Optical Communications Multiple Choice Questions on “Linear & Non-Linear Scattering Losses”.
1. Rayleigh scattering and Mie scattering are the types of _____________
a) Linear scattering losses
b) Non-linear scattering losses
c) Fiber bends losses
d) Splicing losses
Answer: a
Explanation: Rayleigh scattering and Mie scattering both result from non-ideal physical properties of the fiber. These losses may be impossible to eradicate. Linear scattering mechanisms cause the transfer of optical power contained within one propagating mode to be transferred linearly into a different mode.
2. Dominant intrinsic loss mechanism in low absorption window between ultraviolet and infrared absorption tails is ___________
a) Mie scattering
b) Rayleigh scattering
c) Stimulated Raman scattering
d) Stimulated Brillouin scattering
Answer: b
Explanation: Rayleigh scattering results from non-ideal physical properties of fiber. It is a type of linear scattering loss and is difficult or impossible to eradicate. Hence, it is termed as dominant intrinsic mechanism.
3. Rayleigh scattering can be reduced by operating at smallest possible wavelengths.
a) True
b) False
Answer: b
Explanation: Rayleigh scattering results from inhomogeneity of a random nature occurring on a small level compared with the wavelength of light. The Rayleigh scattering is inversely proportional to the wavelength. Thus, as wavelength scattering reduces.
4. The scattering resulting from fiber imperfections like core-cladding RI differences, diameter fluctuations, strains, and bubbles is?
a) Rayleigh scattering
b) Mie scattering
c) Stimulated Brillouin scattering
d) Stimulated Raman scattering
Answer: b
Explanation: Linear scattering also occurs at inhomogeneity which are comparable in size with the guided wavelength. These results from non-perfect cylindrical structures of the waveguide and hence caused by fiber imperfections.
5. Mie scattering has in-homogeneities mainly in ___________
a) Forward direction
b) Backward direction
c) All direction
d) Core-cladding interface
Answer: a
Explanation: In Mie scattering, the scattering in-homogeneities size is greater thanλ/10. Also, the scattered intensity has an angular dependence which is very large. The in-homogeneities are mainly in the direction of guided wavelength i.e. in forward direction.
6. The in-homogeneities in Mie scattering can be reduced by coating of a fiber.
a) True
b) False
Answer: a
Explanation: Mie scattering is a type of linear scattering loss. It results from fluctuations in diameter, differences in core-cladding refractive index, and differences along the fiber length. Therefore, such in-homogeneities can be reduced by controlled extrusion and coating of the fiber.
7. Raman and Brillouin scattering are usually observed at ___________
a) Low optical power densities
b) Medium optical power densities
c) High optical power densities
d) Threshold power densities
Answer: c
Explanation: Raman and Brillouin scattering mechanism are non-linear. They provide optical gain but with a shift in frequency, thus contributing to attenuation for light transmission at a particular wavelength. They can be seen at high optical power densities.
8. The phonon is a quantum of an elastic wave in a crystal lattice.
a) True
b) False
Answer: a
Explanation: A phonon is an elastic arrangement of atoms or molecules in condensed matter. This matter maybe solids or liquids. A phonon is a discrete unit of vibrational mechanical energy given by hf joules;
Where h = Planck’s constant
f = frequency.
9. A single-mode optical fiber has an attenuation of 0.3dB/km when operating at wavelength of 1.1μm. The fiber core diameter is 4μm and bandwidth is 500 MHz. Find threshold optical power for stimulated Brillouin scattering.
a) 11.20 mw
b) 12.77 mw
c) 13.08 mw
d) 12.12 mw
Answer: b
Explanation: The threshold optical power stimulated Brillouin scattering is given by-
PB = 4.4*10-3d2λ2αdBv
Where, PB = threshold optical power
d = diameter of core
λ = wavelength
αdB = attenuation.
10. 0.4 dB/km, 1.4μm, 6μm, 550MHz. Find threshold optical power for stimulated Raman scattering.
a) 1.98 W
b) 1.20 W
c) 1.18 W
d) 0.96 W
Answer: c
Explanation: The threshold optical power stimulated Raman scattering is given by-
PR = 5.9*10-2d2λαdB
Where, PR = optical power for Raman scattering
d = diameter of core
λ = wavelength
αdB = attenuation.
11. Stimulated Brillouin scattering is mainly a ___________
a) Forward process
b) Backward process
c) Upward process
d) Downward process
Answer: b
Explanation: The incident photon in Stimulated Brillouin scattering reduces a phonon of acoustic frequency as well as scattered photon. This produces an optical frequency shift which varies with the scattering angle. This frequency shift is max. in backward direction reducing to zero in forward direction making Stimulated Brillouin scattering a backward process.
12. High frequency optical phonon is generated in stimulated Raman scattering.
a) False
b) True
Answer: b
Explanation: An acoustic proton is generated in Stimulated Brillouin scattering. Raman scattering may have an optical power threshold higher than Stimulated Brillouin scattering.
13. Stimulated Raman scattering occur in ___________
a) Forward direction
b) Backward direction
c) Upward direction
d) Forward and backward direction
Answer: d
Explanation: Stimulated Raman scattering is similar to Stimulated Brillouin scattering except that a high frequency phonon is generated in Stimulated Raman scattering. Stimulated Raman scattering can occur in forward and backward direction as it has optical power threshold higher than Stimulated Brillouin scattering.
14. Stimulated Raman scattering may have an optical power threshold of may be three orders of magnitude ___________
a) Lower than Brillouin threshold
b) Higher than Brillouin threshold
c) Same as Brillouin threshold
d) Higher than Rayleigh threshold
Answer: b
Explanation: Stimulated Raman scattering involves generation of high- frequency phonon. Stimulated Brillouin scattering on the other hand, involves the generation of an acoustic phonon in a scattering process.
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