High Efficient Metadevices For Terahertz Beam Shaping

With the popularity of the concept of 6G,terahertz(THz)technology has attracted the attention of many researchers.So far,THz technology has made remarkable progress,in which THz modulators can achieve various functions through the beam shaping of electromagnetic waves.Compared with traditional bulky THz elements,THz metasurface,as a planar photonic element,can flexibly manipulate electromagnetic wave in the subwavelength scale.Therefore,the THz wavefront modulators based on metasurfaces can facilitate the integration and miniaturization of THz systems.However,due to the inherent Ohmic loss,the efficiency of monolayer plasma metasurface is very low.Multilayer plasma metasurface can achieve highefficiency transmission,but resulting in the complexities of design and fabrication.The all-dielectric metasurface can obtain high transmittance due to its resonant unit with high refractive index,but it also brings reflection loss.Thus,high-efficiency THz metadevices are highly pursued at present.In this paper,we propose an integrated antireflection strategy for transmissive THz metadevices to achieve high-efficiency THz beam shaping.Micro-fabrications are carried out on both surfaces of single silicon wafer separately.On one side,elliptical silicon pillars with the same size are spatially orientated to realize the desired geometric phase.On the other side,uniform circular silicon pillars are set to reduce the reflection loss.With this strategy,several versatile metadevices such as lens,lens array,polarization fork grating,vortex beam generator,Bessel vortex generator and Airy beam generator are demonstrated.The maximum efficiency up to 95% and excellent design flexibility are verified.Our work provides a practical and efficient approach for the development of planar THz metadevices,which play an important role in highperformance THz imaging and communication apparatuses.