Optical heterodyne detection

Optical heterodyne detection is the implementation of heterodyne detection principle using a nonlinear optical process. In heterodyne detection, a signal of interest at some frequency is non-linearly mixed with a reference "local oscillator" (LO) that is set at a close-by frequency. The desired outcome is the difference frequency, which carries the information (amplitude, phase, and frequency modulation) of the original higher frequency signal, but is oscillating at a lower more easily processed carrier frequency.