Understanding the characteristics of different fiber types aids in understanding the applications for which they are used. Operating a fiber-optic system properly relies on knowing what type of fiber is being used and why. There are two basic types of fiber: multimode and single-mode (see box, "Types of Optical Fibers"). Multimode fiber is best designed for short transmission distances, and is suited for use in local area network (LAN) systems and video surveillance. Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems [2].


There are two parameters used to distinguish fiber types, mode and index. The term "mode" relates to the use of optical fibers as dielectric waveguides. Optical fibers operate under the principle of total internal reflection. As optical radiation passes through the fiber, it is constantly reflected back through the center core of the fiber. The resulting energy fields in the fiber can be described as discrete sets of electromagnetic waves. These discrete fields are the modes of the fiber. Modes that propagate axially down the fiber are called guided modes. Modes that carry energy out of the core to dissipate are called radiation modes.

The number of modes allowed in a given fiber is determined by a relationship between the wavelength of the light passing through the fiber, the core diameter ...

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