Multimode vs single-mode fiber (OM3/OM4/OS2): which fiber for which transceiver?
SX/SR optics need multimode fiber; LX/LH/LR need single-mode. How to read the transceiver, match the fiber grade, and get the rated reach.
Optics desk2026-08-27 · 3 min read
A transceiver and the fibre it plugs into must use the same mode. Put a multimode optic on single-mode fibre (or the reverse) and the link fails or loses reach. The optic's suffix tells you which fibre it needs.
Read the suffix
- SX / SR — short reach, 850 nm, multimode fibre.
- LX / LH / LR — long reach, 1310 nm, single-mode fibre (LX/LH can also run multimode with a mode-conditioning patch).
- ER / ZR — extended reach, 1550 nm, single-mode.
Multimode grades (short reach, lower cost)
- OM3 (aqua): laser-optimised, ~300 m at 10G.
- OM4 (aqua/violet): ~400 m at 10G, ~150 m at 100G.
- OM5 (lime): wideband, for SWDM.
Example: the GLC-SX-MMD (SX, multimode) reaches ~550 m on OM2 and up to 1 km on OM3; the SFP-10G-SR reaches 300–400 m on OM3/OM4.
Single-mode grade (long reach)
- OS2 (yellow): 9 µm core, for 1310/1550 nm lasers, 10 km and beyond.
Example: the GLC-LH-SMD and SFP-10G-LR run up to 10 km on OS2.
Connector & practice
Most 1G/10G SFPs use an LC duplex connector. Match optic mode to fibre grade, keep to the transceiver's rated reach, and use clean, correctly-polished patch cords. Every transceiver page on netzspec lists reach, wavelength, fibre type and connector — check before you order.