Planar metallic lens based on an array of slits modified by perpendicular cuts

A novel method for beam focusing in plasmonic lenses with an array of nanoslits perforated on a thin metallic film is proposed. Modifying the nanoslits with perpendicular cuts is utilized to change the effective length of the nanoslits which provides the possibility of manipulating the phase front profile based on the propagation property of the Surface Plasmon Polaritons (SPPs) in the metal-insulator-metal (MIM) waveguides. Using the dispersive finite-difference time-domain (D-FDTD) numerical method, simulations are conducted to explore the beam focusing phenomenon and the performance parameters of the lens include the focal length (FL), full-width half-maximum (FWHM) and depth of focus (DOF). The whole structure is formed on a planar thin film which is convenient for miniaturization and high density integration besides that it can be fabricated simply by well-known techniques such as focused ion beam (FIB) milling.