Switches and Frequency-Agile Sources With Photonic Bandgap Structures

Abstract : The tunable devices are made mostly in bulk silicon (porous silicon one- and two-dimensional photonic bandgap structures) although a few have been made in SOI (two-dimensional photonic bandgap structures). Porous silicon is formed by electrochemically etching a silicon wafer in a hydrofluoric acid-based solution. By choosing the proper silicon doping and controlling the applied current density, it is possible to achieve high quality photonic bandgap structures. Liquid crystals are the active species infiltrated into the porous silicon matrix to enable tuning of the optical properties. Liquid crystals are anisotropic molecules whose refractive index depends on orientation. Either electric field or thermal perturbation can be used to change the orientation of the liquid crystals. Since the optical properties of photonic bandgap structures depend on the refractive indices of the constituent materials, the application of an electric field or heating can be used to control the operation of tunable porous silicon devices.