Dependences of the refractive indices on the proton concentration in H:LiNbO3 waveguides

Proton-exchanged optical waveguides in lithium niobate crystals exhibit a rich variety of structures and phases. It is established that seven H x Li 1− x NbO 3 crystalline phases with a lithium niobate structure may form under various conditions of proton exchange and post-exchange annealing. A method is proposed to determine the proton concentration in the various phases identified. Relationships are established between the structural parameters, the proton concentration, and the ordinary and extraordinary refractive indices of various H x Li 1− x NbO 3 crystalline phases. The results can explain various optical phenomena observed in proton-exchanged waveguides and permit prediction of the characteristics of light-guide structures.