BE/B.Tech .DEGREE EXAMINATION, NOVEMBER/DECEMBER 2008.
Seventh Semester
(Regulation 2004)
Electronics and Communication Engineering
EC1402-OPTICAL COMMUNICATION
(Common to B.E.(Part-time)Sixth semester Regulation 2005)
Time: Three hours Maximum: 100
Answer All Questions
PART-A-(10*2=20 marks)
1. What are the advantages and disadvantages of the ray optics theory?
2. A typical relative refractive index difference for an optical fiber designed for long
distance transmission is 1%.Estimate the numerical aperture for the fiber when the core
index is 1.47.
3. Define group delay.
4. A multimode graded index fiber exhibits total pulse broadening of 0.1 us over a
distance of 15 km. Estimate the maximum possible bandwidth on the link assuming RZ
coding without intersymbol interference.
5. Distinguish direct and indirect band gap materials.
6. An LED has radiative and nonradiative recombination times of 30 and 100 ns
respectively. Determine the internal quantum efficiency.
7. Define responsivity of a photo detector.
8. Compare the performance of APD and PIN diode.
9. What is the significance of rise time budget?
10. Compare doped fiber amplifiers and conventional repeaters.
PART-B---(5*16=80 marks)
11. a) (i) Explain with neat block diagram the fundamentals of optical fiber
communication(8)
(ii) Discuss the mode theory of circular wave guides (8)
or
b) (i) Discuss briefly about linearly polarized modes. (6)
(ii) Draw the structures of single and multimode step index fibers and graded index fiber
with typical dimensions.
(6)
(iii) Mention the advantages of optical fiber communication systems (4)
12. a) (i) Explain the scattering and the bending losses that occur in an optical fiber with
relevant diagrams and expressions (8)
(ii) Discuss polarization mode dispersion and its limitations (8)
or
b) (i) Discuss material and waveguide dispersion mechanisms with necessary
mathematical expressions (8)
(ii) Write brief note on pulse broadening in graded index fibers. (8)
13. a) (i) Draw and explain the different structures used to achieve carrier and optical
confinement in laser diodes
(8)
(ii) Discuss the effects of temperature on the performance of a laser diode (8)
(iii) Give a brief account of the modulation of an LED (4)
or
b) (i) Derive expressions for the power coupled from a surface emitting LED into step
index and graded index fibers (10)
(ii) Explain the mechanical misalignments that can occur between two joined fibers with
necessary diagrams. (6)
14. a) (i) Discuss with necessary expressions the different types of noise that affect the
performance of a photo detector. (10)
(ii) When 3´1011photons each with a wavelength of 0.85 mm are incident on a
photodiode, on an average 1.2´1011 electrons are collected at the terminals of the device.
Determine the quantum efficiency and responsivity of the photodiode at 0.85 mm (6)
or
b) (i) Draw and explain the high impedance preamplifier designs based on BJT and FET
(8)
(ii) Write brief note on Tran impedance amplifier (8)
15. a) (i) Explain the salient features of solitons using relevant expressions and diagrams
(16)
or
b) (i) Discuss the concept of WDM with neat diagram (6)
(ii) Give a brief account of the different types of losses to be considered in the design of
an optical link. (6)
(iii) Draw and explain the basic format of an STS-N SONET frame (4)
Click the following link to download:
http://www.ziddu.com/download/7669136/OpticcommND08.pdf.html
