121 mW single-frequency bismuth-doped fiber MOPA operating at 1460 nm based on ring-cavity seed with saturable absorber filter

In this study, we present an all-fiber single-frequency bismuth (Bi)-doped fiber laser utilizing a fiber-based saturable absorber (SA) filter. To realize stable single-frequency fiber laser (SFFL) operation, Bi-doped germanosilicate fibers (BGDFs) with high gain coefficients were fabricated and incorporated into a ring-cavity configuration. The cavity consists of a 3 m BGDF as the gain medium and a Bi-doped phosphosilicate fiber (BPDF) with low doping concentration as SA. The results showed that the SFFL achieved an output power of 6.1 mW at 1460 nm with a narrow linewidth of 1.8 kHz. Over a one-hour period, the wavelength and power fluctuations were recorded to be 0.022 nm and 0.07%, respectively. A Bi-doped fiber master oscillator power amplifier (MOPA) system was implemented to boost the seed laser to 121 mW with a slope efficiency of 22.4%, and further enhancement was constrained by the maximum pump power. To the best of our knowledge, this work represents the first demonstration of the BGDF-based SFFL with SA, which also obtains the highest output power.