Breaking the spin-orbital angular momentum degeneracy in a novel plasmonic metachain. Plasmonic metasurfaces hold great promise for both fundamental investigation of light's spin-orbit interactions and applied research for nanophotonic chips. However, previous demonstrations fail to distinguish the spin and orbital angular momentum components in a plasmonic field, due to the spin-orbit coupling in a nonparaxial plasmonic field, which leads to the total angular momentum of this field to be degenerate. The total angular momentum is a conserved physical quantity: j=s+l, where s and l are the spin and orbital angular momentum of incident light, respectively. Previous plasmonic metasurfaces can only separate and sort different j, failing to distinguish its spin and orbital components. For instance, both incidences of light with (s=-1, l=1) and (s=1, l=-1) lead to the same total angular momentum of 0 and hence the same plasmonic field formed by previous plasmonic metasurfaces.

This study designed a nanoplasmonic metachain to distinguish any chirality (s) and topological charge (l) of incident light. A plasmonic metachain curvature was designed to achieve the spin-to-orbital conversion, which additionally implements the Pancharatnam–Berry phase through the nanoslit structures. This method demonstrates a flexible way to modulate plasmonic fields in a reconfigurable fashion, which may lead to many benefits across fields of plasmonics, integrated optics, and nanophotonics.

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