Efficient analysis and design of low-loss whispering-gallery-mode coupled resonator optical waveguide bends

TL;DR

This paper presents a rigorous 2D analysis of coupled resonator optical waveguide bends, revealing mechanisms of whispering gallery mode coupling and proposing design strategies to minimize bend losses.

Contribution

It introduces a detailed boundary integral equations method for analyzing finite-size CROW bends and offers novel design guidelines for low-loss optical waveguide bends.

Findings

Differences in WG mode coupling near bends for various microcavity sizes.

Identification of specific bend angles that reduce losses.

Strategies for tuning microdisk radii to optimize bend performance.

Abstract

Waveguides composed of electromagnetically-coupled optical microcavities (coupled resonator optical waveguides or CROWs) can be used for light guiding, slowing and storage. In this paper, we present a two-dimensional analysis of finite-size straight and curved CROW sections based on a rigorous Muller boundary integral equations method. We study mechanisms of the coupling of whispering gallery (WG) modes and guiding light around bends in CROWs composed of both identical and size-mismatched microdisk resonators. Our accurate analysis reveals differences in WG modes coupling in the vicinity of bends in CROWs composed of optically-large and wavelength-scale microcavities. We propose and discuss possible ways to design low-loss CROW bends and to reduce bend losses. These include selecting specific bend angles depending on the azimuthal order of the WG mode and tuning the radius of the microdisk positioned at the CROW bend.