3.1 kW monolithic MOPA configuration fibre laser bidirectionally pumped by non-wavelength-stabilized laser diodes

We report an all-fibre monolithic master oscillator power amplifier configuration fibre laser bidirectionally pumped by non-wavelength-stabilized laser diodes. The Raman Effect and thermal problems can be effectively suppressed by the bidirectional pumping configuration. A small core diameter double-clad ytterbium-doped fibre is utilized in the amplifier for a refined beam quality control. As a result, a maximum output power of 3122 W and an optical-to-optical efficiency of 81.4% are achieved with near-diffraction-limitation beam quality. No mode instability was detected via a photodiode. Also, the output power instability was measured to be less than 0.6% during a continuous operation of 2 h.