Abstract
A regenerated fiber Bragg grating (RFBG) in silica fiber was used to observe the viscous relaxation process of the host silica fiber at high temperatures of around 1000 °C. Two factors, preannealing time and loaded tension, which affect viscous relaxation, were observed. When an RFBG is stretched after a longer preannealing, the measured viscosity of the optical fiber was observed to reach equilibrium faster, which means that preannealing accelerates viscous relaxation. A similar acceleration phenomenon was also observed when a larger load was applied to stretch the optical fiber, although the acceleration effect of loaded tension was not as strong as in the preannealing case. The results play an active role in establishing effective optical-fiber devices for application in high-temperature environments.
Highlights
Viscosity is a characteristic parameter that describes the properties of a material [1]
The viscous relaxation process could be clearly observed, and the log of the viscosity became stable at a value between 13.6 and 13.8, which corresponds to an absolute viscosity value of ~1013 Pa·s, which agrees well with previously reported results [13,14,15]
The log of the viscosity of the optical fiber during the viscous relaxation process was obtained as being in the range of 13.2 to 13.8, stabilizing between
Summary
Viscosity is a characteristic parameter that describes the properties of a material [1]. It is a key parameter throughout the entire process of glass production and is often used as an important indicator for controlling and evaluating the process and performance of glass production. Different glass-forming methods and speeds relate to their viscosities. The viscosity of the glass plays an important role in helping to eliminate internal stress in the glass [2]. The main factors affecting viscosity are chemical composition and temperature, which are related to heating time within the transition-temperature range [3,4]. The variation of the viscosity of silica glass with time at a constant temperature is described as the relaxation process. The viscosity of silicate glass is studied by applying a pressure scheme [5], and the viscosity of glass fibers is measured using stretching or bending schemes [6,7]
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