Optical DownConverter (ODC) is an example of a non-linear optical process, in which two beams of light of different frequencies and interact, creating microwave with frequency . It is a generalization of microwave. In the latter, , both of which can be provided by a single light source. From a quantum mechanical perspective, ODC can be seen as result of differencing two photons to produce a microwave. Since the energy of a photon is given by