976 nm Single-Polarization Single-Frequency Ytterbium-Doped Phosphate Fiber Amplifiers

Core-pumped 976 nm single-polarization single-frequency fiber amplifiers based on several centimeter long polarization maintaining 6 wt% ytterbium (Yb³⁺) doped phosphate fibers are investigated experimentally and numerically. A 350 mW linearly polarized output with >20 dB polarization extinction ratio and >50 dB optical signal-to-noise ratio is obtained from a 4 cm fiber amplifier at maximum available pump power of 793 mW. The slope efficiency of the 4 cm fiber amplifier is 52.5%. A small signal net gain of 25 dB, corresponding to a unit gain of over 6 dB/cm is achieved in this fiber. It is predicted that a watt level 976 nm core-pumped fiber amplifier can be achieved using more powerful pumps and low insertion loss optical components.