Processing-induced defects in optical waveguide materials

The effects of the fiber drawing process and high power (170 mJ/pulse) ultraviolet excimer laser irradiation on defects and defect precursors of silica glasses have been investigated. This study has considered the defects induced by the fiberization process in low-OH silica fibers and their response to ultraviolet excimer laser irradiation. The principal change of the population of defects and defect precursors occurred in the neck-down region where severe conditions such as higher temperatures and shear stresses are encountered. The influence of fiber drawing conditions, in particular, the effect of drawing speed and drawing temperature an the concentration of oxygen-deficient centers (ODCs) has been studied. Drawing speeds ranging from 10 to 180 m/min and drawing temperatures ranging from 1950 degrees C to 2150 degrees C were evaluated. The 215 and 248 nm absorption bands and E' electron spin resonance (ESR) signal intensity initially increased with drawing speed but eventually became invariant. However, both absorption bands and E' ESR signal intensity were insensitive to drawing temperature variations. The]photobleaching of a 248 nm absorption band, due to phototransformation of ODCs by ultraviolet excimer laser irradiation, in fibers is compared to the response of bulk rods from which they have been drawn. These data are interpreted in the context of the processing conditions employed during the investigation. (C) 1998 Elsevier Science B.V. All rights reserved.