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Variable optical attenuation and optical modulation are essential operations in integrated photonic circuits. A new graphene plasmonic gap waveguide structure, which possesses the functions of variable optical attenuator and modulator, is proposed and numerically investigated. The propagation and attenuation modes of the structure can be realized by tuning the gate-voltage. The result shows that it can achieve great modulation depth per micrometer and the working frequency range of 8 THz or more for the variable optical attenuator and the modulator. It also has the advantages of high tolerance, large attenuation range/ modulation depth, wide bandwidth and high integration without crosstalk, which would be promising for high integrated optical circuits. [ABSTRACT FROM AUTHOR]

Graphene metasurface has attracted a lot of attentions due to the unique tunability for exotic electromagnetic properties. In this work, we propose and numerically investigate a tunable metasurface with two non-coplanar and inter-perpendicular graphene nanoribbon arrays. The variation of transmission at different substrate thickness and the coupled mode are analyzed. It is shown that the Rabi-like splitting can be achieved by the coupling between localized and delocalized graphene surface plasmon polaritons. Tunable coupling strength and positions with different gate-voltages have been discussed. The effect of relaxation time and oblique incidences to resonant responses are also investigated. Additionally, we find an optical analogue of a spring, where the spectral dip vibrates around its equilibrium position at a certain wavelength. Our study suggests that the proposed structure is potentially attractive for realization of tunable double-channel filter, optical switch, and variable optical attenuator based on the graphene metasurface. [ABSTRACT FROM AUTHOR]