Defect structure and formation mechanism of drawing-induced absorption at 630 nm in silica optical fibers

This paper presents a study on drawing condition dependences of optical absorption at 630 nm and nonbridging oxygen hole centers (NBOHCs) in optical fibers drawn from low-OH-content synthetic silica glass. The intensity of the 630-nm absorption is proportional to the NBOHC concentration, and the value of the oscillator strength for the NBOHC is 4.2×10−4, which nearly equals the theoretical values. These results confirm that the 630-nm absorption is due to the NBOHCs in low-OH-content silica glass. Furthermore, the 630-nm absorption increases with increasing drawing tension. This drawing tension dependence is explained by applying kinetics of the stress-induced crack growth in metal to the formation of the NBOHCs in the drawing process.