JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 22, NO. 8, AUGUST 2004 1915 -Rays and Pulsed X-Ray Radiation Responses of Germanosilicate Single-Mode Optical Fibers: Inﬂuence of Cladding Codopants Sylvain Girard, Jacques Keurinck, Youcef Ouerdane, Jean-Pierre Meunier, Member, IEEE, Member, OSA, and Aziz Boukenter Abstract—The radiation-induced attenuation (RIA) in ger- manosilicate single-mode optical ﬁbers was measured at 1.55 and 1.31 m after a pulsed X-ray irradiation and at 1.55 m during and after a steady-state -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 s 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 -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. Index Terms—Defects, optical ﬁbers, radiation effects. I. INTRODUCTION T HERE have been to date numerous characterizations of the radiation sensitivities of single or multimode optical ﬁbers. Previous literature has studied the inﬂuence of their compositions on the radiation properties of optical ﬁbers both for -rays [1], [2] and pulsed X-ray [3] environments. The transient exposures were less investigated; only qualitative studies of commercial or prototype optical ﬁbers, provided by ﬁber manufacturers without complete data concerning the fabrication parameters and composition, were performed. This implies that for the transient environment, only the preponderant impact of the core dopants (pure silica or germanium-, nitrogen-doped silica cores) has been studied so far [4], [5]. The exact inﬂuence of the cladding codopants on the germanosilicate ﬁber radiation responses is not yet well documented. For -rays, the effect of varying single-mode ﬁber (SMF) fabrication factors such as core and cladding dopants has been widely studied by Friebele at 1.3 m Manuscript received October 30, 2003; revised May 17, 2004. This work was supported in part by the French Procurement Defense Agency. S. Girard was with the TSI Laboratory, UMR-CNRS 5516, Université Jean Monnet, 42000 Saint-Etienne, France, and also with SAGEM SA, 95101 Ar- genteuil, France. He is now with Commissariat à l’Energie Atomique (CEA), Bruyères-le-Châtel, France (e-mail: sylvain.girard@cea.fr). J. Keurinck is with SAGEM SA, 95101 Argenteuil, France. Y. Ouerdane, J.-P. Meunier, and A. Boukenter are with the TSI Laboratory, UMR-CNRS 5516, Université Jean Monnet, 42000 Saint-Etienne, France. Digital Object Identiﬁer 10.1109/JLT.2004.832435 [6] to improve the knowledge of radiation properties of the light- wave communication systems submitted to nuclear exposure. The preponderant inﬂuence of core dopants is essentially due to the large proportion of light transmitted into the ﬁber core. However, for SMFs and infrared wavelengths such as 1.31 and 1.55 m, the fraction of light guided into the cladding is not negligible, being larger than 20%. The aim of this paper is to determine the inﬂuence of the cladding composition on the ger- manosilicate ﬁber radiation response at 1.31 and 1.55 m. This paper describes a study of the phosphorus (P), germa- nium (Ge), and ﬂuorine (F) codoping inﬂuences on the pulsed X-ray radiation sensitivity of ﬁbers at 1.31 and 1.55 m, as these three elements are widely used in the cladding of stan- dard germanosilicate ﬁbers operating in the third telecommu- nication window 1.55 m . A set of prototype SMFs are tested under transient exposure with well-deﬁned composition and process parameters. The interactions between these three different cladding codopants are also characterized. The tested ﬁbers and the experimental setup are described in Section II. The results of the pulsed X-ray and steady-state -ray irradiation tests are presented in Section III. In the last section, the inﬂuences of Ge-, P-, and F-codoping on the radiation sen- sitivities of germanosilicate optical ﬁbers are discussed. II. EXPERIMENTAL CONDITIONS AND SETUP We tested six different SMF samples with well-known com- positions in order to correlate the nature of dopants to the sensi- tivity of the ﬁbers under irradiation. All the preforms were made by the modiﬁed chemical vapor deposition (MCVD) process with exactly the same preform fabrication and drawing parame- ters. All ﬁbers have a highly Ge-doped core ( 12 wt %) and the same normalized refractive-index proﬁle to ensure an identical contribution of cladding codopants for all tested ﬁbers. Each ﬁber cladding has been codoped by a combination of three ele- ments (Ge, P, and F) at low concentration levels ( 0.3 wt %). We performed electron microprobe analysis (EMPA) at the Centre Technique d’Arcueil, Arcueil, France, facilities, allowing us to detect the nature, concentration, and localization of the dopants and impurities in the transverse section of each ﬁber. The main characteristics of the tested ﬁbers are given in Table I. Pulsed X-ray and -ray tests on optical ﬁbers were performed at the Centre d’Etudes de Gramat facilities, using the X-ray gen- erator ASTERIX [3], [7] and a Co source. The total deposited dose for transient exposures was lower than 1 kGy SiO and the dose rate was greater than Gy s . 0733-8724/04$20.00 © 2004 IEEE