On the benefits of FMF based data center interconnection utilizing MIMO-less PAM-M transceivers

Space division multiplexing (SDM) has been proposed to cost-effectively increase the capacity of optical transmission systems. The cost savings can be realized by introducing some levels of spatial integration of elements. However, spatial densification increases the crosstalk (XT) interactions among spatial channels. The XT is expected to be mitigated by MIMO processing, however, it increases the power consumption which in turn can make MIMO based SDM solutions impractical. This is a major issue for datacenters exploiting SDM solutions. Therefore, removing/lightening the burden imposed by MIMO processing can make SDM a more favorable solution. In this paper, we propose a datacenter interconnection network (DCIN), utilizing PAM-M transceivers, which can circumvent MIMO processing. It can be achieved by designing proper fibers (e.g. elliptical core FMF) in which the likelihood of mixing between mode-groups can be reduced. A key contribution of this work is the development of an analytical model to estimate the maximum reach that PAM-M (M = 4,8) signals can travel through coupled SDM fibers, targeting intra- and inter-DCs applications. We then demonstrate that FMF with MIMO-less PAM-M transceivers can significantly reduce the cabling complexity, and consequently, the cost of DCINs compared to single wavelength multi-mode or single-mode fibers based deployments.