Highly Confining Proton Exchanged Waveguides on Z-Cut LiNbO3 With Preserved Nonlinear Coefficient

We propose a new proton exchange process to reproducibly realize on lithium niobate highly confining (δn_e = 0.1) planar waveguides without degrading the nonlinear coefficient of the crystal. Waveguides were fabricated with different acidic baths and the crystallographic changes, the index profiles and the local SHG response were measured. We show that for certain fabrication conditions, characteristic of the so-called high-index soft proton exchange process, the high-index modification can be obtained without degrading the crystal nonlinear coefficient. This result should open the way to the fabrication of very efficient nonlinear devices.