Enhanced Radiation Resistance of Silica Optical Fibers Fabricated in High O2 Excess Conditions

Seven F-doped-and undoped-silica-core optical fibers were produced by the MCVD-method, the ratio of the O-2 and SiCl4 molar flow rates in the vapor-gas mixture during the fabrication of the perform core being varied among the performs. The fibers were gamma-irradiated to 8.1 kGy (0.75 Gy/s), radiation-induced absorption (RIA) being measured during and after the irradiation in the spectral range 1.1-1.7 mu m. The fiber optical loss spectra were also measured after.-irradiation to 1.31 MGy. Three RIA mechanisms affecting the near-IR region have been revealed, namely, short-wavelength RIA tails due to the Cl-0-center and to the self-trapped holes of the second type (STH2) and a long-wavelength RIA tail due to the self-trapped holes of the first type (STH1). STH2 are argued to result from the strain frozen-in in the fiber glass in the fiber drawing process. The RIA due to STH1 is shown to anticorrelate with the RIA due to STH2. All the RIA mechanisms revealed are shown to be strongly suppressed by providing a high O-2 excess in the vapor-gas mixture during the perform core synthesis. The O-2-excess technique is therefore proposed as a very promising one for the development of radiation-resistant fibers.