Theory and Design of Off-Axis Microring Resonators for High-Density On-Chip Photonic Applications

In this paper, we have developed a theory of an off-axis microring resonator (MRR) with single and multiple off-axis rings. The off-axis inner ring introduces tunable extra notches with many striking features in the transmission spectrum which facilitates its use as efficient modulators and sensors. A few such notches when closely packed have been used to design a compact band rejection filter with improved bandwidth (>10 nm). Moreover, these closely packed extra notches achieved by serially coupled MRRs with off-axis inner rings are tunable to reject arbitrarily chosen WDM channels. Through numerical simulations, based on both transfer matrix method and finite difference time domain method, it has been examined that off-axis MRRs cater superior performances in comparison to the serially coupled conventional MRR with respect to the device size, faster response, and low dispersion. The proposed off-axis MRRs may be used for cluster to cluster interconnects and can have other potential on-chip photonic applications in network layer. Necessary design parameters are computed from the coupled mode theory.