Optical Fibre Communication - Dec 2014

Electronics & Telecomm. (Semester 8)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) Explain three operating windows in optical communication.(5 marks) 1 (b) State the difference between the dispersion shifted and dispersion compensated fiber.(5 marks) 1 (c) Compare direct band gap and indirect band gap semiconductors.(5 marks) 1 (d) Derive expression for responsivity of an intrinsic photo detector in terms of quantum efficiency wavelength.(5 marks) 2 (a) A graded index fiber has a core diameter of 45μ m. Core has a parabolic refractive index profile. The fiber has NA of 0.22 and operating at wavelength of 1.2 μm. Estimate total number of guided mode propagating in the fiber.(10 marks) 2 (b) Explain any one fiber fabrication process with a neat diagram. Compare the different methods of fabrication.(10 marks) 3 (a) Explain all aspect of link power budget and rise time budget.(10 marks) 3 (b) What are the factors that are responsible for optical signal attenuation and dispersion during signal propagation through optical fiber.(10 marks) 4 (a) A silica optical fiber with core diameter large enough to be considered by Ray theory has a core refractive index of 1.5 and cladding refractive index 1.47.
Determine
ii) The NA
iii) The Acceptance angle.(10 marks) 4 (b) With the help of device structure explain the working of LED and LASER with the emphasis on spontaneous and stimulated emission.(10 marks) 5 (a) Describe the various methods of splicing individual fibers together. Enlist the desirable requirements of good fiber conductor.(10 marks) 5 (b) State the working principle of Raman amplifier and state its applications.(10 marks) 6 (a) Explain basic principle of operation of photo detector. Explain the working of PIN diode and APD as photo detector, also compare their performance.(10 marks) 6 (b) Draw and explain block diagram of optical receiver along with various noise sources and relevant equations.(10 marks)

Write short notes on any four:

7 (a) Optical bandwidth and Electrical bandwidth(5 marks) 7 (b) Coherent and Non coherent optical communicator.(5 marks) 7 (c) OTDR(5 marks) 7 (d) Multiplexing of optical signals(5 marks) 7 (e) Linearly polarized modes(5 marks)