Oscillatory coupling between a monolithic whispering-gallery resonator and a buried bus waveguide

TL;DR

This study investigates the oscillatory optical coupling between a monolithic whispering-gallery resonator and a buried bus waveguide, revealing unique vertical coupling behavior through combined theoretical and experimental analysis.

Contribution

It introduces an analytical coupled-mode theory model for vertical resonator-waveguide coupling, validated by experiments and simulations, highlighting oscillatory coupling effects.

Findings

Vertical coupling exhibits oscillatory behavior with respect to the gap.

Experimental data shows oscillations in waveguide transmission and Q-factor.

The coupled-mode theory accurately predicts the observed phenomena.

Abstract

We report on a combined theoretical and experimental study of the optical coupling between a microdisk resonator and a waveguide laying on different planes. While the lateral coupling between a planar resonator and a waveguide is characterized by a unique distance at which the resonant waveguide transmission vanishes because of destructive interference, the vertical coupling geometry exhibits an oscillatory behavior in the coupling amplitude as a function of the vertical gap. This effect manifests experimentally as oscillations in both the waveguide transmission and the mode quality factor. An analytical description based on coupled-mode theory and a two-port beam-splitter model of the waveguide-resonator coupling is developed, which compares successfully both to experimental data and numerical simulations.