[@kevin07nat; @press2007prl], or even through a direct coupling to a one-dimensional mode such as a nanowire [@claudon2010] or a photon crystal waveguide [@hughes2007prl; @shields2011apl; @finley2012prx]. Single-photon nonlinear behavior in the strong light-matter coupling regime has been shown also under resonant excitation [@faraon08nphys; @volz2012nphot], i.e. exploiting the photon blockade effect [@imamoglu97]. The latter occurs in systems where two photons inside a resonant cavity produce an anharmonic shift of its response frequency that is greater than the line-broadening induced by losses and decoherence. Under such conditions, the transmission of a coherent light field is inhibited by the presence of a single-photon within the cavity, until such single-photon state is released: the system converts a low-power coherent state into single-photon streams at the same resonant frequency, thus behaving as a single-photon source. The efficiency of such a source can be assessed by measuring the antibunched $g^{(2)}(0)$ in the transmitting channel, as experimentally shown for the first time with single caesium atoms strongly coupled to an optical Fabry-Pérot cavity [@birnbaum05nat].

A similar device can be realized when using a Kerr-type nonlinear medium, which gives rise to an equivalent response in terms of the degree of photon antibunching of the transmitted field [@rebic04pra]. Theoretical proposals 