Guided Optical Modes in Metal-Cladded Tunable Hyperbolic Metamaterial Slab Waveguides

Abstract

We have theoretically investigated metal-cladded waveguides of tunable hyperbolic metamaterial (THMM) cores, employing graphene sheets as a tunable layer, in terms of guided waves propagation over near- to mid-infrared range, following the effective medium approximation. We have proven that these subwavelength guiding structures offer a number of effects usually not found in other types of waveguides, including controllable propagation gap and number of modes, inversion of power flow direction with respect to phase velocity, TM mode propagation, and absence of the fundamental mode, which occur as a result of controlled change of the guiding layer dispersion regime. This is the first time that the above-mentioned effects are obtained with a single, voltage-controlled waveguiding structure comprising graphene sheets and a dielectric, although the presented methodology allows us to incorporate other tunable materials beyond graphene equally well. We believe that such or similar structures, feasible by means of current planar deposition techniques, will ultimately find their practical applications in optical signal processing, controlled phase matching, controlled coupling, signal modulation, or the enhancement of nonlinear effects.