818 W Yb-doped amplifier with < 7 GHz linewidth based on pseudo-random phase modulation in polarization-maintained all-fiber configuration

Abstract

We present a polarization-maintained (PM), narrow-linewidth, ytterbium (Yb)-doped all-fiber amplifier with the result of continuous-wave 818 W, 85.2% slope efficiency, single-mode beam quality and a 13 dB polarization extinction ratio. It is based on 6.6 GHz pseudo-random binary sequence (PRBS) phase modulation (<7 GHz full width half maximum (FWIIM) laser linewidth) in a simple, three-staged master oscillator power amplifier configuration. The result demonstrates the highest output power per linewidth ratio in the kW regime with a conventional PM 20/400 mu m Yb-doped fiber amplifier. Further studies including the optimization of PRBS parameters and filtered PRBS phase modulation using a low-pass filter will enable <10 GHz, >kW PM high-power fiber lasers in the near future.