Going Coherent to Upgrade Data Centers MMF Links above 100G?

Large Scale Data Centers are still using Multi-Mode Fibers (MMF) for short distance links up to 300 meters, and IEEE is currently working on standardizing a new generation of systems for 100Gbit/s/$\lambda$ transmission using VCSEL+MMF transceivers on OM3 and OM4 fibers. These systems will still be based on IM-DD. In this paper, we experimentally and theoretically investigate on re-using already deployed OM3 and OM4 fibers using commercial coherent transceivers for bit rates up to 400G, showing that the only practical limitation of this solution is connector offsets. We experimentally show a 200G transmission tolerating offsets up to 6 $\mu{\mathrm m}$, and 400G up to 3 $\mu{\mathrm m}$ offset.