Mechanisms of waveguiding in femtosecond laser-structured LiNbO3

Two types of waveguiding have been observed in LiNbO3. Both types of waveguides can be understood based on an analysis of the structural changes of the crystal. Here, waveguiding has been observed at the sides of the modification similar to structures in crystalline quartz. This can be explained by a volume change of the irradiated region and subsequent stress-induced birefringence in the surrounding crystal. Therefore, a model was developed to estimate the change of the focal volume upon irradiation. Based on this, finite element simulations of the resulting stress distribution in the crystalline lattice were carried out. The results illustrate the influence of the modification shape on the guiding properties.