  The polarization entanglement photon pairs generated from the biexciton
cascade decay in a single semiconductor quantum dot is corrupted by the
position-dependent (time-dependent) phase difference of the two polarization
mode due to the fine structure splitting. We show that, by taking voltage
ramping to an electro-optic modulator, such phase-difference can be removed. In
our first proposed set-up, two photons are sent to two separate Pockels cell
under reverse voltage ramping, as a result, the position-dependent phase
difference between the two polarization mode is removed in the outcome state.
In our second proposed set-up, the polarization of the first photon is flipped
and then both photons fly into the same Pokels cell. Since we only need to
separate the two photons rather than separate the two polarization modes, our
schemes are robust with respect to fluctuations of the optical paths.
