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1997 Course Fiber Optic Communication (Elective II)

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Total No. of Questions : 10] [Total No. of Pages : 3 [3764]-1035 P1574 B.E. (EC) FIBRE OPTIC COMMUNICATION (404210) (1997 Course) (Elective - II) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates : 1) Answer any 3 questions from each section. 2) Answers to the two sections should be written in separate books. 3) Neat diagrams must be drawn wherever necessary. 4) 5) Figures to the right indicate full marks. Assume suitable data, if necessary. SECTION - I Q1) a) What are Fiber modes? Explain mode theory for optical fiber in detail. [8] b) Compare SM fiber and Graded index fiber. Explain the requirements for fiber materials. [8] Q2) a) A fiber has normalized frequency is 26.6 and wavelength is 1300nm. If the radius of core is 25 m. Compute numerical aperture? [6] b) Determine the cutoff wavelength for a step index fiber to exhibit single mode operation when the core refractive index and radius are 1.47 and 4.6 m, respectively, with the relative refractive index difference being [6] 0.30%. c) Multimode step index fiber with core diameter of 80 m and index difference of 1.5% at wavelength of 0.85 m. If the refractive is 1.48, find normalized frequency and no. of modes. [6] Q3) a) What is meant by material dispersion? Derive the expression for the pulse broadening due to material dispersion. [8] b) Discuss various kinds of losses that an optical signal might suffer while propagating through fiber. Which is most important one? What is the effect of these losses on light power and pulse shape? [8] P.T.O. Q4) a) A 90 Mb/s NRZ data transmission system that sends two DS3 channels uses a GaAlAs laser diode that has a 1 nm spectral width. The rise time of the laser transmitter is 2 ns. The transmission distance is 7 km over a graded index fiber that has an 800 MHz. km bandwidth distance product. [8] i) If the receiver bandwidth is 90 MHz and the mode mixing factor q = 0.7. What is the system rise time? Does this rise time meet the NRZ data requirement of being less than 70% of pulse width? ii) What is the system rise time if there is no mode mixing in the 7 km link? b) Discuss the different noise sources and disturbances in the optical pulse detection mechanism and derive the expression of S/N ratio. [8] Q5) Answer in brief : (2 marks each) [16] a) What is meant by mode and index profile? b) Mention the advantages of Graded Index fiber. c) What is the need of Cladding? d) What do you mean by polarization mode dispersion? e) How are micro bending losses reduced? f) What is meant by population inversion ? g) Define internal quantum efficiency of an LED. h) What is meant by impact ionization? In APD. SECTION - II Q6) A long haul optical fiber link uses single mode fiber. Find the link length without repeaters while link is operating at 500 Mbps with BER 10 8.[16] a) When A receiver has sensitivity of 30 dBm. b) When other type B receiver has sensitivity of 40 dBm. Conditions are as below : i) No dispersion penalty [3764]-1035 -2- ii) There are two types of transmitters available 1) With Output Power = 3 mW. 2) With Output Power = 0 dBm. Connector loss at each end = 1 dB Splice loss = 0.15 dB/km Attenuation per unit length = 0.35 dB/km Safety margin = 5 dB In length / In path connector loss for two connectors = 1 dB/connector Q7) a) Describe the working principle of PIN photo detector and explain the [8] characteristics of pin diode. b) Explain with neat diagram, construction and working of APD. [8] Q8) a) List out the WDM components. Explain them briefly & list applications of WDM. [10] b) Compare between fusion splicing and mechanical splicing. [8] Q9) a) Discuss with aid of suitable diagram the method used for the measurement of the total attenuation in an optical fiber. [8] b) Discuss the applications of optical fibers in : i) Local area networks. ii) [8] Optical sensor for current measurement. Q10) Write short notes on : [16] a) Edge emitting LED. b) Eye diagram measurement. c) Single Mode Laser. d) Rise Time Budget. rrrr [3764]-1035 -3-

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