Supercontinuum Generation In Optical Fibres

In this work, a high power Ytterbium pump laser was used in a quasicontinuous wave (CW) pump scheme to generate supercontinua in two different optical fibres, a depressed cladding, graded index highly nonlinear fibre (HNLF), and a solid core photonic crystal fibre (PCF). Pumping a 300 m length of the HNLF with a peak pump power of 140 W, a continuum with a spectral flatness of 5 dB over 1000 nm with an average spectral power of 0.33 mW/nm was achieved. Pumping a 28 m length of the PCF gave a spectrum with a spectral flatness of 6 dB over 740 nm with an average spectral power of 1.7 mW/nm. The PCF exhibited two zero dispersion wavelengths (ZDW) and, in addition to the continuum, a broad (80 nm FWHM) high power (330mW) spectral component was generated at 1.98 μm, in the normal dispersion region past the second ZDW. Through computer simulations and an understanding of the physical mechanisms, this was unambiguously understood to be generated through the interaction of solitons and dispersive waves, first the emission of ‘Cherenkov’ radiation by solitons at the ZDW, and then through the interaction of the Cherenkov radiation with solitons in the continuum through soliton FWM. This is the first experimental demonstration of soliton FWM in the context of CW pumped supercontinuum generation.