Graphene-dielectric integrated terahertz metasurfaces

In this paper we discuss graphene-dielectric integrated terahertz metasurfaces as an alternative approach to graphene-metal metamaterials for providing effective control of electromagnetic beam propagation at terahertz wavelengths. Our structures consist of a passive lossless dielectric pattern and a reconfigurable graphene sheet whose terahertz optical conductivity could be actively tuned chemically, electrically, or optically. In particular, we investigate dielectric patterns consisting of pillar- and circular hole arrays and show that via optimizing the geometric dimensions in these patterns it is possible to attain almost complete terahertz absorption at an arbitrary frequency of interest. Furthermore, via either (i) controlling the thickness of a low-index dielectric spacer located between the dielectric pattern and the graphene sheet, or (ii) choosing a material with an appropriate index of refraction when constructing the dielectric pattern, it is possible to control the sensitivity of the overall structure to variations in the graphene sheet conductivity. Full-wave electromagnetic simulations are supported by proof-of-principle experiments on structures fabricated via patterning of a silicon-on-insulator wafer followed by graphene transfer and chemical doping. Overall, the proposed approach can lead to the construction of efficient tunable terahertz absorbers; however, other tailored electromagnetic responses might be also possible via the selection of appropriate dielectric patterns.