Passively mode-locked fiber lasers are capable of generating a variety of optical pulses, depending of the pump power and cavity adjustments, which makes them attractive for research in multidisciplinary fields. In this paper, we analyze the experimental results of a fiber laser operating in passively mode-locked regime. The figure-eight laser cavity configuration uses 4 m of a co-doped Er/Yb double clad fiber, as a gain medium, pumped by a 976 nm diode laser. The cavity is completed by an isolator for ensure unidirectional propagation, two quarter-wave retarders (QWR), and a nonlinear optical loop mirror (NOLM) with 120 m of twisted standard single-mode fiber in the loop acting as saturable absorber. We used a couple of quarter-wave retarders (QWR) QWR1 at the NOLM input and QWR2 into the NOLM loop. By carefully adjusting of the QWRs the laser generates noise-like square pulses at the 1.54 μm range. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental mode with repetition frequency of 1.38 MHz, from which we can obtain the second, third and fourth harmonic in a controlled mode.
We report a linear cavity all-fiber passive Q-switched thulium-doped fiber laser operating at the 2 μm wavelength range. The laser configuration is based on a thulium-doped fiber used as a gain medium and an unpumped segment of holmium-doped fiber which acts as a fiber saturable absorber. The cavity is formed by a fiber optical loop mirror and the flat end facet of the holmium-doped fiber. The fiber segments as saturable absorber is a 1-m long single mode doubleclad holmium-doped fiber. Q-switched pulses are obtained at the wavelength of 2024.5 nm with a pulse width of 1.1 μs. The pulse repetition rate increases as a linear function of the applied pump power. The maximum pulse repetition rate of 100 kHz was obtained with a pump power of 2.4 W.
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.
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