Abstract

Er³⁺ doped single-crystalline layers are particularly interesting active media for compact waveguide lasers emitting at 1.5-1.6 μm [1]. Recently bulk monoclinic potassium double tungstates KRE(WO₄)₂ (RE = Y, Gd, Lu) have been shown to be excellent laser hosts for erbium ions, demonstrating efficient laser performance under direct in-band pumping into ⁴I_13/2 energy level [2]. However, the highest doping level of erbium ions for this crystal is limited to approx. 1 at. % due to concentration quenching effect. This requires engineering of the layer structure to increase refractive index contrast between a layer and a substrate [3].

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