  We present a systematic investigation of lepton pair production through
photon-photon fusion processes in heavy-ion collisions. It is demonstrated that
the dilepton production at a given impact parameter ($b_\perp$) with a fixed
transverse momentum imbalance ($q_\perp$) can be factorized into a unified
formula in terms of the Wigner photon distribution of heavy nuclei. We show
that this framework provides a comprehensive description of all the relevant
data from RHIC to the LHC, with a strong evidence that the quasi-real photon
can be radiated not only from the nucleus as a whole, standing for the coherent
contribution, but also from the sub-structures inside the nucleus, representing
the incoherent contribution. Further predictions are made for the anisotropies
in the correlations between $q_\perp$, $b_\perp$, and the dilepton transverse
momentum ($P_\perp$). This will help us to constrain the photon Wigner
distribution which plays a crucial role to study the gluonic matter of nucleus
at small-$x$ through the diffractive photoproduction processes in heavy ion
collision.
