Properties of phosphorus-related defects induced by γ-rays and pulsed X-ray irradiation in germanosilicate optical fibers

Time dependent radiation-induced attenuation changes of germanosilicate (∼13 wt%) optical fibers have been measured under steady-state γ-ray and pulsed X-ray irradiations. Particularities of phosphorus (P)-codoped cladding fibers for these environments are presented. For each irradiation type, spectral attenuation measurements show that permanent radiation-induced losses at 1.55 μm are due to the infrared absorption band of P1 centers. We assume that particular kinetics of recovery and an increase of attenuation measured for P-codoped fibers, after pulsed X-ray irradiation, are induced by a charge retrapping phenomenon from phosphorous oxygen hole (POH) centers to P1 ones. With this mechanism, we explain the P-codoped fiber characteristics after both types of irradiation. Our study shows that the effect of P-related color centers is increased when the P-codoped cladding (∼0.3 wt%) contains also germanium (∼0.3 wt%).