Design and fabrication of integrated optical waveguide devices

The next generation of all-optical networks requires highly integrated optical devices to realize various optical signal processing and routing functions. An integrated array of optical waveguide devices, also referred to as photonics integrated circuits (PICs), has important potential for these technology areas. Our research work in this area has mainly focused on device prototyping with new functionality, device miniaturization, and development of computer-aided design packages for large-scale and complicated PICs.; The first and main part of this thesis focuses on the multimode interference (MMI)-based imaging devices and their applications in wavelength multiplexing (WDM) systems. In recent years, MMI devices have been of great interest for their application in many complex PICs because of their sometimes, important optical properties and ease of fabrication. The first chapter starts with the analysis of the phase errors of MMI devices that fundamentally determines their imaging performance. The phase-error problem for laser-fabricated MMI devices was experimentally investigated. Based on explicit phase error formula derived, a new optimization design scheme was developed to obtain high-performance large N, N x N MMI devices. The feasibility of this scheme on realistic material systems was proven by using the 3-D wide-angle beam propagation method. The greatly improved performance including low crosstalk and loss was obtained in the simulation for N x N MMI-based phased-array WDM routers.; The second part of my thesis includes research work on prototyping several novel passive and active waveguide devices using laser-writing techniques. A new 3-D laser-etching technique was developed to fabricate high-performance waveguides with different structures, including a smoothly height-tapered structure. Also, a novel technique for electrode design on our waveguides with simple epitaxial-layer structure was simulated and demonstrated. Utilizing both techniques, a tunable Mach-Zehnder-based power splitter was successfully designed and prototyped as an important building block for an optical transversal filter, a large-scale PIC. My effort in prototyping a tunable TE/TM polarization splitter and a two-stage Mach-Zehnder interferometer is also described.; Finally, the design and prototype of an integrated polarization rotator based on the interference of the hybrid modes is presented. The device has advantages in terms of compact size and low loss, and it was fabricated, for the first time for its kind, by both dry and wet etching techniques.