  The optical properties of the charge-ordering ($CO$) phase of the
one-dimensional (1D) half-filled spinless Holstein model are derived at zero
temperature within a well-known variational approach improved including
second-order lattice fluctuations. Within the $CO$ phase, the static lattice
distortions give rise to the optical interband gap, that broadens as the
strength of the electron-phonon ($el-ph$) interaction increases. The lattice
fluctuation effects induce a long subgap tail in the infrared conductivity and
a wide band above the gap energy. The first term is due to the multi-phonon
emission by the charge carriers, the second to the interband transitions
accompanied by the multi-phonon scattering. The results show a good agreement
with experimental spectra.
