Tuning the focus of a plasmonic lens by anisotropic material

A type of tunable plasmonic lens with nanoslits is proposed for subwavelength imaging. The nanoslits array in the plasmonic lens, which have constant depths but varying widths, could generate desired optical phase retardations based on the particular propagation property of the Surface Plasmon Polaritons (SPPs) in the metal-insulator-metal slit waveguides. We numerically demonstrate the tunability of a single plasmonic lens by use of anisotropic materials. Our numerical simulations with finite-difference time-domain (FDTD) technique reveal that the focus length can be controlled easily by imposing constant external electric field. Special characteristic of presented structure gives an opportunity to be used as an efficient element in high integrated optical device.