Highly efficient distributed Bragg deflectors for silicon photonic waveguide devices

Abstract

This thesis focuses on the comprehensive study of integrated photonic couplers pertaining to the category of distributed Bragg deflectors (DBDs) and their implementation in the silicon-on-insulator (SOI) platform. This device converts a channel waveguide mode into a slab confined beam by using a grating formed in the waveguide core. The DBD was first proposed by Stoll in 1978 [Stoll1978]. Stoll foresaw a multitude of applications of DBDs including beam expansion, polarization filtering, beam splitting and modulation. However, DBDs have typically suffered from high insertion losses that hindered their use in practical applications. In this thesis, we develop strategies to dramatically reduce the excess loss and demonstrate various low-loss DBD-based devices in the SOI platform.

First, we developed various tools and methodologies for efficient analysis and design of DBD-based devices. Then, by using these new tools, we found out that off-chip radiation was the primary factor responsible for the excess loss observed in previous works. Subsequently, we propose and develop an original design method based on the single-beam condition, which efficiently suppresses off-chip radiation thus yielding low-loss DBD devices. Based on these original approaches, a low-loss wavelength demultiplexer was designed and experimentally demonstrated. Demultiplexer thermal tunability and flattop response have also been investigated. Finally, we explored the use of DBD devices as feeding elements for grating-based surface-emitting antennas, an application that allows efficient generation of large-area and highly-directional free space beams generated on-chip.