Wavelength converter device for generating a converted radiation at frequency Ωg through interaction between at least one signal radiation at frequency Ωg and at least one pump radiation at frequency Ωg, with an input for the at least one signal radiation at frequency Ωg; a pump light source for generating the at least one pump radiation at frequency Ωg, an output for taking out the converted radiation at frequency Ωg, a structure for transmitting the signal radiation, the structure including one optical resonator having a non-linear material, having an optical length of at least 40*η/2, wavelength η being the wavelength of the pump radiation, and resonating at the pump, signal and converted frequencies Ωp, Ωs, and Ωg. The structure has a further optical resonator coupled in series to the optical resonator, the further optical resonator having a non-linear material, having an optical length of at least 40*η/2, wherein η is the wavelength of the pump radiation, and resonating at the pump, signal and converted Ωp, Ωs and Ωg, wherein by propagating through the structure, the pump and signal radiation generate the converted radiation by non-linear interaction within the optical resonators.