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

Abstract

The defect center causing the 2 eV absorption band induced in pure silica core fibers by 60Co 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.

Effects of light and X-ray irradiation on CdS-doped glass

“…This signal is assigned to a trapped hole on a nonbridging oxygen atom neighboring on an Si atom (≡Si−O·). The ESR signal associated to the nonbridging oxygen atom almost disappears after annealing at 400 • C [11]. This result is consistent with our result.…”

Characterization of defects in waveguides formed by electron irradiation of silica-on-silicon

“…Second, there is a pair of absorption peaks at 650-and 540-nm wavelengths. Because absorption at 650 nm has previously been ascribed to NBOHC defects [11], [24] (even though these normally absorb at wavelengths closer to 630 nm), it is also attributed here to NBOHC's. This conclusion is confirmed by ESR results discussed later and by cathodoluminescence data described elsewhere [25].…”

Origin of the visible absorption in radiation-resistant optical fibers

“…These effects are particularly relevant to an optical absorption (OA) around 2 eV (620 nm) that grows with the deposited dose and constitutes the main contribution to induced losses from 1.5 eV (800 nm) to 3.1 eV (400 nm). Several studies based on optical and ESR experiments [3][4][5] have pointed out that the most important defect absorbing around 2 eV is the non-bridging oxygen hole center, NBOHC (≡Si-O·), but its band shape has never been analyzed in detail. Nagasawa et al [4,5] have asserted that the peak and the FWHM values can change with the OH-group content.…”

“…Several studies based on optical and ESR experiments [3][4][5] have pointed out that the most important defect absorbing around 2 eV is the non-bridging oxygen hole center, NBOHC (≡Si-O·), but its band shape has never been analyzed in detail. Nagasawa et al [4,5] have asserted that the peak and the FWHM values can change with the OH-group content. Later, in similar samples the presence of other absorptions have been proposed in the same spectral region, these bands have been attributed to: the peroxy radical, POR (≡Si-O-O·), [6] and the selftrapped holes, STH (≡Si-Ȯ-Si≡) [7][8][9].…”