Singlemode optical fiber (SMF) and two types of multimode optical fibers (MMF) are schematically shown in Fig.2.8. MMF is categorized into two types by the refractive index distribution in the core, step-index (SI) type optical fiber and GI type optical fiber.

 

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Fig. 2.8. Light propagation and refractive index distribution in SMF and MMF.
(a) SI-SMF, (b) SI-MMF, (c) GI-MMF