Research On The Propagation And Control Of Lightwave In Graphene Nanostructure

Graphene,a two-dimensional monolayer of carbon atoms closely packed in honeycomb lattice,owns the similar functions to those of carbon nanotubes and optoelectronic devices,with outstanding and unique physical properties,and promises extensive applications for new optical functional materials and optoelectronics devices.In this paper,the manipulation mechanisms and laws for Goos-Hanchen(GH)shifts and Group delay properties of the reflected beam from a graphene-on-dielectric surface are investigated.We also researched the scheme to tune the refractive index of metamaterial by graphene.The main research results are listed below:Firstly,the GH shifts of the TM-polarized beam reflected from a graphene-on-dielectric surface near the Brewster angle are theoretically investigated.a physical model between GH shifts and optical conductivity of graphene is built.This model discloses the manipulation mechanisms of GH shifts induced by the optical conductivity of graphene.The addition of controllable optical conductivity of graphene on the surface of the dielectric leads to the controllability of absorption characteristics and plays a critical role in manipulating the GH shifts near the Brewster angle.It is shown that even a single-layer graphene can allow for notable variation of GH shifts.The GH shifts can be enlarged,both positively and negatively,and can be switched from positive to negative by changing the applied gate voltage.Further,the relationship between the GH shifts and the electron-phonon relaxation time is clarified.Secondly,the GH shifts of the reflected beam from graphenes-on-dielectric(or metal)are investigated.For the graphenes-on-dielectric substrates,it is found that GH shifts of the TM-polarized are influenced greatly by the introduced graphene sheets near the pseudo-Brewster angle,for N?6(N is the number of graphene),the GH shifts can become more negative at larger N;however,the GH shifts switches from negative to positive suddenly when N ?7 and the GH shifts become smaller as N increasing.For TE polarization,the GH shifts is still small;however it can also be positive or negative by changing the number of graphene sheets.For the graphenes-on-metal substrates,graphene sheets exert a great impact on the reflectance while has little effect on the GH shifts of both polarizations.Thirdly,the group delay of the optical pulse reflected from the graphene-on-dielectric surface is theoretically investigated.The generation and manipulation mechanisms of the reflected group delay are disclosed.Weak absorption can lead to a large reflected group delay,the introduction of graphene creates the conditions for the generation and manipulation of weak absorption.It is shown that even a single-layer graphene can generate a large and negative reflected group delay near a resonance of the slab.Especially,the group delay time can be negatively enlarged by changing the applied gate voltage.Further,the intrinsic parameters and the number of graphene can also achieve a similar manipulation phenomenon.Finally,by embedding single-layer and multilayer graphene sheet to the spacer layer of fishnet metamaterial(MM),the manipulation properties of the refractive index of graphene-containing MM are disclosed and the dispersion model of composite fishnet structure is established.It is found that the change of optical conductivity of graphene exert a great impact on the amplitude of magnetic resonance while has little effect on the resonant frequency,however,the impact of the change of optical conductivity on electric resonance is very small,so graphene can achieved a flexible manipulation on the magnitude of the effective refractive index of MM,the amplitude of the effective refractive index of MM decreases with the increase of the optical conductivity of graphene.Further,increasing the number of layers of graphene can further reduce the amplitude of effective refractive index of MM.