Dispersionless Phase Discontinuities for Controlling Light Propagation

Ultrathin metasurfaces consisting of a monolayer of subwavelength plasmonic resonators are capable of generating local abrupt phase changes and can be used for controlling the wavefront of electromagnetic waves The phase change occurs. for transmitted or reflected Wave components whose polarization is orthogonal to that of a linearly polarized (LP) incident wave. As the phase shift relies on the resonant features of the plasmonic structures, it is in general wavelength-dependent. Here, we investigate., the interaction of circularly polarized (CP) light at an interface composed of a dipole antenna array to create spatially varying abrupt phase discontinuities. The phase discontinuity is dispersionless that is, it solely depends on the orientation of dipole antennas, but not their spectral response and the wavelength of incident light By arranging the antennas in an array with a constant phase gradient along the interface, the phenomenon of broadband anomalous refraction,is Observed. ranging from visible to near infrared wavelengths. We further. design and experimentally demonstrate an ultrathin phase gradient interface to generate a broadband optical vortex beam based on the above, principle.