Femtosecond distributed soliton spectrum in fibers

Abstract

By pumping a fiber in the anomalous group-velocity dispersion regime with a color-center laser, we generate a femtosecond distributed soliton spectrum with τ ≳ 100 fsec covering a wide spectral range between 1.55 < λ < 1.85 μm. We present a theory to explain the spectrum and use autocorrelations and cross correlations to verify the results experimentally. Modulation instability and the soliton self-frequency shift effect initiate a multisoliton collision process that 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 the exciton ionization time in InGaAs/InP multiple quantum wells for the first time to our knowledge.