Enhanced light absorption in graphene via a liquid-crystalline optical diode

•One-way device based on liquid-crystalline materials for enhanced optical absorption.•Four-fold enhancement of graphene absorption in the optical regime.•Avoidance of parasitic absorption by use of purely dielectric materials.•Tunability of the frequency window of enhanced optical regime by external means, i.e., strain or field (no need to re- manufacture the device in order to operate in a different spectral regime).•Broadband operation of the enhanced-absorption regime.

We demonstrate theoretically that light absorption in graphene can be boosted via a light-trapping mechanism based on a liquid-crystalline optical diode. The optical diode consists of twisted-nematic and nematic liquid-crystalline slabs. In particular, we show that, using a proper optical-diode setup, the absorption in a single graphene layer can be enhanced by a factor of four. By varying the pitch of the twisted-nematic liquid-crystalline slabs comprising the diode, one can tune the operating spectral region of the diode and thus enhance the absorption of graphene within a desired spectral window. Our calculations are based on Berreman's 4×4 method which treats anisotropic, isotropic and/ or inhomogeneous layered systems on equal footing.