Infrared Spectral Dependencies of Pulsed X-Ray Radiation-Induced Attenuation in Single-Mode Optical Fibers J. Bisutti 1,2 , Student Member, IEEE, S. Girard 1 , Member, IEEE, C. Marcandella 1 and J. Baggio 1 , Member, IEEE . Abstract – We investigate the changes of optical absorption at infrared wavelengths induced by pulsed X-ray irradiation on single mode fibers. We focus on the influence of the germanium (Ge) and phosphorus (P) dopants. To do that, we characterize the changes of the radiation-induced attenuation (RIA) at 1310 nm and 1550 nm for shorter times after X-ray pulse (10 -7 -10 -1 s). We also measure the spectral dependence of the RIA (500-2000 nm) from 10 -1 s to several hundreds of seconds. We show that absorption bands peaking at infrared wavelengths mainly explain the RIA at 1310 nm and 1550 nm. In a Ge-doped fiber two infrared absorption bands, not previously reported in literature, are shown to substantially contribute to infrared RIA. In a P-doped fiber, the infrared RIA is explained by using the absorption bands of P-defects previously reported in literature with an un-reported absorption band peaking around 1.43 eV (FWHM=0.41 eV). I. INTRODUCTION HE optical reponse of single-mode optical fibers submitted to a radiative pulse has already been characterized at 1310 nm and 1550 nm Telecom wavelengths in previous studies [1-7]. Pure-silica-core fibers have been shown to exhibit very high transient radiation-induced attenuation (RIA) when subjecting to an high-dose rate pulse (see e.g. [4]). For germanosilicate fibers, it was shown that the P addition into the fiber core or fiber cladding substantially decreases the transient RIA but leads to very high permanent induced-losses. The RIA results from the creation of point defects, also called color centers in the silica glass constituting the fiber core and the fiber cladding. Spectral absorption measurements can give information on the nature of the generated point defects. Indeed, by decomposing the radiation-induced attenuation (RIA) spectra with the help of Gaussian absorption bands associated to the created point defects, it is possible to evaluate the contribution of each point defect to the induced losses. In this paper we study the Manuscript recieved September 7, 2007. J. Bisutti is with the CEA DIF, F91680 Bruyères-le-Châtel, France, and also with the Laboratoire TSI, Université de Saint-Etienne, F42000 Saint-Etienne, France (e-mail: jean.bisutti@cea.fr). S. Girard, C. Marcandella and J. Baggio are with the CEA DIF, F91680 Bruyères-le-Châtel, France (e-mail: sylvain.girard@cea.fr;claude.marcandella@cea.fr;jacques.baggio@cea. fr). influence of Ge and P dopants on the transient RIA of single- mode (SM) fibers at infrared (500-1900nm) wavelengths. For this, we perform two types of transient RIA measurements: short time-resolved measurements (10 -8 -0.1 s) at single wavelengths (1310 nm and 1550 nm) and in-situ spectral measurements (500-1900 nm, ~0.1s to 1000 s). A Super Continuum source, which has an optical power much greater than that of an usual halogen source, has been used, to perform in-situ spectral RIA measurements on single-mode fibers. With this new tool, we will be able to improve our knowledge about the origins of fiber degradation at infrared wavelengths. II. EXPERIMENTAL PROCEDURE A. Tested Optical Fibers The characteristics of the tested SM optical fibers are given in Table I. The #Ge and #Ge/P are commercial off-the-shelf fibers. The #P is a prototype fiber (SR-00-12-28 preform manufactured by the Fiber Optic Research Center, Moscow). TABLE I. CHARACTERISTICS OF SINGLE-MODE TESTED FIBERS Fibers Manufacturer Core/cladding diameter Core dopants Cladding dopants #Ge Corning 8.2 /125 μm Ge (~4%mol) none #P FORC 4/125 μm P (~12-13%mol) none #Ge/P Alcatel 9/125 μm Ge Ge, P, F B. Experimental Setup The tested optical fibers were subjected to transient exposure using the ~1 MeV pulsed X-ray generator ASTERIX from the Centre d’Etude de Gramat in France [8]. The dose rate is >10 9 rad s -1 . All the measurements were performed at room temperature. The tested fibers were coiled to diameters of 60 mm and mated to optical sources and detectors through 30-m fiber pigtails. The radiation responses of the fibers were successively characterized with the two setups represented in Fig. 1. The lengths of the fiber samples were adapted to measure the fiber response on several attenuation decades. The RIA uncertainties are mainly attributed to the dosimetry and are estimated within ±20%. T 978-1-4244-1704-9/07/$25.00 ©2007 IEEE