Step indexed optical fibres

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Aaradhana
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Why are optical fibres step-indexed?
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uberteknik
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(Original post by Aaradhana)
Why are optical fibres step-indexed?
Assuming you understand modes and group velocities?

The optical fibre is a waveguide and step indexing defines it's core and cladding as constant refractive indexes.

The optical wave is guided by total internal reflection and multi-mode fibres suffer from modal dispersion because of the differences in velocities of the modes. i.e. resulting in the arrival of the modes at different times at the end of the transmission path.

Modal dispersion is reduced by grading the refractive index between the core and that of the cladding so that although rays of greater inclination to the fibre axis must travel further, they also travel faster. i.e. the travel times of the different waves are equalised and modal dispersion is therefore reduced.
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Aaradhana
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(Original post by uberteknik)
Assuming you understand modes and group velocities?

The optical fibre is a waveguide and step indexing defines it's core and cladding as constant refractive indexes.

The optical wave is guided by total internal reflection and multi-mode fibres suffer from modal dispersion because of the differences in velocities of the modes. i.e. resulting in the arrival of the modes at different times at the end of the transmission path.

Modal dispersion is reduced by grading the refractive index between the core and that of the cladding so that although rays of greater inclination to the fibre axis must travel further, they also travel faster. i.e. the travel times of the different waves are equalised and modal dispersion is therefore reduced.
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