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


1(a) What are the advantages and disadvantage of optical fiber communication?
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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