Broadband multilayer antireflection coating in THz region

A new approach to the design and the realization of a broadband multilayer anti-reflection (AR) coating is proposed in this study. The binominal multi-section transformer is employed to efficiently determine the thickness and the refractive index of each matching layer, while those layers can be further realized by doping different fraction of subwavelength-size silicon powders (for relatively-high-index layers) or air pores (for relatively-low-index layers) into the low-loss HDPE polymer. Based on this scheme, we design a ten-layer AR coating for widely used silicon wafer. The designed AR coatings are double-side integrated with a 375-μm-thick silicon wafer, which is able to enhance the overall THz transmission to higher than 95.00% from 0.250 THz to 0.919 THz (114.46% bandwidth).