Mode selection in high power cladding pumped fibre lasers with tapered section

Cladding pumped fibre lasers are undoubtedly becoming the most attractive source of high power radiation in the near IR region. The small overlap between the pump and the rare-earth-doped core leads to a small pump absorption, e.g., 1 dB/m. Larger core and absorption is often desirable, especially if (transversally) single-mode operation can be maintained. Thus, single-mode operation following selective excitation of the fundamental mode of large-core multimode fiber amplifiers was recently demonstrated in short fibres [1]. In this paper, we use a simple fiber taper inside a laser cavity with a multimode gain fiber to similarly suppress higher-order modes