The Study Of Tunable Micro-nano Devices Based On Graphene And Multi-layer Structures

With the widely application of micro-nano optical devices,such as plasmon waveguide,spetroscopy and sensing,surface plasmon polaritons(SPPs)become research focus in this area.Graphene,a novel two-dimensional material,can also excite SPPs along the interface between metal and dielectic(GSPPs).In this work,four tunable micro-nano waveguide devices have been proposed based on the theory of SPPs and GSPPs as below:A plasmonic Bragg reflector(PBR)composed of a single-layer graphene-based silicon grating has been numerically studied.An external voltage gating has been applied to graphene to tune its optical conductivity.It is demonstrated that SPP modes on graphene exhibit a stopband around the Bragg wavelengths.By introducing a nano-cavity into the PBR,a defect resonance mode is formed inside the stopband.Multi-defect PBR to adjust the characteristics of transmission spectrum has been further designed.In addition,through patterning the PBR unit into multi-step structure,the insertion loss and suppress the rippling in transmission spectra have been suppressed.A wavelength-sensitive plasmonically induced transparency-like(PIT-like)device consisting of a double-layer graphene-based metal–dielectric–metal(MDM)waveguide is proposed.Initially,monolayer graphene sandwiched in the MDM waveguide has been investigated and the phase-matching equation is utilized to explain the reflected resonant wavelength of the transmission spectra.The PIT-like windows in the transmission spectra of double-layer graphene can be achieved by tuning the applied bias voltage on the graphene layer and the distance between the graphene layer and metal substrate.The high-performance PIT-like devices with a flexible on– off–on effect has been obtained.A grating-coupled Otto configuration consisting of multilayer films including a few layers of graphene and a germanium prism is proposed.A sharp and sensitive Fano resonance appears when a graphene surface plasmon polaritons(GSPPs)mode from the graphene-dielectric interface couple with the planar waveguide(PWG)mode.The classical harmonic oscillator(CHO)has been utilized to explain Fano resonance and the influence of various parameters of the configuration on the reflection spectra have been stuied.The highly sensitive sensor can be achieved by introducing detected materials into Otto structure.In addition,the effects from material loss arising in our designs has been investigated.An angle-insensitive color filters targeting different wavelengths and applications,which can be achieved by metal–dielectric–metal structures has been reported.Certain combinations of metals and dielectrics are selected to achieve efficient angle-insensitive color filters.The type and the depth of the material both have a significant influence on the transmission efficiency.Hope this work could provide some new insights for micro-nano optical studies and applications.