Abstract

Laser sources operating around 2.1 µm are attractive for a range of applications in areas such as remote sensing, free-space optical communication, defense and medicine. Most commonly, holmium-doped fibers pumped by thulium-doped fiber lasers at 1.95 µm are used to reach this spectral regime, but several studies have shown that holmium-doped fiber amplifiers have a much lower efficiency than theoretically possible [1]. Coincidentally, the wavelength 2.1 µm lies close to the peak Raman shift (∼ 13THz in silica) of the 1.95 µm pump. This means that amplifiers can be developed where 2.1 µm light (called Stokes) could be amplified through stimulated Raman scattering (SRS) in a passive fiber instead of through stimulated emission in a Ho-doped fiber.

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