Design And Simulation Of New Optical Devices Based On Micro/nano Gratings

Grating is a kind of optical device,which can make the amplitude or phase of incident light subject to periodic spatial modulation,and is widely used in integrated optics,sensors,filters and other fields.Nowadays,intelligent and complex application systems demand higher functional and performance standards for optical devices based on micro and nano gratings.Therefore,this paper focuses on application scenarios where micro-and nano-devices have low quality factors or are non-tunable.Specifically,it adopts the method of inserting dielectric gratings and applying graphene materials to device mediums in order to study new optical devices with different structures and functions.The main work is as follows:（1）A grating-assisted ultra-narrowband multispectral plasmonic sensor structure is proposed.In response to the problems of large half-width and low quality factor of existing plasmonic resonance sensors,the performance indicators of pure metal grating structures are improved by introducing a dielectric grating.The optical transmission characteristics and sensing characteristics of the proposed metal-dielectric grating resonance sensor structure are numerically simulated,and the effects of structural parameters and incident light polarization state on half-width and sensing characteristics are analyzed.The simulation results show that in the wavelength range of 800-1100 nm,there are two notches in the transmission spectrum of this sensor structure formed by grating diffraction and plasmonic resonance,with corresponding half-widths of 0.35 nm and 0.59 nm,refractive index sensitivities of 525.7 nm/RIU and 475.7 nm/RIU,respectively,and quality factors as high as 1502.00 RIU^-1 and 806.27 RIU^-1.Compared with pure metal gratings,the quality factor of metal-dielectric gratings is improved by two orders of magnitude.（2）A graphene plasma structure which can achieve double tunable electromagnetic induction transparency effect is proposed.Aiming at the problem of poor slow light effect of existing electromagnetic induction transparent devices,this paper designs a tunable electromagnetic induction transparent structure with good slow light effect by combining graphene,thin gold layer and grating.The design studies the optical response of the structure using the finite-difference time-domain method and finds that the electromagnetic induction-like transparency effect is caused by destructive interference between the bright mode of the graphene layer and the dark mode of the gold layer.This phenomenon can be modulated by the Fermi level,which is capable of being dynamically tuned by an applied voltage.The results show that in the terahertz frequency range,the group delay of this structure can reach 0.62 ps,the group refractive index exceeds 1200,the maximum delay bandwidth product is 0.972,and the peak frequency transmittance of electromagnetically induced transparency reaches 0.89,which outperforms most existing devices of similar types.（3）A graphene-based grating narrowband absorber has been proposed,which can achieve tunable dual narrowband perfect absorption in the mid-infrared band.Compared with other similar structures that only study the effect of graphene chemical potential on absorption,this design further discusses the tuning effect of graphene scattering rate on absorption.Simulation results show that in the mid-infrared band,reducing the graphene scattering rate can effectively reduce the full width at half maximum of the absorption peak and increase the structure’s absorption rate.When the graphene chemical potential is 0.7 e V,both absorption peaks can reach 0.98,and the full width at half maximum of the absorption peak can be minimized to 0.16 THz,with a refractive index sensitivity of 7.13 THz/RIU.