicon-based platform by designing, fabricating and characterizing a hybrid silicon-chalcogenide waveguide, which shows significant improvement in terms of nonlinear losses and SBS gain compared to a standard silicon waveguide. The SBS response in photonic waveguides including the silicon-chalcogenide platform is subject to spectral broadening which influences the quality of the devices whose performance are relying on the narrow linewidth of SBS. The spectral broadening is mainly due to structural non-uniformities along the waveguides which affect the local SBS response and consequently deteriorates the strength of the integrated SBS response. Therefore, characterizing those waveguides is of great importance. To address this issue, we employed the principle of distributed SBS sensing to monitor the on-chip waveguides. However, since the waveguides length is on the order of cm and mm, the spatial resolution of the distributed technique needs to be very high, preferably in the sub-mm regime, which is the main goal of this thesis.