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 wavelength drift of these IO devices reported in a previous paper I [Optics Comm. 135 (1997) 385] by surface treatment (hydrophobization) of the waveguides and of the micromachined membranes. The membranes are spanned as `effective-refractive-index-shifting elements' E over surface relief gratings on the planar or rib waveguides. Electrostatic forces cause elastic deflections of an element E and, consequently, changes in the width of a sub-wavelength-wide air gap between the element E and the waveguide. Thus, the effective-refractive-index changes required 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 and of the waveguide enclosing the air gap. The IO nanomechanical devices with response times of μs to ms are fabricated using silicon technology. Their achieved stability is a precondition for potential applications, for example, as wavelength-tunable filters in optical networks.