  The second-order temporal interference of classical and nonclassical light at
an asymmetrical beam splitter is discussed based on two-photon interference in
Feynman's path integral theory. The visibility of the second-order interference
pattern is determined by the properties of the superposed light beams, the
ratio between the intensities of these two light beams, and the reflectivity of
the asymmetrical beam splitter. Some requirements about the asymmetrical beam
splitter have to be satisfied in order to ensure that the visibility of the
second-order interference pattern of nonclassical light beams exceeds classical
limit. The visibility of the second-order interference pattern of photons
emitted by two independent single-photon sources is independent of the ratio
between the intensities. These conclusions are important for the researches and
applications in quantum optics and quantum information when asymmetrical beam
splitter is employed.
