This book gives the synthesis of porous silicon multilayers (PSL) by a simple route called electrochemical etching. The prepared multilayers and their physical characterizations have been carried out. These multilayers have been used to prepare distributed Bragg reflectors and planar microcavities for a potential sensing application. This book also deals with an optical study based on the refractive index deduced by experimental ellipsometric measurements as well as calculating and modeling manners such as the Bruggeman effective medium approximation. (Imprint: Novinka)