Drawing-induced residual stress effects on optical characteristics in pure-silica-core single-mode fibers

Residual stress and its influence on optical characteristics have been investigated for pure-silica (SiO2)-core/fluorine-doped-silica(F-SiO2)-clad single-mode fibers. Theoretical analysis has shown the following: (1) Very high residual stress concentrated at the small-diameter core region is induced by drawing tension because of the viscosity difference between core and cladding. (2) The refractive index in the core is reduced greatly by the residual stress via the photoeleastic effects. (3) The decrease in the refractive index results in the shift of the cutoff wavelength to shorter wavelengths. These characteristic features have been ascertained experimentally in SiO2-core/F-SiO2-clad single-mode fibers drawn at various conditions, indicating the optimum drawing condition and structure for the single-mode fibers.