Abstract

Flame Hydrolysis Deposition (FHD) is a traditional route to deposit layers of doped silica onto the surface of a substrate for planar lightwave circuits. To form a uniform layer of fused glass the deposited soot must be consolidated, typically within a furnace at temperatures between 1200 °C and 1400 °C. This thermal processing is not localised as the temperature of the entire wafer is raised. This could be an issue for thermally sensitive, metallic or active photonic structures. This also limits the materials used for the substrate and requires the silica glass to have sufficient dopants to permit consolidation. CO₂ lasers have previously been used for smoothing and polishing of silica [1,2] and were performed with CO₂ lasers operating with a wavelength of 10.6 µm. Silica however has a large absorption peak between 9 to 9.5 µm [4]. This paper demonstrates that using a CO₂ laser operating at 9.3 µm allows for highly localised heating and consolidation of FHD silica soot on a silicon wafer, this greatly reduces processing time and relaxes the constraints on dopants and substrate used in FHD, and to knowledge of the authors is the first example of FHD consolidation with a 9.3 µm laser.

© 2017 IEEE