Coherent perfect absorption in photonic structures

TL;DR

This paper reviews the phenomenon of coherent perfect absorption (CPA) in photonic structures, presenting a revised theory, experimental demonstrations, and discussing the coexistence of strong coupling and critical coupling regimes for enhanced light absorption.

Contribution

It introduces a comprehensive two-port CPA theory based on scattering matrix formalism and demonstrates the coexistence of strong coupling with critical coupling in photonic systems.

Findings

Demonstrated polaritonic CPA in a metamaterial

Verified elliptical absorption trace experimentally

Showed coexistence of strong coupling and critical coupling

Abstract

The ability to drive a system with an external input is a fundamental aspect of light-matter interaction. The coherent perfect absorption (CPA) phenomenon extends to the general multibeam interference phenomenology the well known critical coupling concepts. This interferometric control of absorption can be employed to reach full delivery of optical energy to nanoscale systems such as plasmonic nanoparticles, and multi-port interference can be used to enhance the absorption of a nanoscale device when it is embedded in a strongly scattering system, with potential applications to nanoscale sensing. Here we review the two-port CPA in reference to photonic structures which can resonantly couple to the external fields. A revised two-port theory of CPA is illustrated, which relies on the Scattering Matrix formalism and is valid for all linear two-port systems with reciprocity. Through a semiclassical approach, treating two-port critical coupling conditions in a non-perturbative regime, it is demonstrated that the strong coupling regime and the critical coupling condition can indeed coexist; in this situation, termed strong critical coupling, all the incoming energy is converted into polaritons. Experimental results are presented, which clearly display the elliptical trace of absorption as function of input unbalance in a thin metallo-dielectric metamaterial, and verify polaritonic CPA in an intersubband-polariton photonic-crystal membrane resonator. Concluding remarks discuss the future perspectives of CPA with photonic structures.