A method of sintering glass preforms for manufacturing planar optical waveguides

摘要

A planar waveguide structure is produced by a process comprising sintering substantially pure SiO₂ layers in a He₂/BCl₃ or He₂/BF₃ atmosphere. This results in the generation of a liquid phase of substantially lower viscosity than that of the deposited silica by itself. Since viscous sintering is enhanced by the presence of this liquid, consolidation occurs at lower temperature, e.g. 1000-1100°C, than those used in the prior art, e.g. 1350-1500° C. Much of the B₂O₃ remains unreacted with the silica particles it helps to sinter, acting like a flux to bring about consolidation. This remaining B₂O₃ is removed at the conclusion of the consolidation procedure by steam treatment at temperatures of 900°C - 1100°C. Some boron is incorporated into the silica layer, changing its Coefficient of Thermal Expansion (CTE) without substantially increasing its index. Thus, this method improves both structure and processing of planar waveguides by reducing the processing temperature and producing a glass which does not bow the substrate and essentially eliminates birefringence resulting in polarization dependent losses. This greatly benefits sophisticated circuits such as those intended for wavelength diversion multiplexing and allows narrow and precisely positional pass bands.