Study of sharp bends in anisotropic potassium double tungstate waveguides

Rare earth ion doped potassium double tungstate gain materials have recently shown a great promise for the development of waveguide amplifiers and lasers exhibiting excellent performance. To enable the use of this material in larger nanophotonic platforms, sharp bends are required. In this work we study the effect of the anisotropy of potassium double tungstates on the bend losses of high contrast waveguides using three different simulation methods. It is concluded that the existence of this anisotropy has not detrimental effect on the bend losses, therefore opening the door to the utilization of this material for integrated nanophotonics

Highly efficient lasers and amplifiers in double tungstates

The double tungstates KY(WO4)2, KGd(WO4)2, and KLu(WO4)2 are excellent candidates for solid-state lasers because of the large transition cross-sections of optically active rare-earth ions doped into these hosts. We grow actively doped KY1-x-yGdxLuy(WO4)2 layers onto KY(WO4)2 substrates by liquid-phase epitaxy. Co-doping the layers with optically inert Gd3+ and Lu3+ ions simultaneously allows for lattice matching and enhanced refractive index contrast with respect to the substrate. Low-loss channel waveguides are microstructured into the layers by Ar+-beam etching, resulting in strong pump- and signal-mode confinement. Yb-doped channel waveguide lasers deliver 650 mW output power at 1 µm. Record-high slope efficiency (85%) and record-low quantum defect (0.7%) for dielectric lasers are achieved. In pump-signal experiments, exploiting highly doped KGd0.447Lu0.078Yb0.475(WO4)2 channel waveguides, we demonstrate a giant optical gain of 950 dB/cm, exceeding the gain previously reported in rare-earth-ion-doped materials by two orders of magnitude and comparable to the gain obtained in semiconductor optical amplifiers

Highly Yb-doped KGd(WO₄)₂ thin-film amplifier

We report record-high small-signal gain of 1050 dB/cm at 981 nm wavelength in a KGd0.425Yb0.575(WO4)2 thin film. The sensitivity of gain to the shift of beam-focus position, which is critical under non-waveguiding conditions, is investigated