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Mode-locked fiber lasers based on Tm-doped and Tm-Ho-codoped silicate fibers have been studied. The first modelocked fiber laser oscillator beyond 2 m was demonstrated. The first mode-locked 2m fiber laser with ~GHz repetition rate was demonstrated. The broadest spectrum (50nm FWHM) was obtained from dispersion managed 2m mode-locked fiber laser. Various operation regimes of mode-locked thulium fiber lasers are presented, as well as all-fiber 2m pulse amplifiers.

A high-spectral-flatness mid-infrared supercontinuum fiber source is presented. It generates highly stable single-mode broadband beam with a FWHM bandwidth of ~600nm and a 20dB-down spectra spanning from 1.8m up to ~ 2.7m. The supercontinuum pulses are emitted from a single-mode fiber with ~15kW peak power and >20GW/cm2laser peak intensity. This compact fiber source, in combination with a commercial mid-infrared optical spectrum analyzer (Yokogawa), offers a powerful tool for mid-infrared component characterization with high spectral resolution.

30ns, 3J Q-switched pulse laser with the repetition rate of 10 kHz at 1950 nm was amplified with a 50cm long piece of thulium(Tm)-doped silicate fiber, and 300J pulses with the pulse width of 20 ns were obtained. The heavily Tm-doped silicate fiber has the cladding-pump absorption of 22dB/m at 793nm and the fiber maintains solid single-mode operation at 1950nm. To further increase output pulse energy, the Q-switched seed was pre-amplified to 20 J with core-pumping at 1567 nm. The power amplifier features of a 55cm long piece of Tm-doped silicate fiber with 21m core. ~600J pulses with peak power up to 28 kW have been achieved. The ASE was suppressed 40dB below the laser pulses due to the short highly Tm-doped silicate fiber. Mode-locked pulses with the pulse energy of 0.3 nJ and the spectral width of 14 nm were amplified with a 30cm long Tm-fiber with 10 m core, pulses with 16kW peak power as well as 20nJ pulses were achieved. With another Tm-doped silicate fiber (22m core), 36nJ pulses with 1.1ps pulse width were obtained in all-fiber configuration. The high peak power pulses at 2 m reported here should be useful for mid-IR generation.

Mid-infrared fiber laser sources have attracted a lot of interest in space and defense applications. We review our latest developments of various fiber laser sources operating near 2m based on Tm3+and Ho3+ions, which include singlefrequency CW laser sources, Q-switched laser sources, mode-locked laser sources. Potential applications of these fiber laser sources are also briefly discussed.