High spectral-efficiency, ultra-low MIMO SDM transmission over a field-deployed multi-core OAM fiber

Space-division multiplexing (SDM) systems based on few-mode multi-core fibers (FM-MCFs) utilize both spatial channels (fiber cores) and modes (optical modes per core) to maximize transmission capacity. Unlike laboratory FM-MCFs or field-deployed single-mode multi-core fibers (SM-MCFs), SDM transmissions over field-deployed FM-MCFs in outdoor settings have not been reported. Therefore, concerns remain that environmental interference and cabling stress could worsen inter-core and intra-core modal crosstalk and impact the performance of SDM systems over FM-MCFs. In this paper, we demonstrate successful bidirectional SDM transmission over a 5-km, field-deployed seven ring-core fiber (7-RCF) with a cladding diameter of 178 μm. Our measurements show no significant differences in attenuation and mode coupling compared to pre-cabling conditions, confirming the fiber’s resilience to environmental disturbances and adaptability to cable deployment. Using the field-deployed 7-RCF, bi-directional SDM transmission is implemented, achieving spectral efficiency (SE) of 2×201.6 bit/(s Hz) which sets a new record in field-deployed fiber cables that is a tenfold increase over previous systems. Furthermore, these results were achieved using a small-scale 4×4 multiple-input multiple-output (MIMO) scheme with a time-domain equalization (TDE) tap number not exceeding 15. These results demonstrate the substantial potential of using SDM techniques to significantly enhance SE and expand capacity in practical fiber-optic transmission applications.