Integrated Photonics Structure for THz Systems Based on Silicon and Photoconductive Material

Abstract

The field of terahertz (THz) technology has been immensely progressed over the past two decades, but integrated on-chip THz circuits and systems are still under development. This thesis is an effort to propose an integrated THz system by trapping a generated photocurrent THz wave and its coupling to the waveguide for on-chip propagation and processing. The proposed system consists of three parts; an optically-excited photoconductive THz source based on low-temperature grown (LT)-GaAs, a photonic crystal nanobeam cavity for THz wave confinement, and its coupling to a waveguide, both are based on a silicon platform. The thesis first investigates how the THz signal is generated by the photomixing techniques. It presents an analytical model to calculate the time-varying photocurrent acting as a THz source. Considering the THz dipole current exciting a cavity, I propose a photonic crystal nanobeam cavity inside a waveguide with high quality factor to confine the THz wave. The design and simulation of such a cavity are presented where the THz field mode has been found in a single-mode regime. Finally, the cavity is coupled to the waveguide using a tapering technique in the photonic crystal structure for efficient coupling and subsequent propagation by modal field matching. The proposed structure exhibits potential applications for integrated THz sources for various on-chip applications such as sensing, spectroscopy, and signal processing.