Coherent optical communications: opportunities & challenges

This paper explores the opportunities and challenges of developing coherent optical transceiver and modem technology and identifies digital and analog application areas of interest. Also, synchronous versus asynchronous detection, heterodyne versus homodyne detection, and on-off keying (OOK) versus complex signaling formats (e.g. Mary PSK or QAM) will be assessed from a system performance/hardware complexity perspective. The laser, modulator, balanced receiver and associated high-speed electronics challenges will be identified. This paper will also outline some of the current limitations of analog intensity modulation direct detection (IMDD) optical transmission systems and point out increasing opportunities for the use of coherent analog modulation and detection technology.