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
the frequency summing is simply a statement that energy is conserved.
The ODC use milimeteric microwave cavity that include photonic crystal that provide by two signal frequency light source. The microwave is detected by the cavity antenna.