Optical-Damage-Resistant Highly Er $^{\bf {3+}}$ -Doped Ti:Er:LiNbO $_{\bf 3}$ Strip Waveguide

We report optical-damage-resistant Ti:Er:LiNbO₃ strip waveguide with high diffusion-doped surface Er³⁺ concentration. The waveguide was fabricated starting from a commercial X-cut congruent LiNbO₃ plate with a two-step technological process in sequence of simultaneous work of Er³⁺ diffusion doping and Li-poor vapor transport equilibration treatment, and fabrication of 6-μm-wide Ti-diffused strip waveguide (Z-propagation). The waveguide retains still the LiNbO₃ phase and has the waveguiding characteristics similar to the conventional Ti:LiNbO₃ waveguide except with a larger loss due to the imperfection of waveguide. Secondary ion mass spectrometry study shows that the Er³⁺ diffusion reservoir was exhausted and the profile is the desired Gaussian-type with a surface concentration 1.0 mol%, which is about two times larger than the value of conventional Ti:Er:LiNbO₃ amplifier. Further optical characterization shows that the waveguide shows stable 1547 nm small-signal gain under the 980 nm pumping without serious photorefractive effect observed. An unsaturated gain 1.7 dB/cm is obtained for the available coupled pump power of 160 mW. With increased pump power, optimized Er³⁺ diffusion condition and degraded loss figure, a higher gain is expected.