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.