Graphene lenses (which has a unique haxegonal 3-D structure that contributes to its unique optical properties) involve sandwiching an insulating barrier of Ta2O5 between two graphene sheets, where the sheets become electrically isolated and exhibited an average Fermi difference of 0.12eV when a current was passed through the bottom layer.
The unique honeycomb 2-D structure of graphene contributes to its unique optical properties. 
