Single-mode vs multimode fiber — how do I choose?
Both are fiber, both beat copper for distance. When is multimode enough and when do I have to pay for single-mode?
1 Answer
Distance decides. Multimode (OM3/OM4, thicker 50µm core, LED/VCSEL light) is fine inside a building: up to ~300–550 m at 10G, and the optics are cheaper. Single-mode (thin ~9µm core, laser light) carries tens of kilometers — it's the only realistic option between buildings or campuses once you pass a few hundred meters. Rule of thumb: same room or same riser → multimode saves money; different buildings → single-mode, no debate. Also remember copper's ceiling: 100 m for twisted pair — every longer run is a fiber conversation. Mixing them up is expensive because the transceivers aren't interchangeable: an SMF optic won't light an MMF run reliably and vice versa.