Hybrid modes in proton exchanged waveguides realized in LiNbO3 , and their dependence on fabrication parameters

In this paper, we present a relation between material structure, hybrid modes, and propagation losses in proton exchanged (PE) LiNbO₃ waveguides. Rutherford backscattering (RBS) and X-ray diffraction studies are used to show that there are two essential reasons for losses and complex behavior in high δn_e PE waveguides. RBS studies show that using benzoic acid melt temperatures below 300°C leads to distorted waveguide layers and propagation losses higher than several dB/cm. At high temperature, the X-ray studies prove that the crystalline order is preserved, but induced strain leads to biaxial exchanged layers, which results in hybrid modes that can have very high losses. Finally, fabrication parameters allowing the realization of high quality, high δn_e, PE waveguides in LiNbO₃ are identified