  We present two-photon interference experiments with polarization-entangled
photon pairs in a polarization-based Franson-type interferometer. Although the
two photons do not meet at a common beamsplitter, a phase-insensitive
Hong-Ou-Mandel type two-photon interference peak and dip fringes are observed,
resulting from the two-photon interference effect between two indistinguishable
two-photon probability amplitudes leading to a coincidence detection. A spatial
quantum beating fringe is also measured for nondegenerate photon pairs in the
same interferometer, although the two-photon states have no frequency
entanglement. When unentangled polarization-correlated photons are used as an
input state, the polarization entanglement is successfully recovered through
the interferometer via delayed compensation.
