Cladding-pumped Yb-doped helical-core fibre lasers and amplifiers

Abstract

Over the last few years there has been very rapid progress in scaling output power from cladding-pumped fibre lasers and amplifiers [1]. One of the key issues to address for further power-scaling of single-mode operation will be to increase the core area in order to avoid the need for excessively long fibres for efficient pump absorption, and to raise the threshold for unwanted nonlinear processes and optical damage, whilst maintaining robust single-mode operation. At the moment, this is generally achieved by employing a multimode large-mode-area core design with a low numerical aperture in combination with bend loss suppression of higher-order modes [2] to promote single-mode operation. However, scaling to higher power levels will require an even larger core diameter and a larger inner-cladding diameter to accommodate more pump power, making it increasingly difficult to coil the fibre with a small enough diameter to use bend-induced loss as an effective means for suppressing higher-order modes. An alternative approach for achieving single-mode operation in a large-core fibre laser/amplifier is to employ a fibre with a helical core trajectory within the inner-cladding. In a preliminary demonstration of this approach, we recently reported a core-pumped Yb-doped helical-core fibre laser with 350mW of single-mode output at 1047nm [3]. Here, we report a highly efficient cladding-pumped Yb-doped helical-core fibre laser at 1043nm with a much higher single-mode output power of ~60.4W and preliminary results for a cladding-pumped Yb-doped helical-core fibre amplifier seeded by a single-mode Yb:YAG laser at 1050nm. ---

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ORCID for J.K. Sahu: orcid.org/0000-0003-3560-6152

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