Photoswitchable exceptional points derived from bound states in the continuum

TL;DR

This paper explores the transition from bound states in the continuum to exceptional points in non-Hermitian systems, demonstrating experimental control and applications in terahertz beam steering.

Contribution

It reveals the transition process from BICs to EPs in a non-Hermitian system and demonstrates dynamic EP switching using external pumping in dielectric metasurfaces.

Findings

Transition from BIC to EP in a two-mode system

Experimental validation in terahertz dielectric metasurfaces

Switchable terahertz beam deflection via EP phase singularities

Abstract

Bound states in the continuum (BICs) and exceptional points (EPs), as two distinct physical singularities represented by complex frequencies in non-Hermitian systems, have garnered significant attention and clear definitions in their respective fields in recent years. They share overlapping applications in areas such as high-sensitivity sensing and laser emission. However, the transition between the two, inspired by these intersections, remains largely unexplored. In this work, we reveal the transition process in a non-Hermitian two-mode system, evolving from one bound singularity to a two-dimensional exceptional ring, where the EP is the coalescent state of the quasi-Friedrich-Wintgen (FW)-BIC. This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band. Furthermore, external pumping induced photocarriers as the dissipative perturbation, facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching. Finally, we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP. These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.