Low-loss ridge waveguides on lithium niobate fabricated by local diffusion doping with titanium

The development of a novel self-aligned photolithographic process is reported enabling selective Ti-deposition on the surface of wet etched ridges on lithium niobate. Thus local diffusion doping of the ridges becomes possible to fabricate optical waveguides. They have surprisingly low propagation losses down to 0.05 dB/cm for TE-polarization (at ～1.55 μm wavelength). The fabrication procedure of locally doped ridge guides in LN and their optical properties are presented in detail.