High-power Er:Yb fiber laser with very high numerical aperture pump-cladding waveguide

Abstract
One watt of laser power at 1535 nm has been generated from an Er:Yb codoped double-clad fiber structure, in which the inner cladding was suspended in air by a large number of thin silica webs. The acceptance numerical aperture (NA) of the inner cladding has been measured over a range of wavelengths, for lengths from 1 up to 100 m. For fiber lengths of ∼40 m, the NA at the pump diode wavelength was 0.88.