Coupling-gap free integrated microresonator: Theory and experimental analysis

Abstract

Microring resonators (MRRs), typically comprising straight and ring waveguides, have played pivotal importance in recent years as far as integrated on-chip systems are concerned. The evanescent coupling in such MRR or solid microdisk resonators is very sensitive to the coupling gap between two waveguides, which affects the resonator’s performance. To overcome the stringent requirement of the gap between two waveguides, we propose a coupling-gap-free, on-chip ellipsoid microresonator. The theoretical framework has been deduced to attain the modal properties of such integrated microresonator geometry, which shows an excellent agreement with the finite difference time domain simulations and experimental results. The absence of a coupling region makes the device uniquely compact and robust, with an insertion loss of ∼5 dB. The resonator’s geometrical dimensions can also be conveniently scaled within certain constraints. The proposed device can be a potential alternative to MRRs and could help in applications such as optical filters, delay lines, on-chip sensing, and many more.