Single-Mode vs Multimode Fiber

Fiber comes in two main types that differ mainly in core size and how light travels through them: single-mode and multimode. The choice affects distance, speed, and cost. Picking the right one for a link is a core skill, and the exam reliably asks you to match each type to its strengths. This lesson compares them clearly so you never mix them up.

A mode is a path that light can take down the fiber. A wide core lets light enter at many angles, so it travels along many paths or modes at once. A very narrow core forces light into essentially one straight path, a single mode. The core diameter is the key difference that gives each fiber type its name and its behavior.