Plasmonic switches based on arrays of plasmonic nanostructures surrounded by VO2 thin films

We describe plasmonic switches consisting of 1-D arrays of plasmonic nanostructures such that they have thin films of vanadium-dioxide (VO2) in the vicinity of the plasmonic nanostructures. A multi-wavelength plasmonic switch is presented based on one dimensional plasmonic, asymmetric narrow-groove nanogratings (ANGN), coated with a thin layer of VO2. Incident optical radiation is coupled into plasmonic waveguide modes in metallic narrow-groove nanogratings leading to a localization of electromagnetic fields inside the narrow grooves. The switching is exhibited due to coating of a thin layer of VO2 - a material whose phase changes from semiconductor to metal on exposure to heat, IR radiation or voltage. As the phase of VO2 changes, it undergoes a change in its dielectric and optical properties. This phase transition in the thin layer of VO2 coated on the nanograting changes the overall optical response from the nanograting, thus exhibiting a switching in the reflectance spectra. The switchability is analyzed through the differential reflectance spectrum which is obtained by subtracting the reflectance spectra of VO2 (M) coated ANGNs from the reflectance spectra of VO2 (S) coated ANGNs. Asymmetry is created in these narrow-groove nanogratings by choosing different values for the narrow-groove gaps. Rigorous coupled wave analysis (RCWA) and finite difference time domain (FDTD) modeling demonstrates that - due to the presence of asymmetric groove widths - the incident light is coupled into plasmonic modes in all the grooves at different resonant wavelengths. The presence of several resonant wavelengths in reflectance spectra of ANGNs gives rise to multiple dips and peaks in the differential reflectance spectra, thus exhibiting multiple switching wavelengths. Thus, these asymmetric plasmonic narrow-groove nanogratings can be employed for switching at multiple wavelengths.