MORE IN Optical Fiber Communication
VTU Electronics and Communication Engineering (Semester 7)
Optical Fiber Communication
May 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) Discuss the advantages of optical fiber communication
6 M
1(b) With the help of neat diagrams discuss the structure of single mode and multi mode step index fibers with appropriate mathematical equations
6 M

2(a) Estimatethe maximum core diameter for an optical fiber with refractive index difference of 1.6 percentage and a core refractive index of 1.48, in order that it may be suitable for single mode operation for an operating wavelength of 0.9μm. Futher estimate the maximum core diameter for a single mode operation when the relative refractive index difference is reduced by a factor of 10. Assume V number as 2.405.
6 M
2(b) Silica has an estimated fictive temperature of 1400K wit an isothermal compressibility of 7×10-11m2N-1. The refractive index and photoelastic co-efficient for silica are 1.46 and 0.286 respectively. Dtermine the theoretical attenuation in decibels per kilometer due to fundamental Rayleigh scattering in silica at optical wavelength of 0.63 μm. Boltzamann's constant is 1.381×10-23JK-1.
8 M
2(c) A step index multimode fiber with a core refractive index of 1.500, a relative refractive index difference of 3 percentage and an operating wavelength of 0.82μm. Estimate the critical radius of curvature at which large bending losses occurs.
6 M

3(a) Explain with the help of neat diagram, distributed-feedback (DFB) laser diode.
6 M
3(b) A double- hetrojunction In GeAsP LED emitting at a peak wavelength of 1310nm has radiative recombination times 30 and 100ns,respectively. The current is 40mA. Find the following:
i) The bulk recombination life time.
ii) The internal quantum efficiency.
iii) Internal power level (assume electron charge as 1.602&time;10-19C)
7 M
3(c) Discuss the operation of pin photodetector with appropriate diagrams.
7 M

4(a) With appropriate mathematical equations explain single-mode fiber joints.
6 M
4(b) Explain fusion splicing of optical fibers with appropriate diagrams.
6 M
4(c) Briefly describe the principal of operation of the following;
i) Expanded beam conductor.
ii) Star couplers.
8 M

5(a) With a schematic diagram, explain the working of an optical receiver.
6 M
5(b) Explain the term receiver sensitivity. Derive an equation for receiver sensitivity in terms of photo detector noise.
8 M
5(c) Discuss coherent detection with relevant block diagram.
6 M

6(a) Discuss subcarrier multiplexing.
6 M
6(b) Explain link power budget with a relevant diagram.
6 M
6(c) Write a short note on;
i) Chirping
ii) Extinction ratio penalty.
8 M

7(a) Explain the principal of operation of WDM with relevant block diagram.
7 M
7(b) Discuss the design and operation of a polarization independent isolator made of three miniature optical components.
6 M
7(c) Explain with help of relevant diagrams various applications of fiber Bragg gratings.
7 M

8(a) With the help of energy level diagrams, explain the working of Erbium-Doped Fiber Amplifiers(EDFA).
10 M
8(b) Write short notes on :
i) SONE / SDH frame formats.