ABSTRACT
Detection of optical signals can be carried out at the optical receiver by direct conversion of optical signal power to electronic current by the photon absorption and generation of electrons in the photodiode. This current is then amplified and converted in to voltage output by a transfer impedance amplifier. This chapter gives a fundamental understanding of coherent detection of optical signals that requires the mixing of the optical fields of the optical signals and that of the local oscillator (LO), a high-power laser, so that their beating product would result in the modulated signals preserving both their phase and amplitude characteristics in the electronic domain. Optical preamplification in coherent detection can also be integrated at the front end of the optical receiver.
