| The goal of integrated optics is to integrate more optical functions, such as modulation, switching, generation, and detection, in one optical chip in a compact form. However, the bend radius required for low-index and low-Delta (index contrast) waveguides, such as silica and polymer waveguides, is typically on the order of multiple millimeters, which limits the compactness of planar lightwave circuits (PLCs). To fully utilize the advantages of these low-index and low-Delta waveguides, such as low propagation loss and low coupling loss to optical fibers, decreasing the bend area is highly desired.; This dissertation focuses on designing very compact waveguide bends for low-index and low-Delta waveguides. The 2-D finite-difference time-domain (FDTD) method is used as a design tool to rigorously evaluate the optical bend performance. Some of the designs have applied a combination of micro-genetic algorithm (muGA) optimization and FDTD methods. Single air-interface bends are shown to have high optical bend efficiency when appropriately designed. The waveguide plane wave expansion theory has been used to explain observed behaviors and suggest alternate geometries for high-efficiency waveguide bends. Among them, the approach using multi-layer structures is particularly promising and versatile to create not only compact bend structures but also splitters.; Both amplitude and polarization beamsplitters have been designed and simulated. Combining waveguide bends and polarization beamsplitters, a system-level device, a waveguide-based depolarizer, has been proposed and experimentally evaluated using bulk optical elements.; Since waveguide bends and beamsplitters are such basic and crucial elements for PLCs, higher-level devices, such as directional couplers, resonators, and arrayed waveguide gratings (AWGs), may be redesigned in a more compact fashion using the components proposed in this dissertation. |
