Optical Communications Interview Questions and Answers for Experienced people on “Stability of the Fiber Transmission Characteristics”.
1. ____________ results from small lateral forces exerted on the fiber during the cabling process.
a) Attenuation
b) Micro-bending
c) Dispersion
d) Stimulated Emission
Answer: b
Explanation: Optical fibers must be designed so that the transmission characteristics of the fiber are maintained after the cabling process. The main problem which occurs in the cabling process is the meandering of the axis of the fiber core on a microscopic scale within the cable form. This phenomenon is called as micro-bending.
2. Microscopic meandering of the fiber core axis that is micro-bending is caused due to ___________
a) Environmental effects
b) Rough edges of the fiber
c) Large diameter of core
d) Polarization
Answer: a
Explanation: Micro-bending can be generated at any stage during manufacturing process, cable installation process or during service. This is mainly due to environmental effects, mainly varying temperatures causing differential expansion or contraction.
3. How many forms of modal power distribution are considered?
a) One
b) Two
c) Three
d) Four
Answer: b
Explanation: Two forms of modal power distribution are considered. The first form is seen when a fiber is excited by a diffuse Lambertian source, and is called as fully filled mode distribution. The second form occurs when, due to mode coupling and attenuation, the distribution of optical power becomes invariant with the distance of propagation along the fiber, and is called as steady-state mode distribution.
4. What does micro-bending losses depend on _____________
a) Core material
b) Refractive index
c) Diameter
d) Mode and wavelength
Answer: d
Explanation: Micro-bending losses cause differential expansion or contraction. These losses are mode dependent. The number of modes is a function inverse to the wavelength of the transmitted light and thus micro-bending losses are wavelength dependent.
5. The fiber should be________________ to avoid deterioration of the optical transmission characteristics resulting from mode-coupling-induced micro-bending.
a) Free from irregular external pressure
b) Coupled with plastic
c) Large in diameter
d) Smooth and in a steady state
Answer: a
Explanation: Micro-bending losses results from environmental effects such as temperature variation. The irregular external pressure deteriorates the quality of transmission through the fiber. Thus, controlled coating and cabling of the fiber is essential in order to reduce the cabled fiber attenuation.
6. The diffusion of hydrogen into optical fiber affects the ______________
a) Transmission of optical light in the fiber
b) Spectral attenuation characteristics of the fiber
c) Core of the fiber
d) Cladding of the fiber
Answer: b
Explanation: The hydrogen absorption by an optical fiber increases optical fiber losses. It forms absorption peaks where the hydrogen diffuses into interstitial spaces in the glass. At high temperatures, these losses can increase and reduced if the hydrogen source is removed.
7. __________ can induce a considerable amount of attenuation in optical fibers.
a) Micro-bending
b) Dispersion
c) Diffusion of hydrogen
d) Radiation Exposure
Answer: d
Explanation: The optical transmission characteristics of the fiber cables can be degraded by exposure to nuclear radiation. The nature of this attenuation depends upon fiber structures, optical intensity, wavelength, etc. The radiation-induced attenuation comprises both permanent and temporary components which makes the exposure irreversible and reversible respectively.
8. The radiation-induced attenuation can be reduced through photo-bleaching.
a) True
b) False
Answer: a
Explanation: Photo-bleaching can be exploited to study the diffusion of molecules. It is used to remove the radiation exposure by quenching auto-fluorescence. It helps to increase signal-to-noise ratio of the fiber and thus reduces attenuation.
9. The losses due to hydrogen absorption and reaction with fiber deposits can be temporary.
a) True
b) False
Answer: b
Explanation: Hydrogen absorption occurs in two mechanisms. First phenomenon affects silica-based glass fibers whereas the second one occurs when hydrogen reacts with the fiber deposits to give P-OH, Ge-OH absorption. These losses are permanent.
10. The losses caused due to hydrogen absorption mechanisms are in the range of ___________
a) 20 dB/km to 25 dB/km
b) 10 dB/km to 15 dB/km
c) 25 dB/km to 50 dB/km
d) 0 dB/km to 5 dB/km
Answer: c
Explanation: The diffusion of hydrogen into optical fiber leads to an increase in optical fiber losses, causing damage to spectral loss characteristics. This phenomenon gets vibrant at higher temperatures. The losses caused due to such absorption are greater than 25 dB/km.
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