Concentric Microresonators Design For Dispersion Engineering and Scalable Electron-Beam Lithography for Si and SiN Photonic Platforms
Silicon (Si) and silicon nitride (SiN) photonic integrated circuits (PICs) are vital platforms for compact, low-loss, and scalable optical systems. In most PIC applications, waveguides, microresonators, and subwavelength gratings (SWGs) serve as the fundamental building blocks for realizing diverse on-chip optical functionalities. Despite extensive advances in design and fabrication, further progress requires new approaches that integrate accurate modeling with robust nanofabrication. This dissertation develops design frameworks and fabrication techniques that expand the performance and integration capabilities of Si and SiN devices. A geometry-guided modeling method is introduced for concentric ring resonators, allowing rapid identification of phase-matched geometries without exhaustive parameter sweeps. This enables dispersion engineering in regimes previously inaccessible. On the fabrication side, a robust subtractive electron-beam lithography (EBL) process is established for the silicon-on-insulator (SOI) platform, enabling reliable pattern transfer from sub-50 nm to micrometer-scale structures. Using this process, corrugated Bragg gratings for optical filtering and subwavelength gratings for refractive-index sensing were fabricated and experimentally validated. A second lithography process was developed for a 300 nm SiN platform, employing a tunable negative-resist system that supports diverse device geometries. Using this process, an exceptional-point (EP) waveguide was demonstrated with symmetric transmission and constant radiation at the EP wavelength. Additionally, a dual-bus racetrack resonator for broadband coupling was fabricated on both Si and SiN platforms using a common design framework. Together, these results advance the design and fabrication of Si and SiN PICs, providing new tools for dispersion control, spectral shaping, and scalable photonic integration. The demonstrated methods lay the groundwork for next-generation photonic technologies spanning communications, quantum information, sensing, free-space beam shaping, and nonlinear optics.
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