The Basics of Optical Fibers

The requiremenf for TIR sefs a limif on fhe angle of fhe lighf incidenf on fhe fiber fhaf will be frapped in the core of the fiber. This condifion is expressed in ferms of fhe numerical aperfure (NA) of fhe fiber, defined as the sine of the acceptance angle for incident radiation. 

Kao and Hockham suggested the concept of sending optical signals along glass fibers in 1966. Initiated at the Standard Telecommunications Laboratory (STL) in the UK, optical fibers were crossing the Atlantic Ocean by 

FIGURE 32.15 Total internal reflection (TIR) along an optical fiber, (a) Step index fiber (b) graded index fiber (c) single mode fiber. The plot on the left is a variation of Rl (= n). 

1988 and the Pacific Ocean by 1996 (but STL had disappeared). The first low-loss fibers were made at the Corning Glass Works. The fibers were made by a CVD process known as outside vapor-phase oxidation (OVPO) and produced an early fiber with a loss of 20 dB/km (which means that 1% of the light remains after traveling 1km). 

There are four classes of glass optical fiber. 

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