Antireflective Characteristics of Sub-Wavelength Periodic Structure with Square Hole

In order to enhance transmittance in the long-wavelength infrared range, the major parameters of periodic sub-wavelength structures (SWS) with square holes on zinc sulfide (ZnS) substrates are designed and analyzed for applications in normal incidence by using rigorous coupled-wave analysis (RCWA) and thin film theory (TFT). Finally the optimal antireflective parameters are achieved. The structures on ZnS substrates are fabricated on the basis of the simulation results by photolithography technology and reactive ion etching technology. A substantial antireflection effect is observed over the wavelength band 8–12 μm by a factor greater than 4.5.