250+ TOP MCQs on Polarization and Answers

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Optical Communications Multiple Choice Questions on “Polarization”.

1. For many applications that involve optical fiber transmission, an intensity modulation optical source is not required.
a) True
b) False
Answer: b
Explanation: In many optical fibers transmission, the cylindrical fibers used generally do not maintain polarization state of light input source not more than a few meters. So for this reason, optical sources intensity modulation is required.

2. The optical source used for detection of optical signal is ____________
a) IR sensors
b) Photodiodes
c) Zener diodes
d) Transistors
Answer: b
Explanation: Optical signal is generally detected by photodiodes because photodiode is generally insensitive to optical polarization or phase of light with the fiber.

3. An optical fiber behaves as a birefringence medium due to differences in ___________
a) Effective R-I and core geometry
b) Core-cladding symmetry
c) Transmission/propagation time of waves
d) Refractive indices of glass and silica
Answer: a
Explanation: In an optical fiber with ideal optically circulatory symmetric core, both polarization modes propagate with same velocities. These fibers have variations in internal and external stress; fiber bending and so exhibit some birefringence.

4. The beat length in a single mode optical fiber is 8 cm when light from a laser with a peak wavelength 0.6μm is launched into it. Estimate the modal birefringence.
a) 1×10-5
b) 3.5×10-5
c) 2×10-5
d) 4×10-5
Answer: a
Explanation: Modal birefringence can be obtained by-
BF = λ/LB = 0.8×10-6/0.08
= 1×10-5
Where
λ = peak wavelength
LB = beat length.

5. Beat length of a single mode optical fiber is 0.6cm. Calculate the difference between propagation constants for the orthogonal modes.
a) 69.8
b) 99.86
c) 73.2
d) 104.66
Answer: d
Explanation: The difference between the propagation constant for two orthogonal modes can be obtained by:
βx – βy = 2Π/LB = 2×3.14/0.06
= 104.66
Where
βx & βy are propagation constants for slow & fast modes resp.
LB = beat length.

6. A polarization maintaining fiber operates at a wavelength 1.2μm and have a modal birefringence of 1.8*10-3. Calculate the period of perturbation.
a) 0.7 seconds
b) 0.6 seconds
c) 0.23 seconds
d) 0.5 seconds
Answer: b
Explanation: The period of perturbation is given by-
T = λ/BF Where λ is operating wavelength, BF = Birefringence, T = period of perturbation.

7. When two components are equally excited at the fiber input, then for polarization maintaining fibers δΓg should be around ___________
a) 1.5ns/km
b) 1 ns/km
c) 1.2ns/km
d) 2ns/km
Answer: b
Explanation: The differential group delay δΓg is related to polarization mode dispersion (PMD) of fiber. This linear relationship to fiber length however applies only to short fiber-lengths in which birefringence are uniform.

8. Polarization modal noise can _________ the performance of communication system.
a) Degrade
b) Improve
c) Reduce
d) Attenuate
Answer: a
Explanation: Polarization modal noise is generally of larger amplitude than modal noise. It is obtained within multimode fibers and so it degrades the performance of the communication system and prevents transmission of analog signals.

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