Abstract
Epitaxially grown, 2.4-microm-thin layers of KY(WO(4))(2):Gd(3+), Lu(3+), Yb(3+), which exhibit a high refractive index contrast with respect to the undoped KY(WO(4))(2) substrate, have been microstructured by Ar beam milling, providing 1.4-microm-deep ridge channel waveguides of 2 to 7 microm width, and overgrown by an undoped KY(WO(4))(2) layer. Channel waveguide laser operation was achieved with a launched pump power threshold of only 5 mW, a slope efficiency of 62% versus launched pump power, and 76 mW output power.
Highlights
The unique property of the family of monoclinic double tungstates, especially KGd(WO4)2, KY(WO4)2, and KLu(WO4)2, to strongly enhance the absorption and emission cross sections of optically active rare-earth ions doped into these host materials is widely recognized, see Ref [1]. and references therein
Rare-earth-ion-doped KY(WO4)2 (KYW) thin layers have been grown by liquid phase epitaxy (LPE) onto undoped KYW substrates [9,10,7]
A channel waveguide laser was demonstrated by strip loading such a planar layer [11], the weak guiding in the horizontal direction led to unreliable performance
Summary
The unique property of the family of monoclinic double tungstates, especially KGd(WO4), KY(WO4), and KLu(WO4), to strongly enhance the absorption and emission cross sections of optically active rare-earth ions doped into these host materials is widely recognized, see Ref [1]. and references therein. This approach makes refractive index contrast and lattice matching constant design parameters over a wide range of Yb3+ doping concentrations, because the Yb3+ ions can replace Lu3+ ions of similar ion radius and electron density Such highly co-doped layers have recently been shown to maintain the favorable spectroscopic properties of the Yb3+ ion and enabled planar waveguide lasing with excellent light confinement and overlap of pump and laser mode, resulting in a record-high slope efficiency of 82.3% and a laser threshold as low as 18 mW of absorbed pump power [17]. (b) Fig. 1. (a) SEM micrograph of a microstructured channel waveguide before overgrowth; (b) measured mode profile of the laser emission (both to scale)
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