Radiation Effects on Silica-Based Optical Fibers: Recent Advances and Future Challenges

Abstract

International audienceIn this review paper, we present radiation effects on silica-based optical fibers. We first describe the mechanisms inducing microscopic and macroscopic changes under irradiation: radiation-induced attenuation, radiation-induced emission and compaction. We then discuss the influence of various parameters related to the optical fiber, to the harsh environments and to the fiber-based applications on the amplitudes and kinetics of these changes. Then, we focus on advances obtained over the last years. We summarize the main results regarding the fiber vulnerability and hardening to radiative constraints associated with several facilities such as Megajoule class lasers, ITER, LHC, nuclear power plants or with space applications. Based on the experience gained during these projects, we suggest some of the challenges that will have to be overcome in the near future to allow a deeper integration of fibers and fiber-based sensors in radiative environments

Neutron-induced defects in optical fibers

“…However, their use in harsh environments associated with ionizing radiation is negative for the optical performance due to the generation of point defects that introduce localized levels within the forbidden band gap thus causing radiation induced absorption (RIA). The radiation effects in silica have been, therefore, the object of intensive studies over the last decades [1].…”

“…Previous studies have shown that pure silica core (PSC) and F-doped fibers exhibit low RIA in the UV-Visible spectral domain for high irradiation doses [1]; they are, for this reason, of particular interest for the design of radiation hardened distributed fiber sensors for nuclear industry.…”

Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels

“…For this aim, fiber-based sensors like those based on fiber Bragg gratings (FBGs) present several advantages, like a faster time response than thermocouples (lower than 1 s) and a high radiation tolerance, as investigated by previous studies [2]. However, radiation is also known to alter the fiber transmission properties as well as the FBG properties [2,3]. Furthermore, the amplitudes and kinetics of these changes are dependent on temperature, as this extrinsic parameter governs the stability of the radiation induced point defects in the silica-based glass at the origin of these macroscopic changes [2,3].…”

“…However, radiation is also known to alter the fiber transmission properties as well as the FBG properties [2,3]. Furthermore, the amplitudes and kinetics of these changes are dependent on temperature, as this extrinsic parameter governs the stability of the radiation induced point defects in the silica-based glass at the origin of these macroscopic changes [2,3]. Another important point, as clearly shown in a paper by Henschel et al [4], is that the radiation sensitivity of a fiber and of an FBG written in this fiber are not directly correlated but will depend on many other parameters like the FBGs' writing technique and conditions as well as the possible hydrogen-loading before inscription [5].…”

“…At the sensor level, the radiation induced attenuation (RIA) is very impacting when the dose increases, as RIA can strongly decrease the sensing length, resulting sometimes in a total loss of the information. To avoid this, specific fibers composition should be used, the most efficient ones being those with pure-silica or fluorinedoped cores [3]. Then, these two types of radiation resistant single-mode fibers are used in this Letter and will be functionalized with FBGs.…”