Thanks to the superiority in controlling the optical wave fronts, plasmonic nanostructures have led to various striking applications, among which metasurface holograms have been well developed and endowed with strong multiplexing capability. Here, we report a new design of multiplexed plasmonic hologram, which allows for reconstruction of multiple holographic images in free space by scatterings of surface plasmon polariton (SPP) waves in different propagation directions. Besides, the scattered polarization states can be further modulated by arranging the orientations of nanoscatterers. By incorporation of the SPP propagation and polarized scattering, a 4-fold hologram with low crosstalk is successfully demonstrated, which breaks the limitation of only two orthogonal states in conventional polarization multiplexers. Moreover, our design using the near-field SPP as reference wave holds the advantage for compact integration. This holographic approach is expected to inspire new photonic designs with enhanced information capacity and integratability.Keywords: holography; multiplexing; polarization; Surface plasmon;

As one of the recent advances of optics and photonics, plasmonics has enabled unprecedented optical designs. Having a vectorial configuration of surface plasmon field, metallic nanostructures offer efficient solutions in polarization control with a very limited sample thickness. Many compact polarization devices have been realized using such metallic nanostructures. However, in most of these devices, the functions were usually simple and limited to a few polarization states. Here, we demonstrated a plasmonic polarization generator that can reconfigure an input polarization to all types of polarization states simultaneously. The plasmonic polarization generator is based on the interference of the in-plane (longitudinal) field of the surface plasmons that gives rise to versatile near-field polarization states on a metal surface, which have seldom been considered in previous studies. With a well-designed nanohole array, the in-plane field of SPPs with proper polarization states and phases can be selectively scattered out to the desired light beams. A manifestation of eight focusing beams with well-routed polarizations was experimentally demonstrated. Our design offers a new route to achieve the full control of optical polarizations and possibly advance the development in photonic information processing.

On the basis of a novel phase modulation method by in-plane diffraction processes, a well-designed nanoarray on metal surface is proposed to realize a broad band focusing (bandwidth ∼100 nm) and a demultiplexing element (resolution ∼12 nm) of surface plasmon polariton (SPP) waves. Moreover, sublattice arrays are developed to achieve an improved demultiplexer and confocal SPP beams. The proposed scheme with implemented functionalities is designed totally in planar dimension, which is free of the SPP coupling process and indicates more practical application in photonic integrations.