UC San Diego

In integrated photonics, cavity resonators play an important role. They are the basis of light sources, which are one of the fundamental building blocks of any integrated circuit. So far, cavities are designed base on their size, shape, and photon lifetime, and requiring any extra features increase their complexity. However, cavities can present some topological behaviors with peculiar characteristics that can enhance their functionalities. Two of these topological behaviors, which are the main focus of this thesis, are Topological insulators (TIs), and Bound states in the continuum (BIC). In the following thesis, we explored theoretically and experimentally the topological singularities in cavities made of periodic structures, and their applications in designing integrated light sources (i.e., lasers). Structures are constructed on a gain material of InGaAsP multiple quantum wells, which emits in the telecommunication wavelength range (λ~1.55 μm), and operates at room temperature.

In the first part of the thesis, we study TIs and design topological cavities for integrated light sources using hybrid photonic crystals (PhCs) with non-zero phase transition between them. Thus the optical wave is fully confined at the boundary of PhCs, and propagates in one direction. The topological cavities can have any arbitrary geometry while preserving high functionality. Furthermore, we demonstrate that topological cavities are able to be used to generate structured lights with very large topological charges, while they maintain small foot-print and no-complexity.

The second part is dedicated to the bound states, which are the type of topological singularities with positive energies in the continuum region. These topological singularities offer many unique characteristics such as tunability of their position in the reciprocal space and carrying non-zero topological charges. Furthermore, the number of singularities can be controlled by crystal symmetry. In this thesis, we present the first experimental demonstration of simultaneously generation and steering multiple vortex beams form an extended PhC cavity.

Our results indicate the application of the topological behavior of cavities as an extra degree of freedom in designing integrated photonic chips with enhanced functionalities.