Plasmon-Induced Transparency And Absorption Properties Of Graphene Optical Microstructures And Application Study

Surface Plasmon Polaritons（SPPs）have been extensively studied in the micro-nano photonics,as a carrier of information and energy,mainly in the interactions between photons and electrons on the surface of metal or insulator.SPPs have a broad development prospect.In recent years,graphene,a two-dimensional material,has become a research hotspot due to its unique physical properties,for example,it exhibits negative dielectric constant in the terahertz band,i.e.,metal-like,leading to the excitation of SPPs in specific wavelength bands.Compared with traditional noble metals,graphene-based SPPs have unparalleled advantages and optical properties:for one,graphene-based SPPs are dynamically tunable,which is more advantageous in practical applications.We indirectly control the permittivity and conductivity of graphene by applying a gate voltage to adjust the Fermi energy level of graphene to achieve dynamically tunable graphene-based SPPs;for another,graphene-based SPPs have the advantage of strong localization and can operate in a wide frequency range.In this paper,we focus on the mechanism of graphene-based SPPs and study the plasmon-induced transparency（PIT）and perfect absorption phenomena based on the excitation of graphene-based SPPs by finite-difference time-domain（FDTD）simulations.The theoretical analysis of multi-PIT based terahertz multimode modulator and the perfect absorption of single-layer graphene microstructure are carried out by using coupled mode theory（CMT）and impedance matching theory.Enhancement properties are numerically simulated and their optical properties are investigated.The main research is as follows:1.A monolayer patterned graphene metamaterial based on silicon/silica substrate and achieved a typical triple plasmon-induced transparency（Triple-PIT）is achieved in terahertz band.The physical mechanism is analyzed by CMT,and the results of CMT calculations are in good agreement with the FDTD simulations.A multimode electro-optical switch can be designed by dynamic tuning,and the modulation degrees of its resonant frequencies are84.0%,87.3%,83.0%,88.1%,and 76.7%.Interestingly,the group index of this structure can be as high as 770 at E_f=0.8 e V,which shows that it can be designed as a slow light device with extraordinary ability.Therefore,the results of this work are of great significance to the research and design of electro-optical switches and slow light devices in the terahertz band.2.A graphene-dielectric-gold hybrid metamaterial is proposed and realizes dual narrow-band plasmon-induced absorption（PIA）in the terahertz region,whose physical mechanism is analyzed using the coupled-mode theory,which agreed well with the finite-difference time-domain simulation.It is found that the Fermi level of graphene can be adjusted to improve the absorptivity when the refractive index（RI）n_d of the chosen dielectric cannot achieve a good absorption effect.In addition,the blue shift of absorption spectrum can be used in the design of dual-frequency electro-optical switches,of which the modulation degree of amplitude（MDA）can reach as high as 94.05%and 93.41%,indicating that this is a very promising electro-optical switch.Most significantly,the RI sensing performance is investigated,which shows an ultra-high absorption sensitivity S_A=4.4°/RIU,wavelength sensitivity Sλ=9.8°/RIU,and phase shift sensitivity Sφ=2691°/RIU.At last,an interesting finding is that the two peaks（R1 and R2）of plasmon-induced absorption show different polarization characteristics（insensitive or sensitive）to the incident light angle;this polarization-sensitive is particularly important for the PIT/PIA-based optical polarizers.Undoubtedly,this work is of great significance to the research and design of terahertz photonic devices and sensors.3.A novel and perfect absorber based on patterned graphene and vanadium dioxide（VO₂）hybrid metamaterial is proposed,which can not only achieve wide-band perfect absorption and dual-channel absorption in the terahertz band,but also realize their conversion by adjusting the temperature to control the metallic or insulating phase of VO₂.First,we analyze the absorption of the proposed structure in the absence of graphene,where the absorption at one frequency point（f=5.956 THz）can reach 100%when VO₂ is in the metallic phase.Notably,when graphene is added above the structure,the 100%absorption is enhanced from one frequency point to a broadband which has a width of 1.683 THz.Secondly,when VO₂ is in the insulating phase,the absorption with graphene metamaterial structure behaves better and forms two high absorption peaks,logging 100%and 90.7%at f₃=5.545 THz and f₄=7.684 THz,respectively.Finally,by adjusting the Fermi level from 0.8 e V to 1.1 e V,it is found that the absorption spectrum is significantly blue-shifted,so that an asynchronous optical switch can be achieved at f _K1=5.782 THz and f _K2=6.898 THz.Furthermore,as the polarization angle of the incident light shifts from 0°to 90°,the absorber exhibits polarization sensitivity at f₃=5.545 THz and polarization insensitivity at f₄=7.684 THz.Therefore,this work provides insights into the new method that increases the high absorption width,as well as the great potential in the multifunctional modulator.