# Optical Communication 7th ND12 EC2402

Question Paper code : 11347
B.E./B.Tech. Degree Examination, November/December 2012
Seventh Semester
Electronics and Communication Engineering
EC 2402/EC 72/10144 EC 702 - Optical Communication and Networking
(Regulation 2008)
(Common to PTEC 2402 - Optical Communication and Networking for B.E. (Part-Time) Sixth Semester Electronics and Communication Engineering - Regulation 2009)

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Part A - (10 * 2 = 20 marks)

1. Calculate the cutoff wavelength of a single mode fiber with core radius of 4µm and ? = 0.003.
2. For a fiber with core refractive index of 1.54 and fractional refractive index difference of 0.01, calculate its numerical aperture.
3. What are the two reasons for chromatic dispersion?
4. What are the most important non-linear effects of optical fiber communication?
5. Compare and contrast between surface and edge emitting LEDs.
6. What is the significance of intrinsic layer in PIN diodes?
7. What is dark current?
8. List out the various error sources.
9. What were the problems associated with PDH networks?
10. Enumerate the various SONET/SDH layers.

Part B - (5 * 16 = 80 marks)

11. (a) (i) Starting from the Maxwell’s equation, derive the expression for the wave equation of an electromagnetic wave propagating through optical fiber. (8 marks)
11. (a) (ii) Derive the ray theory behind the optical fiber communication by total internal reflection. State the application of Snell’s law in it. (8 marks)
Or
11. (b) (i) A Si fiber with silica core refractive index of 1.458, v = 75 and NA = 0.3 is to be operated at 820nm. What should be its core size and cladding refractive index? Calculate the total number of modes entering this fiber. (8 marks)
11. (b) (ii) Derive expression for the linearly polarized modes in optical fibers and obtain the equation for V number. (8 marks)

12. (a) (i) Describe the linear and non-linear scattering losses in optical fibers. (8 marks)
12. (a) (ii) An LED operating at 850nm has a spectral width of 45mm. What is the pulse spreading in ns/km due to material dispersion? What is the pulse spreading when a laser diode having a 2nm spectral width is used? (8 marks)
Or
12. (b) (i) Draw and explain the various fiber alignment and joint losses. (8 marks)
12. (b) (ii) Write notes on fiber splices and connectors. (8 marks)

13. (a) Draw and explain the structure of Fabry-Perot resonator cavity for a laser diode. Derive laser diode rate equations. (16 marks)
Or
13. (b) (i) Draw the structure and electric fields in the APD and explain its working. (8 marks)
13. (b) (ii) What are the three factors that decides the response time of photodiodes? Explain them in detail with necessary sketches. (8 marks)

14. (a) (i) Draw the front end optical amplifiers and explain. (8 marks)
14. (a) (ii) Considering the probability distributions for received logic 0 and 1 signal pulses, derive the expressions for BER and error function. (8 marks)
Or
14. (b) Write notes on the following
(i) Fiber refractive index profile measurement (8 marks)
(ii) Fiber cut off wavelength measurement (8 marks)

15. (a) discuss the concepts of Media Access Control protocols in Broadcast and select networks.(16 marks)
Or
15. (b) (i) Describe the non-linear effects on network performance in detail. (8 marks)
15. (b) (ii) Explain the basics of optical CDMA systems. (8 marks)