We report on high-power thulium-doped fiber amplifiers built using a nanoparticle-doped double-clad, pedestal-style large mode area fiber. The applied nanoparticle doping technique allowed achieving uniform high doping concentrations of Al ₂ O ₃ and Tm ₂ O ₃ across the fiber core. The fiber outer layer was fluorine-doped providing a decrease in pump radiation interaction with the coating, thereby enhancing the reliability of the entire laser system under high-power operation. The laser system operating at a wavelength of 2034 nm delivered an output power of up to 441 W with a slope efficiency of 57.4%, and the electro-optical conversion efficiency of the amplifier was 25%. The 1940-nm-wavelength all-fiber amplifier seeded with a narrowband Tm-doped fiber laser provided an output power of up to 273 W with a slope efficiency as high as 61.8%. In both cases the output spectrum was characterized by a 3-dB spectral bandwidth below 160 pm. Moreover, a special splicing procedure for large mode area fibers transmitting high power radiation was proposed and successfully demonstrated.

A fast gain-switched Tm-doped fiber laser and amplifier system providing stable 17-ns pulses with a 0.64-mJ energy and 35.6-kW peak power at 25 kHz is demonstrated. Then, self-starting mode-locked resembling pulses with duration of <200 ps, recorded within the gain-switched pulse envelope, were achieved in the same laser cavity. By amplifying the pulse train in a Tm-doped fiber amplifier, an average output power of 6.8 W at a ~15-ns full width at half maximum (FWHM) gain-switch envelope and a ~36.9-μJ sub-pulse with a peak power of up to 115.6 kW were demonstrated. To the best of our knowledge, this is the shortest gain-switched and mode-locked-like pulse as well as the highest peak-power that has been demonstrated in this type of laser system. A mid-infrared supercontinuum generation with a total output power of 2.45 W and a cut-off wavelength at 4.4 μm is also reported.

We demonstrate a thulium-doped, mode-locked, all-fiber laser capable of operating in two generation regimes: dispersion-managed soliton and noise-like pulse (NLP). Employing a nonlinear optical loop mirror as an artificial saturable absorber, the oscillator generated optical pulses with a fundamental pulse repetition frequency of ~15.795 MHz. The total net dispersion of the laser cavity had a slightly anomalous group delay dispersion value of −0.016 ps². After appropriate adjustment of a polarization controller, bound states of a dispersion-managed soliton composed of three pulses with fixed soliton separations were also observed. NLP generation, tunable over 35 nm from 1943.5 to 1978 nm, was also presented in the same laser setup. To our knowledge, this is the first report of the generation of tunable NLPs in a mode-locked thulium-doped fiber laser based on a nonlinear loop mirror saturable absorber.

Supercontinuum generation from 1.87 to 4.03 µm in a ZBLAN fiber is reported. A home-made passively mode-locked thulium-doped fiber laser and amplifier, providing 21.4-ps pulses at 81 MHz is used as a pump. The continuum output power is 3.52 W, of which 1.45 and 0.88 W corresponds to wavelengths longer than 3 and 3.5 µm, respectively. A spectrum flatness of 2 dB over a bandwidth of 1710 nm, from 2.02 to 3.73 µm, is also reported. This represents, to our knowledge, the best power conversion in the mid-infrared region and the best spectral flatness for high power supercontinuum generation in ZBLAN fibers directly pumped by 2-µm CW mode-locked fiber lasers and amplifiers.

A mid-infrared supercontinuum generation in a step-index fluoroindate fiber pumped by a Tm-doped fiber amplifier seeded with 1.55 µ m pulses is reported for the first time. By pumping a 9 µ m core fluoride fiber with 3.7 W of power, a broadband supercontinuum with a total output power of 1.41 W and a spectrum extending to 4.1 µ m was demonstrated. It is believed that this is the broadest mid-infrared supercontinuum spectrum with Watt-level time-averaged power generated out of a fluoroindate fiber. The impurities incorporated in the fiber are identified as the main limitation in terms of output power scaling up.