Fiber optic cables are all single-mode

While fiber optic cables can be either single-mode or multimode, the majority of modern long-distance and backbone networks use single-mode fiber.Fiber optic cables transmit data as pulses of light through a glass or plastic core, offering higher bandwidth and longer transmission distances than copper cables . Single-mode fiber has a very small core diameter, typically 8–10 micrometers, allowing only a single light mode to propagate. This minimizes modal dispersion, reduces signal loss, and enables data transmission over distances up to 100 kilometers without the need for signal regeneration . Single-mode fibers are widely used in telecom backbones, data center interconnects, and fiber-to-the-home (FTTH) deployments, accounting for roughly 80% of the global optical fiber market . In contrast, multimode fiber has a larger core, usually 50–62.5 micrometers, which allows multiple light modes to travel simultaneously. This makes multimode fiber suitable for short-distance applications, such as within buildings or data centers, but it suffers from modal dispersion that limits its effective transmission distance . Multimode fibers are often paired with LEDs as light sources, whereas single-mode fibers typically use lasers for long-distance, high-speed transmission . Standards such as G.652 and G.657 define the most common single-mode fibers, ensuring compatibility with modern telecom systems and enabling future upgrades like Dense Wavelength Division Multiplexing (DWDM) without replacing the fiber . Single-mode fibers are also categorized by optical specifications, such as OS1 and OS2, which define attenuation and bandwidth characteristics for different deployment scenarios . In summary, fiber optic cables are not exclusively single-mode, but single-mode fiber is generally preferred for long-distance, high-bandwidth, and backbone network applications, while multimode fiber is used for shorter-range, high-capacity connections within buildings or campuses .