Overview of Evolution:
Pulse shapes itself into a parabolic in a normally dispersive passive fiber. Further evolution, e.g. in the gain fiber, is minimized in order to maintain the parabolic shape. A dispersive delay line (DDL) provides anomalous dispersion to restore the seed for the next roundtrip.
Parabolic shaping occurs in several meters of passive, normally-dispersive fiber. The exact length should be adjusted to match the pulse and gain bandwidths. The gain fiber should be as short as possible (<50 cm) to preserve the parabolic pulse. Anomalous gain is not recommended, and may limit the pulse energy. A DDL (either fiber or grating-based) should be placed after the output coupler, leaving a normal net cavity dispersion. Chirped pulses are obtained at the output, and usually require a GDD on the order of the cavity dispersion to compress.
Output pulses have reached >10 nJ in experiments. Pulse durations are typically several ps, but can be dechirped cleanly to <100 fs outside the cavity. Transform-limited durations are limited by the gain bandwidth.
1. D. Anderson, M. Desaix, M. Karlsson, M. Lisak, and M. L. Quiroga-Teixeiro. “Wave-breaking-free pulses in nonlinear-optical fibers.” Journal of the Optical Society of America B 10, 7 (1993).
2. C. Finot, L. Provost, P. Petropoulos, and D. J. Richardson. “Parabolic pulse generation through passive nonlinear pulse reshaping in a normally dispersive two segment fiber device.” Optics Express 15, 3 (2007).
3. F. Ö. Ilday, J. R. Buckley, W. G. Clark, and F. W. Wise. “Self-Similar Evolution of Parabolic Pulses in a Laser.” Physical Review Letters 92, 21 (2004).
Animation credit: Walter Fu.