Reach depends on fiber type, speed and transceiver:
- Multimode OM3: 300 m at 10G, 100 m at 40/100G.
- Multimode OM4: ~150 m at 10G, ~100–150 m at 40/100G — intra-data-center.
- Single-mode OS2: 10 km with standard “LR” optics, 40 km “ER”, 80 km+ “ZR” or with amplification — inter-site and metro.
The real criterion is not the fiber alone but the optical budget: transmitted power minus attenuation (distance, splices, connectors) must stay above the receiver’s sensitivity. In practice: OM4 inside the building, OS2 as soon as you go outside (campus, metro, dark fiber). Choosing multimode for an inter-site link is the classic mistake that caps distance.