Design of Graphene Photoelectric Devices Based on Photonic Crystal Structures

Author:Bian Li An

Supervisor:liu pei guo


Degree Year:2018





Photonic crystal as an artificial periodic structure has been effectively applied in various devices in recent years.Meanwhile,graphene owning unique photoelectric properties,a two-dimensional material with only one-atom thickness,is becoming a hot topic in many fields.When the photonic crystal and graphene are compounded together,the designed devices will possess all excellent characteristics of both of them,including the smart tunability electrically,ultranarrow or ultrabroad frequency-band response,etc.In this paper,all kinds of terahertz graphene devices are designed referring to absorbing,photoelectric tuning,filtering and so on in the photonic crystal structures.The feature and performance of devices are simulated systematically.Main contents are as follows:1.The one-dimensional graphene photonic crystal is simulated by the modified transfer matrix method.The influences of chemical potential of graphene,incidence angle of electromagnetic wave along with the regulator of dielectric slab on the system transmittance and absorbance are investigated entirely.Based on this,by exploiting the heterostructure and the formed supercell,tunable filter,multiband switch,high-Q filter and multi-stop filter are designed.Besides,the one-dimensional quai-periodic graphene photonic crystal is also constructed by using the Fibonacci sequence.Depending on the quai-periodic structures,a variety of devices are designed including the high-Q filter of heterostructure,the tunable switch with changeable period number,the multi-stop filter exploiting the supercell and the amplifier integrating active medium.2.When one graphene monolayer is embedded into the top mirror of FP resonance cavity,the system achieves the near-unity absorption as well.The phenomena that the number of absorption modes can be added effectively by increasing the number of resonance cavities and the peak-peak distance between modes is controllable flexibly are revealed.A graphene multi-mode absorber is designed by cascading multiple empty cavities behind the FP resonance cavity integrating two graphene monolayers.Such absorber can realize several work-modes.When there is only graphene cavity,two near-unity absorption modes arise.When one empty cavity is cascaded rearwards,three near-unity absorption modes emerge.When two empty cavities are constructed further,four near-unity absorption modes appear.Different absorption modes present different responses to different graphene monolayers,the chemical potential,the geometries of resonance cavities,the period number of reflection mirror,the polarization along with angle of incident wave.3.To enhance the tunability of graphene for Fano resonance of subwavelength grating,the embedded graphene monolayer is replaced by the graphene-dielectric stack.The effects of the alteration of graphene’s conductivity on the equivalent permittivity of the stack is revealed,so that the method improving the system tunablity is established.By tuning the asymmetric transmission spectrum,the switch function is gained.Ultilizing the near-field localization caused by Fano resonance,the tunable absorber is designed.Controlling the chemical potential of graphene and incident light angle jointly,this structure can act as attenuator or modulator as well.4.A graphene absorber with hybrid cavity of FP-Fano resonances is researched.The advantage of graphene-outside-cavity structure is that the shaping in the cavity has no effect on graphene so that the graphene sheet can keep its original physical properties.The method of coexistence of FP-Fano resonances are established.The grating thickness controls the absorption-modes number.The grating period restricts the coupling of FP resonance and Fano resonance.The period number of either-side multilayers around graphene affects fully the absorption response of system.5.The critical coupling theory is applied to design the graphene perfect absorbers.Firstly,using a photonic crystal array achieves the excited FP resonance and Fano resonance simultaneously so that dual-mode absorber is designed.The critical coupling as the essence of perfect absorption is revealed.The influences of the chemical potential of graphene,the thickness of equivalent grating and incident light angle on the coupling of modes are researched.Secondly,the other dual-mode absorber is designed depending on the cascade of graphene cavity and empty cavity with excited FP-FP resonances or FP-Fano resonances.The essence of perfect absorption is emphasized further and the method of modes coupling is proposed again.Employing the perturbation theory,the reason of graphene tuning different modes independently is given.Through these researches in this paper,the advantages of graphene-photonic-crystal composite structure is presented thoroughly.The suggested methods are still useful at higher frequencies,which supply fire-new strategies to design the high-performance devices in the optical communications.