  Blue-enhanced, broadband supercontinuum generation in a 50 um core
fluorine-doped graded-index multimode fiber is demonstrated by pumping with a
1064 nm picosecond source. Multi-octave supercontinuum spectrum extending from
~400 nm to 2,400 nm is achieved in a relatively short fiber. The measured
spectrum and multimode nonlinear properties are compared to those of a
germanium-doped graded-index multimode fiber. It is shown that engineering the
glass composition and thus its chromatic dispersion and absorption
characteristics, provides a novel and effective approach to further controlling
the nonlinear dynamics in highly multimoded parabolic-index fibers.
