  We demonstrate experimentally and support by a theoretical analysis an effect
of asymmetric spectrum broadening, which results from doping of silver
nanoparticles into a heavy-glass matrix, 90(0.5WO3-0.3SbPO4-0.2PbO)-10AgCl. The
strong dispersion of the effective nonlinear coefficient of the composite
significantly influences the spectral broadening via the self-phase modulation,
and leads to a blue upshift of the spectrum. Further extension of the spectrum
towards shorter wavelengths is suppressed by a growing loss caused by the
plasmon resonance in the silver particles. The red-edge spectral broadening is
dominated by the stimulated Raman Scattering.
