ABSTRACT
Detection of optical signals can be carried out at the optical receiver by direct conversion of optical signal power to electronic current in the photodiode (PD) and then electronic amplification. This chapter provides the fundamental understanding of coherent detection (CoD) of optical signals, which requires the mixing of the optical fields of the optical signals and that of the local oscillator (LO), a high-power laser so that its beating product would result in the modulated signals preserving both its phase and amplitude characteristics in the electronic domain. Optical preamplification in CoD can also be integrated at the front end of the optical receiver.
