Excitation and manipulation of both magnetic and electric surface plasmons.

Abstract

Surface plasmons (SPs) is the cornerstone in terahertz (THz) near-field photonics, which play crucial roles in the miniaturization and integration of functional devices. The excitation and manipulation of SPs, however, is currently restricted to electric SPs paradigm, while magnetic SPs receive less attention despite the importance of magnetic light-matter interactions. Here, a scheme is proposed to simultaneously convert the propagating waves in free space into magnetic and electric SPs using a single ultracompact device. First, a plasmonic structure composed of connected slit rings is designed and demonstrated to support both electric and magnetic SPs, which is ascribed to the two distinct eigenmodes of oscillating electrons and vortex currents, respectively. Second, with the assistance of an anisotropic and gradient metasurface, orthogonal linear polarized components of incident THz beams are coupled into different electric and magnetic SP channels with little crosstalk. Furthermore, by encoding two distinct polarization-dependent phase profile into the metasurface, it is shown that the resulting meta-device can individually tailor the wavefronts of magnetic and electric SPs, thus simultaneously engineering magnetic and electric near-field distributions. This work can pave the road to realize bi-channel and on-chip devices, and inspire more integrated functionalities especially related to near-field manipulations of magnetic SPs.