ABSTRACT
Most current IR detectors that have been considered in the previous chapters are used in the direct detector mode. In direct detection the output electrical signal is linearly proportional to the signal power. As such, no information regarding the phase of the signal is retained in the electrical output. A heterodyne detection, in contrast, produces an output signal proportional to the electric field strength of the signal and thus the phase of the optical field is preserved in the phase of the electrical signal. Infrared heterodyne detection have been used primary in pas sive heterodyne radiometry and in CO2 laser applications.
