Which type of optical fiber is primarily used for long-distance communication?

Single-mode fiber is primarily used for long-distance communication due to its design, which allows light to travel through a single path or mode. This construction significantly reduces light reflection and scattering, enabling signals to maintain their strength and clarity over long distances, often exceeding tens of kilometers. The core of single-mode fiber is very narrow, typically around 8 to 10 micrometers in diameter, which helps eliminate modal dispersion—an issue that can impact signal quality when various light modes interact within the fiber.

In contrast, multi-mode fiber, although suitable for shorter distances due to its wider core (approximately 50 to 62.5 micrometers), experiences greater modal dispersion as multiple light modes propagate through the fiber, leading to signal loss over longer spans. Plastic optical fiber, while useful for some applications due to its flexibility and ease of handling, also does not provide the performance required for long-distance communication when compared to single-mode fiber. Standard coaxial cable, while effective for certain types of electrical signal transmission, is not utilized in optical communication and therefore does not pertain to the question about optical fibers.