Mechanical Stress in Rare-Earth-Doped Laser Fibers

摘要

Mechanical stress can significantly influence the optical and mechanical properties of fibers. We present results ofnondestructive measurements of thermal stress in rare-earth-doped optical fibers, which are related to the dopingvariations across the fiber cross section and the preparation conditions. The samples are preforms and fibers with a largeytterbium doped core that were prepared by an alternative glass forming process, which is capable to realize bigger ratiosof core to cladding diameter than the MCVD-method. To the best of our knowledge, this is the first time measurementsof stresses and birefringence were made on such active optical fibers and their preforms. The results are compared toprevious results on ytterbium-doped samples fabricated by the MCVD-technology. From the resultant stress profile, wecould calculate the stress induced index changes that are relevant for the light propagation in optical fibers, and discussthe reasons for the observed mechanical stress. In addition, we could evaluate the samples regarding their changes inthermal expansion coefficient induced by doping with one or more oxides in several concentrations and different ratios.We confirmed our earlier result that the active doping component ytterbium generates much higher stress than othercommon dopants like aluminum, phosphorus or boron.