Radiation hardness of present optical fibres

Optical fibers find rapidly growing use also in the nuclear industry. The dependence of their radiation-induced loss on fiber type, wavelength, temperature, light power, dose rate, and radiation type (gamma rays, neutrons) is pointed out and test results of modern (1989 - 1993) single mode (SM), graded index (GI), multimode stepindex (MM SI), and polymer optical fibers (POF) are presented. Continuous 60 Co gamma irradiation of the SM fibers with a dose rate of about 1.5 Gy/s up to a final dose of 10 6 Gy led to radiation-induced losses of only 0.85 to 1.3 dB/10 m at 1300 nm wavelength and temperatures around 30 degree(s)C, whereas the GI fibers had losses of 1.3 to 2 dB/10 m under the same conditions. The lowest radiation-induced loss show MM SI fibers with pure SiO 2 core of high OH-content: about 0.15 dB/10 m around 850 nm and about 0.1 dB/10 m around 1060 nm (10 6 Gy, equals 30 degree(s)C). POF with a core made of polymethyl methacrylate also have loss increases of 6 Gy increased by about 2% (MM SI) up to about 10% (SM). 14 MeV neutron irradiations seem to cause higher losses and reduced breaking stress, compared with 60 Co gamma irradiations up to the same total dose.