Thermochromic modulation of surface plasmon polaritons in vanadium dioxide nanocomposites.

We propose and implement a new concept for thermochromic plasmonic elements. It is based on vanadium dioxide (VO₂) nanocrystals located in the near field of surface plasmon polaritons supported by an otherwise unstructured gold thin film. When the VO₂ undergoes the metal-insulator phase transition, the coupling conditions for conversion of light into propagating surface plasmon polaritons change markedly. In particular, we realize thermochromic plasmonic grating couplers with substantial switching contrast as well as tunable plasmonic couplers in a Kretschmann configuration. The use of VO₂ nanocrystals permits highly repetitive switching and room temperature operation. Simulations based on the actual dielectric function of our VO₂ nanocrystals agree well with the experiment.