All Optically Written Planar Germanosilicate Waveguide Gratings

Abstract

Photo-induced index changes in germanosilicate glass is a well known effect and has provided the basis for much recent activity on photoinduced refractive index gratings in fibres1. Since then, very large (>10-3) index changes in hydrogen loaded waveguide structures have been observed and used as the basis for patterning channel waveguides2 and directional couplers3. Recently, we have demonstrated waveguide structures patterned in PECVD grown material without the aid of hydrogen loading4,5, and in this paper we report the fabrication of all optically patterned buried waveguide grating structures, again without the aid of hydrogen loading. This demonstrates that the achievable index changes (without hydrogen loading) in this material is large enough to simultaneously support both waveguide and grating structures. The elimination of hydrogen loading is an important practical issue because, unlike fibres, planar waveguides need anomalously large overcladding layers to prevent rapid out diffusion of hydrogen during writing.