High-gain and thermally stable Er/Yb-doped waveguide amplifiers in low-hydroxyl phosphate glasses fabricated by femtosecond laser writing

Phosphate glasses offer exceptional rare-earth solubility for photonic integration, yet conventional fabrication faces hydroxyl quenching, mode mismatch, and thermal instability. We adopted femtosecond laser direct writing (FLDW) technology to overcome these limitations in optimized Er/Yb co-doped multi-component phosphate glass. Thanks to reduced hydroxyl content and enhanced thermal conductivity, the LP01-mode waveguide exhibits a propagation loss of less than 0.5 dB/cm in the C-band, with temperature rise under strong pumping limited to 8.3 K. With bidirectional pumping, a net gain of 15.10 dB at 1550 nm and a gain coefficient of 5.03 dB/mm (8-fold higher than melt-quenched counterparts) were achieved. The platform achieves a remarkable on-chip amplification density of 2.1 dB/mm 3 and a quantum yield of 42.1%, surpassing semiconductor optical amplifiers in linearity and nonlinear tolerance, establishing a robust foundation for advanced integrated photonic systems.