Strong reduction of propagation losses in LiNbO3 ridge waveguides

•LiNbO3 ridge waveguides with propagation losses lower than 0.2 dB/cm.•Only three steps of fabrication, without the need of cleanroom facilities.•An improved characterization setup for the evaluation of propagation losses.

We propose optimized processes for the reproducible production of LiNbO3 ridge waveguides with propagation losses lower than 0.2 dB/cm. The performances are achieved for both Z-propagating and Y-propagating waveguides, TE and TM polarizations, in X-cut LiNbO3 congruent substrates, and could be easily extrapolated to Z-cut substrates. The fabrication procedure is composed of three steps: titanium deposition, optical grade dicing and diffusion at high temperatures, so that lithography or cleanroom facilities are not required. The reproducible smooth waveguides with low propagation losses result from the diffusion step, which is performed after the production of the ridges. We also show how the losses can be evaluated from the Fabry–Perot effect in the waveguides, without any assumption on the input and output reflection coefficients.