The numerical aperture (N.A.) of a graded-index multimode fiber is an important parameter that is a direct measure of a fiber's light gathering efficiency and sensitivity to microbending loss. Two standardized measurement methods are commonly used to obtain a fiber's numerical aperture. In the first method the N.A. is calculated from a measured value of delta, the fractional difference between the peak refractive index of the core n1 and that of the cladding n2. Delta is obtained along with the fiber's core diameter from its refractive-index profile.
© 1985 Optical Society of AmericaPDF Article