Propagation characteristics of femtosecond pulses in erbium-doped monomode optical fibers

The spectral and temporal characteristics of femtosecond optical pulses (durations of ~120 fs, wavelength of 1.5 μm) propagating in erbium-doped monomode fibers have been experimentally studied in detail. Distinct spectral broadening and shifting processes have been observed for three types of fibers (two different dopant concentrations and one erbium-free sample for comparison). Whereas only a small amount of spectral broadening occurs in the Er-free fiber, there is a major spectral extension (1.3-1.7 μm) for the low-doped erbium fiber, in which a self-phase-modulation mediated four-wave-mixing process has been observed. Autocorrelation data for the exiting pulses indicate the existence of strong pulse shaping and breakup effects in the Er-doped fibers