  In the late 80's, Ou and Mandel experimentally observed signal beatings by
performing a non-time resolved coincidence detection of two photons having
interfered in a balanced beam splitter [Phys. Rev. Lett 61, 54 (1988)]. In this
work, we provide a new interpretation of the fringe pattern observed in this
experiment as the direct measurement of the chronocyclic Wigner distribution of
a frequency Schr\"odinger cat-like state produced by local spectral filtering.
Based on this analysis, we also study time-resolved HOM experiment to measure
such frequency state.
