Widely Tunable Dual-Wavelength Fiber Laser in the 2 μm Wavelength Range

In this paper, we demonstrate a widely tunable dual-wavelength fiber laser, which is based on a thulium-doped fiber and volume Bragg gratings triggering the emission wavelengths in the 2-μm band. A continuously tunable wavelength separation range (Δλ), from 1 to 144 nm (0.08–11.47 THz) is demonstrated, with > 4.5 W of output power over the tuning range. The laser emission exhibits a linewidth (FWHM) lower than 0.1 nm independent from wavelengths and Δλ, with more than 45 dB of a signal-to-noise contrast. A maximum output power of 7 W is obtained for shorter Δλ (1–14 nm), corresponding to a slope efficiency of 33% with respect to the incident pump power at 790 nm.