$gamma$ -Rays and Pulsed X-Ray Radiation Responses of Germanosilicate Single-Mode Optical Fibers: Influence of Cladding Codopants

The radiation-induced attenuation (RIA) in germanosilicate single-mode optical fibers was measured at 1.55 and 1.31 mm after a pulsed X-ray irradiation and at 1.55 mm during and after a steady-state g-ray irradiation. The influence of codoping the fiber cladding with germanium (Ge), phosphorus (P), and fluorine (F) on the sensitivity of Ge-doped core fibers was characterized. P-codoping makes it possible to decrease the RIA for short times (10/sup *6/ s*10/sup *3/ s) post- pulse. However, P-codoped fibers exhibit larger values of permanent RIA than P-free fibers after transient exposure and are inadequate for a steady-state environment. The impact of F-codoping depends on the other codopants incorporated in the fiber cladding, but its addition seems to be deleterious for the radiation hardening of the germanosilicate fiber at the two tested wavelengths. Ge-codoping increases the sensitivity of P-, F-codoped fibers under X-rays and steady-state g-ray irradiation, whereas it decreases the RIA in F-doped ones. Some hypotheses on the creation mechanisms and properties of the color centers related to these three codopants are proposed.