Page 195 - Sensors and Control Systems in Manufacturing

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Cha p te r
T h ree

FIGURE 3.30 Structure of optical fi ber.

glass, and the cladding structure composed of glass or plastic. Each
layer has a different index of refraction, the core being higher. The
difference between the index of refraction of the core material n and
1
that of the surrounding cladding material n causes rays of light
2
injected into the core to continuously reflect back into the core as they
propagate down the fiber.
The light-gathering capability of the fiber is expressed in terms of
its numerical aperture NA, the sine of the half angle of the acceptance
cone for that fiber. Simply stated, the larger the NA, the easier it is for
the fiber to accept light (Fig. 3.31).

FIGURE 3.31 Numerical aperture (NA) of an optical fi ber.