Fabrication method of low-loss large single mode ridge Ti:LiNbO₃ waveguides

We present a method for fabrication of smooth ridge waveguides by wet etching technique, using a special mixture of acids and applying a pretreatment procedure. By implementing this method, we fabricated 4.5 μm-deep large single mode ridge waveguides with walls and edges roughness comparable with the roughness of the non-etched regions, namely, less than 20 nm. Optical extra losses caused by the ridge creation were measured by the Fabry Perot technique and were 0.2 dB/cm@TM and 0.7 dB@TE for 1550 nm wavelength. Surface roughness, morphology, etching rates and propagation losses are presented and compared to the characteristics achieved by previously reported wet etching recipes.