Research On Tunable Devices Using Graphene Stacks

Made up of carbon atoms,graphene is an ideal two-dimensional nanomaterial,which has ultra-high electron mobility and thermal conductivity,excellent electrical conductivity,ideal light transmittance and other peculiar physical properties.External bias voltage or chemical doping can dynamically regulate the electrical conductivity of graphene surface,which makes graphene gain a broad application in the fields of photoelectric detectors,ultra-sensitive sensors and transparent conductive films.Graphene stack is formed by alternative monolayer graphene and dielectric layer,such as Al₂O₃ and MgF₂.Graphene stack can keep the electrical properties of single-layer graphene as well as increase the carrier concentration greatly,which can overcome the weak resonance response,insensitive modulation,and unstable structure in monolayer graphene.As a result,a series of tunable functional devices based on graphene stack are designed in this study,such as terahertz metamaterials,antennas,optical switches,modulators,absorbers and so on.Meanwhile,the optoelectronic response characteristics and performance of these devices are also analyzed by simulation results.The main research contents of this paper are as follows:1.The equivalent medium method is used to verify that terahertz metamaterials based on graphene stack are significantly improved in modulation performance,compared with single-layer graphene metamaterials;The effects of filling factor and oblique incidence on tunable properties of terahertz metamaterials are also analyzed.2.By optimizing the reflection loss and relative bandwidth,the graphene stack is embedded into the medium layer of microstrip line and fabricate to a terahertz microstrip slot antenna,which has high integration,broadband,low loss and dynamic adjustable working frequency.3.A light switching is formed by the combination of graphene stack,optical waveguide and photonic crystal nano-beam cavity,which can achieve prefect switching effect by adjusting the chemical potential of graphene;Using the perturbation theory of the dielectric resonator,the cause of the blue shift of the resonant wavelength in the waveguide with the increase of chemical potential is explained.4.By embedding the graphene stack into the coupling defect cavity of the photonic crystal waveguide,a tunable coupled-resonator-induced transparency effect is achieved,and its physical mechanism is analyzed with the modified time-domain coupling mode theory.On this basis,a multimode tunable coupled-resonator-induced transparency effect can be achieved by increasing the number of coupling defect cavities,and the modulus can by tuned with the chemical potential of graphene.5.A photonic crystal nanobeam cavity with Bragg reflector is designed.By tuning the chemical potential to match with the critical coupling condition,the cavity can realize a more than 99.7%absorption rate,which means a perfect absorption.6.The graphene stack is combined with multiperiod grating to realize ultra-wideband wave absorption of 780nm to 5351.6nm by using graphene's strong surface plasmon resonance response.Through the studies in this paper,the advantages of using graphene stack in terahertz and optical devices to achieve dynamic tunability are fully demonstrated,which supply fire-new strategies to design the high-performance devices in the optical communications.