Photosensitization of optical fiber and silica-on-silicon/silica waveguides

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Abstract
Localized heating with a flame is shown to be a simple and effective method for substantially augmenting the photosensitivity of high-silica optical waveguides to (UV) light. The method increases the photosensitivity of standard (Ge-doped core) telecommunications fiber by a factor greater than 10 (photoinduced ΔnUV > 10−3) and renders strongly photosensitive the cores of high-quality Ge:SiO2-on-Si and Ge:SiO2-on-SiO2 planar waveguides that were negligibly photosensitive before treatment. We have written large-modulation-depth Bragg gratings, in both fiber and planar optical waveguides photosensitized by our method, using KrF (249-nm) radiation incident upon the waveguides through a zero-order-nulled phase mask. It is noteworthy that photosensitization by our method is achieved with a negligible increase in loss at the three principal optical communication windows.