Near diffraction limit output of a coiled 20/400 μm Yb-doped fiber laser

This paper presented a near diffraction limit output of YDFL employing 20/400 μm gain fiber. By coiling the fiber at different radius, different beam quality output was obtained. Combined with the BPM analysis, including the impact of fiber bending and the eccentric core loss induced by fusion splicing on beam quality, the bending radius was optimized to be 4.5 cm. Then, two optimized bending fiber parts were added in our FL system. Accordingly, an excellent beam quality output of M² = 1.06 under the output power of 50 W was achieved successfully.