Manipulating Light on Wavelength Scale

Abstract

Light, at the length-scale on the order of its wavelength, does not simply behave as "light ray", but instead diffracts, scatters, and interferes with itself, as governed by Maxwell's equations. A profound understanding of the underlying physics has inspired the emergence of a new frontier of materials and devices in the past few decades. This thesis explores the concepts and approaches for manipulating light at the wavelength-scale in a variety of topics, including anti-reflective coatings, on-chip silicon photonics, optical microcavities and nanolasers, microwave particle accelerators, and optical nonlinearities. In Chapter 1, an optimal tapered profile that maximizes light transmission between two media with different refractive indices is derived from analytical theory and numerical modeling. A broadband wide-angle anti-reflective coating at the air/silicon interface is designed for the application of photovoltaics. In Chapter 2, a reverse design method for realizing arbitrary on-chip optical filters is demonstrated using an analytical solution derived from Chapter 1. Example designs are experimentally verified on a CMOS-compatible silicon-on-insulator (SOI) platform. Among this device’s many potential applications, the use for ultrafast on-chip pulse shaping is highlighted and numerically demonstrated. In Chapter 3, the concept of tapering is applied to the design of photonic crystal cavities. As a result, the scattering losses of cavities are suppressed, and light can be localized in a wavelength-scale volume for a long life-time. In Chapter 4, photonic crystal cavity-based nanolasers with low power consumption are demonstrated with two different prototypes-photonic crystal nanobeams and photonic crystal disks. The use of graphene is also explored in this chapter for the purpose of electrically-driven nanoscale light-emitting devices. In Chapter 5, photonic crystal cavities at millimeter wavelength for particle acceleration applications are developed. In Chapter 6, a novel design of dual-polarized mode photonic crystal cavities, and its potential for difference-frequency generations are examined.