Influence of aluminium-phosphorus codoping on optical properties ofytterbium-doped laser fibers

摘要

Ytterbium-doped high-power fiber lasers with high beam quality are promising devices for a variety of applications.Extreme power load and complicated fiber structures make great demands on material properties and preparationtechnology. Recently, with the further increase of output power, the problem of photodarkening has been identified as acritical issue for fiber laser devices. Detailed knowledge of optical properties of materials and fibers are needed for thesuccessful development of laser fibers, aimed at increasing efficiency and power. It is well known that the properties of silica based rare earth doped fibers can be influenced and remarkably improvedby the incorporation of further dopants. Here, the influence of combined aluminium-phosphorus codoping on the opticalproperties of Yb doped laser fibers was investigated. Preforms and fibers were prepared by MCVD and solution dopingboth with phosphorus and aluminium excess. The samples were characterized concerning the radial distribution ofrefractive index and dopant concentrations and the absorption and emission properties in the UV/VIS/NIR region. Theobserved spectral effects and active properties (laser efficiency, photodarkening) were correlated with changes in thefiber composition. It could be shown, that the combined doping leads to effects which deviate from a simple additivityand which can be beneficially utilized for the improvement of the laser fiber performance.