Radiation effects of 14 MeV neutrons on germanosilicate and phosphorus-doped multimode optical fibers J. Bisutti a,b, * , S. Girard a , J. Baggio a a CEA/DIF, BP12, F91680 Bruye ` res-le-Cha ˆtel cedex, France b Laboratoire TSI, UMR-CNRS 5516, F42000 Saint-Etienne, France Available online 7 February 2007 Abstract We report the radiation-induced effects of 14 MeV neutrons on the transmission properties (300–900 nm) of germanosilicate (Ge) and phosphorus (P)-doped multimode optical fibers. We showed that all optical fibers, especially those containing P in their core or cladding, exhibit strong radiation-induced attenuation levels. Our results suggest that phosphorus-oxygen-hole centers govern the radiative response of P-codoped fibers in the visible to near-infrared range. Germanosilicate P-free fibers exhibit an induced attenuation decreasing from the ultraviolet to the near-infrared wavelengths that can be associated with GeX, Ge(1) and Ge-NBOH centers. Ó 2007 Elsevier B.V. All rights reserved. PACS: 78.70.g; 61.72.Ji; 61.80.x Keywords: Optical fibers; Radiation effects; Optical spectroscopy; Absorption; Silica; Radiation 1. Introduction The responses of single-mode and multimode optical fibers have been widely studied under continuous c-rays [1]. However fewer results are available concerning their behaviors under neutron exposures. Under c-rays, ioniza- tion leads to the creation of point defects in the silica glass constituting the fiber core and cladding. These defects, also called color centers, can imply both light emission through luminescence, and the decrease of the transmission proper- ties of the waveguide [2]. In the case of neutron irradiation the generation of defects can result from both atomic dis- placements and indirect ionizing effects [3,4]. To evaluate the vulnerability of optical links that will operate in the Laser Me ´gajoule facility [5], we have to ensure their radiation-tolerance to the mixed environment (X-rays, c-rays and 14 MeV neutrons) associated to the fusion experiments. For specific plasma diagnostics with high temporal resolution, the response of graded-index multimode optical fibers to neutron exposures has to be investigated. The constraints of using graded-index wave- guides is that the ‘radiation-hard’ pure-silica-core fibers can not be used. The germanium (Ge) and phosphorous (P) dopants are classically used to modulate the silica refractive-index of multimode optical fibers. In this paper we present the influences of these two elements on the 14 MeV neutron radiation responses of three different fibers. 2. Experimental procedure 2.1. Tested samples Table 1 gives the characteristics of the tested multi- mode fibers. Two samples are commercial fibers with Ge-doped cores with and without P-codoping in their clad- dings. The third fiber core is only doped with phosphorus. All our samples have acrylate coatings of 250 lm dia- meters. 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.10.013 * Corresponding author. Address: CEA/DIF, BP12, F91680 Bruye `res- le-Cha ˆ tel cedex, France. Tel.: +33 1 69 26 43 46/54 29 ; fax: +33 1 69 26 70 53. E-mail address: jean.bisutti@cea.fr (J. Bisutti). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 461–465