Experimental demonstration of flexible plasmonic spin-Hall effect and its application on coherent control

Optical spin-Hall effect (OSHE) is a spin-dependent transport phenomenon of light. Here, the spin of light is associated with the circular polarization. Although being observed one decade ago [1], OSHEs are usually extremely weak and in uncontrollable manner owning to the inability to fully control the spin-orbit coupling. Recently, with the development of metasurfaces, the spin-dependent splitting of light beam can be significantly enhanced by using metamaterials [2]. Many attentions have been paid to the spin-orbit interaction (SOI) of light using geometric-phase enabled optical and plasmonic systems. However, these previous works on OSHE only demonstrated simple and symmetric splitting of the two spins [1–4], far from the capability to generate independent OSHEs, which can then work coherently together for more flexible and tunable functionalities. Here, we present a plasmonic metasurface consisting of an array of nano-slots with tailor-made orientation profiles to generate independent surface plasmon polariton (SPP) patterns on the metasurface with the two incident spins [5]. For example a “cross” pattern for one spin and a “triangle” pattern for another as incidence. With such flexible control of OSHEs, we also demonstrate that it is possible to make the two spins work coherently together by controlling the relative phase between the two polarizations. It allows us to play motion pictures, for example, to write a letter “b” with a series of picture frames by varying the phase difference between the two spins. Our work may stimulate more applications in near-field optics, such as optical integrated circuits, tip-free near-field scanning optical microscopy, and plasmonic tweezers to trap and move micron size particles.