| FIBRE OPTICS COMMUNICATION |
| PAPER NO. 2 |
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| PUT ON: Dec, 2002 |
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EC-422 FIBRE OPTICS COMMUNICATION (B.Tech 8th Semester, 2122) Time : 3 Hours Maximum Marks : 60 NOTE:- This paper consist of Three Sections. Section A is compulsory. Do any Four questions from Section B and any two questions from Section C Section-A Marks : 20 1(a) Explain Goos-Haeuchen shift in optical fibres. (b) Define acceptance angle. (c) What is meant by beat length ? (d) What is graded index fibre ? (e) Explain the term intramodal dispersion. (f) What are indirect band gap semi-conducters ? (g) Explain the term simulated emission. (h) What is modulation bandwidth in optical communication ? (i) What do you mean by quantam efficiency ? (j) What do you understand by multiplication factor of an Avalanche photodiode ? Section-B Marks:5 Each 2. Estimate the fibre core diameter for a single mode step index fibre which has a mode field diameter of 11.6 µm, when normalized frequency is 2.2. 3. Whenthe mean optical power launched into an 8 km of fibre is 120 mW, the output mean optical power is 3 µW. Determine : (a) the overall loss in db. (b) the signal attenuation per kilometre. 4. A single mode optical fibre has an attenuation of 0.5 db km-1when operating at a wavelength of 1.3 µm. The fibre core diameter is 6 µm, and the laser source bandwidth is 600 MHz. Compare the threshhold optical powers for stimulated Brillouin and Raman scattering. 5. Determine the cut off wavelength for step index fibre to exibit single mode operation when the core refractive index and radius are 1.46 and 4.5 mm respectively, while the relative refractive index difference being 0.255. 6. A graded index fibre with a parabolic refractive index profile which has a dia. of 50 µm and number aperture of 0.2. Estimate the total number of guided modes propagating in the fibre when it is operating at a wavelength in the fibre when it is operating at a wavelength of 1 µm. Section-C Marks : 10 Each 7. Discuss the advantages of optical fibre communication system. 8. Briefly describe what is meant by the following terms when they are used in relation to injection lasers : (a) relaxation oscillator (b) frequency chirp (c) partition (d) mode hopping. 9. Describe with the aid of a suitable diagram, the mechanism of giving the emission of light from an LED. Discuss the effects of this mechanism on the properties of the LED, in relation to its use as an optical suorce for communication. |
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