Effects of Radiation on Optical Fibers

Optical fibers have many advantages over metallic lines such as broad bandwidth, low-loss, immunity from interference due to electromagnetic induction, etc. They can be used to implement ultra-fast pulse signal transmission over a long distance under the circumstance with sophisticated electromagnetic radiation. However, while optical fibers are exposed in nuclear radiation environments, changes in their optical properties will occur thus resulting in deterioration of system performance eventually. Optical fibers will be required to withstand exposure to nuclear environments. Since optical fibers were applied in nuclear radiation environments as signal transmission media, people began to study effects of radiation on optical fibers, to measure the changes of optical fiber parameters, e.g. radiationinduced loss, irradiation damage recovery time and to analyze the effecting factors (Mattern et al., 1974; Evans et al., 1974; Golob et al., 1977; Friebele et al., 1978, 1979, 1980). Research results are used to evaluate the variation degree of optical fiber system performance and their working lives under nuclear circumstance, and to search methods for reducing radiation-induced loss (Tsunemi et al., 1986; Akira et al., 1988). As a result, anti-radiation optical fibers are developed subsequently. With the application of anti-radiation optical fibers, the degradation of performance will be reduced and the system life will be extended accordingly. On the other hand, radiation detecting systems based on the parameter changes above-mentioned are established to monitor the ambient radiation doses of underground nuclear exploders, space-aircrafts, radiation reactors and other nuclear facilities (Ramsey et al., 1993; Moss et al., 1994; Tighe et al., 1995; Fernadndez et al., 2002; May, 2006). When radiation projects to optical fibers, three effects will produce: (1) Increase of optical fibers absorption loss. The additional loss caused by radiation of photons and electrons with lower energy corresponds with the mechanism of color center. The color center spectrum lies usually within the visible and near-infrared wavelength regions, and it is resonant absorption that leads to additional loss. Neutron or alpha particle radiation absorbed by optical fibers can also cause additional loss. It will mainly damage optical fiber matrix structure and produce atomic structure defects and release electrons. (2) Changes of optical fiber refractive index. As a result, boundary conditions will no longer fully meet the optical fiber waveguides, and increase of evanescent field coupling energy will lead to additional loss. (3) Development of optical fiber luminescence. It is usually considered to be fluorescence or Cerenkov effects. It is very difficult to detect the light due to its weak intensity along optical fiber axis.