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What is NA?
(Numerical Aperture)
Numerical Aperture (NA) is a dimensionless parameter that describes the light-gathering and light-guiding capability of an optical fiber. It defines the range of angles over which light can enter the fiber and still be guided through its core.
NA is determined mainly by the refractive index difference between the fiber core and cladding. It is an important parameter when selecting and coupling light into optical fibers, particularly for multimode and high-power applications.
HOW Numerical Aperture Works
The principle can be understood through three main steps:
Light acceptance
Light entering the fiber within a specific range of angles is guided by the core. This range is known as the acceptance angle and is directly related to the fiber's NA.
Core-cladding interface
The difference in refractive index between the core and cladding determines whether light remains confined within the core through total internal reflection.
Mode propagation
For a given core diameter and wavelength, a higher NA generally allows the fiber to support more propagation modes. This makes NA particularly important when coupling light efficiently into multimode fibers.
