OM1 vs OM3 vs OM4 vs OS2: Which Fiber Optic Cable Do You Need?

Fiber optic cable naming looks like alphabet soup — OM1, OM3, OM4, OS2, LC, SC, ST — but the decision tree behind it is short. Answer two questions and you're done: how far does the link run, and what do your transceivers expect?

Multimode vs single mode: the first fork

Multimode fiber (OM1–OM4) has a wider core (50 or 62.5 microns) that carries light from inexpensive VCSEL transceivers. It's the default for links inside a building: server room runs, switch-to-switch links between floors, rack-to-rack in a lab. The trade-off is distance — bandwidth drops as runs get longer.

Single mode fiber (OS2) has a tiny 9-micron core that carries a single mode of laser light for kilometers. Campus links between buildings, metro runs, and anything past a few hundred meters belongs on OS2. The cable itself is cheap; the laser optics on each end cost more than multimode optics.

One rule with no exceptions: you cannot mix them. A multimode cable between two single mode transceivers (or vice versa) is not a slower link — it's a dead one. Match the cable to the optics you own.

The multimode grades

  • OM1 (62.5/125, orange) — the legacy grade. Fine for 1Gbps up to ~275 m, but 10Gbps only survives about 33 m. Buy it to match existing OM1 plant, not for new installs.
  • OM3 (50/125, aqua) — laser-optimized. 10Gbps to 300 m, and 40/100Gbps to 100 m over parallel optics. The sensible floor for any new multimode run.
  • OM4 (50/125, aqua) — same construction as OM3 with tighter specs: 10Gbps to 400 m and 40/100Gbps to 150 m. The small price difference over OM3 buys headroom you'll be glad of at the next speed upgrade.

Connectors: LC, SC and ST

LC is the small-form connector that fits SFP/SFP+/QSFP transceivers — if you're plugging into a modern switch or NIC, you almost certainly want LC on at least one end. SC is the larger square push-pull connector common on older patch panels, media converters and ONTs. ST is the round bayonet-twist connector found on legacy panels and industrial gear. Mixed plant is normal, which is why patch cables come in every combination — LC-LC, LC-SC, LC-ST, SC-SC, SC-ST and ST-ST.

Duplex, and a note on Uniboot

Most links need two strands — transmit and receive — so standard patch cables are duplex. Uniboot LC cables run both strands through a single jacket and connector body, roughly halving cable bulk in dense patch fields, and allow polarity reversal without tools.

Quick answers

  • Server room, 10G, under 300 m: OM3 or OM4 duplex LC-LC.
  • Same rack or row: OM4 LC-LC in 1–5 m lengths; short is tidy.
  • New switch to an old SC patch panel: LC-SC multimode matching the installed grade.
  • Between buildings, or anything over 400 m: OS2 single mode with connectors matching your optics.
  • Legacy ST panel: match ST on the panel end, LC or SC on the equipment end.

Browse our full fiber optic cable collection — every listing states the grade, core size, connector pair and available lengths. Unsure what your transceiver takes? Ask us with the optic's model number and we'll match it.

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