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UBC Theses and Dissertations

Silicon photonic waveguide Bragg gratings Wang, Xu


Silicon is the most ubiquitous material in the electronics industry, and is now expected to revolutionize photonics. In just over ten years, silicon photonics has become a key technology for photonic integrated circuits. By taking advantage of silicon-on-insulator (SOI) wafers and the existing complementary metal-oxide semiconductor (CMOS) fabrication infrastructure, silicon photonic chips are now being delivered with low cost and rapidly increasing functionality. This thesis presents the integration of a fundamental optical device - Bragg grating - into SOI waveguides. Various types of waveguides and grating structures have been investigated. All designs are fabricated using CMOS foundry services. We have also explored various applications using the fabricated devices. From the beginning, we focused on strip waveguide uniform gratings, as these are the most simple to design and fabricate. We have studied many design variations, supported by experimental results. In parallel, we have provided insight into practical issues and challenges involved with the design, fabrication, and measurement, such as the lithography effects, thermal sensitivity, and wafer-scale nonuniformity. We then introduce phase-shifted gratings that can achieve very high quality factors and be employed in various applications. We have also demonstrated sampled gratings and the Vernier effect in strip waveguides. To obtain narrow-band gratings, we propose the use of a rib waveguide. We also propose a multi-period grating concept by taking advantage of the multiple sidewalls of the rib waveguide, to increases the design flexibility for custom optical filters. The wafer-scale data shows that rib waveguide gratings have better performance uniformity than strip waveguide gratings, and that the wafer thick- ness variation is critical. Additionally, we have demonstrated very compact Bragg gratings using a spiral rib waveguide. Finally, we demonstrate slot waveguide Bragg gratings and resonators, which has great potential for sensing, modulation, and nonlinear optics. We have also developed a novel biosensor using a slot waveguide phase-shifted grating that has a high sensitivity, a high quality factor, a low limit of detection, and can interrogate specific biomolecular interactions.

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