Fabrication of electrochromically tunable photonic crystals

Tunable photonic crystals offer an interesting possibility to adjust the photonic band gap (PBG) as per requirement. Various methods of achieving this have been tried that include polarization of liquid crystals, thermal effects and more. Electrochromic (EC) materials in which a reversible optical property change can be induced with the application of a small electric field offer a novel possibility to tune the PBG in a controlled and reversible way. The reversible chemical change and the ensuing change of optical constants in these periodically arranged EC materials make the PBG tunability possible. In a recent work we have demonstrated for the first time the PBG tunability of EC materials deposited in the form of periodic inverse opals. This earlier work was carried out with the well known Tungsten Trioxide (WO₃) EC thin films into which lithium intercalation was done by a dry lithiation method. In the present work we report on the fabrication of a simple tunable photonic crystal device based on electrochemical insertion/extraction of lithium based on WO₃ inverse opals.