Optical limiting effects in hybrid electromechanical-metallo-dielectric Ag/ZnO photonic band gap structures

We study a combination of nonlinear interactions and electromechanical switching in one-dimensional metallo-dielectric photonic band gap (PBG) structures. The structure, which is composed of two similar stacks consisting of ZnO and Ag alternating layers separated by an air layer of tunable thickness, is arranged to take advantage of both active and passive transmission control mechanisms. Active transmission control is provided by the activation of electromechanical switches, and acts on a time scale of microseconds. Passive transmission control is based on the onset on nonlinear two-photon absorption in the ZnO layers for high incident intensities, and occurs on a time scale of picoseconds. Preliminary samples were prepared to show that the two degrees of freedom can be implemented in a metallo-dielectric structure. The reduction of transmittance with increasing incident intensity was demonstrated in Ag/ZnO samples realized by means of dual ion beam sputtering technique. Electromechanical transmission control was instead demonstrated in a metallo-dielectric structure composed of thermally evaporated Ag/MgF₂ multilayer stack which contained an air gap. We therefore show that the combination of the nonlinear behavior exhibited by ZnO and modulation of an air gap results in a more responsive, faster device, with stronger attenuation and higher contrasts in the transmission of light between "on" and "off states. We conclude that this kind of structure has great potential for broadband optical limiting and switching applications.