The modal dispersion in a fiber is 20 ns/km. what will be the overall pulse spread in 10 km long fiber? Assume material dispersion to be zero

The modal dispersion in a fiber is 20 ns/km. what will be the overall pulse spread in 10 km long fiber? Assume material dispersion to be zero Correct Answer 200 ns

Concept:

Dispersion can be defined as the spreading out of light pulse when light propagates down the fiber. Dispersion can be of three types modal dispersion, material dispersion, and waveguide dispersion. 

Model dispersion in multimode fibers:

• Multimode fiber is an optical fiber that enables multiple light modes to be propagated as they have a much larger core size. 
• Each mode ray travels a different distance as it propagates, therefore the ray arrives at different times at the fiber output.
• So the light pulse spreads out in time which can cause signal overlapping.

Calculation:

Given that,

Modal dispersion over distance = 20 ns/km

Fiber distance = 10 km

∴ The overall pulse spread in 10 km long fiber will be::

= (20 ns/km) × (10 km)

= 200 ns

Important Points

Model dispersion is not a problem in single mode fibers since there is only one mode that can travel in the fiber.