A review of high-speed coherent transmission technologies for long-haul DWDM transmission at 100g and beyond

Over the past five years, coherent transmission technologies have delivered more than an order of magnitude improvement in the capacity- reach product for long-haul DWDM transmission systems. This article provides a working definition of "coherent transmission" based on current market realities; provides a functional model for beyond 100G coherent systems, and then examines five key technologies that will deliver beyond 100G: evolving transmitter technologies, including Nyquist pulse shaping and nonlinear compensation of transmitter devices; nonlinear compensation for the propagation effect; further advances in FEC technology; flexible grid DWDM and coherent super-channels. In each case we explain the factors in terms of optical or electronic component performance that are most likely to result in system performance limitations, and discuss engineering strategies to mitigate those limitations.