Evaluation of residual stress and viscosity in SiO₂-core/F- SiO₂ clad single-mode optical fibers from Brillouin gain spectra

A new method is presented for evaluating residual stress and viscosity in SiO₂-core/F-SiO₂ clad single-mode optical fibers from Brillouin gain spectra. The residual stress, which strongly influences refractive index and density in the core, is found theoretically and experimentally to be closely related to Brillouin frequency shift. The residual stress and viscosity calculated from the Brillouin frequency shift agree well with those measured with the photoelastic method. As a result, the average residual stress of long-length optical fibers can be obtained by this evaluation method.