Basic Introduction of Optical Fiber- Refractive Index

Some of the questions that arise about the optical fibers (OF) are:

  1. What is the structure of an optical fiber?
  2. How does light propagate along a fiber?
  3. What materials are used to make optical fibers?
  4. What is the process of making the OF?
  5. What is the signal loss or attenuation loss in optical fibers?


Prior to the year 1980, most communications technologies involved some type of electrical transmission mechanism. The era of electrical communications started in 1837 with the invention of the telegraph by F. B. Morse. Later in 1867, Graham Bell developed a fundamentally different device that could transmit the entire voice signals in an analog form.

As research & development progressed, the first installed optical fiber links which appeared in the late 1970s were used for transmitting telephony signals at about 6Mb/s over distances of around 10km.

Advantages of Optical Fibers

  1. Long distance transmission
  2. Large information capacity
  3. Small size and low weight
  4. Enhanced safety
  5. Increased signal security

Basic Optical Laws and Definitions

(a) Refractive index

Refractive index or index of refraction.

The speed of light is related to the frequency “ν” and the wavelength “λ” by

c=\nu \lambda

The ratio of the speed of light in a vacuum to that in the matter is the index of refraction “n” of the material and is given by



Refractive index for air = 1

Refractive index for water = 1.33

Refractive index for Silica Glass = 1.45

Refractive index for diamond = 2.42

The large value of refractive index means a small value of the speed of light in medium comparative to the vacuum.


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