Monoclinic double tungstate lattice matched epitaxial layers for integrated optics applications

In this work we report on the activation of KY 1−x−yGdxLuy(WO4)2 lattice matched epitaxial layers with Er3+ and Tm3+ ions. The epilayers posses low enough lattice mismatch as well as high enough refractive index contrast with respect to the KY (WO4)2 substrates, which are key parameters for the fabrication of high quality optical waveguides. A structural study revealed that there are two types of lattice matched KY 1−x−yGdxLuy(WO4)2 compositions, one with a negative lattice mismatch, - 0.53×10−3, corresponding to KY 0.58Gd0.22Lu0.20(WO4)2, and the second one with a positive lattice mismatch, 0.55×10−3, which corresponds to KY 0.75Gd0.18Lu0.07(WO4)2. However, the refractive indices corresponding to the first one were greater than those of the second composition. We then chose the composition with a negative lattice mismatch for doping with Er3+ and Tm3+ active ions, both with percentages of 1% at. and 3% at. Epitaxial growth of the active lattice matched layers on b oriented KY (WO4)2 substrates was obtained without loosing structural quality compared with the passive compositions. Waveguiding demonstration was observed by recording the dark mode spectra at different wavelengths.