vacancy disordering, quantum dots, quantum wells, all-optical, electro-optical, multimode interference, photonic integrated circuit, monolithic integration
The application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered advantages such as a very compact device footprint, low polarization sensitivity, large bandwidth and relaxed fabrication tolerances when compared with conventional single-mode waveguide formats. The first portion of this dissertation focuses on the characterization of the materials and material processing techniques for the monolithic integration of In0.15Ga0.85As/GaAs self-assembled quantum dots (SAQD) and InGaAsP/InGaAsP multiple quantum wells (MQW). Supplemental methods for post-growth bandgap tuning and waveguide formation were developed, including a plasma treatment process which is demonstrated to reliably inhibit thermally induced interdiffusion of Ga and In atoms in In0.15Ga0.85As/GaAs quantum dots. The process is comparable to the existing approach of capping the SAQD wafer with TiO2, while being simpler to implement along-side companion techniques such as impurity free vacancy disordering. Study of plasma-surface interactions in both wafer structures suggests that the effect may be dependent on the composition of the contact layer. The second portion of this work deals with the design, fabrication, and the testing of MMI switches which are used to investigate the limits of electrical current control when employing SAQD as the active core material. A variable power splitter based on a 3-dB MMI coupler is used to analyze the effects of sub-microsecond electrical current pulses in relation to carrier and thermal nonlinearities. Electrical current controlled switching of the variable power splitter and a tunable 2 x 2 MMI coupler is also demonstrated. The third part of this dissertation explores the response of In0.15Ga0.85As/GaAs SAQD waveguide structures to photogenerated carriers. Also presented is a simple, but effective, design modification to the 2 x 2 MMI cross-coupler switch that allows control over the carrier distribution within the MMI waveguide. This technique is combined with selective-area bandgap tuning to demonstrate a compact, working, all-optical MMI based switch.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Bickel, Nathan, "Electro-optical And All-optical Switching In Multimode Interference Waveguides Incorporating Semiconductor Nanostructures" (2010). Electronic Theses and Dissertations. 4282.