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This study presents a framework for optimizing the core pitch of multi-core fibers (MCFs) in bidirectional MCF-based space-division multiplexing elastic optical networks (SDM-EONs). Existing studies have predominantly adopted hexagonal-lattice core layouts for the MCF structure and have overlooked indirect inter-core crosstalk (IC-XT), which can be the dominant impairment in bidirectional MCF-based SDM-EONs. In this study, existing IC-XT calculation models are re-evaluated, demonstrating that square-lattice-structure (SLS) MCFs are preferable for bidirectional MCF-based SDM-EONs, and an “XT-free condition” is derived to determine the optimal core pitch. Numerical simulations on three network topologies (EURO28, Kanto11, and TMN12) under multiple resource-allocation strategies reveal that the blocking probability is minimized whenever the XT-free condition is satisfied, independent of topology size or resource-allocation policy. For standard-cladding 4-core SLS MCFs, optimal core pitches (34.4, 34.0, and 30.7 µm) yield a minimum lightpath blocking probability, acceptable IC-XT, and ITU-T recommendation-compliant splicing loss. The proposed framework provides a general method for MCF design and offers valuable insights into realizing high-core-count MCF-based SDM-EONs. Beyond immediate design implications, the proposed framework may serve as a foundation for redefining benchmarking standards in resource-allocation models and guiding the future standardization of MCF designs.
Seki et al. (Thu,) studied this question.