  We present a concentration and purification scheme for nonmaximally entangled
pure and mixed porization entangled state. We firstly show that two distant
parties Alice and Bob first start with two shared but less entangled photon
pure states to produce a four photon GHZ state, and then perform a 45
polarization measurement onto one of the two photons at each location such that
the remaining two photon are projected onto a maximally entangled state. We
further show the scheme also can be used to purify a class of mixed
polarization-entangled state.
