Size-dependent viscosity of silica optical fiber under high temperature

Abstract

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.

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“…This fact can have a significant impact on optical characteristics. The residual stresses level is consistent with the data obtained in [58].…”

“…Cui et al [58] note the importance of considering the viscoelasticity of silica-based optical fibers to improve and optimize their performance characteristics. The aim of their study was to evaluate the influence of fiber size (diameter) on the selection of fictitious temperatures.…”

“…Glass transition temperatures should be considered as a transformation range [52,60]. In [58], a formula is given to calculate the notional temperature, according to which the fictional temperature is approximately 1630 • C for a 80 µm diameter fiber. However, the formula does not take into account the chemical composition of the glass and the surface properties.…”