Which fiber is designed to carry a single light path with a core diameter of about 8–105 microns?

• A. Single-mode Fiber
• B. Multi-mode Fiber
• C. Fiber (Generic)
• D. MT-RJ Connector

Answer: (A)

In optical fibers, the number of light paths that can propagate depends on the core diameter. A very small core confines light to a single path, so only one mode travels—this is single-mode fiber. Its core is around 8 to 10 microns in diameter, which minimizes modal dispersion and supports long-distance, high-bandwidth transmission. Larger-core fibers support multiple light paths, causing modal dispersion and limiting distance and speed; those are the multi-mode fibers with core sizes commonly around 50–62.5 microns. A generic "fiber" or a connector type like MT-RJ isn’t describing a fiber type itself, so they don’t match the idea of carrying a single light path. Therefore, the fiber designed for a single light path is single-mode fiber.