OPTICAL FIBRE COMMUNICATION (OFC) DECEMBER 2010 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

OPTICAL FIBRE COMMUNICATION (OFC) DECEMBER 2010 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

Con.5606-10.                                                                                                       GT-8568 

                                                           (3 Hours)                                     [Total Marks:-100]

N.B: (1) Question No.1 is compulsory.
        (2) Attempt any four questions out of remaining six questions. 
        (3) Assume any suitable data wherever required but justify the same.
        (4) Figures to the right indicate full marks.

1. Answer the following in brief:-
     (a) What is the meaning of 'Avalanche' in the term Avalanche photodiode? [5 Marks]
     (b) Describe three types of optical fibers. For each type give typical core and cladding diameters.
          Sketch their Refractive Index Profile. [5 Marks]  
     (c) What do you mean by optical wave guide? How it is different from Electrical
          Waveguide? [5 Marks] 
     (d) Explain spontaneous emission and stimulated emission. [5 Marks]

2. (a) Derive an expression of Numerical Aperture of optical fiber in terms of Refractive
         Indices. [10 Marks] 
         A silica optical fiber with a core diameter large enough to be consider by Ray Theory analysis
         has a core Refractive Index of 1.50 and cladding Refractive Index of 1.47.
         Determine:- (i) The critical angle at the core-cladding interface.
                           (ii) The numerical Aperture for fiber.
                           (iii) The Acceptance Angle in Air for the fiber.
     (b) Explain the 'Different Modes' that can be supported by an optical fiber. [10 Marks]

3. (a) Compare and contrast, using suitable diagram, the Outside Vapour-Phase Oxidation(OVPO)
          process and the Modified Chemical Vapour Deposition(MCVD) technique for  preparation
          of Low Loss Optical fibers. [10 Marks]
    (b) Describe with the aid of suitable diagrams, three common techniques used for the Mechanical
          splicing of optical fibers. [10 Marks]

4. (a) When a light pulse propagates through the optical fiber, attenuation of the signal (light pulse)
          takes place. [10 Marks] 
          List the important factors responsible for Power Loss in optical fiber. Explain each factor
          in brief.    
    (b) A Multimode step Index fiber has a Numerical Aperture of 0.3 and a core Refractive
         Index of 1.45. The material dispersion parameter for the fiber is 250 ps nm⁻¹ km⁻¹ which
         makes material dispersion the totally dominating intramodal dispersion mechanism. Estimate:
         (i) The Total RMS pulse broadening per kilometer when the fiber is used with an LED source
         of RMS spectral width 50 nm and (ii) The corresponding Bandwidth-length product for the
         fiber. [10 Marks]  

5. (a) Explain and compare pin diodes with Avalanche Photo Diode(APD) with the help of suitable
         Electric field diagrams. [10 Marks]
    (b) With the help of receiver configuration circuit diagram, explain the working of optical receiver.
          Also derive the expression for output pulse. [10 Marks] 

6. (a) List the important point-to-point link design used in optical communication. Explain each in
         brief. [10 Marks]  
    (b) Explain with suitable diagram the Cutback Method for total fiber attenuation
         measurement. [10 Marks]

7. Write short notes on any three of the following:- [20 Marks]
     (a) Wavelength Division Multiplexing (WDM)
     (b) Linearly Polarised Modes
     (c) Optical Time Domain Reflectometer (OTDR)
     (d) Laser Diode