High Temperature Effects in Fused Silica Optical Fibers

Abstract

Fire-resistant fiber optic cables used in safety and monitoring systems playing an essential role in fire fighting and building evacuation procedures are required to temporarily maintain optical continuity when exposed to fire. However, the use of fused silica fiber at temperatures between 800C and 1000C is associated with two highly undesirable phenomena. Thermal radiation (incandescence) of optical fibers, with its intensity and spectral distribution being proportional to additional attenuation observed in the fiber’s hydroxyl absorption bands (“water peaks”) is one of them. The other consists in penetration of thermal radiation from the surroundings into the fiber, due to defects in glass, causing light scattering and resulting in fiber brittleness. Thermal radiation is a source of interference in fiber attenuation measurements performed during fire tests and affects normal operation of fiber optic data links in the event of a fire. In this article, results of laboratory tests performed on a telecom single mode and multimode fibers subjected to temperatures of up to 1000C are presented. Keywords—fire-resistant fiber optic cable, fire test, fused silica optical fiber, incandescence spectrum, thermal deterioration, thermal radiation.