Silicon-based tantalum pentoxide ridge waveguide with high erbium concentration

High Erbium-doped tantalum pentoxide (Er:Ta2O5) films with different Er-doping concentrations was fabricated on silica-on-silicon substrate. The fabricating method of Er-Ta co-sputtering and following thermal oxidation was first proposed. The influence of high Er-doping concentration on refractive index of Er:Ta2O5 films was evaluated by prism coupler. The results indicate that the refractive index of Er:Ta2O5 films decreases slightly while Er-doping concentration increases and the films do not show anisotropy obviously. On this basis,0, 2.5, 5, 7.5 mol% Er-doped Ta2O5 ridge waveguides were successfully fabricated on Si substrate. The waveguides were observed to be single-mode at 1 550 nm wavelength. Propagation loss of 0.6, 1.1, 2.5, 5.0 dB/cm at 1 600 nm wavelength was estimated using cut-off method, respectively. Although no crystallization of Er2O3 was found among the fabricated Er:Ta2O5 films, Er3+ could affect the crystallinity of Ta2O5 and then increase the propagation loss of the waveguide. Finally net optical gain of 3.1 dB/cm at 1 531 nm was demonstrated in a 2.5 mol% Er:Ta2O5 ridge waveguide when pumped with 980 nm laser.