In 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.

This paper reports on the radiation induced attenuation of light at 1310 nm and 1550 nm in 12 commercially available single mode (SM) optical fibers. The fiber samples are exposed to gamma rays from a ⁶⁰Co source and to a high energy physics radiation field. The attenuation is studied as a function of total dose, dose rate, light power and temperature. Radiation hard fibers from one manufacturer show an extraordinary low attenuation for light at 1310 nm that does not exceed 5 dB/km even after a total dose of 1 MGy. 2500 km of this type of fiber have been produced by the manufacturer and quality assurance measurements of the production batches are presently ongoing.

This review focuses on silica-based optical fibers, guiding light through the total internal reflection mechanism, that are currently used in telecommunications and sensor networks. Section I briefly introduces the fiber and fiber sensor technologies. Section II presents their various applications in radiation environments. In section III, the radiation effects on optical fibers are explained, first at a microscopic scale, with the description of point defects generated by irradiation. Then, the macroscopic consequences of the appearance of these point defects are discussed, in particular the phenomena of radiation-induced attenuation (RIA), radiation-induced emission (RIE) and radiation-induced refractive index change (RIRIC). RIA impacts nearly all applications under irradiation. We then detail the various parameters, intrinsic or extrinsic to the optical fibers that influence their amplitudes and kinetics. This improved knowledge paved the way for the radiation hardening of optical fibers through various approaches, either at material, component or system levels, that are described in section IV. Recent advances are presented for passive and for active rare-earth doped optical fibers and systems. Then, the use of fiber optic sensors is introduced, starting in section V with the latest advances in radiation-hardened point or distributed sensors. Then, the potential of this technology for radiation detection, beam instrumentation and dosimetry applications is assessed in section VI. Finally, the future prospects and the main challenges to be met in order to accelerate the implementation of this technology in the harshest environments are discussed.

The process of selecting, manufacturing, and installing a large quantity (2500 km) of commercially available radiation tolerant specialty fibers is described. Radiation tests of various types of fibers from different manufacturers provided sufficient understanding of the radiation effects to select the best performing fiber type. Systematic verification of a sample of each preform assured a constant quality of the series production and allowed assessing the impact of small variations in the manufacturing process on the radiation hardness and the optical transmission characteristics. The fiber cable installation technique based on microjetting and plastic cable ducts has been validated for areas with high levels of radiation.

The radiation-induced Bragg wavelength shift (BWS) was measured with type I gratings made of 12 fibers with very different composition, i.e., of fibers with an extremely different radiation-induced attenuation. With two of the fibers fabrication parameters like laser intensity, hydrogen loading, and annealing conditions after grating inscription were varied. With another fiber type I and type II gratings were made by a completely different process. With gratings made under identical conditions of the 12 fibers the radiation-induced BWS only varied by about a factor of three. Varying the fabrication parameters led to BWS differences up to nearly a factor of ten.