Design, fabrication, and characterization of a low-index center and trench-assisted 7-ring-core 5-mode-group fiber for dense space-division multiplexing

An optimized design of 7-ring-core 5-mode-group fiber for mode-group-based dense space-division multiplexing (DSDM) is proposed. It is found that decreasing the refractive index of the center and trench of each ring core can increase the available ring-core thickness and meanwhile suppress the radial higher-order modes. Based on the simulation, a fiber, with a thicker ring core and a relatively low refractive index contrast at the ring-core boundaries, is found of higher mode purity and lower macro-bending-caused mode coupling. In the experiment, the seven cores of the fabricated fiber have low transmission losses around -0.25 dB/km with only a few fluctuations. The three higher-order mode groups (MG(2,1), MG(3,1), and MG(4,1)) are verified to be in a weak-coupling state (crosstalk of which are less than -12 dB) over a transmission length of 23 km. (c) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement