PhD Defense by Chirag M. Patil

Title: Experiments on Glide-Symmetric Photonic-Crystal Waveguides

Abstract: This thesis is intended to report the research outcome of the fabrication and characterization of glide-symmetry photonic-crystal waveguides on a silicon-on-insulator (SOI) platform. The glide-symmetry waveguide has the potential to offer new functionalities in the realm of chiral quantum-optics. These waveguides can support circularly polarized light, which is important for observing chiral behavior. Additionally, the presence of a band-crossing at the Brillouin-zone edge offers an interesting feature.

Silicon is a promising substrate for fabricating both active and passive nanophotonic devices, and has a huge potential for building integrated photonic-circuits. An optimized recipe to fabricate photonic-crystal slab waveguides on SOI platform has been described. Major challenges and drawbacks have been investigated and reported. The devices are optically characterized and measured to study the various properties of the photonic-crystal waveguides. A free-space optical characterization setup is built to perform transmission measurements on resonators and photonic circuits. Measurements are performed on more than 150 devices for statistical averaging on an ensemble of photonic-crystal waveguides. The transmission of glide-symmetry resonator structures exhibits clear signs of slow-light behavior. The group index is extracted, compared with the theoretical prediction and its implications are discussed.

Further, a novel criterion to qualitatively measure the localization length is also proposed. Localization length is a key parameter to detect the onset of Anderson localization in disordered systems. The Thouless criterion clearly distinguishes localized and non-localized modes by making a connection between fluctuations in conductance with localization. This criterion is explored and combined with systematic variation of sample size to extract the localization length in a simplified manner. This method is also verified experimentally, hence underpinning our claim.