Beaming of light through depth-tuned plasmonic nanostructures

A nanostructure comprising dielectric/Ag interface with central slit surrounded by grooves is presented for beam focusing and collimating. Desired phase retardations of the beam emerging through slits are manipulated by tuning the depth of grooves. Numerical simulations are performed through a finite-difference time-domain (FDTD) algorithm. Results reveal the suitability of parabolic depth-tuned structure for enhanced transmission and beam collimation. Enhanced transmission and beam collimation are the result of transportation of electromagnetic energy in the form of surface plasmon polariton (SPP) waves.