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1994
Conference Paper
Title
Radiation hardness of present optical fibers
Abstract
Optical fibres find rapidly growing use also in the nuclear industry. The dependence of their radiation-induced loss on fibre 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 fibres (POF) are presented. Continuous 60Co gamma irradiation of the SM fibres with a dose rate of about 1.5 Gy/s up to a final dose of 10E6 Gy led to radiation-induced losses of only 0.85 to 1.3 dB/10 m at 1300 nm wavelength and temperatures around 30 øC, whereas the GI fibres had losses of 1.3 to 2 dB/10 m under the same conditions. The lowest radiation-induced loss show MM SI fibres with pure SiO2 core of high OH-content: about 0.15 dB/10 m around 850 nm and about 0.1 dB/10 m around 1060 nm (10E6 Gy, about 30 øC). POF with a core made of polymethyl methacrylate (PMMA) also have loss increases of < about 0.1 dB/10 m (670 nm, ro om temperature ), but only up to gamma dose values < about 800 Gy. The breaking stress of allglass fibres after 10E6 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 60Co gamma irradiations up to the same total dose.