Optical Communications Multiple Choice Questions on “Fiber Dispersion Measurements”.
1. ___________ measurements give an indication of the distortion to the optical signals as they propagate down optical fibers.
a) Attenuation
b) Dispersion
c) Encapsulation
d) Frequency
Answer: b
Explanation: Dispersion measurements provide the exact parameters to truly determine the quality and degradation to the optical signals. It gives an indication of the distortion to the optical signals as they propagate down the optical fibers.
2. The measurement of dispersion allows the _________ of the fiber to be determined.
a) Capacity
b) Frequency
c) Bandwidth
d) Power
Answer: c
Explanation: Dispersion measurements give an indication of distortion, which in turn determines the information carrying capacity of the fiber. This information carrying capacity of the fiber is purely dependent on the bandwidth of the fiber.
3. How many types of mechanisms are present which produce dispersion in optical fibers?
a) Three
b) Two
c) One
d) Four
Answer: a
Explanation: There are three major mechanisms which produce dispersion in optical fibers. These are: Material dispersion, waveguide dispersion and intermodal dispersion.
4. Intermodal dispersion is nonexistent in ________ fibers.
a) Multimode
b) Single mode
c) Step index- multimode
d) Al-GU
Answer: b
Explanation: Intra-modal as the name suggests need multimode fibers to propagate. In single mode fibers, only one mode is there to propagate. Hence, Intermodal dispersion is nonexistent in single mode fibers.
5. In the single mode fibers, the dominant dispersion mechanism is ____________
a) Intermodal dispersion
b) Frequency distribution
c) Material dispersion
d) Intra-modal dispersion
Answer: d
Explanation: In single mode case, the dominant dispersion mechanism is chromatic. Chromatic dispersion is called as intra-modal dispersion.
6. Devices such as ___________ are used to simulate the steady-state mode distribution.
a) Gyrators
b) Circulators
c) Mode scramblers
d) Attenuators
Answer: c
Explanation: The dispersion measurements on the fiber are performed only when the equilibrium mode distribution is set up within the fiber. Hence, filters or scramblers are used to simulate the steady state mode distribution.
7. How many domains support the measurements of fiber dispersion?
a) One
b) Three
c) Four
d) Two
Answer: d
Explanation: Fiber dispersion measurements can be made in two domains. These are time domain and frequency domain.
8. The time domain dispersion measurement setup involves _____________ as the photo detector.
a) Avalanche photodiode
b) Oscilloscope
c) Circulator
d) Gyrator
Answer: a
Explanation: The time domain fiber dispersion measurement involves the pulses to be received by the photo detector in order to determine the distortion in the optical signals. These pulses are received by avalanche photodiode.
9. In pulse dispersion measurements, the 3dB pulse broadening for the fiber is 10.5 ns/km and the length of the fiber is 1.2 km. Calculate the optical bandwidth for the fiber.
a) 32 MHz km
b) 45 MHz km
c) 41.9 MHz km
d) 10 MHz km
Answer: c
Explanation: The optical bandwidth for the fiber is given by –
Bopt = 0.44/3dB pulse broadening
Where, 0.44 = constant.
10. Frequency domain measurement is the preferred method for acquiring the bandwidth of multimode optical fibers.
a) True
b) False
Answer: a
Explanation: Bandwidth is usually the difference in the frequency. Frequency domain measurement is usually the best method in order to find the bandwidth of the multimode optical fibers.
11. Intra-modal dispersion tends to be dominant in multimode fibers.
a) True
b) False
Answer: b
Explanation: Intra-modal dispersion is dominant in case of single mode fibers. In case of multimode fibers, intermodal dispersion comes handy and is dominant.
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