HIGH-TEMPERATURE EFFECTS IN FLUORINE-DOPED, FUSED SYNTHETIC SILICA FIBERS

Effects caused by exposure oflarge-core, fluorine-doped, step-index si lica optical fibers to high temperatures were studied experimentally i n controlled laboratory conditions. A fiber was located partially insi de a temperature-controlled electric tube furnace and irradiated from the end by a light source. The Light source was either an incandescent halogen lamp or a blackbody radiator. The influence of fiber temperat ure on the angular distribution of the radiation in the fiber and the coupling and propagation of thermal radiation in the fiber was studied . With increasing temperature the profile of the angular distribution of the radiation was transformed irreversibly from a Chinese hat profi le to a much flatter one, This effect was pronounced at 1000 degrees C and above. Radiation from the furnace was found to propagate in the f iber as an attenuating mode at temperatures above 800 degrees C. Most of the radiation exited the fiber at angles beyond but close to the ac ceptance angle. Calculations show that thermal self-radiation of the f iber is negligible. The physical explanations fur these effects are di scussed and practical conclusions are drawn. (C) 1997 Optical Society of America.