# Chromatic Dispersion MCQ || Chromatic Dispersion in optical fiber Questions and Answers

2. ________ is the spreading of light pulse as its travels down the length of an optical fiber.

1. Transmission
2. Dispersion
3. Diffusion

Explanation:

Dispersion is the spreading of the light pulse as its travels down the length of an optical fiber. Optical fiber dispersion describes the process of how an input signal broadens/spreads out as it propagates/travels down the fiber. Normally, dispersion in fiber optic cable includes modal dispersion, chromatic dispersion, and polarization mode dispersion.

4. In waveguide dispersion, refractive index is independent of ______________

1. Bit rate
2. Index difference
3. Velocity of medium
4. Wavelength

Explanation:

• The waveguide dispersion occurs because the propagation constant is a function of the fiber parameters (core radius and difference between refractive indices in fiber core and cladding) and at the same time is a function of wavelength.
• The longer the wavelength, the more power in the cladding.
• The effect of waveguide dispersion on pulse spreading can be approximated by assuming that the refractive index of a material is independent of wavelength.
• In material dispersion, the refractive index is a function of optical wavelength. It varies as a function of wavelength.
• In wavelength dispersion, group delay is expressed in terms of normalized propagation constant instead of wavelength.

5. ______  dispersion occurs because the propagation constant is a function of the fiber parameters.

1. Intramodal Dispersion
2. Chromatic Dispersion
3. Waveguide Dispersion
4. Intermodal Dispersion

Explanation:

• The waveguide dispersion occurs because the propagation constant is a function of the fiber parameters.
• Waveguide dispersion occurs because a single-mode fiber confines only about 80 percent of the optical power to the core.
• The dispersion thus arises, since the 20 percent of the light propagating in the cladding travels faster than the light confined to the core.
• The amount of waveguide dispersion depends on the fiber design since the modal propagation constant β is a function of a/ (the optical fiber dimension relative to the wavelength λ; here a is the core radius.)

6. For no overlapping of light pulses down on an optical fiber link, the digital bit rate BT must be ___________

7. Which of the following are types of optical fiber dispersion?

1. Intramodal Dispersion
2. Waveguide Dispersion
3. Material Dispersion
4. All of the above

Explanation:

The term dispersion describes the pulse broadening effect in fibres.

The types of dispersion are

1. Intramodal Dispersion
2. Material Dispersion
3. Waveguide Dispersion
4. Intermodal Dispersion
5. Polarization mode Dispersion

9. The total dispersion produced by the fiber depends directly on its ______.

1. Bandwidth
2. Length
3. Power
4. Refractive Index

Explanation:

Dispersion is the spreading of the light pulse as its travels down the length of an optical fiber. Dispersion limits the bandwidth or information-carrying capacity of a fiber.

The total dispersion produced by the fiber depends directly on its length. So, dispersion is typically measured in nanoseconds per kilometer (ns/km).

11. ________ is also called as intermodal dispersion.

1. Waveguide Dispersion
2. Material Dispersion
3. Polarization mode Dispersion
4. Chromatic Dispersion

Explanation:

• Intramodal dispersion is also called chromatic dispersion because it depends on the range of wavelengths transmitted by a fiber.
• Chromatic dispersion is the sum of two components: waveguide dispersion and material dispersion.
• Unlike intermodal dispersion, chromatic dispersion can be positive or negative.
• When material dispersion, which is always negative, is added to waveguide dispersion, the total can be positive or negative.
• The two components of chromatic dispersion can also cancel each other, yielding zero dispersion.

12. What is pulse dispersion per unit length if for a graded-index fiber, 0.1μs pulse broadening is seen over a distance of 13 km?

1. 6.12ns/km
2. 7.69ns/km
3. 10.29ns/km
4. 8.23ns/km

Explanation:

Dispersion is the spreading out of light pulses as they travel along with fiber. It occurs because the speed of light through a fiber depends on its wavelength and the propagation mode.

In its simplest sense, dispersion measures pulse spreading per unit distance in nanoseconds or picoseconds per kilometer. Total pulse spreading, Δt, is

Δt = Dispersion × Distance

Given

Pulse Broading = 0.1 μs = 0.1 × 10-6

Distance = 13 km

Dispersion = (0.1 × 10-6)/13 = 7.69 ns/km.

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