(under subclass 189) Subject matter wherein the received wave is combined with a locally generated wave in a nonlinear device to produce sum and difference frequencies at the output.
(1) Note. This is also called a beat demodulator.
(2) Note. Any further breakdown of the output of the demodulator will use electrical signals since the intermediate frequency (IF) output is outside the frequency spectrum of optical signals.
(3) Note. An electrical or optical oscillator used in combination with a heterodyne optical receiver is classified in this subclass.
