An Image Band Interpretation of Optical Heterodyne Noise

Optical heterodyning and homodyning (heterodyning to hueband) have been studied by varioul authors. 1-3 The intermediate frequency or baaeband aignal that ia obtained by ideal optical heterodyning or bomodyning coneieta of the signal that would be expected from classical analysis plus an added puuian quantum noise. The variance of thia quantum noise is twice as large in the heterodyning case as it is in the homodyning case. Since classically beterodyning need not have a noise disadvantage over homodyning, this result at first eeem puzzling. We shall show below that the disadvantage of heterodyning can be interpreted as an unavoidable “image band” quantum noise. We shall argue this both heuristically and formally uaing quantum field theory.