Multimode fiber must be two-core

Multimode fiber typically has a single core, not two cores.

Multimode fiber (MMF) is designed with a single, relatively large core—usually 50 or 62.5 microns in diameter—surrounded by cladding, which allows multiple light modes to propagate simultaneously within that single core . The large core diameter simplifies alignment and installation, making MMF ideal for short- to medium-distance data transmission in enterprise networks, data centers, and campus environments . The concept of "two cores" refers to dual-core fiber modules, where two separate fiber cores are used in a single cable or connector to allow simultaneous bidirectional data transmission or increased bandwidth. This is independent of whether the fiber is single-mode or multimode . In other words, a multimode fiber can be manufactured as a single-core or multi-core cable, but the standard multimode fiber itself has only one core per fiber strand .

Key Points:

• Core vs. Mode: Multimode refers to the ability of the fiber to carry multiple light paths (modes) within a single core, not the number of cores .
• Single-core MMF: Most multimode fibers used in networking are single-core, supporting hundreds of guided modes .
• Multi-core fibers: Some specialized fibers may have two or more cores, but this is a separate design choice for higher capacity or redundancy, not a standard feature of multimode fiber . In summary, multimode fiber usually has one core, and the "multi" in multimode refers to multiple light paths within that core, not multiple physical cores. Dual-core or multi-core fibers exist but are distinct configurations used for specific applications.