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Thursday, 15 November 2012

Optical fiber communications-model question paper for B.E/B.Tech/M.E/M.Tech/MSc



1(a) Write a note on linear, elliptical and circular polarization. (6 Marks)
(b) Differentiate between step index fiber and graded index fiber. (4 Marks)
(c) Explain vapour-phase axial deposition method of optic fiber fabrication. (6 Marks)
(d) A signal passes through three cascaded amplifiers, each of which has a 5 dB gain. What is the total gain in dB? By what numerical factor is the signal amplified? (4 Marks)
2(a) Write notes on modal delay and group delay. (6 Marks)
(b) What is material dispersion? Explain. (6 Marks)
(c) Define external quantum efficiency. (4 Marks)
(d) An optical fiber 40 km long has a loss of 0.4 dB/km. What is the minimum input power to maintain an optical power of 2mW at the receiving end? (4 Marks)
3(a) Explain different lensing schemes for coupling improvement. (6 Marks)
(b) What is connector return loss? Explain. (4 Marks)
(c) Explain the construction and working of Avalanche photodiode. (6 Marks)
(d) Quantum efficiency of a silicon avalanche photodiode is 65% at a wavelength 900 nm. If an optical power of 0.5 mW produces a multiplied photocurrent of 10mA, determine the multiplication. (4 Marks)
4(a) Explain the working of high impedance amplifier and transimpedance amplifier. (6 Marks)
(b) What is an eye diagram? Explain. (4 Marks)
(c) Write notes on homodyne detection and heterodyne detection. (6 Marks)
(d) If a bit-corrupting noise burst lasts for 2ms, how many bits are affected at data rates of 10 Mb/s, 100 Mb/s and 2.5 Gb/s? (4 Marks)
5(a) What is extinction ratio penalty? Explain. (4 Marks)
(b) Explain the term ‘Chirping’. (4 Marks)
(c) Explain multichannel amplitude modulation and multichannel frequency modulation. (6 Marks)
(d) Calculate the optical modulation index of a laser for frequency division multiplexing of 60 FM signals. 30 of these signals have a per channel modulation index 3% and remaining 30 signals have per channel modulation index 4%. (6 Marks)
6(a) What is wavelength division multiplexing? Explain the operational principles. (8 Marks)
(b) Differentiate between a 2×2 fiber coupler and 2×2 waveguide coupler. (8 Marks)
(c) A DWDM optical transmission system is designed to have 100 GHz channel spacings. How many wavelength channels can be utilized in the 1536 to 1556 nm spectral band? (4 Marks)
7(a) Explain the construction and working of Erbium doped fiber amplifier, EDFA. (6 Marks)
(b) Explain the significance of Raman scattering in the design of Raman fiber amplifiers. (4 Marks)
(c) What is stimulated Brillouin scattering? Explain. (6 Marks)
(d) A single mode fiber has an attenuation of 0.55 dB/km at 1310 nm and 0.28 dB/km at 1550 nm. Compare the effective lengths of this fiber at 1310 nm and 1550 nm. (4 Marks)
8(a) Explain different network topologies with neat sketches. (8 Marks)
(b) Explain the terms optical packet switching and optical burst switching. (4 Marks)
(c) Explain the three layers of optical performance monitoring. (4 Marks)
(d) Show that when using an OTDR, an optical pulse width of 5 ns or less is required to locate a fiber fault to within ± 0.5 m of its true position. (4 Marks)

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