Suppressing amplified spontaneous emission in high-power 1018-nm monolithic fiber laser by decreasing the feedback from the inner reflections

We showed that decreasing the feedback that comes from the inner reflections of counter-propagating light could suppress the amplified spontaneous emission (ASE) in the output of 1018-nm fiber lasers. With a simulation model to solve the power spectrum of multiple signals, we calculated the values of the feedback required for aimed power scaling. We realized low feedback by modifying the counter-propagating side of the setup, which included a home-made cladding light stripper on a no-core fiber that was angle-cleaved. With that, we demonstrated a 1018-nm monolithic fiber laser producing 506.4 W with 1.58-M2 beam quality, 84.9% optical–optical efficiency, and 148-pm linewidth. The maximum intensity of the ASE noises was >50dB lower than that of the 1018-nm signal, which could allow further power scaling with safety and stability.