We demonstrate a widely tunable, mode-locked fiber laser capable of producing sub-picosecond pulses between 1705 and 1805 nm. The 100 nm tuning range is achieved by using intracavity acousto-optic tunable filter. The laser delivers highly stable pulses via self-starting hybrid mode-locking triggered by frequency-shifting and nonlinear polarization evolution.

We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 µm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 µJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M = 1.09).

We demonstrate the first 1.7 μm bismuth-doped fiber laser generating ultrashort pulses via passive mode-locking. Pulse operation has been achieved for both anomalous and normal dispersion of the laser cavity owing to broadband characteristics of carbon nanotube saturable absorber. The laser delivered 1.65 ps pulses in net anomalous dispersion regime. In normal dispersion regime, the laser delivered 14 ps pulses which could be compressed to 1.2 ps using external fiber compressor.

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We demonstrate a 1.44-μm bismuth-doped master oscillator-power amplifier (MOPA) system for generating femtosecond pulses. The cavity of master oscillator comprises dispersion-compensating fiber for detuning the total dispersion to the normal regime and a carbon nanotube saturable absorber for triggering the mode-locked operation. The described multifunction bismuth fiber amplifier performs energy scaling, large spectral broadening, and pulse compression. The results show that the large chirp superimposed on the pulses in the bismuth oscillator with normal dispersion can be effectively suppressed in a subsequent bismuth power amplifier with anomalous dispersion and high nonlinearity, resulting in high-quality pulses with record duration of 240 fs. An all-fiber design provides a practical solution that avoids the need for supplementary pulse stretching and compression.