Optical Fiber Structures

The principles explained in 'The Principles of Optical Fiber' apply to optical fiber with a "step index" (SI) structure. This is the structure used for most POFs. On the other hand, quartz fiber used for telephone lines uses a "graded index" (GI) structure for increased transmission volume. In GI-POF, the index of refraction progressively increases toward the center of the optical fiber. Therefore, it utilizes the principle of refraction, not reflection as in the previous example. This method is the same as what occurs when light refracts at the surface of water. GI fiber uses this principle to progressively change the track of the light to contain it within the fiber. This type of fiber is suitable for high-speed, high-volume transmission.