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  1. Can some one please explain in simple words that what is effective refractive index?

  2. How it is different from the refractive index?

  3. And how we can calculate the effective refractive index?

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Here is nice explanation – freude Jun 26 '13 at 11:58
The term "effective refractive index" is also used in the theory of composite media like photonic crystals in different meaning. – freude Jun 26 '13 at 11:59
+1 Welcome to physics SE! Consider marking an answer, that helped you by clicking the green check at the answer. This removes the question from the unanswered questions list. – Stefan Bischof Aug 6 '14 at 6:46

The refractive index $n$ of a homogenous medium can be looked at as a measure of the delay which light propagating through the medium experiences, compared to the propagation of light in vacuum. For example, glass has a refractive index of about 1.3, meaning light waves propagate about 1.3 times slower in water than in vacuum. A refractive index is a property of the material itself.

Now an effective refractive index can be given for an optical component (e.g. a waveguide) as a measure of the overall delay of a light beam in that component. This is not a property of the material the optical fibre is made of, but an effective property of the optical fibre altogether.

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Thanks for your answer but can you please explain little more that what do you mean by overall delay of light beam in that component ??? It is little confusing and do you have any idea that how to calculate the effective refractive index ?? – Rizwan Jun 26 '13 at 11:35
@Rizwan, the effective index takes into account the different paths light rays can take inside, for example, a fiber. Even in a homogeneous fiber (same material and index everywhere) you have more than one dimension in which light propagates, giving a dispersion in the possible paths and thus in the time necessary to go from one end to the other. Other components may have more complex structures but you also can compare the time between the signal output and the signal input and define an effective index as if it were a homogeneous material where light is propagating. – Andrestand Nov 2 '15 at 13:41

In fiber optic measurement the effective refractive index is calculated as follow:

RI eff=(L opt* RI opt)/L eff

where: L eff is the cable or physical distance between two know even on the OTDR L opt is the optical distance between two known events

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You haven't really explained anything useful here. – Brandon Enright Aug 6 '14 at 4:59

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