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A graded indexed optical fiber has a parabolic refractive index profile (ฮฑ = 2). If the fiber has a numerical aperture = 0.22 the total number of guided modes at a wavelength of 1310 nm is given by :


33) A graded indexed optical fiber has a parabolic refractive index profile (ฮฑ = 2). If the fiber has a numerical aperture = 0.22 the total number of guided modes at a wavelength of 1310 nm is given by :

  • (1) 174
  • (2) 1740
  • (3) 119
  • (4) 274
Answer: Option A
Solution 
Normalized frequency, V = 2*pi*a/ฮป * NA     [a = core radius = 25 micrometer]
= 26.38
and, number of guided modes,
M = V^2 / 4 = 171 

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