Hybridization engineering in Er‐activated silicate glass fiber for high repetition rate and sub‐100 fs mode‐locked laser

Abstract Femtosecond mode‐locked lasers (MLLs) with hundreds of megahertz repetition rate are of broad interest due to the relatively large longitudinal mode interval. The performance of MLL is dominated by the active fiber, and candidates with both high gain and high compatibility with inactive silica fiber are urgently required. Herein, we propose and demonstrate an Er‐doped hybridized silicate glass fiber (EHSGF) for nonlinear polarization rotation‐based high‐repetition‐rate MLL. The fiber is derived from silica and hybridized with Y and Al elements, which enables providing a rich chemical environment for the active Er dopant. As a result, EHSGF with heavily doped Er 3+ ions and a high gain coefficient of 2 dB/cm can be realized. In addition, it exhibits excellent chemical affinity with the Si‐O, and the fiber can be directly fused with commercial silica fiber without a bridge component. We design and build a stable MLL device with a fundamental repetition rate up to 318.94 MHz by using only 9.5 cm EHSGF without any special integrated devices. The central wavelength is around 1565 nm with a 3 dB width of 32 nm, and the direct output pulse duration is 87 fs, which is close to the transform limit. The measured root mean square power fluctuation remains below 0.039% during continuous 12‐h operation. We believe this research provides a new strategy for the development of highly doped Er‐doped fibers and high‐repetition‐rate laser systems.