What does 'numerical aperture' in fiber optics describe?

Numerical aperture is a crucial concept in fiber optics that relates to the light acceptance angles of a fiber. Specifically, it is a dimensionless number that quantifies the ability of a fiber optic cable to gather and transmit light. The numerical aperture defines the range of angles over which the fiber can accept incoming light, which directly influences the fiber's efficiency and performance.

A higher numerical aperture allows the fiber to accept light from a wider range of angles, making it advantageous in applications where light input may not be perfectly aligned with the fiber. This characteristic is essential in determining how much light can be effectively transmitted through the fiber, impacting the overall signal quality and transmission distance.

In this context, the other options do not accurately represent what numerical aperture signifies. While the length of fiber, light speed, and amount of light transmitted are all important aspects of fiber optics, they do not describe the angle-related properties that the numerical aperture specifically addresses. Thus, the connection of numerical aperture to light acceptance angles is key to understanding its role in fiber optic technology.