The Research Of Plasmon Induced Transparency Based On Graphene Structures

Surface plasmas,also known as surface plasmons(SPPs),are a mixed oscillating pattern of incident photons acting on the surface of metal and dielectric with free electrons.Because SPPs can overcome the traditional diffraction limits and localize the light in the nanometer scale range,it is very advantageous to design subwavelength photon devices.Interestingly,researchers found that graphene also supports SPPs waves.Graphene plasmons have been extensively investigated theoretically and experimentally.Graphene is a promising candidate plasmon material in the terahertz to mid-infrared spectral range,Compared to metal plasmonics,GPs possess higher confinement,longer relative propagating distances and easier electrostatic tunablility.plasmon-induced transparency(PIT),as an analog of electromagnetically induced transparency(EIT)in atomic systems,has been demonstrated in graphene structures.These active systems have aroused extensive attentions in recent years since it exhibit promising applications in integrated photonic circuits,including slow light devices,plasmonic switches and optical sensors.In this paper,we design and study several kinds of graphene structures to realize the PIT effect by using finite-difference time-domain(FDTD)method.The main contents of the work and the results are as follows:PIT effect is realized for the mid-infrared region only by using two parallel graphene nanostrips.The weak hybridization between the two bright modes results in the novel PIT optical response.The performance of the PIT system can be controlled by changing the geometry parameters of graphene nanostrips.At the same time,the resonance frequency of transparency window can be dynamically tuned by varying the Fermi energy of the graphene nanostrips via electrostatic gating instead of re-fabricating the nanostructures.Moreover,a figure of merit(FOM)value as high as 12 is achieved in the proposed nanostructures based on the performed sensitivity measures.Such proposed graphene-based PIT system may open up avenues for the development of compact elements such as tunable sensors,switchers,and slow-light devices.PIT effect is achieve in a graphene system which is composed of a graphene strip and a graphene disk.Interestingly,the modulation of the PIT transparency window can be achieved by changing not only the gap distance of the two resonators but also the polarization angle of the excitation light.The three-level plasmonic system is employed to well explain the formation mechanism of PIT effect.The analytical results show good consistence with the numerical calculations.Moreover,the PIT resonant wavelength and group delays of incident waves can be dynamically tuned by varying the Fermi energy of the graphene.We propose an easily-integrated structure based on dual coupled graphene ring resonators(GRRs)to achieve plasmon-induced absorption(PIA)effect.A temporal coupled mode theory(CMT)is utilized to verify the simulation results.The novel structure shows a high group delay as high as-1.2 ps.In addition,the dual coupled GRRs can be easily used to design a plasmon-induced transparency(PIT)nanostructure,in which,the outstanding slow light feature is obtained.The pronounced PIA and PIT resonance are easily modified by adjusting the geometric parameters and the Fermi energy of graphene nanostructure.