The 1.6 µm transition in Er3+ ions can be useful for many applications, such as LIDAR, spectroscopy and laser cavity pumping. However, the small cross section of erbium and the occurring of concentration quenching are detrimental to the efficiency of this transition for direct-diode pumping near 976 nm . A commonly used solution to increase pump absorption in erbium-doped silica fibers is to integrate ytterbium as codopant. Nonetheless, this method has the effect of raising the refraction index of the core as well as generating parasitic emission around 1 µm . In turn, some recent studies codoped ytterbium fiber core with AlPO4 glass structure in order to reduce the occurrence of ion quenching while preserving a low numerical aperture . To our knowledge, this method of doping has however never been demonstrated for an ytterbium-free erbium-doped fiber laser.
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