Metasurfaceshavebecomeanewphotonicstructureforprovidingpotentialapplicationstodevelopintegrateddeviceswithsmallthickness,becausetheycanintroduceanabruptphasechangebyarraysofscatterers.Tobeappliedmorewidely,activemetasurfacedevicesarehighlydesired.Here,atunableterahertzmeta-leuswhosefocallengthisabletobeelectricallytunedby-4.45λisdemonstratedexperimentally.Thelensconsistsofametallicmetasurfaceandamonolayergraphene.Duetothedependenceoftheabruptphasechangeofthemeta-surfaceonthegraphenechemicalpotential,whichcanbemodulatedusinganappliedgatevoltage,thefocallengthischangedfrom10.46to12.24mmwhenthegatevoltageincreasesfrom0to2.0V.Experimentalresultsareingoodagreementwiththetheoreticalhypothesis.Thistypeofelectricallycontrolledmeta-lenscouldwidentheapplicationofterahertztechnology.
