Fabrication of monolithic microlenses in ytterbium doped microstructured optical fibers

Ytterbium doped microstructured optical fibers have many advantages for fiber amplifiers. Due to air-clad structures, high-power microstructured optical fiber laser systems require stricter end-facet treatment than that of conventional fiber laser systems. Here, we fabricated microlenses in ytterbium doped double-cladding microstructured optical fibers by a CO₂ laser. The surface power density of the MOF tip can be reduced by 2 quantity levels theoretically. The theoretical and experimental investigation is carried out to study effect of minor and major axis semidiameter of ellipsoidal microlenses on coupling efficiency. The experimental coupling efficiency was over 88%. Results indicated that this microlens combines the end cap scheme and pump coupling. The proposed fabrication method is helpful for high mechanical stability, well reproducibility and miniaturization of the high-power rare earth-doped microstructured optical fiber laser systems.