Dual-channel graphene-based optical metasurface switch at telecommunication wavelengths

We theoretically present the concept of a dual-channel optical metasurface switch, operating at the telecommunication wavelengths of 1.53 μm and 1.57 μm. The switching exploits two Fano resonant peaks produced by two pairs of asymmetric silicon nano-bars stacked vertically- with each pair acting as optical resonators. We have explored two types of asymmetricity in silicon nano-bars viz. asymmetry in width and length. The Fano resonances of these silicon nano-bars could be tuned independently between ‘ON’ and ‘OFF’ states by changing the Fermi potential (Ef) of the graphene sheet placed beneath each optical resonator. Transmission greater than 55% at a potential of Ef =0.75 eV refers to the switch in the ON state, and less than 55% refers to switch in the OFF state for Ef =0 eV. We also demonstrate four possible combinations of the optical switch viz. “ON-ON, ON-OFF, OFF-ON, OFF-OFF” depending on the potential applied to the corresponding graphene sheet. The contrast ratio is 12.54 dB and 18.42 dB for the two switches at 1.53 μm and 1.57 μm respectively.