Accurate Nanofabrication Techniques for High-Index-Contrast Microphotonic Devices

Abstract

High-refractive-index-contrast microphotonic devices provide strong light confinement allowing for sharp waveguide bends and small dielectric optical resonators. They allow dense optical integration and unique applications to optical filters and sensors but present exceptional complications in design and fabrication. In this work, nanofabrication techniques are developed to address the two main challenges in fabrication of high-indexcontrast microphotonic devices: sidewall roughness and dimensional accuracy. The work focuses on fabrication of optical add-drop filters based on high-indexcontrast microring-resonators. The fabrication is based on direct-write scanning-electronbeam lithography. A sidewall-roughness characterization and optimization scheme is developed as is the first three-dimensional analysis of scattering losses due to sidewall roughness. Writing strategy in scanning-electron-beam lithography and absolute and relative dimensional control are addressed. The nanofabrication techniques developed allowed fabrication of the most advanced microring add-drop-filters reported in the literature. The sidewall-roughness standarddeviation was reduced to 1.6 nm. The field polarization and the waveguide cross-sections minimizing scattering losses are presented. An absolute dimensional control accuracy of 5 nm is demonstrated. Microring resonators with average ring-waveguide widths matched to 26 pm to a desired relative width-offset are reported.