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VTU Electronics and Communication Engineering (Semester 7)
Optical Fiber Communication
June 2015
Total marks: --
Total time: --
INSTRUCTIONS
(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) With neat block schematic explain the working of an optical fibre transmission link? Briefly explain the characteristics and operating ranges of a key optical fibre link components.
10 M
1 (b) Design a single mode guide for operating at λ=1.3μm with fused silica core n1=1.458 with NA=0.3. Specify n2 and 'a' for the mode. Will the guide still be single mode if λ0.82μm. If not how many modes will exist.
4 M
1 (c) With neat sketches, explain with reference to ray optics
i) NA ii) Skew rays
iii) Acceptance angle.
6 M

2 (a) Explain the following parameters: i) Absorption
ii) Group delay iii) Scattering loss iv) Chromatic dispersion v) Bending loss.
10 M
2 (b) The mean optical power lunched into an optical fibre link is 1.8mw and the fibre attenuation is 1.8dB. Determine the maximum possible link length without repeaters when the minimum optical power level required at detector is 4μW. Calculate the power received in dBm after 10km.
4 M
2 (c) Describe and explain signal distortion in optical fibers.
6 M

3 (a) With neat sketches, explain the characteristics and function of the double hetero structure device.
6 M
3 (b) A double heterojunction InGaAsP, LED emitting a peak wave length of 1310nm has radiative and non-radiative recombination times of 30 and 100ns respectively. The drive current is 40mA. Calculate the bulk recombination life time, internal quantum efficiency, internal power level.
4 M
3 (c) Compare the operating characteristics of the Si, Ge and InGaAs with PIN and APD diodes.
6 M
3 (d) A silicon APD has quantum efficiency of 75% at a wavelength of 900nm. Suppose 0.8μw of optical power produce a multiplied photocurrent of 10μA. Find the multiplication factor.
4 M

4 (a) Explain the function of a good connector? With neat sketches, explain the biconical ferrule connector.
6 M
4 (b) A four port multipart fibre FBT coupler has 60μw optical power launched into port 1. The measured output power at ports 2, 3 and 4 are 0.004, 26.0 and 27.5μw respectively. Determine the excess loss, the insertion loss between the input and the output ports, the cross talk and the split ratio of the device.
4 M
4 (c) With neat sketches, explain the role and types of splicing techniques used in OFC.
6 M
4 (d) A GIF has a parabolic RI (α=2) and a core diameter of 50μm. Estimate the insertion loss due to a 3μm lateral misalignment at a fibre joint when there is index matching and assign
i) Uniform illumination of all guided modes only
ii) Uniform illumination of all guided modes and leaky modes.
4 M

5 (a) With neat sketches, explain the power full measurement tools for accessing the data handling ability of a digital transmission system.
8 M
5 (b) Explain the various noise and disturbance associated with the signal detection system.
6 M
5 (c) Write a note on analog receiver.
6 M

6 (a) With neat sketches explain the optical power loss model for a point to point link.
8 M
6 (b) Explain the basic elements of an analog link and the major noise cntribution.
8 M
6 (c) Explain the basic concept of sub carrier multiplexing.
4 M

7 (a) Explain the concept an basic tuning option of a tuneable lasers and depict the relation between tuning range, channel spacing and source spectral width.
6 M
7 (b) Explain the operation of 4×4 OADM.
4 M
7 (c) Explain the operation of Etalon. Design 4 channel multiplexing using TTF.
10 M

8 (a) Explain the possible applications of optical amplifier.
4 M
8 (b) With neat sketches, explain the simplifier energy level an various transition process of Er3t in silica.
6 M
8 (b) Explain the basic formats of STS N connect frame and STM-N-SDH frame.
5 M
8 (c) Write a note on high speed light wave links.
5 M

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