Electrically Tunable Optical Absorption in a Graphene-based Salisbury Screen

TL;DR

This paper demonstrates an electrically tunable optical absorption device using a graphene-based Salisbury screen, achieving significant absorption modulation at mid-infrared wavelengths through electrical gating.

Contribution

It introduces a novel graphene Salisbury screen with active electrical tuning of absorption, combining spectroscopic measurements and theoretical modeling for analysis.

Findings

Achieved ~6% change in optical absorption via gate bias tuning.

Designed for maximum absorption at 3.2 micrometers using a silica spacer.

Validated the tuning mechanism with transfer matrix and coupled mode theory.

Abstract

We demonstrate a graphene-based Salisbury screen consisting of a single layer of graphene placed in close proximity to a gold back reflector. The light absorption in the screen can be actively tuned by electrically gating the carrier density in the graphene layer with an ionic liquid/gel. The screen was designed to achieve maximum absorption at a target wavelength of 3.2 micrometer by using a 600 nm-thick, non-absorbing silica spacer layer. Spectroscopic reflectance measurements were performed in-situ as a function of gate bias. The changes in the reflectance spectra were analyzed using a Fresnel based transfer matrix model in which graphene was treated as an infinitesimally thin sheet with conductivity given by the Kubo formula. Temporal coupled mode theory was employed to analyze and intuitively understand the observed absorption changes in the Salisbury screen. We achieved ~ 6 % change in the optical absorption of graphene by tuning the applied gate bias from 0.8 V to 2.6 V, where 0.8 V corresponds to graphene's charge neutrality point.