Size-dependent viscosity of silica optical fiber under high temperature

Viscosity of optical fiber plays an important role in high temperature applications in harsh environments. A size-dependent viscosity phenomenon of silica optical fiber under high temperature is observed by the stretching method with in-fiber regenerated fiber Bragg gratings (RFBGs). Higher viscosity is derived from optical fiber with larger diameters. The mechanisms of this size-dependent relationship of high temperature viscosity of silica optical fiber are discussed, and the difference in fictive temperature of silica optical fibers is considered as the mainly contribution. An equivalent fictive temperature of optical fiber at a metastable structure state is used to explain the difference in equilibrium viscosity. Then the relationship between equilibrium viscosity and fictive temperature for silica optical fiber at 1000 °C is derived.