  Optomechanical system is a promising platform to connect different notes of
quantum networks, therefore, entanglement generated from it is also of great
importance. In this paper, the parameter dependence of optomechanical and
optical-optical entanglements generated from the double-longitudinal-mode
cavity optomechanical system are discussed and two quadrapartite entanglement
generation schemes based on such a system are proposed. Furthermore, 2N or
4N-partite entangled states can be obtained by coupling N cavities with N-1
beamsplitter(BS)s, and these schemes are scalable in increasing the partite
number of entanglement. Certain ladder or linear structures are contained in
the finally obtained entanglement structure, which can be applied in quantum
computing or quantum networks in the future.
