Single-Mode Er-Yb Fiber with 20 μm F-P2O5-SiO2 Core

Er-Yb fibers are routinely used for generation of watt-level signal near 1.55 μm. Such fibers typically have core doped with a high P 2 O 5 concentration (required for efficient energy transfer from Yb3+ to Er3+ ions) which result in a high core numerical aperture (NA) of about 0.2. As a results single-mode Er-Yb fibers has a small core diameter (∼5 μm) and they are not suitable for high peak power applications. In the current communication we report on development of Er-Yb fibers with a low core NA based on highly fluorine doped P 2 O 5 -SiO 2 glass.