ELECTRO-NANOMECHANICALLY WAVELENGTH-TUNABLE INTEGRATED-OPTICAL BRAGG REFLECTORS - PART II - STABLE DEVICE OPERATION

We demonstrate stable operation of electro-nanomechanically wavelength -tunable integrated-optical (IO) Bragg reflectors. We eliminated the w avelength drift of these IO devices reported in a previous paper I [Op tics Comm. 135 (1997) 385] by surface treatment (hydrophobization) of the waveguides and of the micromachined membranes. The membranes are s panned as 'effective-refractive-index-shifting elements' E over surfac e relief gratings on the planar or rib waveguides. Electrostatic force s cause elastic deflections of an element E and, consequently, changes in the width of a sub-wavelength-wide air gap between the element E a nd the waveguide. Thus, the effective-refractive-index changes require d for device operation are induced. As the cause of the drift effect, we identified the small but finite ionic electric conductivity of the nanometer thick adsorbed water film on the surfaces of the element E a nd of the waveguide enclosing the dr gap. The IO nanomechanical device s with response times of mu s to ms are fabricated using silicon techn ology. Their achieved stability is a precondition for potential applic ations, for example, as wavelength-tunable filters. in optical network s. (C) 1998 Elsevier Science B.V.