Ultrasensitive Higher-Order Exceptional Points via Non-Hermitian Zero-Index Materials

TL;DR

This paper demonstrates the realization of higher-order exceptional points in non-Hermitian zero-index materials with multiple open channels, leading to ultrasensitive responses suitable for advanced sensing.

Contribution

It introduces a novel approach to achieve higher-order EPs in open scattering systems using wave interference in non-Hermitian zero-index materials, expanding the fundamental understanding and potential applications.

Findings

Identified three types of third-order EPs: lasing, reflecting, and absorbing.

Near the absorbing EP, observed ultrasensitivity with drastic output change.

Showed potential for arbitrary-order EPs in open scattering systems.

Abstract

Higher-order exceptional points (EPs) in optical structures enable ultra-sensitive responses to perturbations. However, previous investigations on higher-order EPs have predominantly focused on coupled systems, leaving their fundamental physics in open scattering systems largely unexplored. Here, we harness wave interference to realize higher-order EPs in non-Hermitian zero-index materials connected to multiple open channels. Specifically, we show that a three-channel model can give rise to three interesting types of third-order EPs: lasing EP, reflecting EP, and absorbing EP. Notably, near the third-order absorbing EP, we show ultrasensitivity -- a drastic change in output power in response to perturbations at the operating frequency -- in a purely lossy system. These findings pave the way for achieving higher-order and even arbitrary-order EPs in open scattering systems, offering significant potential for advanced sensing applications.