Analysis of heterodyne detection in the frequency domain

As opposed to previous works, our research on heterodyne detection is performed in the frequency domain. Based on the planar wave, it is pointed out that the current amplitude of a heterodyne signal is proportional to the spectrum value of the quantum efficiency function of a detector, and the frequency corresponding to the value is decided by the beam's incident angle. The spectrum of the quantum efficiency function has a low-pass characteristic, and its cut-off frequency is determined by the diameter of the photosensitive surface. Consequently, the strength of the heterodyne signal current depends on the position of a specific frequency in the passband. Our study method is extended to the arbitrary wave and proven to be still effective. According to our analyses, it is concluded that, in addition to the energy decline of interference field, the main cause of performance deterioration resulting from various influential factors can be generally explained as a spectrum mismatch between the interference field and the quantum efficiency function. Based on the Gaussian wave mode, the fact is illustrated by making theoretical deductions, in which the effects of the misaligned angle and beams' spot position offset are treated as examples. Our work provides the possibility of introducing frequency-domain theories into further studies on heterodyne detection.