Femtosecond Distributed Soliton Spectrum in Fibers.

By pumping a fiber in the anomalous group velocity dispersion regime with a color center laser, we generate a femtosecond distributed soliton spectrum with tau >~100fsec covering a wide spectral range between 1.55 lambda 1.85microns. We present a theory to explain the spectrum, and use auto- and cross-correlations to verify experimentally the results. Modulation instability and the soliton self-frequency shift effect initiate a multi-soliton collision process which results in narrow, high intensity solitons. An ensemble average over these solitons, which start from noise and frequency shift by different amounts, yields the observed broad spectra. We use the fiber output in pump-probe experiments, measuring for the first time the exciton ionization time in InGaAs/InP multiple quantum wells.