Optical Vortex Transmutation with Geometric Metasurfaces of Rotational Symmetry Breaking

The free-space optical vortex transmutation is realized by using geometric plasmonic metasurfaces with the designed noncanonical vortex phase profiles possessing discrete rotational symmetries of finite order. Based on the introduced continuous-to-discrete rotational symmetry breaking in metasurfaces, the vortex transmutation phenomena are observed behind the metasurfaces from the near-field to far-field diffraction in free space. The near-field optical beam profile represents the input vortex, while in the far field the input vortex is diffracted into the central output vortex with topological charge determined by the transmutation rule and the symmetrically distributed off-axis vortices with unity topological charge bifurcating from the input vortex, with the total orbital angular momentum conserved. The demonstrated free-space optical vortex transformation will promise many potential applications related to optical communication, particle manipulation, and quantum information processing.