  Based on the four wave mixing, a three mode nonlinear system is proposed. The
single photon blockade is discussed through analytical analysis and numerical
calculation. The analytical analysis shows that the conventional photon
blockade and unconventional photon blockade can be realized at the same time,
and the analytical conditions of the two kinds of blockade are the same. The
numerical results show that the system not only has the maximum average photon
number in the blockade region, but also can have strong photon anti-bunching in
the region with small nonlinear coupling coefficient, which greatly reduces the
experimental difficulty of the system. This optical system which can realize
the compound photon blockade effect is helpful to realize the high-purity
single photon source.
