Joint Residual Stress/Refractive Index Characterization of Large-Mode-Area Erbium-Doped Fibers

The residual stress (RS) and refractive index (RI) distributions of large-mode-area (LMA) erbium-doped fibers (EDFs) are measured for the first time using a high-resolution three-dimensional index-stress distribution measurement method. The effects of fiber manufacturing, cleaving, and arc fusion splicing of a commercially available LMA EDF are concurrently characterized at state-of-the-art stress, index, and spatial resolutions. RS induced via fiber manufacturing results in RI changes as large as 1.2 ×10^-4 RI units through the photo-elastic effect. The relaxation of RS within ~ 30 μm of a cleaved end-face reverses the stress-induced RI changes formed during fiber manufacturing. After fusion splicing, an even larger stress-induced RI change of 3.5 ×10^-4 RI units results over an axial distance on the order of millimeters. The diffusion of core dopants reduces the maximum core RI by as much as 21.7% along a transition region length of ~ 400 μm. These measurements represent the first of many required to develop future ultra LMA EDFs where RS effects and dopant diffusion are absolutely critical for fiber design and performance.