Numerical Aperture (NA) | Alker Fibre Optic Specialists

Numerical Aperture (NA)

The sine of half the angle over which a fibre can accept light multiplied by the refractive index of the medium containing the light. For air, the index is almost equal to 1.
NA also describes the angular spread of light from a central axis, as in exiting a fibre, emitting from a source, or entering a detector.

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