Non-Destructive 2D Profiling of Refractive Index and Dopant Distributions in Yb-Doped Glass Preforms

High-power fibre lasers are used in advanced manufacturing, owing to their high efficiency and beam quality. However, further power scaling is limited by the onset of nonlinear effects [1], prompting the development of fibres with more complex refractive index (RI) [2] and dopant profiles [3]. RI and dopant measurements can be made on drawn fibres [4], but commercial preform characterisation equipment can measure only the preform RI profile. Commonly used methods to measure Yb distribution, such as electron microprobe analysis, destroy the studied sample. A profiler has been developed previously, to simultaneously measure RI and dopant distribution without destructing the preform [5]. We report the development of this device, extending the characterisation of dopant distribution to asymmetric preforms by capturing a 2D profile of the preform core.