Radiation Effects on Pure Silica Core Optical Fibers by γ-Rays: Relation between 2 eV Band and Non-Bridging Oxygen Hole Centers

The defect center causing the 2 eV absorption band induced in pure silica core fibers by 60 Co γ-rays is discussed. The 2 eV band and non-bridging oxygen hole center (NBOHC, SI–O·) show almost the same thermal annealing characteristics. The peak wavelength of the 2 eV band in low-OH (≦6 ppm) fibers is 630 nm, but shifts to shorter wavelengths according to the amount of OH group the sample contains, and appears at 600 nm in high-OH (≧700 ppm) fibers. The peak shape is broader in high-OH fibers than in low-OH fibers. This shift and broadening is attributable to a hydrogen bond between NBOHC and a hydrogen atom. Based on the above results, the defect center responsible for the 2 eV band is considered to be NBOHC.

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