  We report on the in-plane anisotropy of the electronic response in the
spin/charge/orbital ordered phase of a half-doped layered-structure manganite.
The optical conductivity spectra for a single domain of Eu$_{1/2}$%
Ca$_{3/2}$MnO$_{4}$ unambiguously show the anisotropic charge dynamics which
well corresponds to the theoretical calculation: the optical conductivity with
the polarization along the zigzag ferromagnetic chain direction exhibits a
smaller gap and a larger intensity at lower energies than that of the
perpendicular polarization mostly due to the charge/orbital ordering and the
associated quantum interference effect.
