# The core diameter of multimode step index fibre is 50 μm.The numerical aperture is 0.25. Calculate the number of guided modes at an operating wavelength of 0.75 μm. - Applied Physics 2

Numerical

The core diameter of multimode step index fibre is 50 μm.The numerical aperture is 0.25. Calculate the number of guided modes at an operating wavelength of 0.75 μm.

#### Solution

d = 50 x 10-6

N.A = 0.25

λ = 0.75 x 10-6

V = (πd)/λ x N.A

= (π  x  50  x  10^(−6))/(0.75  x  10^( −6)

= 52.36

Nm = (V^2)/2
= 1370.8
= 1370

 Number of modes = 1370
Concept: Numerical Aperture
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