Optical Communications Questions and Answers – Material Absorption & Fiber Bend Losses In Silicon Glass Fibers

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This set of Optical Communications Questions and Answers for Freshers focuses on “Material Absorption & Fiber Bend Losses In Silicon Glass Fibers”.

1. Which of the following statements best explain the concept of material absorption?
a) A loss mechanism related to the material composition and fabrication of fiber
b) A transmission loss for optical fibers
c) Results in attenuation of transmitted light
d) Causes of transfer of optical power
View Answer

Answer: a
Explanation: Material absorption is a loss mechanism that results in dissipation of transmitted optical power as heat in a waveguide. It can be caused by impurities or interaction with other components of the core.
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2. How many mechanisms are there which causes absorption?
a) One
b) Three
c) Two
d) Four
View Answer

Answer: b
Explanation: Absorption is a loss mechanism. It may be intrinsic, extrinsic and also caused by atomic defects.

3. Absorption losses due to atomic defects mainly include ___________
a) Radiation
b) Missing molecules, oxygen defects in glass
c) Impurities in fiber material
d) Interaction with other components of core
View Answer

Answer: b
Explanation: Atomic defects are imperfections in the atomic structure of fiber material. Atomic structure includes nucleus, molecules, protons etc. Atomic defects thus contribute towards loss of molecules, oxygen, etc.

4. The effects of intrinsic absorption can be minimized by ___________
a) Ionization
b) Radiation
c) Suitable choice of core and cladding components
d) Melting
View Answer

Answer: c
Explanation: Intrinsic absorption is caused by interaction of light with one or more components of the glass i.e. core. Thus, if the compositions of core and cladding are chosen suitably, this effect can be minimized.

5. Which of the following is not a metallic impurity found in glass in extrinsic absorption?
a) Fe2+
b) Fe3+
c) Cu
d) Si
View Answer

Answer: d
Explanation: In the optical fibers, prepared by melting techniques, extrinsic absorption can be observed. It is caused from transition metal element impurities. In all these options, Si is a constituent of glass and it cannot be considered as an impurity to glass itself.
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6. Optical fibers suffer radiation losses at bends or curves on their paths.
a) True
b) False
View Answer

Answer: a
Explanation: Optical fibers suffer radiation losses due to the energy in the bend or curves exceeding the velocity of light in the cladding. Hence, guiding mechanism is inhibited, which in turn causes light energy to be radiated from the fiber.

7. In the given equation, state what αr suggests?
a) Radius of curvature
b) Refractive index difference
c) Radiation attenuation coefficients
d) Constant of proportionality
View Answer

Answer: c
Explanation: Above equation represents the fiber loss. This loss is seen at bends and curves as the fibers suffer radiation losses at curves. These radiation losses are represented by a radiation attenuation coefficient (αr).

8. A multimode fiber has refractive indices n1 = 1.15, n2 = 1.11 and an operating wavelength of 0.7μm. Find the radius of curvature?
a) 8.60μm
b) 9.30μm
c) 9.1μm
d) 10.2μm
View Answer

Answer: b
Explanation: The radius of curvature of the fiber bend of a multimode fiber is given by
optical-communication-questions-answers-material-absorption-fiber-bend-losses-silicon-glass-fibers-q8
Where, Rc = radius of curvature
n1, n2 = refractive indices
λ = wavelength.

9. A single mode fiber has refractive indices n1=1.50, n2 = 2.23, core diameter of 8μm, wavelength = 1.5μm cutoff wavelength = 1.214μm. Find the radius of curvature?
a) 12 mm
b) 20 mm
c) 34 mm
d) 36 mm
View Answer

Answer: c
Explanation: The radius of curvature of the fiber bend of a single mode fiber is given by-
optical-communication-questions-answers-material-absorption-fiber-bend-losses-silicon-glass-fibers-q9
Where R = radius of curvature,
n1, n2 = refractive indices,
λc = cutoff wavelength,
λ = operating wavelength.
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10. How the potential macro bending losses can be reduced in case of multimode fiber?
a) By designing fibers with large relative refractive index differences
b) By maintaining direction of propagation
c) By reducing the bend
d) By operating at larger wavelengths
View Answer

Answer: a
Explanation: In the case of multimode fibers, radius of curvature is directly proportional to core refractive index and operating wavelength. In order to reduce the macro bending losses, the operative wavelength must be small and fibers must have large relative refractive index difference. Losses are inversely proportional to refractive index differences.

11. Sharp bends or micro bends causes significant losses in fiber.
a) True
b) False
View Answer

Answer: a
Explanation: Sharp bends usually have a radius of curvature almost near to the critical radius. The fibers with the radius near to the critical radius cause significant losses and hence they are avoided.

Sanfoundry Global Education & Learning Series – Optical Communications.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn