  We present a convenient and efficient scheme to generate arbitrarily
multipartite continuous-variable entanglement via mechanical oscillator
displacement induced by two strong input pump fields in the conventional
single-cavity optomechanical system. It is shown that multipartite entanglement
among the outputs of the two pump fields and any number of relatively weak
probe fields can be realized and optimized when the two pump fields with
suitable amplitude ratio and relative initial phase are, respectively, tuned to
the red and blue mechanical sidebands of a single cavity mode and each probe
field is red-detuned by the mechanical frequency with respect to a different
neighboring cavity mode. This method can, in principle, be extended to flexibly
and conveniently generate arbitrarily multiple nondegenerate bright entangled
fields by using only coherent laser fields, and may find promising applications
in realistic quantum communication and networks.
