Effect of polarization on symmetry of focal spot of a plasmonic lens

Abstract

When one uses a metallic nanostructure to excite surface plasmon polaritons (SPPs) for subwavelength focusing, there is the distinct shape of the light emerging from the plasmonic lens in the transverse directions due to 2D confinement of SPPs. To study the tuning of symmetry of a focal spot, we consider an annular plasmonic lens incident with a polarized plane wave having various polarization states, including circular polarization (CP), elliptical polarization (EP), and radial polarization (RP), compared to linear polarization (TM). We find that plasmonic modes are independent of the polarization approach and the different polarization states enable to tune transverse electric field. More specifically, for CP case where the phase function Re[exp(itheta)]=0, the total-electric-field intensity is distributed uniformly in the transverse plane, while for RP case where the phase function Re[exp(itheta)]=1, a significant intensity contrast is observed in the two diagonal directions. We show an agreement between the analytical description and numerical simulation.