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Networking Fundamentals · Foundational

Single-Mode Fiber (SMF)

Fiber with a very small core (about 9 microns) that carries a single light path, supporting distances of tens to hundreds of kilometers.

Definition

SMF uses laser sources at 1310 nm or 1550 nm, avoids modal dispersion and offers the highest bandwidth over distance. Its jacket is typically yellow (OS1/OS2 grades). Optics for SMF historically cost more than multimode optics, though the gap has narrowed.

Example

A 40 km metro link uses single-mode fiber with 10GBASE-ER optics.

Exam tip

Single-mode = small core, laser, long distance, yellow jacket.

Don't confuse it with

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