7-Ring-Air-Core Trench-Assisted Fibre Supporting >300 Radially Fundamental OAM Modes Across S+C+L Bands

Recently, high-speed optical communication systems have achieved fundamental capacity limitation by using time-, wavelength-, and polarization-division multiplexing technologies. As a recently explored property of light, mode division multiplexing (MDM) and space division multiplexing (SDM) have great potential to break the capacity limitation for the next-generation communication systems. Orbital angular momentum (OAM) beam is one kind of structured light with a "doughnut" intensity distribution and theorectically infinite topological charge [1] – [3] . Advanced multiplexing technique of combining MDM technology based on OAM modes with SDM in the multicore fibres (MCF) can be utilized to further improve the data-transmission rate and spectral efficiency. In this work, we propose and design a multi-ring-air-core trench-assisted fibre with 7 rings each supporting 58 OAM modes (i.e. 406 ones in total) at 1550 nm. Moreover, the improvement of the introduced low-index trench region on the communication system’s performance is numerically analyzed for the OAM 1,1 mode, and the results show that -77.37 dB low-level crosstalk can be achieved after 100-km fibre propagation.