Reflective chiral meta-holography: multiplexing holograms for circularly polarized waves

By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.However,holography with circularly polarized waves remains complicated as the achiral building blocks of existing meta-holograms inevitably contribute to holographic images generated by both left-handed and right-handed waves.Here we demonstrate how planar chirality enables the fully independent realization of high-efficiency meta-holograms for one circular polarization or the other.Such circular-polarization-selective meta-holograms are based on chiral building blocks that reflect either left-handed or right-handed circularly polarized waves with an orientation-dependent phase.Using terahertz waves,we experimentally demonstrate that this allows the straightforward design of reflective phase meta-holograms,where the use of alternating structures of opposite handedness yields independent holographic images for circularly polarized waves of opposite handedness with negligible polarization cross-talk.

Two-dimensional control of light with light on metasurfaces

The ability to control the wavefront of light is fundamental to focusing and redistribution of light,enabling many applications from imaging to spectroscopy.Wave interaction on highly nonlinear photorefractive materials is essentially the only established technology allowing the dynamic control of the wavefront of a light beam with another beam of light,but it is slow and requires large optical power.Here we report a proof-of-principle demonstration of a new technology for two-dimensional(2D)control of light with light based on the coherent interaction of optical beams on highly absorbing plasmonic metasurfaces.We illustrate this by performing 2D all-optical logical operations(AND,XOR and OR)and image processing.Our approach offers diffractionlimited resolution,potentially at arbitrarily-low intensity levels and with 100 THz bandwidth,thus promising new applications in space-division multiplexing,adaptive optics,image correction,processing and recognition,2D binary optical data processing and reconfigurable optical devices.

All-optical dynamic focusing of light via coherent absorption in a plasmonic metasurface

Vision,microscopy,imaging,optical data projection and storage all depend on focusing of light.Dynamic focusing is conventionally achieved with mechanically reconfigurable lenses,spatial light modulators or microfluidics.Here we demonstrate that dynamic control of focusing can be achieved through coherent interaction of optical waves on a thin beam splitter.We use a nanostructured plasmonic metasurface of subwavelength thickness as the beam splitter,allowing operation in the regimes of coherent absorption and coherent transparency.Focusing of light resulting from illumination of the plasmonic metasurface with a Fresnel zone pattern is controlled by another patterned beam projected on the same metasurface.By altering the control pattern,its phase,or its intensity,we switch the lens function on and off,and alter the focal spot’s depth,diameter and intensity.Switching occurs as fast as the control beam is modulated and therefore tens of gigahertz modulation bandwidth is possible with electro-optical modulators,which is orders of magnitude faster than conventional dynamic focusing technologies.