Critical coupling vortex with grating-induced high quality optical Tamm states

TL;DR

This paper explores how dielectric gratings on Bragg reflectors can support optical Tamm states that become bound states in the continuum, leading to critical coupling with zero reflectance, explained via coupled mode theory.

Contribution

It introduces the concept of vortex-induced critical coupling in optical Tamm states supported by dielectric gratings, revealing new conditions for bound states in the continuum.

Findings

Bound states in the continuum can be achieved with dielectric gratings on Bragg reflectors.

Critical coupling occurs at the vortex core of the reflection amplitude.

Coupled mode theory explains the emergence of the vortex in the reflection space.

Abstract

We investigate optical Tamm states supported by a dielectric grating placed on top of a distributed Bragg reflector. It is found that under certain conditions the Tamm state may become a bound state in the continuum. The bound state, in its turn, induces the effect of critical coupling with reflectance amplitude reaching an exact zero. We demonstrate that the critical coupling point is located in the core of a vortex of the reflection amplitude gradient in space of wavelength and angle of incidence. The emergence of the vortex is explained by the coupled mode theory.