Structure Design And Properties Of Metamaterials With Tunable Plasmon Induced Transparency

Metamaterials constitute of specially synthesized unit cell,usually in the wavelength or subwavelength range.When the incident light wave couples with the unit cell,the free electrons on the surface can produce the surface plasmon polaritons under the periodic driven of the electromagnetic wave.The special control of light propagation is realized by the design of the micro-nano structure,which has good application in information transmission,light integration and optical sensing.There are many kinds of unit cells to realize metamaterials,such as metal,metal and dielectric materials,graphene,Dirac semimetals and transparent oxides.Among them,the phenomenon of plasmon induced transparency refers to the formation of a narrow transmission peak at the transparent window to further realize the dynamic regulation of the transmission spectrum amplitude,phase,resonance peak and other characteristics.And it has good applications in sensors,filters and slow light devices.In this paper,based on the finite element method,the metamaterial structure is constructed with graphene,Dirac semimetal and gain medium to realize the dynamic regulation of the spectrum.The research results are listed as follows:1.A novel metamaterial structure composed of asymmetric double L graphene strips is proposed to achieve plasmon induced transparency in terahertz region.The structure consists of two L graphene strips of different sizes and asymmetrical arrangement.A transparent window appears in the absorption spectrum due to the weak hybridization between the two resonators.And the window can be dynamically modulated by adjusting Fermi energy and graphene mobility.In addition,the reflection and absorption spectrum are analyzed in detail,and the absorption rate is close to 0.5.The sensitivity of the transparent window is linearly related to the refractive index of the surrounding medium.In terms of dispersion performance,the group index of this structure can reach 1125,showing good slow light performance.2.A periodic arrangement of graphene metamaterials in terahertz region was designed to achieve tunable PIT effects using different carrier mobility.the structure comprises a pair of graphene strips and a split ring resonant?SRR?.The formation of the transparent window is attributed to the near-field coupling between the two resonators.The transmission spectra at different mobility were numerically fitted using the oscillator mode to further verify the accuracy and reliability of the results.Switching modulation of the PIT transparent window can be achieved by carrier mobility.As the carrier mobility increases,the PIT transparent window becomes more obvious.Accordingly,the plasmon induced absorption can also be achieved synchronously,and its absorption rate is as high as 0.5.In addition,the group delay increases with the increase of mobility,and it can reach to 1.57 ps.3.Tunable and enhanced optical properties of graphene metamaterials are investigated,which composed of?resonators and hollow rectangular resonators.The unit is arranged periodically on the dielectric substrate.The obvious PIT window can be generated due to the destructive interference between the?and hollow rectangular resonators,and the resonant frequency as well as the number of transparent windows can be adjusted by polarization angle.Padding a gain medium into the graphene metamaterials,the intrinsic loss of the system can be greatly compensated,and the resonant intensity gets amplified to achieve a dramatic stimulated emission of radiation with a low gain thresholds.In addition,the resonance intensity of the peak can be adjusted by adjusting the polarization angle,and the tunable nano-laser phenomenon can be realized.4.Dynamic manipulation of plasmon induced transparency based on Dirac semimetal metamaterials is investigated elaborately.The structural elements consist of a vertical strip and a resonator arranged periodically on the Si O₂substrate.By observing the transmission spectrum and the corresponding electric field distribution,the near-field coupling between the two bright mode resonators leads to the appearance of a transparent window.And the Fermi energy can be flexibly controlled by non-contact mode,showing obvious blue shift as the Fermi energy increases.Modulation of optical switch by changing polarization angle is proposed for the first time.The slow light characteristics of the structure are analyzed by calculating the phase and group delay.And verify that the PIT transparent window can be regulated by geometric parameters.The sensor performance of structures under different substrates was also considered.