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VTU Electronics and Communication Engineering (Semester 7)
Optical Fiber Communication
December 2016
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

7 M
1(b) Derive necessary mathematical condition that the angle of incidence "θ" must satisfy for the optical skew ray to propagate in a step index fiber.
8 M
1(c) Calculate the number of modes of an optical fiber having diameter of μm, n1=1.48, n2=1.46 and wavelength 'λ' of 820 nm.
5 M

2(a) Explain the Different types of absorption losses in optical fiber.
6 M
2(b) Derive an expression for pulse spreading due to material dispersion which is a function of wavelength and time delay.
8 M
2(c) Explain different types of bending losses in optical fiber.
6 M

3(a) Draw the cross section of GaALAS double hetero structure LED energy band diagram and refractive index variation. Explain their importance.
7 M
3(b) Derive an expression for lasing condition and hence for optical gain in LASERS.
8 M
3(c) With proper sketwch briefly explain the structure of RPAD photodiode.
5 M

4(a) Show that optical power coupled into a step index fiber due to an LED with lambartian distribution is given by P=ps(NA)2 for rs≤a, with usual notations.
7 M
4(b) What are different types of mechanical misaligments?
5 M
4(c) Explain briefly the various fiber splicing techniuques.
8 M

5(a) With a neat diagram, explain the operation of transimpedance preamplifier equivalent circuit.
6 M
5(b) Derive an expression for receiver sensitivity and also explain quantum limit.
8 M
5(c) Discuss how the eye diagram is powerful measurement tool for assessing the data handling capability in digital transmission system.
6 M

6(a) Explain with block diagram, the elements of analog link. List the signal impariments in analog systems.
6 M
6(b) Explain sub-carrier multiplexing techniques in optical fiber communication.
4 M
6(c) Briefly explain the rise time budget analysis with its basic elements contribute to system risetime.
10 M

7(a) With a neat sketch explain WDM scheme.
5 M
7(b) Derive an expression for difference in length in MZI multiplexers.
9 M
7(c) Write a note on optical add | drop multiplexers.
6 M

8(a) Explain in detail the amplification mechanism with energy level diagram in an EDFA.
10 M
8(b) With suitable diagrm describe SONET/SDH optical network function.
10 M

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