Graphene surface plasmon waveguides incorporating high-index dielectric ridges for single mode transmission

We report a novel plasmonic waveguide by incorporating a uniformly-biased graphene sheet over a high-index ridge. The fundamental mode in the proposed waveguide concentrates in the low-index low-loss gap, which is easier to excite and leads to longer propagation length than that of graphene ribbon waveguides׳, where the field is mostly confined at the high-loss graphene edges. The single mode transmission can be achieved at far-infrared regime without the hard-to-fabricate, ultra-narrow ribbon that results in extra material loss. Instead of the reflection mechanism at the ribbon edges, the optical field is laterally confined by the effective index difference of graphene plasmons due to the ridge. The results based on the effective index method (EIM) have been validated by finite-element simulations at each stage. Rapid design and optimization is carried out by EIM without requiring further extensive numerical computations. The presented waveguide might be employed in integrated wafer-scale photonic systems to enable high performance graphene-based devices.