Controlling The Light With Plasmonic Metasurfaces

Surface plasmons(SPs)are waves that exist at the interface between two materials whose real parts of the dielectric functions are opposite in sign(e.g.a metal-dielectric interface,including a metal sheet in air).They are the combinations of electromagnetic waves and the surface electron oscillations.There are two types of SPs:surface plasmon polaritons(SPPs)at planar interfaces,and localized surface plasmons(LSPs)for the closed surfaces of small particles.SPs have tight spatial confinement and high local field intensity.They have shown great potential in sub-wavelength optics.The properties of SPs can be tailored by constructing nano-structures at the interfaces.Plasmonic metasurfaces are the materials that comprise artificial sub-wavelength metal nano-structures.On the basis of the concept of LSPs,one can control the light by altering the materials and the geometries of the nano-structures.Metasurfaces have achieved many interesting optical properties such as anomalous reflection and refraction,focusing,hologram,etc.In this paper,we design and demonstrate three metasurfaces.Their properties are studied by theoretical analyses along with numerical simulations.We obtain a uni-directional source of SPPs,high-efficiency anomalous refraction,and a multi-functional metasurface.They are expected to be useful in integrated optical devices.First,we introduce a uni-directional source of SPPs.We use aperture antennas with different geometries to excite the SPPs.These SPPs will be superposed.By carefully designing the geometric parameters and the distances between the antennas,we can obtain the constructive interference in one direction with the destructive interference in the opposite direction,and finally realize a uni-directional SPP.The metasurface may be used as a source of SPPs in integrated optical devices.Then,we show a three-layered metasurface for highly efficient anomalous refraction.The metasurface utilizes Fabry-Perot resonance to raise the efficiency.It contains metal antennas to steer light and a metal grating that acts as a polarizer.The efficiency is over 15 times higher than that of the single-layered metasurface.This three-layered design is expected to open the sights of raising the efficiency of transmitted light.Last,we design and demonstrate a multi-functional plasmonic metasurface.The metasurface contains gold bars aligned in different directions,a gold ground plane,and a silica spacer.These anisotropic building blocks produce a phase gradient and their responses vary with the handedness of the circular polarization.Our results mainly contain following three progresses:We realize anomalous reflection and optical rotation simultaneously,which demonstrates the multi-function of the metasurface;we clearly show the conditions of the reflection coefficients for ideal performance,which may benefit the geometric designing of the building blocks;we exhibit the simulated results of different incident wavelengths,different incident angles,and different rotation angles,which indicate that the metasurface can be effective in many situations.We believe that these results may be useful in changing optical paths and achieving optical rotation within a small volume.