A photonic device and a continuous-wave THz signal generator using such photonic device. The photonic device includes an input waveguide arranged to receive input waves of at least two input frequencies and to generate photons at an output frequency associated with the at least two input frequencies; an output waveguide coupled to the input waveguide and arranged to collect the generated photons at the output frequency; wherein the output waveguide is further arranged to facilitate an amplification of the generated photons as the generated photons propagates along the output waveguide and arranged to output an amplified signal at the output frequency.