Splice loss of single mode fiber as related to fusion time, temperature, and index profile alteration.

The lower bound in loss for fusion splices is ~0.01 dB due principally to lateral offset of the cores and alteration of the index profile. This study shows the effects on loss of viscous flow and diffusion of the glass constituents during fusion, defining their time-temperature dependencies and changes in index profile. The activation energy for coalesence of the splice is 139 kcal/mole agreeing with that for viscous flow of fused silica. The minimum in splice loss follows completion of visible activity at the surface of the join and appears to be controlled by viscous flow since the activation energy at that point is 161 kcal/mole and within the range for silica. Index profile determinations of splices show that alteration takes place overlaping the period of coalesence and becoming increasingly servere as heating is continued past minimum loss. Separate studies of simulated splices indicate activation energies for diffusion of the core-cladding constituents of 50-75kcal/mole. Diffusivities of these constituents can be obtained from the index profiles, however sufficient data is not presently available for an accurate determination. It is intended to supplement these initial efforts with additional data in order to more fully understand these interactions and be able therefore to optimize fiber structrues having more desirable splicing characteristics with respect to low loss.