The role of glass composition in the 3D laser fabrication of lithium niobate single crystal in lithium niobosilicate glass

Spatially selective growth of lithium niobate (LiNbO3) crystals deep within lithium niobosilicate (LNS) glass can be achieved via femtosecond laser irradiation, wherein these crystals could serve as optical elements in photonic integrated circuits. In practice, it is challenging to achieve continuous, single-crystal growth of LiNbO3 within LNS glass. This work reports on progress in overcoming this challenge by exploring how the formation of single-crystal LiNbO3 is influenced by the incongruent composition of the glass matrix. An investigation of the parameter space of glass composition ((100 – x) LiNbO3 – x SiO2 for x = 22, 26, 30, and 34), laser scanning speed, and laser power leads to the observation of several growth modes: continuous growth at an optimal speed, segmented growth below it, and polycrystalline growth above it. For certain glass compositions, a balance of long incubation time and high crystal growth rate results in the ability to grow indefinitely long (∼cm) single crystal lines at the optimal scanning speed. Guidance for predicting which glass compositions are most suitable for single crystal growth based on the LNS composition diagram is provided.