AFL, Corning Incorporated, Sumitomo Electric Industries, Ltd., and TeraHop PTE. LTD. today announced the completion of the SDM4 Multicore Fiber Multi-Source Agreement (SDM4 MCF MSA) and the public release of the SDM4 Multicore Fiber MSA Technical Specifications, Version 1.0.
The specification defines 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.
By reaching agreement on a common fiber specification, the participating companies have completed the objective established for the MSA: to provide an industry-defined technical foundation for multi-vendor interoperability and future international standardization of four-core multicore fiber.
"This specification establishes a common technical foundation that can help accelerate adoption of multicore fiber across the industry," said Antonio Castano, Chair, SDM4 MCF MSA. "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."
A common fiber design for higher-density optical infrastructure
The continued scale-out of AI infrastructure is increasing the number and density of optical connections required within data centers and across data center campuses. Multicore fiber can provide multiple independent optical paths within a standard fiber cladding, offering a potential path toward greater connection density.Key elements defined in the SDM4 MCF MSA include:
• A four-core, square-lattice 2×2 core arrangement with a core pitch of 40 ± 1 µm
• A nominal cladding diameter of 125 µm
• Optical characteristics suitable for O-band short-reach applications
• Crosstalk limits of −40 dB or less at 1 km and 1310 nm for both adjacent and diagonal core pairs
The specification also provides measurement principles and informative guidance on core numbering, rotational alignment, polarization mode dispersion, and marker configurations.
A foundation for broader industry standardization
With publication of the specification, the SDM4 MCF MSA establishes a stable, industry-aligned technical baseline for interoperable SDM4 multicore fiber. The specification is intended to serve as a durable foundation for multi-vendor implementation, industry adoption, and related standards-development activities. Consistent with its role as a stable industry reference, frequent revisions to the MSA specification are not anticipated. Future evolution of requirements for this class of fiber is expected to be advanced through relevant international standards-development organizations, informed by the published specification.The publicly available specification may serve as a technical reference and foundation for discussions on multicore fiber standardization within ITU-T and IEC, and as a technical reference for discussions on optical transceiver and interface standardization by organizations such as IEEE.
The SDM4 Multicore Fiber MSA Technical Specifications, Version 1.0 are available at:
• AFL: AFLglobal.com
• Corning: Corning® Multicore Fiber Solutions website
• Sumitomo Electric: https://sumitomoelectric.com/press/2026/09/prs038
• TeraHop: TeraHop.com
About the SDM4 MCF MSA
The SDM4 Multicore Fiber Multi-Source Agreement is an industry-led agreement defining common technical requirements for a four-core multicore fiber designed for short-reach O-band optical links. The agreement was created to support multi-vendor interoperability and provide a technical foundation for future international standardization of multicore fiber.Publication of the SDM4 Multicore Fiber MSA Technical Specifications, Version 1.0, completes the objective of the MSA. The specification will remain publicly available as an industry reference.