Fabrication techniques of lithium niobate waveguides

In the paper, the most commonly used fabrication techniques of optical waveguides in lithium niobate are reviewed. Diffusion processes such as out-diffusion of lithium oxide from the crystal surface, in-diffusion of metals, ion exchange and proton exchange, and ion implantation are analysed. The characteristics of LiNbO3 optical waveguides prepared by the different technological procedures, are reported in relation with the fabrication conditions. High quality optical waveguides on lithium niobate can be produced by Ti in-diffusion in a dry O2 atmosphere at temperatures above 1000¿¿C for long diffusion times (>10 h). However, despite the large amount of research done in this field, correlations between optical properties and structural characteristics have not yet been established.