Singlemode fiber (SMF) has a very small core—around 8 to 10 microns —that allows only a single light mode to travel directly through the cable. Because the light does not bounce around, signal distortion is minimal, enabling long-distance transmission with high bandwidth. Let's break down these terms in simple, clear language with practical examples. 2-core o In optical modules, "core". There are two main types of fiber optic cables: single mode and multimode. Multimode fiber has a bigger core. It works well for short distances. What Is. But not all fiber cables are created equal: multimode (MM) and single mode (SM) fibers are the two primary types, each engineered for specific use cases, from short-range data center connections to transcontinental telecom backbones.