Optical aging characteristics of borosilicate clad fused silica core fiber optical waveguides

Very low transmission loss fiber optical waveguides have been developed during the past two years which have pure fused silica cores surrounded by borosilicate glass claddings. A recent study of the binary borosilicate glass system revealed that the low refractive index values which can be achieved with this glass and which are essential for the fiber cladding application occur only when the glass is quenched. Annealing causes the refractive index to increase to a less acceptable value. Although fibers are naturally quenched during drawing, there is a legitimate concern that the cladding might spontaneously anneal at its operating temperature in an unacceptably short time. The details of the annealing time−temperature relationship are determined in the present work and effective lifetimes for borosilicate clad fibers are predicted. It is concluded that lifetimes in excess of 100 years should be expected if the fiber operating temperature does not exceed 60 °C.