Fiber Types & Classifications

Singlemode Fiber Overview

Singlemode fiber allows only one mode (path) of light to propagate through its core. This eliminates modal dispersion entirely, enabling very high bandwidth over very long distances. Singlemode fiber is the standard choice for telecommunications, long-haul networks, CATV, and any application requiring distances beyond a few hundred meters.

Core Size

The core size of standard singlemode fiber is approximately 8-10 micrometers (um). This tiny core diameter is what restricts propagation to a single mode. The cladding diameter is standardized at 125 um for both singlemode and multimode fiber.

Mode Field Diameter (MFD)

Mode field diameter is the effective optical width of the singlemode core - the area where light actually travels. The MFD is slightly larger than the physical core diameter because the light extends slightly into the cladding. MFD is an important specification for singlemode fiber because it affects splice loss and connector coupling. When splicing two fibers with different MFDs, the mismatch causes additional loss.

For standard singlemode fiber at 1310 nm, the MFD is typically about 9.2 um. At 1550 nm, it expands slightly to about 10.4 um because longer wavelengths spread more into the cladding.

Standard singlemode fiber has a core of approximately 8-10 um and supports only one mode of light. Mode field diameter describes the effective optical width where light actually propagates, and it is slightly larger than the physical core.