Athermalization of a silica-based waveguide with a UV-induced Bragg grating on a crystallized glass substrate

To realize athermal glass films, formation of Ge-B-SiO₂ and F-B-SiO₂ films by plasma-enhanced chemical vapor deposition (PECVD) was examined on several substrates with various thermal expansion coefficients. Waveguide Bragg gratings were fabricated by irradiation with a KrF excimer laser light through a phase mask. A temperature dependence of the Bragg wavelength as low as 4 pm/°C was obtained in a 6GeO₂-13B₂O₃-81SiO₂ (mol%) core and 13B₂O₃-87SiO₂ (mol%) cladding waveguide or in a 13B₂O₃-87SiO₂ (mol%) core, 6GeO₂-13B₂O₃-81SiO₂ (mol%) grating layer and 6F₂-10B₂O₃-84SiO₂ (mol%) cladding waveguide on crystallized glass substrates with a thermal expansion coefficient of -2.0 × 10^-6/°C. Such temperature sensitivity is one third of conventional waveguide Bragg grating devices.