What is the refractive index?

The refractive index refers to how much light bends, or refracts, when it passes from one medium into another. This property is crucial in optical fibers, as it determines how light travels through the fiber. When light moves from air (or a vacuum) into the denser material of the fiber, the speed of light decreases, and it bends at the interface between the two materials. The refractive index is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium, which directly relates to the bending of light.

This property is fundamental for designing optical systems, including fiber optics, because it affects how light is guided through the fiber and how effectively signals can be transmitted with minimal loss. A higher refractive index indicates that light will bend more sharply when entering the medium, which is essential for maintaining total internal reflection in fiber optic cables.

Other options do not accurately capture the essence of refractive index. For instance, measurements of light speed in a vacuum pertain to the fundamental properties of light rather than its interaction with materials. Signal loss over distance relates to attenuation and other factors, while the thickness of the fiber addresses physical dimensions rather than optical properties like refractive index.