Radiation resistant characteristics of optical fiber, 4

A modified GI type optical fiber, the core of which was doped with boron and fluorine, was fabricated for trial to improve defects of limitation of employable wavelengths for transmission, which were usually found in the SI-type OP fibers, the core of which were made OT pure quartz fiber. This report describes results of radiation resistivity characteristics of the modified GI type optical fiber at the standpoint of practicability. Experimental work was carried out for continuous measurement of light transmission characterics and of wavelength dependency of light transmission loss during γ-ray irradiation from 60Co γ-ray source, Results by employing the test specimen of the modified GI type optical fiber made by the MCVD method showed several advantages in comparison with a conventional GI-type optical fiber doped with Ge and P. The modified GI type fiber had a better radiation dose rate effect, photobleaching effect and restoration capability after irradiation. Formation of color center was accelerated by shorter wavelength rays and it was found more suitable to employ light of 1.3 μm of longer wavelength 0.85 μm of the conventionally employed rays. Transmission loss increase by 1 MR irradiation was 100 dB/km and 250 dB/km for 65 MR. The latter value was restored to 100 dB/km after 30 hours of irradiation, and it was concluded that the radiation resistivity was significantly improved. It should be improved, however, that transmission loss is still higher of one order in the modified GI type fiber than the modified SI type fiber. (Takagi, S.)