Pathway interference in a loop array of three coupled microresonators

TL;DR

This paper investigates a loop array of three coupled microresonators, revealing phase-sensitive interference effects in light transmission and reflection, with potential applications in nanoparticle detection and refractive index sensing.

Contribution

It introduces the concept of pathway interference and phase sensitivity in a loop microresonator system, supported by analytical and numerical Maxwell's equations simulations.

Findings

Transmission and reflection spectra show phase-dependent interference effects

The system's optical properties are highly sensitive to coupling and scattering phase changes

Potential for high-precision nanoparticle and refractive index sensing

Abstract

A system of three coupled toroidal microresonators arranged in a loop configuration is studied. This setup allows light entering the resonator setup from a tapered fiber to evolve along a variety of different pathways before leaving again through the fiber. In particular, the loop configuration of the resonators allows for an evolution which we term roundtrip process, in which the light evolves from one resonator sequentially through all others back to the initial one. This process renders the optical properties of the system sensitive to the phases of all coupling and scattering constants in the system. We analyze the transmission and reflection spectra, and interpret them in terms of interference between the various possible evolution pathways through the resonator system. In particular, we focus on the phase dependence of the optical properties. Finally, we discuss possible applications for this phase sensitivity induced by the roundtrip process, such as the measurement of the position of a nanoparticle close to one of the resonators, and the measurement of changes in the refractive index between two resonators. Our analytical results for the applications are supported by proof-of-principle calculations based on finite-difference-time-domain solution ofMaxwell's equations in two dimensions on a grid.