Question

The core diameter of multi-mode step index fiber is 60 micrometer. The difference in refractive index is 0.013. The core refractive index is 1.46. Determine the number of guided modes when the operating wavelength is 0.75 micrometer​​

Answer 1

direct answer: the no of modes are 1200

Answer 2

Given,

Core diameter of multi mode step index fiber =60 micrometer

Difference in refractive index=0.013

Core refractive index=1.46

To Find,

The number of guided modes when the wavelength is 0.75

Solution,

n1=1.46

n2=1.46+0.013

   =1.473

D=60micrometer

wavelngth=0.75micrometer

NA=√n2²-n1²

  =√1.473²-1.46²

 =0.19

Number of modes=1/2×((π×D×NA)/lambda))²

                              =1/2×((3.14×60×10^-6×0.19)/0.75×10^-6)²

                              =1200

Hence, the number of guided modes are 1200.