High efficient ultra-broadband anti-reflection coating on silicon for infrared applications

In this work, we describe an efficient design and fabrication process of anti-reflection (AR) coating over 1400 nm spectral interval from 3.4 mu m to 4.8 mu m at mid wave infrared (MWIR) on silicon optics with only 3 layers which have overall physical thickness less than 1 mu m. Multi-layer AR coating consisting of aluminum oxide (Al2O3) and germanium (Ge) layers as low (n(L)) and high (n(H)) index materials respectively are coated by plasma assisted e-beam evaporation on silicon substrates with well optimized process parameters. AR coating on silicon is the first one reported by exhibiting record average transmission more than 99.7% over 1400 nm broadband spectral interval in mid-wave infrared (MWIR) with minimum number of layers. Moreover, number of layers and overall thickness for our design enables a cost effective solution for low process cycle in mass production of AR coated silicon optics.