Digital signal processing in high-speed optical communications

Electronic digital signal processing is currently introduced in various subsystems of modern optical high-speed transceivers. Traditionally, electronic processing was basically limited to tasks like MUX/DEMUX, clock and data recovery and various synchronization loops as well as analog circuitry like modulator drivers or limiting amplifiers. In order to deal with advanced systems and with the need for increased performance at long reach and higher speed, additional signal processing requirements have appeared. Examples are FEC and electronic equalizers (EDC), electronic pre-compensation, differential encoders, clock and carrier recovery, and polarization control. Recent challenges employ pure digital processing, where ADCs and DACs are required, like OFDM (orthogonal frequency division multiplexing) modulation or MLSE (maximum likelihood sequence estimation) equalizers. In this paper some of these signal processing algorithms are considered in detail and their impact on performance and cost in terms of implementation effort is reviewed.