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Commonly confused · Networking Fundamentals

Single-Mode vs Multimode Fiber: What's the Difference?

Single-mode fiber has a tiny core that carries one light path, usually from a laser, so it reaches many kilometers. Multimode fiber has a larger core that carries many light paths, usually from LEDs or VCSELs, so modal dispersion limits it to a few hundred meters.

Single-Mode Fiber (SMF)

Full definition
vs

Multimode Fiber (MMF)

Full definition
Single-Mode FiberMultimode Fiber
Core diameterAbout 8-10 microns50 or 62.5 microns
Light sourceLaserLED or VCSEL
DistanceUp to tens of kilometersTypically up to about 300-550 meters at 10 Gbps
DispersionMinimal modal dispersionModal dispersion limits distance
Jacket color (common)YellowOrange (OM1/OM2) or aqua (OM3/OM4)
CostCable is inexpensive; optics cost moreCheaper optics, shorter reach
Typical useCampus backbones, WAN, carrier linksInside buildings and data centers
Remember it

Single-mode is a single laser beam going far; multimode is many beams bouncing a short way.

Exam tip

Questions give a distance and ask which fiber to use: long runs between buildings or kilometers mean single-mode. Jacket color identification (yellow vs orange/aqua) also appears.

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