Thulium-doped fiber laser using two FOLMs with a high birefringence fiber in the loop

We report a linear cavity all-fiber Thulium-doped fiber (TDF) laser with tunable narrow linewidth operating near to 2 μm of wavelength. The TDF is pumped with a laser source at 1567 nm. The cavity is delimited by two fiber optical loop mirrors (FOLM) with high birefringence fiber in the loop (Hi-Bi FOLM) with different periodical wavelength-dependent reflection periods. The wavelength tuning range for the generated laser line of ~44.3 nm depends on the Hi-Bi FOLM with long wavelength period of 54.4 nm. The generated laser spectral width, less than 0.05 nm, is determined by the Hi- Bi FOLM with narrow-band wavelength period of 1 nm. Discrete wavelength tuning is achieved by wavelength reflection displacement of the narrow-band Hi-Bi FOLM by temperature variation on the high birefringence fiber loop. The temperature changes are performed with a temperature electronic controller/meter with resolution of 0.06°C in a temperature range from 22.87 to 49.12°C. Dual-wavelength generation with a wavelengths separation of ~47 nm is also obtained at the single wavelength tuning limits.