We analyze the state of type-I SPDC polarization in nonlinear uniaxial crystals using a coordinate system connected with a pump beam. The entanglement loss due to the Migdall effect is examined. The analytical expressions for polarization components of the signal and idler waves for the frequency-degenerate regime are obtained. The numerical results for BBO crystal are also adduced.
42.65.Lm Parametric down conversion and production of entangled photons
42.70.Mp Nonlinear optical crystals
Department of Physics, International Laser Center, M.V. Lomonosov Moscow State University, Moscow, 119991 Russia