Linearly-Polarized Mode-locked Yb³⁺-doped Phosphate Fiber Ring-Cavity Laser at 976 nm

Compact and robust linearly-polarized pulsed laser sources at 976 nm are in great demand for high-efficiency harmonic generation of blue and deep ultraviolet lasers. In this paper, we report a semiconductor saturable absorber mirror mode-locked fiber ring-cavity laser at 976 nm, in which only 2.4 cm highly ytterbium-doped phosphate fiber was used as the gain fiber. Fundamental mode-locking operation with 5-ps pulses at a repetition rate of 16.53 MHz and with average output power of 2 mW was obtained at a pump power of 215 mW. The pulse energy and peak power of the mode-locked pulses were estimated to be 0.12 nJ and 24.4 W, respectively. The polarization extinction ratio was measured to be 21.5 dB.