  Exciton fine-structure splittings within quantum dots introduce phase
differences between the two biexciton decay paths that greatly reduce the
entanglement of photon pairs generated via biexciton recombination. We analyze
this problem in the frequency domain and propose a practicable method to
compensate the phase difference by inserting a spatial light modulator, which
substantially improves the entanglement of the photon pairs without any loss.
