11. ________ is also called as intermodal dispersion.
Waveguide Dispersion
Material Dispersion
Polarization mode Dispersion
Chromatic Dispersion
Answer: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?
6.12ns/km
7.69ns/km
10.29ns/km
8.23ns/km
Answer: 2. 7.69ns/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.
13. A multimode graded-index fiber exhibits a total pulse broadening of 0.15μs over a distance of 16 km. Estimate the maximum possible bandwidth, assuming no intersymbol interference.
4.6 MHz
3.9 MHz
3.3 MHz
4.2 MHz
Answer:3. 3.3 MHz
Explanation:
The digital bit rate and pulse duration are always inversely proportional to each other.
$B_{T}<\frac{1}{2\tau }$
Where
BT = bit rate
2Γ = duration of pulse.
$B_{T} = \frac{1}{2\times0.15\times 10^{-6} }$
BT = 3.3 MHz
14. The optical source used in fiber is an injection laser with a relative spectral width σλ/λ of 0.0011 at a wavelength of 0.70μm. Estimate the RMS spectral width.
1.2 nm
1.3 nm
0.77 nm
0.98 nm
Answer:3. 0.77 nm
Explanation:
λRMS is the RMS spectral width of the source, in nm (the RMS spectral width is the standard deviation of the curve of power density versus wavelength)
The relative spectral width σλ/λ= 0.01 is given. The RMS spectral width can be calculated as follows:
Given
Wavelength = 0.70μm = 0.70 × 10-6
σλ/λ = 0.0011
σλ = 0.0011λ
= 0.0011 × 0.70 × 10-6
= 0.77 nm.
15. Dispersion is measured in the unit of time in ______
Second
Nanosecond
Picosecond
Both 2 and 3
Answer:4. Both 2 and 3
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.
Dispersion is measured in the unit of time either in nanoseconds or picoseconds. The total dispersion produced by the fiber depends directly on its length. So, dispersion is typically measured in nanoseconds per kilometer (ns/km).
16. The non-zero-dispersion-shifted fiber was introduced in the year ______.
2000
1990
1960
1940
Answer.1. 2000
Explanation:-
The non-zero dispersion-shifted fibers (NZ-DSF) become more prevalent in the marketplace in mid-1990 system designers are interested in ensuring compatibility with the existing fiber plant.
The non-zero-dispersion-shifted fiber was introduced in the mid-1990s to provide wavelength division multiplexing applications. In the year 2000, the dispersion profile for non-zero-dispersion-shifted fiber was introduced.
Nondispersion-shifted single-mode fiber, sometimes referred to as standard single-mode fiber, was the first single-mode optical fiber type in widespread use in telecommunications systems.
Nondispersion-shifted single-mode optical fiber normally has a simple step-index profile. It has a nominal zero-dispersion wavelength in the 1300 nm transmission window.
17. A multimode step-index fiber has a source of RMS spectral width of 60nm and the dispersion parameter for fiber is 150psnm-1km-1. Estimate RMS pulse broadening due to material dispersion.
12.5ns km-1
9.6ns km-1
9.0ns km-1
10.2ns km-1
Answer.3. 9.0ns km-1
Explanation:-
Pulse broadening due to material dispersion results from the different group velocities of the various spectral components launched into the fiber from the optical source.
Calculation
The RMS pulse broadening per km due to material dispersion is given by
σm = σλLM
Where
σλ = rms spectral width = 60 nm
L = length of fiber = 1 Km
M = dispersion parameter = 150psnm-1km-1
= 60 × 1 × 150
= 9.0nskm-1
18. The variant of non-zero-dispersion-shifted fiber is called as __________
Dispersion flattened fiber
Zero-dispersion fiber
Positive-dispersion fiber
Negative-dispersion fiber
Answer.4. Negative-dispersion fiber
Explanation:-
Nonzero-dispersion-shifted fiber (NZ-DSF) is sometimes simply called nonzero-dispersion fiber (NZDF) and a variant of this fiber type is negative-dispersion fiber (NDF).
Nondispersion-shifted single-mode fiber, sometimes referred to as standard single-mode fiber, was the first single-mode optical fiber type in widespread use in telecommunications systems.
Nondispersion-shifted single-mode optical fiber normally has a simple step-index profile. It has a nominal zero-dispersion wavelength in the 1300 nm transmission window.
19. The amount of dispersion in Nonzero Dispersion-shifted single-mode fiber is controlled by ________
Managing Zero dispersion Wavelength
Managing Characteristic dispersion slope
Both 1 and 2
None of the above
Answer.3. Both 1 and 2
Explanation:-
The amount of dispersion in Nonzero Dispersion-shifted single-mode fiber is controlled by managing the zero-dispersion wavelength and characteristic dispersion slope through the careful manipulation of the fiber’s complex index profile.
One characteristic of these fibers is that the light carrying region of the fiber is proportionally smaller than non-dispersion-shifted single-mode fibers. This results in a higher power density at a given source power level, which if severe enough can mitigate improvements in the fiber’s nonlinear performance.
The latest generation fibers are designed with a larger mode-field diameter to lower the transmitted power density, thereby reducing nonlinear effects.
20. A multimode fiber has RMS pulse broadening per km of 12ns/km and 28ns/km due to material dispersion and intermodal dispersion resp. Find the total RMS pulse broadening.
30.46ns/km
31.23ns/km
28.12ns/km
26.10ns/km
Answer.1. 30.46ns/km
Explanation:-
The overall dispersion in multimode fibers comprises both chromatic and intermodal terms. The total RMS pulse broadening σT is given by
σT = (σ2c + σ2n)½
where
σc is the intramodal or chromatic broadening
σn is the intermodal broadening caused by delay differences between the modes
