Which fiber type has a core diameter of about 8 to 10 microns and supports the highest bandwidths and longest distances without repeaters?

Which fiber type has a core diameter of about 8 to 10 microns and supports the highest bandwidths and longest distances without repeaters?

• A. Copper
• B. Coaxial
• C. Multi-mode
• D. Single-mode fiber

Answer: (D)

The core idea here is how the way light travels inside a fiber affects how much data you can send and how far it can go without needing repeaters. A fiber with a very small core—about 8 to 10 microns—forces light to take essentially a single path, so there’s almost no modal dispersion. With only one propagation mode, the signals don’t spread out in time as they travel, which means you can push for higher bandwidths over much longer distances before the signal degrades. That’s why single-mode fiber is preferred for long-haul communications: it minimizes distortion and attenuation over distance, letting repeaters be spaced far apart. In contrast, fibers with larger cores, like multi-mode types, let light travel in multiple paths. Those different paths have slightly different travel times, so the signal bits smear together (modal dispersion) and you lose bandwidth. Over shorter distances this is fine, but it limits how much data you can send reliably and how far you can go without repeaters. Other media such as copper or coaxial cables don’t offer the same combination of very small core, single-path propagation, and low dispersion, so they can’t reach the same high bandwidths over long distances as single-mode fiber.

The core idea here is how the way light travels inside a fiber affects how much data you can send and how far it can go without needing repeaters. A fiber with a very small core—about 8 to 10 microns—forces light to take essentially a single path, so there’s almost no modal dispersion. With only one propagation mode, the signals don’t spread out in time as they travel, which means you can push for higher bandwidths over much longer distances before the signal degrades. That’s why single-mode fiber is preferred for long-haul communications: it minimizes distortion and attenuation over distance, letting repeaters be spaced far apart.

In contrast, fibers with larger cores, like multi-mode types, let light travel in multiple paths. Those different paths have slightly different travel times, so the signal bits smear together (modal dispersion) and you lose bandwidth. Over shorter distances this is fine, but it limits how much data you can send reliably and how far you can go without repeaters. Other media such as copper or coaxial cables don’t offer the same combination of very small core, single-path propagation, and low dispersion, so they can’t reach the same high bandwidths over long distances as single-mode fiber.