  We numerically study supercontinuum (SC) generation in photonic crystal
fibers pumped with low-power 30-ps pulses close to the zero dispersion
wavelength 647nm. We show how the efficiency is significantly improved by
designing the dispersion to allow widely separated spectral lines generated by
degenerate four-wave-mixing (FWM) directly from the pump to broaden and merge.
By proper modification of the dispersion profile the generation of additional
FWM Stokes and anti-Stokes lines results in efficient generation of an 800nm
wide SC. Simulations show that the predicted efficient SC generation is more
robust and can survive fiber imperfections modelled as random fluctuations of
the dispersion coefficients along the fiber length.
