Principles of Communication: Optical Fibre MCQ

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Optical FibreHardQuestion 20324

Question

In an optical fibre system, chromatic dispersion causes pulse broadening because:

A
Different wavelengths travel at different speeds in the fibre material (different n)
Correct
B
The core and cladding have different refractive indices
C
The light source is not coherent
D
Modal noise adds to the signal

Correct answer

Different wavelengths travel at different speeds in the fibre material (different n)

Explanation

Chromatic (material) dispersion: n = n(λ) (dispersion relation of glass). A source with spectral width Δλ causes pulse broadening Δτ = D × L × Δλ where D is dispersion coefficient (ps/nm/km). At 1310 nm, D ≈ 0 for standard SMF (zero-dispersion wavelength). At 1550 nm, D ≈ 17 ps/nm/km — requires dispersion-compensating fibre for long links.

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