Lapping and Polishing of Crystalline KY(WO₄)₂: Toward High Refractive Index Contrast Slab Waveguides

Rare-earth ion-doped potassium yttrium double tungstate, RE:KY(WO₄)₂, is a promising candidate for small, power-efficient, on-chip lasers and amplifiers. Thin KY(WO₄)₂onglass layers with thicknesses ranging between 0.9 and 1.6 m are required to realize on-chip lasers based on high refractive index contrast waveguides operating between 1.55 and 3.00 µm. The crystalline nature of KY(WO₄)₂ makes the growth of thin, defect-free layers on amorphous glass substrates impossible. Heterogeneous integration is one of the promising approaches to achieve thin KY(WO₄)₂onglass layers. In this process, crystal samples, with a thickness of 1 mm, are bonded onto a glass substrate and thinned down with an extensive lapping and polishing procedure to the desired final thickness. In this study, a lapping and polishing process for KY(WO₄)₂ was developed toward the realization of integrated active optical devices in this material.