Design And Fabrication Of Metamaterial Absorber Based On Paticle Swarm Optimization

In recent years,the research of uncooled infrared detectors based on micro-electromechanical systems(MEMS)has made significant progress.the further improvement of the performance and functions of existing infrared detectors depends largely on the introduction of new physical mechanisms and new device structures.Metamaterials is a research field of electromagnetics.It is an artificial structure composed of periodic or non-periodic arrangements of sub-wavelength units.At optical frequency,the alliance of metamaterials with the fields of plasmonics and nanophotonics can further advance the possibility of controlling light propagation,radiation,localization and scattering in unprecedented ways.Metamaterials redefine the way we understand light,such as negative refractive index,Breakthrough of diffraction limit,perfect absorber,etc.Based on the theory of surface plasmon and using the unique properties of metamaterials,this paper designs a perfect absorber in the infrared band to achieve broadband absorption and polarization selective characteristics,and builds an "integrated optical information processing and photoelectric conversion" imager architecture based on metamaterials.The electromagnetic simulation results show that the absorption wavelength can be shifted according to the structural characteristics of the material in a wide range of wavelengths,and broadband absorption can be achieved through a variety of coupling methods.At the same time,due to the asymmetry of the structure,such as two-dimensional gratings,it’s polarization dependent.We can achieve both polarization imaging and multi-color detection.Specifically,this paper uses FDTD software to analyze the period P,the refractive index of the dielectric layer n,the height of the dielectric layer H,the top gold structure height,the top gold nanostrip width W and their influence on absorption peak and wavelength.And we can set extinction ratio,bandwidth or other fitness functions to achieve long-wavelength infrared broadband absorption and other different design goals.We use the micro-nano processing technology: FIB and EBL to set ideal fabrication constrains,such as a fixed top-layer gold structure with a height of 50 nm and a strip pitch greater than 50 nm.The particle swarm algorithm optimization results show that in the 8-14 um band,the overall absorption rate reaches 68.94%,and the polarization selection ratio is 34.266.Considering that the atmospheric transmittance curve is low at 12-14 um,our optimization results in the 8-12 um band show that the absorption rate reaches 80.41%,however the overall absorption rate in the long wavelength band drops to 62.5%,and the polarization selection ratio is 39.69.Furthermore,we optimized two sub-bands: 8-11 um and 11-14 um.Considering the crosstalk between the band signals,the overall absorption rate is still higher than 80%,and the polarization selection ratios are all above 40.The MIM infrared absorber is designed at pixed-level,which lays the foundation for the wavelength selective and polarization selective functions of infrared detection,and is expected to be applied to a new generation of infrared detectors.