Broad Bandwidth from Frequency Shifting Solitons in Fibers.

By pumping a fiber in the anomalous group velocity dispersion regime with a color center laser, we generate femtosecond pulses with tau > ~ 100fsec covering a wide spectral range between 1.55 lambda 1.85microns. Cross-correlation measurements prove the lack of correlation between different parts of the spectrum. Computer simulations show that modulation instability and the soliton self-frequency shift effect initiate a multi- soliton collision process which results in narrow, high intensity, fundamental solitons. The observed broad spectra correspond to an ensemble average over these solitons, which start from noise and frequency shift by different amounts.