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SYNERGY INSTITUTE OF ENGINEERING AND TECHNOLOGY
SHORT QUESTIONS
Department: - ECE
Subject: - Optical Fiber Comm.
Semester: - 7th
Session:-2005-2009
1. Define the bandwidth of an optical Amplifier.
2. What is difference between optical and electrical noise?
3. What is difference between step index and graded index fiber?
4. What is input- output characteristics of a photodiode.
5. How does light radiation occur in semiconductor material?
6. What light sources are called Lambertian?
7. What is channel spacing for WDM with 40 channels?
8. What do you mean by microbending and macro bending losses?
9. State the advantages and disadvantages of fiber optic communication system
10. Draw the basic block diagram of fiber optic communication and explain it.
11. What is EDFA?
12. Write causes associated with the quantum or shot noise in photodector?
13. Write three key processes in laser action.
14. Explain the significance of optical amplifiers.
15. Explain quantum noise current.
16. Explain total internal reflection.
17. Explain in brief graded index fibers.
18. Write the general dimension of the core and clad for the single mode fiber and
multimode fiber.
19. Define single mode fiber.
20. State the advantages of fiber optic communication system.
21. State the disadvantages of fiber optic communication system.
22. Define mode in optical propagation.
23. Write the two advantages of using LED as a source.
24. Write the advantages of using graded index fibers.
25. Define windows in optical communication system
26. Define critical angle of incidence.
27. Explain the significance of Numerical Aperture.
28. Define acceptance angle.
29. Write the criteria in choosing the cladding material.
30. Define mode coupling.
31. What are the modes that exist in step index fiber?
32. Define mode field diameter.
33. Define cutoff wavelength.
34. Write one difference between in matched and depressed cladding design.
35. Explain SNR at the optical receiver.
36. Write disadvantages of Avalanche photodiode.
37. Explain information capacity of optical fiber.
38. Define mode delay factor.
39. Write principle of photodetection.
40. What should be the requirement for high performance detector?
41. Write the photodetector requirements in terms of operating life, temperature and
compatibility.
42. Explain in brief the construction of photodetectors.
43. Define impact Ionization?
44. Define Responsivity.
45. Define Quantum efficiency.
46. Define the terms diffusion length and carrier lifetime?
47. Why semiconductor photodiode are used in fiber optic communication system.
48. Define modulation Bandwidth?
49. Write three factors that limit the speed of response of photodiode.
50. Define Multiplication Factor.
51. Write two criteria that are important for the performance and compatibility
requirements of detectors.
52. Explain various modulation techniques in fiber optic communication system.
53. On what factors does modulation Bandwidth of LED depends upon?
54. What is the difference between optical Bandwidth and electrical Bandwidth?
55. Explain wavelength Division Multiplexing.
56. Explain in brief Intensity modulated system.
57. Explain briefly various sources of attenuation.
58. Explain briefly bending losses.
59. Define attenuation in optical fiber.
60. Define Intermodal Dispersion.
61. Explain briefly microbends?
62. Explain the sources of scattering losses.
63. State carrier to noise ratio.
64. Define dispersion.
65. Define chromatic dispersion.
66. How Mie scattering can be reduced?
67. Explain briefly the function of preamplifiers.
68. Explain briefly Rayleigh scattering loss.
69. Explain Intersymbol interference.
70. Explain in brief spot attenuation measurement.
71. Explain material absorption loss measurement.
72. Define Bit error rate.
73. Which parameter effect ultimate Bandwidth of photodetectors.
74. Write cutoff wavelength of light for intrinsic semiconductor material.
75. Write principle noise encountered in photodetectors.
76. Explain Quantum noise current.
77. Write the causes associated with the Quantum or shot noise in photodetectors.
78. Explain the significance of optical amplifiers.
79. Define Lineraly Polarlized modes.
80. Determine cutoff wavelength for step index fiber to exhibit single mode operation
when core RI and radius are 1.46 & 4.5m and relative RI difference is equal to
0.25%.
81. What is the relation between WDM and TDM?
82. Write the formula for a step index refractive –index profile.
83. Why is it necessary to meet the total internal reflection requirement inside an
optical fiber?
84. Why we need to know the acceptance angle?
85. What is the difference between phase and group velocity.
86. What is the relationship between bit rate and Bandwidth?
87. What are two major stages of the fiber fabrication?
88. Calculate the numerical aperture, NA, of a single mode fiber where n1=1.4675d
n2=1.4622.
89. What is principle of action in LED?
90. Explain the splices in fiber.
91. Explain the connectors in fiber.
92. What are advantages of using LEDs as a source?
93. What are the drawbacks of using LEDs as a source?
94. What are advantages of laser as compared to LEDs.
95. Explain the working of photodiode.
96. Explain the operation of EDFAs.
97. What is the gain in EDFAs.
98. Expalin the components of fiber optic Networks.
99. What is the power relationship of photodiodes?
100.
Explain the ray theory.
LONG QUESTIONS
Department: - ECE
Subject: - Optical Fiber Comm.
Semester: - 7th
Session:-2005-2009
1. Draw the basic block diagram of fiber optic communication and explain it.
2. State the advantages and disadvantages of fiber optic communication system.
3. What are the various types of attenuation factors in fiber optic communication.
Suggest proper remedies
4. What is the role of fiber optic communication technology in modern tele
communication scenario.
5. Name and explain three basic techniques used to couple light from an LED into
optical fiber.
6. Explain the principle of operation of quantum well laser diode.
7. With the help of proper diagram, explain the construction, principle of operation
and difference between step index fibers and graded index fibers.
8. Calculate the internal quantum efficiency of a 1.3m surface emitting LED at a
forward current of 100mA, assuring that 7.5% of the LEDs. Output power is
coupled into an optical fiber.
9. List and compare the main properties of both stimulated and spontaneous
emission.
10. Explain the Intramodal and Intermodal dispersion?
11. Explain the working principle of LEDs.
12. Explain the various optical detectors.
13. Explain the APD?
14. What do you understand by internal quantum efficiency of the LEDs? Derive the
expression.
15. Explain optical transmitter circuit and optical receiver circuit.
16. Give the theory of semiconductor lasers and derive an expression for threshold
current.
17. Compare the performance of laser diode versus LED in fiber optic
communication. Discuss the radiation pattern and model properties of Led.
18. Explain the Avalanche multiplication theory. What are advantages of Avalanche
photodiode over other photodiodes?
19. Explain the working of a p-I-n photodiode. Discuss its responsivity and quantum
efficiency.
20. When 3 X 1011photons each with a wavelength of 0.85m are incident on a
photodiode, on average 1.5 X 1011 electrons are collected at the terminals of the
device. Determine the quantum efficiency and responsivity of the photodiode at
the wavelength of 0.85m.
21. A multimode step index fiber has the relative refractive index of difference of 1%
and a core refractive index of 1.5. The number of modes propagating at a
wavelength of 1.3m is 1100. Estimate the diameter of the fiber core.
22. Given below the certain parameters of silica:
Fiction temperature = 1400k
Isothermal compressibility = 7 X 1011 m2 N-1
Refractive index = 1.46
Photoelastic coefficient = 0.286
Boltzman constant = 1.381 X 1011JK-1
Determine attenuation due to fundamental Rayleigh scattering in dB per km at a
wavelength of 0.63m.
23. What are the various types of optical fibers? List the applications of each.
24. Derive the expression for S/N in case p-I-n photodector under various conditions.
25. Define various types of lasers.
26. Explain the different structures of LEDs.
27. Explain the transmitter unit of the fiber optic communication system.
28. Explain the receiver unit of the fiber optic communication system.
29. What is the total pulse spreading by modal and chromatic dispersion.
30. Explain the Electromagnetic mode theory.
31. A singlemode fiber has the following parameters:
Core diameter (d) = 8.3m
Core Refractive index = 1.4692
Relative index =0.36%.
Calculate the V- number at the 1550nm operating wavelength.


Calculate the pulse spreading caused by waveguide dispersion at the 1550nm
operating wavelength if spectral width = 0.5nm and L = 1km.
Explain the various bending losses.
34. Explain the characterstics of the LEDs.
35. The radiative and nonradiative recombination lifetimes of the minority
carriers in the active region of a double heterojunction LED are 60ns and 100ns
respectively. Determine the total carrier recombination lifetime and the power
internally generated within the device when the peak emission wavelength is
0.87m at a drive current of 40mA.
36. Explain the optical detection principle.
37. Explain the factors, which limit the speed response of a photodiode.
38. Explain the linear and nonlinear scattering.
39. Explain the Ray theory.
40. Explain the limitations and remedies for chromatic dispersion.
41. Explain the splices and connectors in the fiber.
42. Explain the operation of EDFAs.
43. What is principle of action in LEDs and laser?
44. Explain the population inversion, stimulated emission and spontaneous
emission.
45. Explain the noise and gain phenomena in the EDFA.
46.explain Explain how Chriped-fiber Bragg grating works as dispersion –
compensating device.
47.Write the difference between stimulated brillouin scattering and stimulated
Raman scattering.
48.What is the solution for the intermodal dispersion problem in singlemode
fiber.
49. Explain the intrinsic and extrinsic loses.
50. Explain the Transmitter and Receiver module in the fiber optic
communication system.