Amplification combination of Er³⁺ and Tm³⁺ emissions in titanium-diffused lithium niobate strip waveguide

Erbium(Er)/thulium(Tm)-codoped active lithium niobate(LiNbO₃) channel waveguides were fabricated by titanium diffusion following erbium/thulium co-diffusion doping in an X-/Z-cut LiNbO₃ substrate with an initial congruent/Li-deficient composition. We show that the waveguide is in an initial congruent or Li-deficient composition environment, remains LiNbO₃ crystalline phase, is monomode at the 1.5 µm wavelength region under either the transverse electric or the transverse magnetic polarization, and has a loss < 0.5 dB/cm. The X-cut/Z-propagation scheme can effectively suppress the photorefractive effect, while the Z-cut/Y-propagation scheme cannot. Codoping with thulium effectively promotes the resistance to optical damage. An optical gain of 0.8/0.1 dB/cm is attained for the 1547(erbium)/1450(thulium) nm small-signal, showing that erbium/thulium codoping enables to combine the emissions of the two ions and realize the S+C+L broadband amplification or lasing by using 980 and 795 nm laser diodes as the pump sources.