Lithium niobate ridge waveguides fabricated by wet etching
The fabrication of LiNbO3 ridge waveguides etched by a mixture of HF and HNO3 using chromium (Cr) stripes as masks is reported. Smooth etched surfaces are obtained by adding some ethanol into the etchant. Under-etching is nearly avoided by annealing the sample with the Cr masks before the wet etching process. Low-loss monomode ridge guides with a height of up to 8 pm and a width between 4.5 and 7.0 mu m are demonstrated. As an example, the propagation losses in a 6.5-mu m-wide and 8-mu m-high structure are 0.3 dB/cm for transverse-electric and 0.9 dB/cm for transverse-magnetic polarization, respectively, at 1.55-mu m wavelength.