CALIENT Technologies

Move the light, not the fiber

Multi-Mode or Single-Mode Fiber for Data Centers?

Selecting the appropriate fiber cabling for a Data Center (DC) is both a financial and a strategic decision. DCs have a choice between multi-mode fiber (MMF) and single-mode fiber (SMF). The shorter distances and slower data rates (i.e., below 25 Gbps) of earlier DC architectures, made it financially feasible to use multi-mode fiber. Also in the past, the comparatively high cost of pluggable optics discouraged DCs from using SMF over MMF.

smtformmfbluered Picture credit:

Currently, three changes are favoring single-mode fiber:

  • Data rates are increasing from 10 Gbps to 40 Gbps, 100 Gbps and beyond
    • DCs that deployed OM1 and OM2 fibers have had to upgrade to OM3 and OM4 multi-mode fibers to support higher rates
    • As data rates grow greater than 100 Gbps, OM3 and OM4 will also have to be upgraded
  • Intra-DC distances are increasing
    • With DCs getting larger, intra-DC distances are increasing; as such, the distance limitations of OM3 and OM4 will constrain growth
  • Silicon photonics is reducing the cost of serial optics
    • The silicon photonics manufacturing process is driving down the cost of serial optics. The industry is nearing cost parity when the price of fiber is factored into cost estimates.
    • Intel® recently announced that it is launching silicon photonics for datacenter traffic management (see

Facebook has worked with the industry to develop a single-mode, fiber-optic cabling solution that operates over greater distances, at a much lower cost, than the longer-haul, single‑mode fiber which has historically been available for 100 Gbps links.

smformmfgraph Graph source: “Datacenters to Get A High Fiber Bandwidth Diet,” March 18, 2016, Timothy Prickett Morgan, The Next Platform

DCs have to look at cabling costs versus not being able to scale and offer newer services. With intra-DC distances getting longer and capacities expanding to 40 Gbps and higher, a DC equipped with multi-mode fiber is analogous to a competitive runner using ill-fitting shoes—it’s questionable whether he’ll finish the race and if he does, he won’t be competitive. To compete successfully, DCs will have to transition to a fiber plant that will support scale, longer distances and higher capacities. At present, SMF is the best means for achieving this goal.

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