L-band short-cavity fiber lasers based on home-made highly Er ³⁺ -doped silica fiber

L-band (1565-1625 nm) single-frequency and high-repetition-rate mode-locked Er³⁺-doped fiber lasers based on short cavities are attractive for applications in optical communications, remote sensing, and bioimaging due to their favorable spectral and temporal characteristics. However, the L-band lies at the long-wavelength edge of the Er³⁺ emission spectrum, where the available gain is significantly lower than that in the C-band, posing a fundamental challenge for realizing high-performance short-cavity lasers. To address this challenge, we systematically investigate L-band short-cavity fiber lasers enabled by a home-made highly Er³⁺-doped silica fiber fabricated using a modified chemical vapor deposition process combined with solution doping. A distributed Bragg reflector (DBR) single-frequency laser employing only a 3 cm-long gain fiber achieves stable operation at 1590 nm with an output power of 10.5 mW and a linewidth of approximately 6 kHz. In addition, a semiconductor saturable absorber mirror (SESAM)-based linear cavity incorporating an 8.4 cm-long segment of the same fiber delivers stable mode-locked pulses at 1584 nm with a repetition rate of 1.24 GHz and a pulse duration of 566 fs. These results demonstrate that the tailored, highly Er³⁺ doping fiber effectively overcomes the intrinsic low-gain limitation of the L-band, enabling compact, centimeter-scale fiber lasers operating in both single-frequency and ultrafast regimes, and highlight the potential of this material platform for high-performance L-band laser sources.