Green Wavelength-Tunable and High Power Ho<sup>3+</sup>-Doped Upconversion Fiber Lasers
Shuaihao Ji, Xiuji Lin, Meina Chen, Xiaofeng Rong, Huiying Xu, Wensong Li, Zhiping Cai
Abstract
Tunable coherent light source emitting at the visible region has long been recognized as a key asset, especially with a monolithic design involved, for the increasing number of emerging applications in the scientific research and industrial manufacturing. Here, an efficient 640 nm solid-state laser is used as a pump source, and the fiber end-facet mirrors construct a fiber laser resonator. We experimentally developed green wavelength-tunable Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped all-fiber upconversion lasers, which corresponds to the transitions originating from the Stark levels within thermally-coupled <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> S2, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> F4 states and terminating on the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> I8 ground state. Moreover, a high power 236 mW and a high efficiency 38.9% of green upconversion fiber laser operating at 544 nm was demonstrated, and the output power achieved is six-times higher than before. Such compact tunable and high power green fiber lasers are very attractive for the practical applications in optical communications, spectroscopy, sensing, and optical switching devices.