Traditional unit for fiber diameter?

• A. Meters
• B. Millimeters
• C. Microns
• D. Nanometers

Answer: (C)

Fiber diameters are on a tiny scale, so we use micrometers as the measuring unit. One micrometer (µm) is one millionth of a meter, which puts typical optical fiber sizes in a practical range to read and compare. For example, the core of a common single-mode fiber is about 8–10 µm across, while the surrounding cladding is about 125 µm in diameter. Describing these sizes in meters would give numbers like 0.000008 m or 0.000125 m, which are harder to interpret at a glance. Nanometers would be too fine for standard fiber dimensions and are more suited to nanoscale features or wavelengths, not the everyday diameter specs of most fibers. So micrometers are the traditional, most convenient unit for stating fiber diameter.