In a multimode fiber (step index), number of modes passing at an operating wavelength of 1300 nm are 1000, the refractive index of the core is 1.50 and that of the cladding is 1.48. The value of core diameter is:

 

29) In a multimode fiber (step index), number of modes passing at an operating wavelength of 1300 nm are 1000, the refractive index of the core is 1.50 and that of the cladding is 1.48. The value of core diameter is:

• 1. 600 nm [Option ID = 2945]
• 2. 1.4 μm [Option ID = 2946]
• 3. 125 μm [Option ID = 2947]
• 4. 4.25 μm [Option ID = 2948]

Answer: C

Solution

number of multimode, M = V^2/2

and multimode density V = pi*d/λ * sqrt(n1^2 - n2^2)

given,

M = 1000, n1 = 1.50, n2 =1.48

M = V^2/2

or, V^2 = 2000

V = pi*d/1300*10^(-9) * sqrt(1.50^2 - 1.48^2)

or, 2000 = {pi*d/1300*10^(-9) * sqrt(1.50^2 - 1.48^2)}^2

or, d = 75.6 micrometer

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