Module 2 : Ray Model
Lecture : Ray Model
5. Numerical Aperture: This parameter tells us that if we take an optical fiber and put it in front of an optical source then how
  much light is collected by the fiber from the source. Smaller the value of N.A, smaller the value of (maximum launching angle) and smaller is the power accepted by the fiber. In other words, if the light is available from various directions from the source, only a portion of light is accepted by an optical fiber and the remaining part of the light is rejected by it.
6.
If we want good light launching efficiency then should be as large as possible. Since is related to the
 

difference of the squares of the refractive indices of the core and the cladding, the difference of squares of the refractive indices should be as large as possible.

So, for good launching efficiency, should be large compared to . Since the material for the optical fiber has been chosen as glass, the refractive index of the core is practically fixed to about 1.5.

The only choice therefore we have is to reduce the refractive index of the cladding for good launching efficiency. Since (i.e., no cladding) is the minimum possible value, it suggests that the cladding is an undesirable feature. In the first look it then appears that the cladding is only for mechanical support.

   
4.
DISPERSION
1.

The amount of light accepted by an optical fiber is only one of the parameters in optical communication. A more
 

important parameter is the data rate which the fiber can handle since the primary purpose here is to send information from one point to another.

 

Figure (4)
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