Inter-mode reactive coupling induced by waveguide-resonator interaction

TL;DR

This paper investigates how a waveguide coupled to a microresonator causes reactive inter-mode coupling, leading to unique Fano lineshapes, validated through theory, simulations, and experiments.

Contribution

It introduces the concept of waveguide-induced reactive inter-mode coupling in microresonators, supported by theoretical analysis, numerical simulations, and experimental validation.

Findings

Reactive coupling causes Fano lineshapes in transmission spectra

Theoretical predictions match numerical simulations and experiments

Waveguide-resonator interaction induces off-diagonal Lamb shift-like effects

Abstract

We report on a joint theoretical and experimental study of an integrated photonic device consisting of a single mode waveguide vertically coupled to a disk-shaped microresonator. Starting from the general theory of open systems, we show how the presence of a neighboring waveguide induces reactive inter-mode coupling in the resonator, analogous to an off-diagonal Lamb shift from atomic physics. Observable consequences of this coupling manifest as peculiar Fano lineshapes in the waveguide transmission spectra. The theoretical predictions are validated by full vectorial 3D finite element numerical simulations and are confirmed by the experiments.