Observation of coherent perfect absorption at an exceptional point

TL;DR

This paper experimentally demonstrates a novel type of exceptional point in optical microcavities where absorption properties degenerate, leading to perfect absorption and unique spectral features, opening new avenues in non-Hermitian physics.

Contribution

It introduces and experimentally verifies a new kind of exceptional point based on absorption degeneracy in dissipative optical microcavities, distinct from traditional resonance degeneracies.

Findings

Achieved perfect absorption at an exceptional point.

Observed anomalously broadened absorption lineshape.

Distinguished conditions for resonant and absorbing exceptional points.

Abstract

The past few years have witnessed growing interests in exceptional points (EPs) in various domains, including photonics, acoustics and electronics. However, EPs have mainly been realized based on the degeneracy of resonances of physical systems; distinct degeneracies occur relating to the absorption properties of waves, with distinct physical manifestations. Here we demonstrate this physically different kind of exceptional point, by engineering degeneracies in the absorption spectrum of optical microcavities with dissipation. We experimentally distinguish the conditions to realize a resonant EP and an absorbing EP. Furthermore, when the optical loss is optimized to achieve perfect absorption at such an EP, we observe an anomalously broadened lineshape in the absorption spectra, as predicted by theory. The distinct scattering properties enabled by this type of EP creates new opportunities for both the fundamental study and applications of non-Hermitian singularities.