B.S.T.J. Briefs: An Image Band Interpretation of Optical Heterodyne Noise
01 January 1971
Optical heterodyning and homodyning (heterodyning to baseband) have been studied by various authors. 1-3 The intermediate frequency or baseband signal t h a t is obtained by ideal optical heterodyning or homodyning consists of the signal that would be expected from classical analysis plus an added gaussian quantum noise. The variance of this quantum noise is twice as large in the heterodyning case as it is in the homodyning case. Since classically heterodyning need not have a noise disadvantage over homodyning, this result at first seems 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 using quantum field theory.