Near-stoichiometric Ti: Sc: LiNbO₃ strip waveguide for integrated optics

We demonstrate near-stoichiometric Ti:Sc:LiNbO₃ strip waveguide fabrication starting from a congruent LiNbO₃ substrate with a technological process in sequence of Sc³⁺- diffusion-doping, Ti diffusion, and post Li-rich vapor transport equilibration. We show that the waveguide is in a near-stoichiometric composition environment, well supports singlemode propagation at 1.5 μm wavelength under both TE and TM polarizations, shows considerable polarization dependence, and has a loss ≤ 0.4/0.7 dB/cm for TE/TM mode. The Ti⁴⁺ surface profile can be fitted by a sum of two error functions, the depth profile can be fitted by a Gaussian function, and the Sc³⁺-profile part which has a concentration above the threshold of photorefractive damage entirely covers the waveguide, showing that the waveguide is expected to be optical-damage-resistant.