Mode Division Multiplexing (MDM) Based Hybrid PON-FSO System for Last-Mile Connectivity

In this work, we have demonstrated mode division multiplexing (MDM) based high-speed passive optical network (PON) and free-space optical (FSO) hybrid link for providing a practical solution to last-mile bottleneck issues. The proposed hybrid link has a PON with fiber length of 10 km and 20 km, integrated with an FSO system capable of supporting high-speed connectivity for end-users within the link range of 100–1000 $m$. Also, MDM has been incorporated as a part of the strategy to improve the performance of FSO links under adverse atmospheric conditions. Four different Laguerre-Gaussian (LG) modes i.e. LG 00, LG 01, LG 10, and LG 11, have been used here with each mode capable of supporting user data of 10 Gbps. Among various modes, the proposed link has demonstrated promising results for LG 00 mode as compared to other modes. Additionally, in contrast to conventional FSO links, it has been observed that the MDM-FSO link is a highly reliable solution for delivering high-speed last-mile connectivity. However, for FSO links with link range typically beyond 700 $m$, the use of the non-MDM transmission is highly recommended.