ABSTRACT
This chapter introduces the concept of homodyne detection and heterodyne detection of light in the framework of electromagnetic wave theory of radiation, including Maxwell’s continuous picture and Einstein’s quantized granularity picture of light. Optical homodyne detection and heterodyne detection are both adapted from radio frequency modulation technology. Unlike standard photodetection, homodyne detection and heterodyne detection measure the signal radiation, which may have modulated complex amplitude, by mixing with radiation of a reference frequency, which is usually generated by a local oscillator. Roughly speaking, in homodyne detection the reference frequency equals that of the input signal radiation; in heterodyne detection, the reference light is frequency-shifted. The design and working mechanism of specific spectrum analyzers can be quite different from each other. Nevertheless, the output reading of modern spectrum analyzers can be roughly divided into two categories: linear normal spectrum and nonlinear power spectrum.
