Extreme Miniaturization of Silicon Add–Drop Microring Filters for VLSI Photonics Applications

We theoretically and experimentally investigated the performance of silicon-on-insulator (SOI) microring add–drop filters in the limit of extreme miniaturization for potential application in very dense integration of silicon photonic devices. Rigorous numerical analyses were performed to predict the theoretical limit of achievable intrinsic quality factors as the microring radius is scaled down to 1 $\mu\hbox{m}$. Experimental measurements of fabricated SOI microring resonators showed that ultracompact add–drop microring filters with radii as small as 1 $\mu \hbox{m}$ can be achieved with a free spectral range exceeding 80 nm and an insertion loss of only 1 dB. These devices are also shown to exhibit intrinsic quality factors approaching the theoretically achievable limit set by the bending loss in ultracompact microring resonators.