Ultra-low-bending-loss trench-assisted ring-core fiber

Telecom is in need of bend-insensitive fibers to decrease the overall fiber attenuation for long-haul applications. We propose 2-LP mode trench-assisted-ring core fiber (TA-RCF) and 3-LP mode TA-RCF structures, which result in ultra-low macro-bending losses (Ma-BL). The low bending loss of TA-RCF is demonstrated by designing and comparing standard and trench-assisted 2-LP (supports 3 spatial and 6 degenerate modes) and 3-LP (supports 5 spatial and 10 degenerate modes) RCF structures. Our design achieves extremely low Ma-BL at a 15 mm bend diameter at trench distances of (26.5-31.5) µm for 2-LP and (17.5-22.5) µm for 3-LP. The effective refractive index variation for the 2-LP TA-RCF is found to be in the range of (1.3×10^-3)-(2.3×10^-3), whereas for the 3-LP TA-RCF, it lies between (1×10^-3)-(2.3×10^-3), which results in low mode coupling. To anticipate reduced MIMO-DSP complexity at the receiver side, we have used the RCF refractive index profile, which supports only one radial order mode in a mode group (MG). The designed fibers' modal properties were analyzed using COMSOL Multiphysics, commercially available software based on the finite element method.