Spatial division multiplexing in the short and medium range: From the datacenter to the fronthaul

Abstract

This paper reports the experimental performance of spatial division multiplexing (SDM) optical transmission systems. These SDM systems are intended to support key short- and medium-range low-latency applications as optical fronthaul in cellular networks, point-to-point optical backhaul and baseband optical links in datacentre applications. In particular, the experimental demonstration of optical fronthaul of 3GPP LTE-A wireless supporting up to 4×4 MIMO on a 4-core multicore fibre (MCF) is reported. The results indicate that successful multiple-antenna transmission is achieved at 150 m MCF range. SDM implementation in SSMF by modal multiplexing is a complementary approach to MCF and is also experimentally investigated. The key limiting factor in this case is the optical mode conversion stage. An efficient mode-conversion coupler is proposed and evaluated for 850 nm and 1550 nm operation. For 1550 nm, a coupler has been fabricated in silicon-on-insulator (SOI) technology. Few-mode transmission performance is analysed considering the propagation of two LP mode groups. The experimental results indicate that the SDM system is suitable for short-range datacentre applications operating at 850 nm where integration capability is of great importance, and medium-range point-to-point optical backhaul links operating at 1550 nm can also benefit from the proposed device architecture.