Broadband plasmonic switches based on nanodisc-dimers with progressively increasing diameters on a plasmonic film with a VO2 spacer

Abstract

In this paper, we propose active broadband plasmonic switches based on a periodic array of metallic dimers of nanodiscs with progressively increasing diameters on a gold coated SiO 2 substrate with a VO2 thin film as a spacer between the nanodiscs and the underlying plasmonic substrate. Periodic arrays based on unit cells with plasmonic nanodisc dimers of varying diameters are employed to couple multiple wavelengths of the incident radiation into the plasmonic modes of the nanostructure, which results in a broadband plasmonic response. We employ a vanadium dioxide (VO2) thin film as a spacer between these periodic sets of plasmonic nanodisc-dimers and the underlying gold coated substrate to achieve broadband switching. On exposure to voltage, infrared light or heat, the VO2 spacer layer changes from its semiconducting state to its metallic state. This transformation leads to significant changes in its optical properties leading to changes in the reflectance spectra of the proposed nanostructure. This results in an efficient switching action over wide range of wavelengths spanning the C, L and U bands of optical communication. We demonstrate a broadband extinction ratio of 5 dB over an operating wavelength range of 650 nm spanning from 1460 nm to 2110 nm, and a broadband extinction ratio of 4 dB over an operating wavelength range of 702 nm spanning from 1432 nm to 2134 nm. In addition, we demonstrate the trade-off between the extinction ratio and the operating wavelength range of these switches. An exhaustive analysis of these switches has been carried out using finite difference time domain (FDTD) modelling to demonstrate that the spectral range over which switching can be achieved by employing these switches can be varied by varying the geometrical parameters of the proposed switches and thus these switches offer the flexibility of being employed for different wavelength regimes. These switches can be potentially employed in optical communication networks or as switching elements in plasmonic circuits.