What does the numerical aperture (NA) measure?

The numerical aperture (NA) specifically measures the ability of an optical fiber to capture light. It quantifies the light-gathering capability of a fiber optic cable, which is crucial for determining how much light can enter the fiber and how effectively the fiber transmits that light. A higher numerical aperture indicates a greater ability to capture light from a wider range of angles, which is vital for the performance and efficiency of fiber optics in various applications.

In essence, the NA is derived from the refractive indices of the core and the cladding of the fiber and gives insight into the fiber's performance in transmitting signals. Understanding the numerical aperture is fundamental for selecting the appropriate type of fiber for specific applications, as it can impact bandwidth and transmission distance.