Research On Filters And Absorbers Based On Micro-nano Structure

In recent years,the study of micro and nano structured optical devices has become an inevitable topic in the field of system integration and chip fabrication,where filters and absorbers have received a lot of attention due to their excellent performance in the field of optical communication and optical imaging.To date,various structures of filters and absorbers have been proposed,but their optical performance is still far from the standard for practical applications,so how to improve their optical performance is the focus of this paper.In this paper,two filters and two absorbers are proposed according to the micro-nano structure,and the structure is simulated and analyzed theoretically by using the finite-difference time-domain（FDTD）method.The specific content of this paper is shown as follows:（1）Two bandstop filters are designed based on MIM plasma waveguide filters.The relationship between wavelength and transmittance is investigated.A combined double square ring and rectangular filter is designed based on the mutual enhancement of the filtering effect by the resonators.The minimum transmittance is significantly improved compared to the square ring structure.The filter is composed of a straight waveguide and two square resonators embedded with silver nanorods has high filtering efficiency and sensitivity,and the filter can be used as a refractive index sensor.（2）A new type of active tuned vanadium dioxide（VO₂）dual broadband terahertz dual function absorber is proposed.By adjusting the conductivity of VO₂,the absorption optical rate and absorption bandwidth can be perfectly modulated.The physical mechanism of the double broadband absorption and tunable absorption is elucidated by applying impedance matching theory and electric field distribution.Furthermore,its superior features includ both polarisation insensitivity and maintaining stable absorption at a wide angle of oblique incidence.（3）Individually frequency and amplitude tunable metamaterial absorber with sensing functions based on strontium titanate（STO）and graphene.The optical properties of the designed structure were simulated and numerically calculated using FDTD and Coupled mode theory（CMT）methods.The results show that under the condition of changing temperature of strontium titanate and the Fermi energy level of graphene,the absorber frequency and absorbance can be tuned.When the temperature of STO is stabilised at 300 K,double narrow-band absorption can be changed to single narrow-band absorption by changing the Fermi level of graphene,when the Fermi level of graphene changes from 0.1e V to 0e V.The physical mechanism of the absorption and active tuning is analysed by electric field distribution and impedance matching theory.The effect of polarization direction and incident angle on the absorber performance is also investigated.In addition,the structure can be used as a refractive index sensor in the terahertz range.