Efficient 960 nm single-frequency all-fiber MOPA laser incorporating a semiconductor optical amplification seeded by an ultrashort-cavity Yb ³⁺ -doped fiber oscillator

Generating a single-frequency fiber oscillator (SFFO) below 970 nm with Yb³⁺-doped fiber presents a significant challenge due to the small ratio between emission to absorption cross-sections and severe signal reabsorption, particularly in short linear-cavity configuration. To address this, we demonstrate an efficient single-polarization single-frequency all-fiber master oscillator power amplifier (MOPA) laser at 960 nm seeded by an ultrashort cavity Yb³⁺-doped phosphate fiber (YPF) oscillator, and boosted by a semiconductor optical amplifier (SOA). The 960 nm seed oscillator features a distributed Bragg reflector short cavity constructed with a 7-mm-long, highly-YPF with a large emission cross-section. By elevating the cavity temperature to 70 °C, a stable single-longitudinal-mode operation with an output power of 1.7 mW and a wavelength tuning range of 100.9 GHz are obtained from the fiber oscillator. Subsequent power amplification using an SOA scaled the final output power to 209 mW. In addition, the MOPA system exhibits excellent performance metrics: an optical signal-to-noise ratio exceeding 54 dB, a laser linewidth less than 5.05 kHz, and a relative intensity noise lower than -140 dB/Hz at frequencies over 50 MHz. To the best of our knowledge, this represents the shortest wavelength operation achieved from a Yb³⁺-doped SFFO. These outstanding results pave the way for expanding the application of single-frequency lasers into the sub-970 nm spectral region with high power, narrow linewidth, and low noise.