  We propose and experimentally demonstrate two-photon interference effects in
a Mach-Zehnder interferometer in which two different kinds of two-photon states
are prepared by introducing a time delay between the two input photons. The
two-photon states are simultaneously prepared in a symmetrically superposed
state with two temporally separated photons in two different spatial modes or
in the same spatial mode within the interferometer. We observe two-photon
interference fringes involving both the Hong-Ou-Mandel interference effect and
the interference of path-entangled two-photon states simultaneously in a single
interferometric setup. The observed two-photon interference effect can provide
a simultaneous observation of the interferometric properties of the
single-photon and two-photon wavepackets
