Optical Tamm State Based On Graphene And Its Application In Micro/Nano-structured Optoelectronic Devices

In recent years,optical Tamm state(OTS)is a kind of surface wave confined on the interface of two different media.Because it has the characteristics of being easily excited and strongly localized to electromagnetic waves,which attracted much attention of researchers.Compared with surface Plasmon resonance(SPR),it can be excited without a specific angle of incidence and it can be directly excited by TE(transverse electric)polarization,it also has a local field enhancement effect.Therefore,it has potential application in realizing compact optoelectronic devices.As we know,photonic crystal heterostructures and metal-distributed Bragg reflector(DBR)structures are typical structures for observing OTS,but their applications in optoelectronic devices limited by the extremely high loss coefficient of metal,narrow band response and difficulty in active regulation.In recent years,the emergence of graphene has provided a new idea of solving this problem.Graphene has metal-like characteristic,which can excite OTS under TE and TM(transverse magnetic)polarization.Its flexible tuning characteristics,huge nonlinear conductivity,fast response time and ultra-thin atomic layer thickness provide a new idea for realizing ultra-compact and adjustable nonlinear optoelectronic devices.At the same time,based on the graphene-DBR structure to excite the OTS to obtain the local field enhancement,we can realize the micro/nano-sturctured optoelectronic devices with excellent performances.It has very realistic scientific significance in photoelectric applications.We mainly study the OTS based on graphene-DBR and its application in micro/nano-structured optoelectronic devices,including control OTS,the group delay,Goos-Hanchen displacement,and biosensor,photonic spin Hall effect and bistability.The innovative results are as follows:(1)We demonstrate the physical mechanism of OTS at the interface between graphene and a dielectric Bragg mirror in the THz frequency band.Based on such mechanisms,we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency.Moreover,we show that the OTS is dependent on the optical conductivity of graphene,making the graphene–DBR structure a good candidate for dynamic tunable OTS device in the THz frequency range.(2)We theoretically propose a configuration composed of the gold-1D PC with graphene.By exciting OTS via the gold-1D PC to generate the spin-dependent splitting.Moreover,we introduce the graphene to make the photonic spin Hall effect controllable.The maximum spin-dependent splitting can be achieved 18?m through setting appropriate parameters of the proposed configuration for TM-polarization.Our results may open up a new idea for regulating the photonic spin Hall effect and has potential applications in the fields of spin-controlled optics.(3)The low-threshold optical bistability(OB)of a reflected light beam at terahertz frequencies is achieved by using a multilayer structure where monolayer graphene is coated on 1D PC separated by a top layer.This low-threshold OB phenomenon originates from the enhancement of the electrical field owing to the excitation of OTS at the interface between the graphene and 1D PC.Moreover,the bistable behavior of the proposed structure is proved sensitive to the optical condunctivity of graphenen,thus making this configuration a prime candidate for future experimental investigation at the terahertz range.(4)A high sensitivity optical biosensor at terahertz frequencies is achieved by using a composite structure where monolayer graphene is coated on 1D PC separated by a sensing medium.This high sensitivity phenomenon originates from the excitation of optical resonance at the interface between the graphene and 1D PC.By selecting appropriate parameters,the maximum sensitivity?407.36~o/RIU is obtained.We believe the proposed configuration is promising for fabricating graphene-based biosensor devices and other applications in the terahertz band.(5)We have shown that a giant Goos–H?nchen shift and group delay of a light beam reflected at terahertz frequencies can be achieved by graphene-1D PC structure.This giant Goos–H?nchen shift and group delay originates from the enhancement of the electrical field,owing to the excitation of OTS at the interface between the graphene and 1D PC.It is shown that the Goos–H?nchen shift and group delay in this structure can be significantly enlarged negatively and can be switched from negative to positive due to the tunability of graphene's conductivity.Moreover,the numerical simulation results have testified its validity under the condition of finite beam width.