Optimized Design Method for Trench-Assisted Grade-Index Ring-Core Fiber with low DMD and large A_(eff)

摘要

We propose a kind of trench-assisted graded-index ring-core fiber (TA-GI-RCF) with a low refractive index rod deployed in the center of the core, which supports three LP modes (LP_(01), LP_(11) and LP_(21)) transmission. There are two difficulties about designing TA-GI-RCF, one is to depart LP_(21) mode from LP_(02) mode because their effective indices are too close which makes it difficult to realize only three LP modes transmission; the other one is how to make sure these three LP modes reach the receiver end with low differential mode delay (DMD), so that the computation complexity of multi-input multi-output (MIMO) digital signal process (DSP) can be reduced. At first, we realize the separation of LP_(21) mode and LP_(02) mode in TA-GI-RCF by enlarging the size of low refractive index rod. We next investigate the influence of the TA-GI-RCF structural parameters on DMD and DMD slope, and find that a graded-index core and a low refractive index rod can flexibly tune the DMD, and a trench can flexibly control the DMD slope. Through optimizing the core parameters, we find that the design region of a is 1.01~2.23 and that of Δ_1 is 0.28%~0.46% at r_1=30 jμm, where a is the profile exponent and Δ_1 is the relative refractive index difference between core and cladding. Simulation results show that TA-GI-RCF can achieve the effective area (A_(eff)) of LP_(01) mode over 2000 μm~2 and the |DMD| between LP_(01) mode and LP_(11) mode is <100 ps/km over C+L band. Above all, we can achieve three LP modes transmission in TA-GI-RCF with low DMD over whole C+L band and large A_(eff).