Designing Appointed and Multiple Focuses With Plasmonic Vortex Lenses

A plasmonic vortex lens (PVL), which enables to focus the spin or orbital angular momentum to a specific spatial position in the form of a plasmonic vortex, has been widely studied. Here, we present a specific PVL structure to focus the surface plasmon polariton wave on an arbitrary spatial position. Both analytical and numerical analyses are presented. The plasmonic field of our PVL is an approximate Bessel beam. In particular, the PVL can focus the input beam into a zeroth-order Bessel beam with a central peak. Based on this principle, multiple focuses by combining multiple different PVLs are designed. We can freely control the focuses just by changing the input modes. Owing to the tuning ability of the focuses, these findings can motivate the applications for optical trapping, optical data, and digital display on chip.