Study Of Light Absorbers Based On Metal-Dielectric Micro/Nano Structures

Metamaterial absorbers have become a research hotspot in the field of micro/nano optics in recent years.It can be divided into narrowband absorber and broadband absorber according to the absorption bandwidth.Narrowband absorbers are usually used in optical sensing,while broadband absorbers are widely used in solar cells,photoelectric detection,imaging and other fields.At present,people have designed many narrowband and broadband absorbers with different surface shapes and absorption mechanisms for micro/nano structures,and the research bands have also expanded from the initial microwave and terahertz bands to infrared,visible and ultraviolet bands.Micro/nano structure absorbers usually only need subwavelength physical thickness,but can achieve good enhanced absorption performance,which is beneficial to the on-chip integration and packaging of optical components,so they have great advantages in applications.However,for the metal-dielectric micro/nano structures,functionalized absorbers with high absorption efficiency and manufacturing advantages are still to be developed.In this paper,based on the Finite-Difference Time-Domain(FDTD)method,several novel metal-dielectric micro/nano structure absorbers have been numerically simulated and theoretically analyzed.The main research contents are as follows:1.An ultrabroadband,omnidirectional,and polarization-insensitive absorber based on cascaded nanorod arrays(CNAs)is numerically demonstrated,and an average absorptivity of98.2% with a relative absorption bandwidth(RAB)of 149.8% can be achieved in the0.38-2.65 ?m wavelength range.This structure only needs a few pairs of metal/dielectric layers to obtain excellent absorption performance.The excellent absorption characteristics are attributed to the synergistic effect of localized surface plasmon(LSP)resonance and plasmonic resonant cavity(PRC)modes.We investigated the absorption properties of the CNA-based metasurface by using the impedance theory,which indicates that the impedance of the structure matches well with the impedance of the free space from the visible to near-infrared wavelength range.In addition,the absorption properties of the CNA-based metasurface are robust to the variation of the structural parameters and the metal/dielectric materials,and ultrabroadband absorption performance can be maintained within 0°-60° for both TM and TE modes.2.A novel ultrabroadband absorber based on encapsulated T-shaped metasurface(ETM)is designed and fabricated.The ETM is composed of Cr thin film,T-shaped polymethyl methacrylate(PMMA)nanostructure and Cr substrate on quartz glass sheet.The average absorption of simulated and experimental results in the whole visible spectrum from 400 nm to 800 nm are over 96.3% and 89.4%,respectively.Three-dimensional power loss density distributions of the proposed structure have been investigated to analyze the ultrabroadband light absorption mechanism.The spectrum of numerical simulation shows that the absorption bandwidth and efficiency are insensitive to the change of geometric parameters and incident angle.Moreover,the absorption bandwidth can be well maintained when the polarization angle changes from 0° to 90°.The designed ultrabroadband absorber is compact,and the thickness of the ultrathin Cr film is less than 1/20 of the wavelength of the incident light.It has many potential applications,such as solar energy collection and integrated photovoltaic devices.3.A novel polarization insensitive ultrabroadband absorber is theoretically simulated and experimentally demonstrated,which is a two-dimensional trapezoidal array structure composed of metallic nickel.The combination of the LSP resonance excited near the upper bottom of the trapezoid and the narrow gap between the lower bottoms of the adjacent trapezoid and the propagating surface plasmon resonance(PSP)excited at the waist of the trapezoid leads to enhanced absorption.This structure can achieve broadband absorption from ultraviolet to visible wavelength range(306.2-726.5 nm),with an average absorption efficiency of 95.7%.When the incident angle of TM polarized light is 60°,the absorption of this wavelength range is still greater than 70%.The change of the polarization angle hardly affects the absorption performance of the structure.In addition,the proposed ultrabroadband absorber is made of high temperature resistant material nickel,which greatly improves the thermal stability of the structure,and does not need to use precious metals,so the manufacturing cost is low.