Enhanced Radiation Resistance of Silica Optical Fibers Fabricated in High O $_{\bf 2}$ Excess Conditions

Seven F-doped- and undoped-silica-core optical fibers were produced by the MCVD-method, the ratio of the O2 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 γ-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 μm. The fiber optical loss spectra were also measured after γ-irradiation to 1.31 MGy. Three RIA mechanisms affecting the near-IR region have been revealed, namely, short-wavelength RIA tails due to the Cl0-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 STH 1 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 O2 excess in the vapor-gas mixture during the perform core synthesis. The O2-excess technique is therefore proposed as a very promising one for the development of radiation-resistant fibers.