Improved setup and procedure for benchmarking of photodarkening in ytterbium doped silica fibers

This paper presents a new setup and a corresponding procedure for the accurate measurement of photodarkening in ytterbium doped fibers. The core-pumping scheme enables the use of short samples and a low pump power and the automation of the measurement permits long-term tests for an effective benchmarking of fibers with low photo-degradation. Exploiting temperature-controlled components and coherent detection, this arrangement allows the measurement of transmission drops below 2% over hundreds of hours. For the first time, a long-term photodarkening experiment (up to 450 h) has been carried out and correlated to the drop in output power experienced by a laser using the same type of fiber, demonstrating that the system can be employed in pre-compliance testing of active fibers prior to their use in a laser configuration. (paper)