Design and fabrication of low-loss antireflection structures for Si windows in 10–30 THz

We report on the design, fabrication, and characterization of low-loss antireflection (AR) structures for Si windows in 10–30 THz. Based on scattering-matrix simulations and effective medium theory, optimal Si filling ratios are presented for AR structures composed of Si-rod arrays and holey-Si films with different periods. To reduce the difficulties in fabrications, we fabricated Si rod arrays with optimal AR parameters. Experiments show that by using a single layer of AR structure, the transmission of Si wafer can be enhanced by 38% at 20 THz, agreeing well with numerical simulations.