  Generation of polarization-entangled photon pairs with a precise timing
through down-conversion of femtosecond pulses is often faced with a degraded
polarization entanglement quality. In a previous experiment we have shown that
this degradation is induced by spectral distinguishability between the two
decay paths, in accordance with theoretical predictions. Here, we present an
experimental study of the spectral compensation scheme proposed and first
implemented by Kim et al. in 2002. By measuring the joint spectral properties
of the polarization correlations of the photon pairs, we show that the spectral
distinguishability between the down-converted components is eliminated. This
scheme results in a visibility of 97.9+/-0.5% in the polarization basis without
any spectral filtering.
