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We report for the first time an all-fiber laser system that generates tunable Watt-level femtosecond pulses at around 2 microm without an external pulse compressor. The system is based on amplification of a Raman shifted Er-doped fiber laser in a Tm-doped 25-microm-core fiber. We obtain 108-fs pulses at 1980 nm with an average power of 3.1 W and a pulse energy of 31 nJ. The peak power at the output of the amplifier is estimated as ~230 kW, which to the best of our knowledge is the highest peak power obtained from a femtosecond or a few-picosecond amplifier based on any doped fiber. The amplified output is frequency-doubled to produce 78-fs pulses at 990 nm with an average power of 1.5 W and a pulse energy of 15 nJ. We demonstrate broad wavelength tunability around 2 microm as well as around 1 microm.

The generation of cubicon pulses from an Yb fiber chirped pulse amplification system at pulse energies up to 200 microJ is demonstrated. After pulse compression 650 fs pulses with a pulse energy of 100 microJ are obtained, where pulse compression relies on the compensation of third-order dispersion mismatch between the stretcher and compressor via self-phase modulation of the cubicon pulses in the fiber amplifier. Values of self-phase modulation well in excess of pi can be tolerated for cubicon pulses, allowing for the nonlinear compensation of very large levels of dispersion mismatch between pulse stretcher and compressor.

We present a theory of ultrashort-pulse difference-frequency generation (DFG) with quasi-phase-matching (QPM) gratings in the undepleted-pump, unamplified-signal approximation. In the special case of a cw (or quasi-cw) pump, the spectrum of the generated idler is related to the spectrum of the signal through a transferfunction relation that is valid for arbitrary dispersion in the medium. The engineerability of this QPM-DFG transfer function establishes the basis for arbitrary pulse shaping. Experimentally we demonstrate QPM-DFG devices operating in a frequency-degenerate type II configuration and producing pulse-shaped output at 1550 nm from 220-fs pulses at 1550 nm.

An optically integrated self-referenced frequency comb laser is demonstrated. The system consists of a passively-modelocked Er-fiber laser, a butt-coupled periodically poled lithium niobate (PPLN) waveguide phase-sensor and an electronic feedback loop for carrier-envelope-offset (CEO) phase stabilization. The fceo-beat-signal has a linewidth of 62 kHz and is detected with a S/N-ratio of 40 dB, with greatly reduced pulse energy requirements compared to bulk crystal phase-sensors. To our knowledge this is the first self-referenced frequency-comb system entirely based on guided-wave technology.