  We theoretically investigate the spectral entanglement of a multiphoton
source generated from the cascade emissions in the cascaded cold atomic
ensembles.\ This photon source is highly directional, guaranteed under the
four-wave mixing condition, and is also highly frequency-correlated due to
finite driving pulse durations and superradiant decay constants.\ We utilize
Schmidt decomposition to study the bipartite entanglement of the biphoton
states projected from the multiphoton ones.\ This entropy of entanglement can
be manipulated by controlling the driving parameters and superradiant decay
rates.\ Moreover the projected biphoton states in the cascaded scheme can have
larger entanglement than the one produced from only one atomic ensemble, which
results from larger capacity in multipartite entanglement.\ This cascaded
scheme enables a multiphoton source useful in quantum information processing.\
It also allows for potential applications in multimode quantum communication
and spectral shaping of high-dimensional continuous frequency entanglement.
