FIBRE OPTICS COMMUNICATION(paper no. 1) by SURESH KUMAR.....sureshkumarthegreat@yahoo.com

FIBRE OPTICS COMMUNICATION

PAPER NO. 1

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PUT ON: MAY , 2003

                                               EC-422
                          FIBRE OPTICS COMMUNICATION
                             (B.Tech 8th Semester,2063)
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) Explian the term evanescent field.
(b) What are skew rays ?
(c) What do you mean by the term modal birefringence ?
(d) What do you understand by degenerate modes in optical transmission ?
(e) What is meant by cut-off wavelength of the optical fibre ?
(f) Explain the term intermodel dispersion.
(g) Explain the term spontaneous emission.
(h) Define LED internal quantam efficiency.
(i) What do you mean by responsivity ?
(j) List three factors limiting the speed of response of a photodiode.

                                              Section-B                                          Marks:5 Each

2. A multimode step index fibre has a relative refractive difference of 1% and a core refractive index of 1.5.
    The number of modes propagating at a wavelength of 1.3 µm is 1100. Estimate the diameter of the fibre core.
3. A Multimode graded index fibre exibits total pulse broadening of 0.1 µs over a distance of 15km. Extimate :
    (a) the max. possible bandwidth
    (b) the pulse dispersion per unit length
    (c) the bandwidth length product for the fibre.
4. Given below certain parameters of silica :
    Fictive temperature = 1400 K
    isothermal compressibility = 7 x 10¹¹ m²N^-1
    Refractive index = 1.46
    Photoelastic coefficient = 0.286
     Boltzmann constant = 1.381 x 10^-23 Jk^-1
    Determine attenuation due to fundamental Rayleigh scattering in decibles per kilometer at a wavelength of 0.63 m.
5. Explain the terms mode field diameter and spot size.
6. A graded index with a parabolic refractive index has a core refractive index of 1.5 and relative index difference of 1%.
    Estimate the maximum core diameter which allows single mode operation at a wavelength of 1.3 m.

                                               Section-C                                        Marks : 10 Each

7. Discuss the optical fibre communication system in detail elobrating the role of each component in it.
8. Discuss the mechanism of optical feedback to provide oscillations and hense amplification within the lazer.
    Indicate how this provides a distinctive spectral O/P from the device.
9. Discuss the various types of losses in optical fibres.

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