Broadband Omni-resonant Coherent Perfect Absorption in Graphene

TL;DR

This paper demonstrates a broadband omni-resonant coherent perfect absorption technique using graphene in a planar cavity, significantly enhancing absorption over a wide spectrum by pre-conditioning incident light.

Contribution

It introduces a novel method for achieving broadband CPA by angular dispersion and cavity placement, challenging conventional placement requirements.

Findings

Optical absorption in graphene boosted from 1.6% to 60%.

Achieved ~70 nm bandwidth in visible spectrum.

Analytical model confirms cavity placement flexibility.

Abstract

Coherent perfect absorption (CPA) refers to interferometrically induced complete absorption of incident light by a partial absorber independently of its intrinsic absorption (which may be vanishingly small) or its thickness. CPA is typically realized in a resonant device, and thus cannot be achieved over a broad continuous spectrum, which thwarts its applicability to photodetectors and solar cells, for example. Here, we demonstrate broadband omni-resonant CPA by placing a thin weak absorber in a planar cavity and pre-conditioning the incident optical field by introducing judicious angular dispersion. We make use of monolayer graphene embedded in silica as the absorber and boost its optical absorption from ~1.6% to ~60% over a bandwidth of ~70 nm in the visible. Crucially, an analytical model demonstrates that placement of the graphene monolayer at a peak in the cavity standing-wave field is not necessary to achieve CPA, contrary to conventional wisdom.