Group Delay Spread Calculation Based on Individual Core-Mode-Based Supermode Analysis for Randomly Coupled Multi-Core Fiber

We propose a group delay spread (GDS) calculation for randomly coupled multi-core fiber (RC-MCF) based on simple core-mode analysis for a single-core structure, which avoids the time-consuming two-dimensional supermode calculation. The differential mode delay (DMD) and coupling efficiency between supermodes required for GDS calculation are derived from the individual core-mode properties through the mode basis transformation from the core-modes to the supermodes, which is applicable for an arbitrary number of cores and layout. After calculating the GDS properties of 4-, 7-, and 12-core RC-MCFs, we found that the proposed method well describes the GDS dependence on fiber parameters such as core pitch, bending radius, and core structure, which are essential for optimizing RC-MCF design.