  We propose a single photon source based on a pair of weakly nonlinear optical
cavities subject to a one-directional dissipative coupling. When both cavities
are driven by mutually coherent fields, sub-poissonian light is generated in
the target cavity even when the nonlinear energy per photon is much smaller
than the dissipation rate. The sub-poissonian character of the field holds over
a delay measured by the inverse photon lifetime, as in the conventional photon
blockade, thus allowing single-photon emission under pulsed excitation. We
discuss a possible implementation of the dissipative coupling relevant to
photonic platforms.
