J. Opt. 16, 105005 (2014)
Almir Wirth Lima and Antonio Sérgio Bezerra Sombra at the University of Ceará in Brazil have theoretically proposed a scheme for realizing a nanophotonic switching cell that takes advantage of the unique electronic properties of graphene. It is well known that the transportation of electrons in graphene sheets is governed by the Dirac equation and that they propagate as if they were massless. Furthermore, the Dirac-cone-shaped dispersion characteristics of graphene can be modified using an externally applied voltage. The authors build on these two properties to design a switching cell that operates in the infrared and terahertz frequency ranges. The device comprises a directional coupler and two graphene nanoribbons that are used as waveguides. They are separated vertically and embedded in a boron nitride substrate — a material chosen due to its low impact on the properties of graphene. When optical power is fed into one of the two ports, bar operation (in which power exits from the opposite end of the same waveguide) or cross operation (power exits from the adjacent waveguide) of the cell is determined by the value of the graphene nanoribbon's dielectric constant. The externally applied voltage changes the chemical potential, allowing the dielectric constant to be fine-tuned to the desired value.
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