Flat Helical Nanosieves

Compact and miniaturized devices with flexible functionalities are always highly demanded in optical integrated systems. Plasmonic nanosieve has been successfully harnessed as an ultrathin flat platform for complex manipulation of light, including holography, vortex generation, and nonlinear processes. Compared with most of the reported single‐functional devices, multifunctional nanosieves might find more complex and novel applications across nanophotonics, optics, and nanotechnology. Here, a promising roadmap for nanosieve‐based helical devices is experimentally demonstrated, which achieves full manipulations of optical vortices, including its generation, hybridization, spatial multiplexing, focusing and nondiffraction propagation, etc., by controlling the geometric phase of spin light via over 121 thousands of spatially rotated nanosieves. Thanks to such spin‐conversion nanosieve helical elements, it is no longer necessary to employ the conventional two‐beam interferometric measurement to characterize optical vortices, while the interference can be realized natively without changing any parts of the current setup. The proposed strategy makes the far‐field manipulations of optical orbital angular momentum within an ultrathin interface viable and bridges singular optics and integrated optics. In addition, it enables more unique extensibility and flexibility in versatile optical elements than traditional phase‐accumulated helical optical devices. A nanosieve array is endowed with the abilities of full manipulations of electromagnetic waves. Its phase encoding is especially investigated in beam forming/steering, imaging, and many other significant applications. Based on the double‐ring nanosieves, a novel class of helical optical devices is proposed and demonstrated with a (almost) complete set of various designs for vortex generation, multiplexing, interaction, focusing, and interference.