Microoptical applications of porous silicon superlattices

Using reflectance measurements we have investigated the dependence of the refractive index of porous silicon layer structures on the formation current density for different substrates. Based on these results various kinds of optical interference filters were fabricated. We have formed samples consisting of discrete single layers with different porosities as well as samples with continuous variations of the refractive index (rugate filters). Using this technique the fabrication of anti-reflectance coatings with low reflectance over a wide range of wavenumbers becomes possible.