  We perform an analysis of the optomechanical entanglement between the
experimentally detectable output field of an optical cavity and a vibrating
cavity end-mirror. We show that by a proper choice of the readout (mainly by a
proper choice of detection bandwidth) one can not only detect the already
predicted intracavity entanglement but also optimize and increase it. This
entanglement is explained as being generated by a scattering process owing to
which strong quantum correlations between the mirror and the optical Stokes
sideband are created. All-optical entanglement between scattered sidebands is
also predicted and it is shown that the mechanical resonator and the two
sideband modes form a fully tripartite-entangled system capable of providing
practicable and robust solutions for continuous variable quantum communication
protocols.
