Transport and lasing in topological photonic systems

Abstract

This thesis concerns the study of novel topological transport phenomena in photonic systems, particularly in valley photonic crystals, Weyl semimetals and photonic Chern insulators; and lasing in a valley photonic crystal.

In the first part of the thesis, I present our study of an electrically pumped quantum cascade laser based on the topological edge states of a valley photonic crystal operating in THz frequency regime. The topological protection of lasing modes allows for irregular laser cavity design with robust mode spacings arising from the running wave nature of topological lasing modes that resist the formation of localized standing-waves.

In the second part, I present our work on near field imaging of topological edge modes of a valley photonic crystal slab operating in infrared regime.

The third part of the thesis describes our study of beam displacements in a Weyl semimetal. Beams in Weyl semimetals undergo both lateral (Goos-Hänchen shift) and transverse (Imbert-Fedorov shift) displacements upon reflecting off a gapped medium. We show that the displacement forms a half-vortex structure in momentum space. The center of the half-vortex is determined by the Fermi arc which provides a way to use bulk transport to probe the topological characteristics of a Weyl semimetal.

In the last part of the thesis, I present our study of mode delocalization in a photonic Chern insulator. In contrast to trivial two-dimensional insulators, where all modes are localized when disorder is present, a single extended mode survives in Chern insulators up to a critical disorder strength. We study this phenomena in a photonic Chern insulator platform which is promising for direct experimental probing.