300+ TOP Optical Communications and NETWORKING UNIT WISE Important Questions Answers

Optical Communications and NETWORKING UNIT WISE Important Questions Answers :-


1. A point sorce of ligth is 12 cm below the surface of a large body of water (n = 1.33). What is the radius of the largest circle on the water surface through whichthe light can emerge?
2. Consider a parabolic index waveguide with n1 =1.75 ,n2 = 1.677 and core radius
25 micro meter. Calculate the numerical aperture at the axis and at a point 20
micro meter from the axis
3. Define numerical aperture of a step index fiber
4. Define mode-field diameter
5. Commonly available single mode fibers have beat lengths in the range 10 cm < Lp <2 m . What range of refractive index diffrences does this correspond to? (for
wavelength = 1300 nm)
6. Define mode field diameter
7. What is the fundamental parameter of a single mode fiber?
8. A step index fiber has a normalized frequency V = 26.6 at 1300 nm wavelength.
If the core radius is 25 pm, find the numerical aperture.
9. (i) Diacuss the signal distortion in single mode fibers
(ii) Discuss pulse broadening in graded index fibers with necessary equations
10. (I) Discuss the propagation modes in single -mode fiber
(ii) Discuss the structure of graded index fiber
11. (i) What is meant by ‘material dispersion’? Derive its expression
(ii) Discuss the pulse broadening in graded index fiberss
12. (a) What are fiber modes? Explain mode theory for optical fibers in detail.
(b) Compare Single mode fibers and Graded index fibers. Explain the requirements
for fiber materials.

13. Write the expression for the effective number of modes guided by a curved
multimode fiber of radius ‘a’
14. Define normalized propagation constant
15. Give expression for the effective number of modes guided by a curved multimode fiber
16. What are the causes of absorption
17. Find the coupling loss for two fibers having core refractive index profiles alpha E = 2.0 and alpha R = 1.5 .18. What causes mode coupling
19. Mention the two causes of intra-modal dispersion.
20. Define fiber loss.
21. (i) Briefly explain the evolution of fiber optic system
(ii) Compare the configuration of different types of fibers .
22. (b)(i) Derive modal equation
23. (ii) Discuss the modes in step- index fibers
24. (a) (i) What is meant by material dispersion?
(ii) Derive an expression for material dispersion
(iii) Derive the expression for wave guide dispersion
(b) Discuss the pulse broadening in graded index fibers
25. (i) List the advantages of optical fiber comminication
(ii) Draw the elements of an optical fiber transmission link and explain
26. OR
27. (i) Discuss the mode theory of circular waveguide
28. (a) 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?
(b) What is mode coupling? Discuss pulse broadening in Gl fibers.
29. Draw the three key transistion process involved in laser action
30. Write the concept of indirect bandgap semiconductor materials
31. What is meant by hetero junction?
32. What is meant by indirect band gap semi conductor material?
33. Give example for direct and indirect semiconductor materials
34. Calculate the ratio of stimulated emission rate to the spontaneous emission
rate for a lamp operating at a temperature of 100 K . Assume average operating
wavelength is 0.5 micro meter
35. Compare LED and LASER.
36. What is meant by population inversion
37. (a) Draw the structures of edge-emitting LED and surface emitting LED and
explain the operation
(b) (i)Discuss the LASER diode principle , modes and threshold conditions

38. (a) Draw the structure of edge emitting and surface emitting LEDs and explain
(b) Discuss the laser diode structures and radiation patterns
39. (a)(i) What is meant by heterojunction ? Give example.
(ii) Derive the internal quantum efficiency of an LED
40. (b) (i) Explain optical feedback and laser oscillation.
41. (ii) Derive the threshold condition for lasing
42. (a) With neat diagram explain the construction and working of high radiance
surface emitting LED.
(b) Discuss about modulation of Laser diodes. Why thermoelectric cooler are used
in Laser diodes?

43. Define responsivity of photodiode.
44. Define quantum efficiency of a photodetector
45. Define responsivity
46. A given APD has a quantum efficiency of 65 % at a wavelength of 90 nm . If 0.5 micro watt of optical power produces a multiplied photocurrent of 10 micro Ampere, find the multiplication
47. Define long wavelength cutoff of a photodiode
48. What is meant by quantum limit?
49. A photodiode is constructed of GaAs, which has band gap energy of 1.43 eV at
300 K. What is meant by long wavelength cutoff?
50. What are the benefits of a trans-impedance amplifier?
51. (a) Draw the schematics of pin photodiode and APD and explain.
(b) Explain the fundamental receiver operation in optical communication
52. (a) An InGaAs pin photodiode has the following parameters at a wavelength of
1300 nm : I D = 4 nA, ? = 0.9, RL = 1000 ohms and the surface leakage current is
negligible. The incident optical power is 300 nw (- 35 dBm), and the receiver
bandwidth is 20 MHz . Find the various noise terms of the receiver
(b) Discuss the performance of digital receiver by defining the probability of
53. (a) Discuss the principle of operation of APD wiht neat circuit diagram. Also
discuss the requirements of photo detector.
(b) Discuss the fundamentals of receiver operations with neat block diagram
54. (a) What is known as quantum limit? A digital fiber optic link operating at
850 nm requires a maximum BER of 10*9. Find the minimum incidental optical power
Po to achieve this BER at a data rate of 10 Mb/s for a simple binary level
signaling scheme. (ry: 1), [1/r : B/2].
(b) Discuss in detail digital receiver performance calculation and sensitivity
calculation in detail.

55. List the sysyem requirements neede in analyzing a point -to- point link
56. Write the concept of solution
57. What is meant by solitron?
58. What is meant by modal noise?
59. Write the basic concept of solition generation
60. Write the concept of link power budget
61. List the key requirements needed in analyzing a link.
62. Define Modal Noise.
63. (a) Explain various types of fiber splicing techniques and fiber connectors
(b) (i) Explain the operational principles of WDM
64. (ii) Explain the rise-time budget.
65. (a) (i) Discuss the operational principles of WDM
66. (ii) Describe the key features of WDM
(b) Explain the rise-time budget of a fiber –optic point – to – point link
67. (a) Draw the point-to -point fiber optic link and discuss the system
(b) Discuss the principle ,requirement and applications of WDM
68. (a) What are the system consideration in point to point links? Explain in
(b) Discuss in detail Fiber splicing and connectors. Explain the operation
principles of WDM.

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