VTU Electronics and Communication Engineering (Semester 7)
Optical Fiber Communication
June 2013
Total marks: --
Total time: --
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Discuss the advantages and disadvantages of OFC.
6 M
1 (b) Explain Mode Field Diameter(MFD) of a single mode fiber.
6 M
1 (c) Differentive between glass fiber and plastic fiber.in case of glass fiber how RI can be varied
4 M
1 (d) A SI multimode fiber with a NA of 0.20 supports approximately 1000 modes at an 850 nm wavelength.
What is the diameter of its core?
how many modes does the fiber support at 1320 nm?
how many modes does the fiber support at 1550 nm?
4 M

2 (a) Explain the "pulse dispersion " with suitable diagram and differentiate MMSIF, MMGIF and SMF by their information carrying capacity with reason.
6 M
2 (b) Discuss the following for optical fibers:
Extrinsic absorption.
Material dispersion.
8 M
2 (c) Optical power launched into fiber at transmitter end is 150?w.The power at the end of 10km length of the link working in first window is -38.2 dBm.Another s/m of same length working in second window is 47.5?w.Same length s/m working in third window has 50% of launched power.calculate fiber attenuation for each case and mention wavelenghth of operation.
6 M

3 (a) A double-hetero junction "InGaAsP" LED emitting at a peak wavelenghth of 1310 nm has radiative and non radiative recombination times of 25 ns and 90 ns respectively. The drive current is mA.
Find the internal quantum efficiency and tne internal power.
If the RI of the light source material is n=3.5. Find the power emitted from the device.
6 M
3 (b) Discribe the following terms relating to LASER:
Extenal quantum efficiency.
wavelength spacing.
6 M
3 (c) Explain the three factors which affects the response time of a photodiode.
8 M

4 (a) Discuss the different lensing scheme used to improve the source-to-fiber couplin efficiency,with the necessary skethes.
6 M
4 (b) For a surface emitting LED has radiance of 150W(cm2.sr) and radius of emitting area is 35?m.Calculate the optical power coupled to the fibers with
a1=25?m and NA=0.20.step index
a2=50?m and NA=0.20,step index.
6 M
4 (c) Difine fiber splicing.Explain different types of splicing with neat sketches
8 M

5 (a) Explain the different types of front-end amplifires in optical receiver.
6 M
5 (b) with a neat sketch,explain how system performance information can be obtained from the eye diagram
8 M
5 (c) Write a short note on burst-mode recevers.
6 M

6 (a) fFollowing are the parameters of a point-to-point optical link:
optical power launched :+3dBm
sensitivity of detector:-32dBm
source/detector connector loss:1dB
Lenghth of optical cable:60km
Cable attenuation:0.3dB/km
Jumper cable loss:3dB
Connector loss at each fiber joint(two at each transmitter and receiver end beacause of the jumper cables) computer the power margin of the link using spread method.
6 M
6 (b) Explain the basis element of analog link with different noise contribution
9 M
6 (C) What is sub carrier multiplexing?Explain
5 M

7 (a) Expain the need of isolator in optical network .Give its principle of operation also.
6 M
7 (b) Explain the operational principle and implementation of WDM.
8 M
7 (c) Brifly discuss dielectric thin-film filters.
6 M

8 (a) Expain the three main amplifire types.
6 M
8 (b) Describe:
SONET /SDH rings .
SONET/SDH networks.
Frame formate of STS-1 SONET.
10 M
8 (c) An EDFA amplifire produces ps.out=27dBm for an input ps.in=2dBm at 1542 nm.
find the amplifire gain.G
What is minimum pump power required.
4 M

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