Optical modules, the core components enabling optical-electrical conversion, are widely used within data centers. With the continuous evolution of network architectures, the number of optical modules required per server rack has increased significantly. In this paper we review key technological milestones in system embedded optical interconnects in data centers that have been achieved between 2014 and 2020 on major European Union research and development projects. Much of this increase in traffic is dominated by video services. Linear pluggable optics (LPO) is garnering more attention as a way to quickly and efficiently move data in and out of server racks, but a lack of standards for connecting the optical modules is slowing adoption at a time when there is growing pressure to reduce power in data centers.
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