What Is Multimode Fiber?_
Multimode fiber (MMF) uses a larger core than single-mode fiber, allowing multiple light modes to propagate simultaneously, which limits reach due to modal dispersion. It is the standard media for intra-cluster GPU scale-out networking links, such as InfiniBand or Ethernet, connecting GPUs within a rack or across adjacent racks. OM3, OM4, and OM5 grades support increasing bandwidth over limited distances, with OM5 designed for shortwave wavelength division multiplexing.
Technical Details
Multimode fiber is typically terminated with MPO connectors (e.g., 12- or 24-fiber arrays) for parallel optics, using 850 nm VCSEL transceivers. OM4 and OM5 grades support high-bandwidth links (e.g., 100 Gbps, 200 Gbps, 400 Gbps) over typical reaches of up to a few hundred meters, depending on transceiver type and link budget. In GPU clusters, multimode fiber is used exclusively for scale-out networking (InfiniBand or Ethernet), not for NVLink, which remains copper within the rack. Cable assemblies must meet insertion loss and return loss per the relevant standard (e.g., TIA-568.3).
How Leviathan Systems Works with Multimode Fiber
Leviathan Systems field crews run and terminate multimode fiber trunks between GPU racks and leaf switches, using MPO cassettes and patch panels. We verify polarity and loss with an OLTS during commissioning to ensure fabric performance.
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