We experimentally study chaos synchronization in unidirectionally coupled vertical-cavity
surface-emitting semiconductor lasers (VCSELs) with polarization-preserved and
polarization-selected optical injection. The measurements show, in agreement with
theoretical predictions, that the maximum cross coefficient of 0.884 obtained with
polarization-preserved optical injection is significantly higher than the maximum cross
coefficient of 0.724 obtained with polarization-selected optical injection.