  We consider the optical properties of the half-filled AB-stacked bilayer
graphene with the excitonic pairing and condensation between the layers. Both
intra and interlayer local Coulomb interaction effects have been taken into
account and the role of the exact Fermi energy has been discussed in details.
We have calculated the absorption coefficient, refractive index, dielectric
response functions and the electron energy loss spectrum for different
interlayer Coulomb interaction regimes and for different temperatures.
Considering the full four-band model for the interacting AB bilayer graphene, a
good agreement is achieved with other theoretical and experimental works on the
subject, in particular, limiting cases of the theory. The calculations,
presented here, permit to estimate accurately the effects of excitonic pairing
and condensation on the optical properties of the bilayer graphene. The
modifications of the plasmon excitation spectrum are discussed in details for a
very large interval of the interlayer interaction parameter.
