Researchs On Infrared Optical Devices Based On Graphene Metasurface

In recent years,metasurface technology has become one of the hot research directions in the field of optical communication.Metasurface is a synthetic material that combines photonics and nanotechnology to achieve flexible regulation of the amplitude,phase and polarization state of light,resulting in device effects such as beam deflection,wavefront focusing and polarization transformation.Conventional metasurface optical systems are mostly composed of metal and dielectric materials.The high loss,resonance dispersion and nano-scale fabrication difficulties of metal metasurfaces limit their wide application in the field of metasurfaces.The medium metasurface also has the disadvantages of single function and poor adjustability.Graphene is a two-dimensional metamaterial with a hexagonal arrangement of carbon atoms in a honeycomb,exhibiting unique optoelectronic properties that have attracted our attention with its high carrier mobility,metal-like negative dielectric constant and tunable Fermi energy levels.Graphene metasurface devices using graphene and metasurface compositions can be flexibly regulated by methods such as gate pressure regulation and chemical doping,single and multi-layer structures can be easily obtained by nanoprinting and lithography.In addition,the ultra-thin nature of graphene greatly reduces the loss of light propagation on the graphene metasurface.The details of the graphene-based metasurface study are as follows:(1)A multifunctional tunable terahertz graphene metasurface was designed;a new multifunctional,broadband,efficient and tunable metasurface device was designed using graphene metasurface technology.The local plasma resonance of the graphene strip and the Fabry-Perot resonance of the dielectric layer work together to change the reflected wave phase of the unit structure by adjusting the graphene fermi energy,thus achieving 360° phase coverage of the metasurface system.Based on this360° phase coverage,we first designed a multi terahertz refractive focusing mirror with an effective broadband focus of 5THz,6THz,7THz and a focal length of 200?m.In order to demonstrate the flexible control effect of the focusing mirror,we also achieved an accurate movement of 100?m above and below the focal spot.In addition,we have achieved anomalous reflections at different angles(±16°)using a specific phase gradient method.These results demonstrate that our device architecture is an excellent metasurface optical simulation system that is flexible and tunable,broadband efficient,and has multifunctional effects.(2)A polarization converter based on graphene metasurface was investigated.In the first work on the graphene metasurface single-band cell structure,we unexpectedly discovered the polarization transformation effect of the structure,which can effectively change the polarization properties of light.Based on this structure,we designed and simulated an ultra-thin,broadband,highly efficient polarization converter by means of a complex graphene pattern.In order to obtain more excellent device simulations,a cross-sectional 1.5-?m-long graphene strip was added to the2.9-?m strip to investigate the polarization conversion capability of the new structure.The new metasurface structure has an ultra-wide band(4-9THz)polarization conversion bandwidth and a stable polarization conversion rate of over 95%.In addition,the Fermi energy of graphene can be dynamically tuned to change the polarization transition properties of the structure.This dynamic polarization conversion using graphene metamaterial can be used in many optical fields such as3 D imaging,sensing,communication,etc.