Supercontinuum spectral control

Supercontinuum (SC) generation in photonic crystal fibers (PCFs) is a cutting-edge phenomenon extensively studied in recent years. SC has found many scientific and technological applications. The control of the SC spectral characteristics is crucial in most of them. Supercontinuum generation is typically generated by accessing the anomalous dispersion regime of the fiber, i.e., when the group velocity dispersion coefficient is lower than zero, beta₂<0. The recent achievement of soft-glass PCFs, namely, PCFs made up of a transparent material that shows higher nonlinear response than the widely used fused silica, opens new possibilities in SC generation at the normal regime, beta₂>0. The shift from the anomalous to the normal dispersion regime is discussed in this paper and this fact allows the recognition of a procedure, based on fiber-dispersion design, to control at least to some extent the spectral characteristics of the broadband SC generated by soft-glass PCFs. As a byproduct, a PCF geometry is identified that provides an ultrawide (over an octave) and very flat SC when pumped with a commercial Er-doped femtosecond fiber laser.