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UBC Theses and Dissertations

Sub-wavelength grating components for silicon-on-insulator platform Wang, Yun


This dissertation is a theoretical and experimental study of sub-wavelength grating (SWG) based photonic devices for the silicon-on-insulator (SOI) platform, including high-efficiency sub-wavelength grating couplers (SWGCs), broadband SWGCs, broadband SWG directional couplers, and an SWG polarization splitter-rotator. High-efficiency SWGCs with improved operating bandwidths and sup- pressed back reflections have been demonstrated to couple light into and out of SOI based photonic integrated circuits (PICs). One-dimensional SWGs have been proposed and experimentally demonstrated for the first time to make fully-etched grating couplers, which have performances comparable to the state-of-the-art fully-etched grating couplers, but with better fabrication tolerance, reduced fabrication complexity, and less cost. A theoretical study of the operating bandwidths for grating couplers has been presented and a design methodology has been demonstrated for designing SWGCs with design-intent operating bandwidths. SWGCs with 1-dB bandwidths up to 90 nm have been demonstrated, which have improved the operating bandwidth of fully-etched grating couplers by a factor of 3. Such broadband SWGCs are essential components for applications such as wavelength-division multiplexing (WDM) PICs and bio-sensing. Compact directional couplers, with dimensions about 10 times smaller than its alternatives, i.e., adiabatic couplers and multimode interference couplers have been demonstrated for various power splitting ratios. The operating bandwidths of our directional couplers have been improved by a factor of 2 as compared to conventional directional couplers. The dispersion properties of SWGs have been explored and applied to engineer the wave- length dependancy of conventional directional couplers for broad operating bandwidths, which is the first experimental demonstration of such devices. Polarization splitter and polarization rotators are essential components to address the polarization diversity of PICs. An ultra-compact mode- coupling based polarization splitter-rotator (PSR), which combines functionalities of a polarization splitter and a polarization rotator, with dimensions 15-20 times smaller than its alternative, i.e., mode-evolution based PSRs, has been experimentally demonstrated for the first time, where an asymmetric waveguide system consisting of a strip waveguide and an SWG waveguide were used to improve the fabrication tolerance of such devices. A measured peak polarization conversion efficiency of −0.3 dB with crosstalks below −10 dB over the C-band has been achieved.

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