SDM4 multicore fiber MSA publishes 1.0 spec for four-core MCF interoperability

AFL, Corning, Sumitomo Electric, and TeraHop have completed the SDM4 Multicore Fiber Multi-Source Agreement and published version 1.0 of its technical specification, defining a common four-core multicore fiber design aimed at short-reach links in AI data centers and campus networks.

The SDM4 Multicore Fiber MSA Technical Specifications, Version 1.0 set common geometrical, optical, mechanical, and measurement requirements for a four-core multicore fiber intended for “AI data centers, campus networks and other short-reach optical links.” The group says the goal of the MSA was to provide an industry-defined foundation for multi-vendor interoperability and future international standardization of four-core multicore fiber.

On the physical and optical side, the spec calls for a four-core, square-lattice 2×2 core arrangement with a core pitch of 40 ± 1 µm, and a nominal cladding diameter of 125 µm. It targets O-band short-reach applications and sets crosstalk limits of −40 dB or less at 1 km and 1310 nm for both adjacent and diagonal core pairs. The document also includes measurement principles and informative guidance covering core numbering, rotational alignment, polarization mode dispersion, and marker configurations.

For data center engineers, the practical point is straightforward: standardizing a multicore fiber geometry and its measurable limits is what enables multi-vendor optical ecosystems to form around it. But moving from a published fiber spec to deployable infrastructure still depends on the rest of the link, including connectors, transceivers, and interface specifications that can take advantage of multiple cores in a consistent way.

Antonio Castano, chair of the SDM4 MCF MSA, said: “By aligning around a shared four-core fiber design, we are enabling interoperability while supporting the increasing connectivity demands of AI data centers and campus networks.” The group also notes that frequent revisions to the MSA specification aren’t anticipated, and that future evolution is expected to progress through international standards-development organizations, with the published document serving as a reference for work in bodies including ITU-T, IEC, and IEEE.

The companies involved include AFL, Corning, Sumitomo Electric, and TeraHop.