Bidirectional mobile fronthaul based on wavelength reused MDM

In this paper, we propose a cost effective wavelength reused mode-division-multiplexing (MDM) system for high speed symmetrical bidirectional mobile fronthaul application. At the base band unit (BBU) pool, one of the spatial modes is used to transmit signal carrier while the others are used for downstream signal channels. At the remote radio unit (RRU) side, the signal carrier is firstly mode demultiplexed and then selected to be reused as modulation carrier for all the upstream signal channels. Thanks to the low mode crosstalk characteristic of the mode multiplexer/demultiplexer (MUX/DEMUX) and few-mode fiber (FMF), the signal carrier and each signal channel can be effectively separated. The spectral efficiency (SE) is significantly enhanced when multiple spatial channels are used. With the proposed scheme, we demonstrate a proof of concept intensity modulated 4×25-Gb/s 16-QAM orthogonal frequency division multiplexing (OFDM) transmission over 10-km FMF using low modal-crosstalk two-mode FMF and MUX/DEMUX with error free operation.