  We propose a novel scheme for realizing single-photon blockade in a weakly
driven hybrid cavity optomechanical system consisting of a nonlinear photonic
crystal. Sub-Poissonian statistics is realized even when the single-photon
optomechanical coupling strength is smaller than the decay rate of the optical
mode. The scheme relaxes the requirement of strong coupling for photon blockade
in optomechanical systems. It is shown that photon blockade could be generated
at the telecommunication wavelength.
