M.Sc. (Semester IV) (CBCS) Examination Nov/Dec-2018
Electronics Science
OPTIC FIBER COMMUNICATION
Time: 2½ Hours Max. Marks: 70
Instructions: Q.1 and Q.2 are compulsory
Answer any three questions from Q.3 to Q.7.
All questions carry equal marks.
Use of nonprogrammable calculator is allowed.
Q.1 Select the most correct alternative 14
Numerical aperture of multimode step index fiber is
0.16 to 0.5 0.2 to 0.5
1 to 2 0.8 to 1
If mean optical launched power is 120 length of fiber is 8 km and
output power is 3 what will be the signal attenuation per km?
16dB/km 2dB/km
20dB/km 29dB/km
Core diameter of single-mode step index fiber is
100 to 1000 10 to 30
2 to 10 140 to 400
Stimulated Raman scattering can occur in both the directions in
an optical fiber.
all backward
forward and backward forward
Ideal fiber couplers should distribute light among the branch fibers with no

Scattering loss Joint Loss
Fresnel reflection Attenuation
The modulation bandwidth of LEDs is generally determined by
the doping level
the reduction in radiative lifetime
the parasitic capacitance
all of the above
The ratio of number of electrons collected and number of incident photons
is
quantum efficiency responsivity
fidelity scattering
Avalanche photodiodes have more sophisticated structure than the
PN photodiode photodiode
heterodyne detector phototransistors
Total internal reflection occurs in optical fiber, if incident angle is
critical angel.
greater than less than
equal to undefined
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SLR-VH-245
10) FDDI connectors in optical fibers gives db loss.
0.70 -1.00 0.20-0.70
0.01-0.19 0.50-0.90
11) Homo-junction LED devices have quantum efficiency.
100% 70%
50% 10%
12) The mechanism by which light at may be considered to
propagate down an optical fiber with low loss.
less than 900 − θc greater than 900 − θc
equal to or less than 900 − θc less than 1800 − θc
13) may be defined as the ratio of the slow carrier transit time (or
lifetime) ts to the fast carrier transit time tf.
Equalization Bit duration
Photoconductive gain Sampling rate
14) The channel loss is increased with
splice losses connector losses
both a and b thermal fluctuations
Q.2 Answer the following.
Explain your idea of attenuation in optical fiber communication, 05
Explain refractive index profile of graded index fiber. 05
What is a PN photodiode? 04
Q.3 Explain and derive a numerical aperture of the OFC. 08
A silica optical fiber with a core diameter large enough to be considered
by ray theory analysis has a core refractive index of 1.50 and a cladding
refractive index of 1.47. Determine:
the critical angle at the core-cladding interface;
the NA for the fiber;
the acceptance angle in air for the fiber
06
Q.4 Explain different types of optical fiber. 08
Discuss the plasma-activated chemical vapor deposition. 06
Q.5 What are fiber alignment and joint loss? 10
Discuss the expanded beam connectors. 04
Q.6 Discuss the optical emission from the semiconductor. 08
Explain in detail mechanical splices. 06
Q.7 Explain material absorption and the types of material absorption. 08
What is responsivity? Discuss. 06