MMF-based Data Center Interconnect using Commercial Coherent Transceivers

In this manuscript we present an experimental analysis of a multi-mode fiber (MMF) link based on coherent detection. We propose the use of a commercial coherent transceiver to increase the transmission speed of a short-reach optical communication system over 300 m OM3 fiber. The performance of the system is studied in terms of bit rate as a function of the power budget margin (PBM) defined as the extra attenuation that can be introduced on the optical path. We investigate polarization multiplexed (PM) QPSK and 16-QAM modulation formats achieving up to 400 Gbps net bit rate transmission. Moreover, we analyze the impact of the lateral offset introduced by the connectors between MMF segments, showing decreasing PBM for increasing lateral offset. Nevertheless, PBM in excess of 28 dB for PM-QPSK modulation at 100G and 200G, 23 dB for 200G PM-16QAM modulation and 16 dB for 400G PM-16QAM, shows that commercial coherent transceivers can be used on MMF links up to much higher bit rates than those achieved by current VCSEL+direct detection based systems, provided that connections along the MMF have connectors connectors with offsets in the 3 $\mu m$ to 6 $\mu m$ range.