Contents I. Introduction
With the recent spread of on-demand video services and cloud-based applications, data traffic on intra- and inter-data center fiber links has been growing exponentially [1]. Optical links for short-reach applications such as data center interconnects (DCIs) demand low-power consumption, high-spectral efficiency, dispersion-tolerance, and low-cost optical transceivers [2]. Polarization-multiplexed digital coherent optical transmission can increase the capacity but is not preferable for DCI applications because of the hardware complexity and the cost. Single-polarization intensity modulation-direct detection (IM-DD) is a low-cost solution. However, because the degree of freedom for modulation is limited only to the optical intensity, the capacity increase is challenging. Moreover, electronic dispersion compensation (EDC) at the receiver becomes so difficult that fiber dispersion limits the reach or the capacity [3].
