Large-mode area erbium-doped tantalum pentoxide waveguide amplifier with high on-chip net gain

We report a high-performance erbium-doped tantalum pentoxide (Er³⁺: Ta₂O₅) large-mode-area (LMA) waveguide amplifier fabricated by direct etching of the gain medium. The device achieves strong optical confinement and high pump-signal overlap (>98.6%) while maintaining propagation loss of 0.7 dB/cm after annealing. Under 140 mW total pump power at 980 nm, the 2.75-cm-long amplifier delivers a maximum on-chip signal enhancement of 38.1 dB at 1530 nm and 24.1 dB at 1550 nm, corresponding to net gains of 8.6 and 9.6 dB, respectively, with gain exceeding 3 dB/cm across the C-band. Large-signal measurements show a maximum output power of 2.4 mW (1.25 dB net gain), confirming stable high-power operation enabled by the LMA design. A minimum noise figure of 5.68 dB is achieved at 1550.5 nm. This device not only overcomes the fabrication challenges associated with Er³⁺: Ta₂O₅ and validates its amplification potential, but also demonstrates excellent large-signal amplification performance, highlighting its strong potential for compact, high-output, and low-noise on-chip optical amplification in integrated photonic systems.