| In recent years,magneto-optical photonic crystals?MOPCs?has attracted much attention.The changes of dielectric tensor or permeability tensor of magneto-optical material caused by magneto-optical effect can break time-space inversion symmetry,which bring out non-reciprocal transmission properties of electromagnetic waves.Nonreciprocal devices based on MOPCs are widely used in optical communications,optical integrated chips and so on due to their high integration,high stability,high isolation,and high response speed.In addition,to achieve the dynamic control of photonic bands,graphene with the advantages of low loss and externally adjustable optical parameters can be used in a one-dimensional layered structure,which may greatly enhance the application of photonic crystals.Graphene is insensitive to the incident angle of electromagnetic waves,and the layered graphene structure can achieve omnidirectional band gap.Graphene photonic crystals have become the focus of current research due to their unique properties.The research work of this paper mainly includes the following aspects:Aiming at the shortcomings of traditional photonic devices with only a single non-reciprocal channel,MOPCs with defect layer was designed.Due to the asymmetry of the structure,non-reciprocal transmission of electromagnetic waves can be achieved when the directions of the applied magnetic field on both sides of the defect layer are the same or opposite.The relation between the defect layer thickness and the number of non-reciprocal channels was analyzed,and 6 non-reciprocal channels were realized in the case of the thickness of defect layer 4400?m.The influence of the incident angle of the electromagnetic wave on transmission properties of the proposed structure was also studied,it shows that the difference of defect mode frequencies in the two directions reaches up to maximum when the incident angle is around 65°.A one-dimensional graphene magneto-optical photonic crystal structure?AGBG?N D?AGBG?N was constructed.The structure contains dielectric materialSiO2layers A,graphene layers G,YIG layers B,and an air defect layer D.One-way defect modes in the Bragg band gap can be realized.Compared to ordinary MOPCs,the period number of the proposed structure is smaller.The influence of the defect layer thickness and the graphene chemical potential on transmission properties of graphene magneto-optical photonic crystals was studied by using the transmission matrix method.The results also show that the photonic bands strongly depend on graphene chemical potential.The non-reciprocal transmission properties can be dynamically controlled by varying the graphene chemical potential via a gate voltage,and the non-reciprocal channel will be shifted to higher frequency with the increasing of graphene chemical potential.A simple structure of one-dimensional graphene magneto-optical photonic crystals?BG?ND?BG?Nwas proposed.The structure contains only graphene layers G,YIG layers B and an air defect layer D.When the period number N is 2,one-way defect modes with a transmittance close to100%can be achieved in graphene induced band gaps.Meanwhile,a broad photonic conduction band can be obtained between the graphene-induced band gap and the Bragg gap,and with the period number increasing the photonic conduction band can split into multiple channels.The influence of graphene chemical potential on the conduction band was analyzed,and with graphene chemical potential increasing,new band gaps will appear among the photonic conduction bands.The proposed graphene magneto-optical photonic crystals can be used to manufacture non-reciprocal or multi-channel photonic devices such as magneto-optical isolators,multi-channel filters,etc. |
PDF Full Text Request