Theoretical study of the quantum noise in phase-sensitive heterodyne detection with a bichromatic local oscillator
A traditional heterodyne detector, as a phase-insensitive device, suffers the well-known 3 dB noise penalty caused by image sideband vacuum. In contrast, a heterodyne detector with a bichromatic local oscillator, as a phase-sensitive device, should be exempted from the 3 dB noise penalty, in spite of the existence of the image sideband vacuum. Assuming coherent light at the input, we develop in this work a theory to describe the quantum nature of the phase-sensitive heterodyne detector, in a good agreement with experiment. The absence of the quantum noise of the image vacuum modes in the heterodyne detector may be explained by that the studied detector senses only a single field of light, i.e., the signal field, according to the theory developed.