RESUMO
We design and fabricate a dual-step-index ring-core fiber (RCF) for orbital angular momentum (OAM) mode transmission. It has been proven that the proposed novel, to the best of our knowledge, dual-step-index ring-core structure can suppress the spin-orbit coupling and cut off the radial higher-order modes when the mode number becomes very large. In experiments, we demonstrate that the fabricated fiber can support OAM8,1 with the interferometric method, where four higher-order mode groups are weakly-coupled. We also measure the loss of each mode according to the cut-back method and the loss can achieve <0.3 dB/km for the OAM modes with an order from |l| = 1 to |l| = 5. The exploration of this novel optical fiber structure may provide ideas and knowledge for the improvement of the optical fiber communication capacity.
RESUMO
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 (MG2,1, MG3,1, and MG4,1) are verified to be in a weak-coupling state (crosstalk of which are less than -12 dB) over a transmission length of 23 km.
