Ultra-high Q planar silicon microdisk resonators for chip-scale silicon photonics

TLDR

Substrate leakage loss has historically required undercut structures, but we demonstrate that the substrate can serve a beneficial role for passive chip‑scale and active electronic integration. We fabricate and experimentally characterize an ultra‑high‑Q microdisk resonator on a silicon‑on‑insulator platform while investigating how the substrate influences its performance. Two disk‑on‑substrate architectures were optimized and fabricated, and their resonance spectra were compared to theoretical and simulated models to analyze waveguide‑cavity coupling conditions. The devices exhibit a Q of ~3×10⁶ (propagation loss 0.16 dB cm⁻¹), the highest reported for this size on‑substrate resonators, with critical coupling observed at an unloaded Q of ~0.7×10⁶ and good agreement between experiment and theory.

Abstract

We report the fabrication and experimental characterization of an ultra-high Q microdisk resonator in a silicon-on-insulator (SOI) platform. We examine the role of the substrate in the performance of such microdisk resonators. While substrate leakage loss has warranted the necessity of substrate undercut structures in the past, we show here that the substrate has a very useful role to play for both passive chip-scale device integration as well as active electronic device integration. Two device architectures for the disk-on-substrate are studied in order to assess the possibility of such an integration of high Q resonators and active components. Using an optimized process for fabrication of such a resonator device, we experimentally demonstrate a Q approximately 3 x 10(6), corresponding to a propagation loss approximately 0.16 dB/cm. This, to our knowledge, is the maximum Q observed for silicon microdisk cavities of this size for disk-on-substrate structures. Critical coupling for a resonance mode with an unloaded Q approximately 0.7 x 10(6) is observed. We also report a detailed comparison of the obtained experimental resonance spectrum with the theoretical and simulation analysis. The issue of waveguide-cavity coupling is investigated in detail and the conditions necessary for the existence or lack of critical coupling is elaborated.