Nanoporous silicon multilayers for terahertz filtering

We describe the fabrication, simulation, and measurement of a terahertz (THz) filter composed of nano-porous silicon multilayers. Using electrochemical etching, we fabricated a structure composed of alternating high- and low-index layers that achieves 93% power reflectivity at the target wavelength of 1.17 THz, with a stopband of 0.26 THz. The measured reflection and transmission spectra of the multilayer filter show excellent agreement with calculations based on the refractive indices determined separately from single-layer measurements. This technique could provide a convenient, flexible, and economical way to produce THz filters, which are essential in a variety of future applications. (C) 2009 Optical Society of America