An optical heterodyne mixer providing image-frequency rejection

This paper describes an optical heterodyne mixer which detects a desired signal at frequency
f_{LO} \pm f_{IF}
while rejecting interference from any signal at the image frequency
f_{LO} \pm f_{IF}
. Implementation of the mixer is relatively simple. Its performance is insensitive to fluctuations in the optical dimensions of the circuit. This mixer is particularly attractive for communication systems using wavelength division multiplex techniques.