I. Introduction
Data centers have become the main point of infrastructure for information and communication technology (ICT) services, for example, cloud storage, social networking, and video streaming. However, the growth of data centers has led to increasing load on three key resources. The first one is the increasing power consumption, where each data center can consume several megawatts [1]. The second one is increasing data traffic; Cisco estimated global data centers to reach 19.5 Zbytes/year by the end of 2021, while only 6.0 Zbytes/year in 2016 [2]. The third one is the physical upscaling of data centers, with the need for “hyperscale datacenters” to support heavy amounts of data traffic. Optical interconnects that eliminate energy loss and limited bandwidth problems of metal wiring have become commonly used this decade, with their potential for high capacity at low-cost well investigated.