Design And Optical Characteristics Research Of Nano Antenna Based On Cross Fractal

Nano-antennas are the extension products of traditional antennas in the optical frequency band,which has attracted the attention of many researchers because they can couple incident beams to spatial scales that are much smaller than the diffraction limit.Generally,researchers build structural models using stacking,alignment,and combinations of common geometric patterns in traditional design methods for optical nano-antennas.In order to obtain excellent experimental results,iterative parameter adjustment,scanning,and optimization are repeated.The workload is huge and inefficient.But the appearance of fractal geometry can well suppress the calculation complexity of the structure size and improve the simulation efficiency.Furthermore,the nano-antennas designed by the classical fractal theory can widen the frequency band,which is mainly determined by the self-similarity of fractal geometry.In this paper,a simple “cross” is used as the basic fractal iterative unit,and a cross-slots fractal nano-antenna and a three-dimensional multilayer cross-fractal nano-metamaterial absorber are designed to achieve excellent optical characteristics.Firstly,a fractal nano-antennas with cross-gaps are proposed in view of the low transmittance and narrow frequency band of traditional antennas,and the influence of their extraordinary optical transmission characteristics and physical parameters on the extraordinary transmission characteristics are studied by the time domain finite difference method(FDTD).The nano-antenna takes the precious metal silver as the main material of the antenna,and makes a simple cross-fractal etching iteration on the surface of the silver material.In general,the nano antenna can be regulated by changing the physical parameters of the nano antenna.The results show that the fractal cross-slots structure is more miniaturized,and realizes extraordinary optical transmission and full 2 phase control of transmission beam,and the transmittance is higher than the uniform cross-slots structure,the full width at half maximum(FWHM)is wider,and the highest transmittance is up to 99.51%.By adjusting the physical parameters,the transmission spectrum exhibits red-shift or blue-shift characteristics,achieving controllability of the transmission spectrum.When h=50 nm,the full width at half maximum is about 356 nm,and the transmittance is still as high as 95.66%,is generally higher than traditional structures,and the peak transmittance is still greater than 74% at large incident angles(70°).In short,the cross-slots fractal nano-antenna has the characteristics of wide frequency,controllable and adjustable,and more miniaturized structure compared with other nano-antenna structures,and realizes extraordinary optical transmission,and has more extensive applications.Secondly,a three-dimensional cross-shaped fractal nano-metamaterial absorber was proposed in view of the disadvantages of low absorptivity and narrow wavelength band of nano-antenna,and its absorption mechanism and absorption characteristics were systematically studied by FDTD.The absorber takes the layer of metal gold as the base layer,the silicon ring filled with the metal iron material as the middle layer,and the cross fractal layer stacked with two iron-silicon layers as the upper layer.In the absorber,the solar energy is captured by the upper cross fractal column and the silicon ring filled with iron in the middle layer.The results show that the absorber shows an absorptivity higher than 91% in the band of 400 to 2000 nm,and the absorption bandwidth is 133%.In addition,the proposed absorber is polarization independence and has a maximum angle of incidence of 76°.Since the iron material in the metamaterial absorber is easily oxidized and rusted,the iron is replaced with nickel having excellent characteristics such as corrosion resistance and high temperature resistance,and obtaining an improved nano-metamaterial absorber.The improved metamaterial absorber not only eliminates the susceptibility to corrosion of the above structure,but also maintains polarization independence and high absorptivity,and expands the incident angle to 79 °,which can be used in many applications.