High-Q exterior whispering gallery modes in a metal-coated microresonator

TL;DR

This paper introduces a novel exterior plasmonic whispering gallery mode in a metal-coated microresonator that exhibits high quality factors at room temperature and can be used for highly sensitive biosensing applications.

Contribution

It presents the design and analysis of exterior whispering gallery modes with high Q-factors, enabling efficient excitation and strong coupling with interior modes for biosensing.

Findings

High-Q exterior modes localized on the microresonator surface.

Efficient excitation of exterior modes by tapered fiber.

Biosensor sensitivity up to 500 nm per refractive index unit.

Abstract

We propose a kind of plasmonic whispering gallery modes highly localized on the exterior surface of a metal-coated microresonator. This exterior (EX) surface mode possesses high quality factors at room temperature, and can be efficiently excited by a tapered fiber. The EX mode can couple to an interior (IN) mode and this coupling produces a strong anti-crossing behavior, which not only allows conversion of IN to EX modes, but also forms a long-lived anti-symmetric mode. As a potential application, the EX mode could be used for a biosensor with a sensitivity high up to 500 nm per refraction index unit, a large figure of merit, and a wide detection range.