  We experimentally observed optical precursors in optically pumped crystals
using polarization-based interference. By switching the user-programmable
medium among the fast light, slow light and no-dispersion regimes, we observed
an unchanged polarization states for the wavefronts. The robust
polarization-encoded information carried by wavefronts suggests that precursors
are the preferred carriers for both quantum and classical information in
communication networks.
