An apparatus with either a graphene sheet or an epsilon-near-zero layer sandwiched in a waveguide structure and a tuning device. The tuning device is configured to selectively control application of at least first and second gate voltages across the waveguide structure. The graphene sheet has a first dielectric constant which is zero and the waveguide structure operates at a first absorption state and a first propagation distance with application of the first voltage by the tuning device and has a second dielectric constant and the waveguide structure operates at a second absorption state and a second propagation distance with application of the second voltage. The second dielectric constant is larger than the first dielectric constant, the second absorption state is smaller than the first absorption state, the second propagation distance is longer than the first propagation distance, and the second voltage which is zero or smaller than the first voltage.