Annexure I

Question Bank I

Course: B.TechBranch: ECESemester and Session 8th / Jan- may 2011Subject Code and Name: EC-404 OFCSubject Teacher: Harsimran jit kaur/ Priyanka MalhotraTopics Covered:

Geometrical-Optics Description; Step-Index Fibers, Graded Index Fibers, Wave Propagation; Maxwell’s Equations, Fiber Modes, Single-Mode-Fibers, Dispersion in Single-Mode Fibers; Group Velocity Dispersion, Material Dispersion, Wave guide Dispersion, Higher-order Dispersion, Polarization-Mode Dispersion, Dispersion-Induced Limitations; Basic Propagation Equation, Chirped Gaussian Pulses, Limitations on the Bit Rate, Fiber Bandwidth, Fiber Losses; Attenuation Coefficient, Material Absorption, Rayleigh Scattering, wave guide Imperfections, Nonlinear Optical effects; Stimulated Light Scattering, Nonlinear Phase Modulation, Four Wave Mixing, Fiber Manufacturing; Design Issues, Fabrication Methods, Cables and Connectors

Section A

1. Among Microwaves and light waves which have high bit rate distance product? Why?

2. Mention the three advantages of optical fiber as wave guide over conventional.3. Mention the advantages of Graded Index fiber.4. Write the expression for the refractive index in Graded index fiber.5. Define Numerical Aperture of step index fiber.6. Define TIR?7. What is the need of Cladding?8. Define V number?9. Give the relation between rays and modes?10. Define MFD?11. Define Bi refrigence and beat length?12. Consider a parabolic index wave guide with n1=1.75,n2=1.677 and core radius

52µm. Calculate the numerical aperture at the axis and at a point 20µm from the axis.

13. Why do we prefer step index single mode fiber for long distance communication?14. Alight ray is incident from glass to air. Calculate critical angle?15. An optical signal has lost 55% of its power after traversing 3.5 km of fiber. What

is the loss in dB/km of this fiber?16. What are the causes of absorption?17. List the basic attenuation mechanisms in an optical fiber.18. Mention the two causes of intramodal dispersion.19. Define fiber loss.20. What do you mean be polarization mode dispersion?

Section B

1. What is meant by wave-guide dispersion? Derive the expression for the same.2. What is meant be material dispersion? Derive the expression for the pulse

broadening due to material dispersion. 3. Explain with suitable diagrams the different mechanisms that contribute to

attenuation in optical fibers. 4. When the mean optical power launched into an 8km length of fiber is

120 µW, the mean optical power at the fiber output is 3µ W.Determine

(1) Overall signal attenuation in dB/km and (2) The overall signal attenuation for a 10km intervals, each giving an attenuation of 1dB.

5. Discuss in detail intermodal dispersion of multimode step index fiber with relevant expression and diagrams.

6. 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?

7. A 6 km optical link consists of multimode step index with a core refractive index of 1.5 and a relative refractive index difference of 1%. Estimate the delay difference between the slowest and fastest modes at the fiber output and the rms broadening due to intermodal dispersion on the link. Also derive the expression involved in it..

8. A multi-mode step index fiber with core diameter of 60m & a relative refractive index difference equal to 1% is operated at a wavelength of 0.80m. If the refractive index of core is 1.5.Determine

a. Normalized frequency for the fiberb. Approx. number of modes if will support.

9. An optical fiber made of silica glass has a relative refractive index difference of 0.45% and acceptance angle for fiber in the core is 0.115radians. Find the speed of light inside the fiber core.

10. A multi-mode step index fiber has a core refractive index of 1.5 & relative refractive index difference equal to 1%. If the number of modes propagating at a wavelength of 1.3m is 1100. Find the diameter of the core.

11. A multi-mode graded index fiber has an acceptance angle of 8° & launching takes place from the air. If the refractive index at the core axis is 1.52 then determine the value of relative refractive index difference.

12. A single-mode fiber has a core diameter of 10m & is coupled to laser diode that produces 1.3m light. The refractive index of core glass is 1.55. Determine

a. Max. value of normalized refractive index difference b. Refractive index of cladding glassc. Acceptance angle for the fiber.

13. A graded index with 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

14. Explain briefly non-linear optical effects.15. Discuss Maxwell’s equation.16. Calculate the cut off condition wavelength for step index single mode fiber having

core and cladding radius as 13.2 and 32 µm respectively. The core and cladding refractive indices are 1.55 and 1.45 respectively. Operating wavelength is 0.75µm.

17. A SI fiber has core refractive index of n1 = 1.445, and a cladding index of n2 = 1.440. The normalized frequency is 2.2 If the source wavelength is 1.3 µm:

a) What is the core radius of this fiber?b) What is the numerical aperture (NA) of this fiber?c) What is the spot-size of this fiber?d) How many modes can propagate in this fiber? Briefly explain your answer.

18. Discuss the signal distortion in single mode fibers. 19. Discuss in detail intermodal dispersion of multimode step index fiber with

relevant expression and diagrams.20. The material dispersion in an optical fiber is defined by d²n/d²is 4*10-²m-². Find

pulse broadening per kilometer due to material dispersion within the fiber when it is illuminated with a led source with a peak wavelength of 0.9m and an rms spectral width of 45nm.

Section C

1. Numerical Aperture gives __________ collecting ability of the fiber.2. Micro bending losses can be reduced by _________________3. Single mode fibers are not affected by____________4. Connectors are used to make ___________5. Four wave mixing is a type of _____________loss phenomenon associated with

optical fiber communication6. Optical fiber system of information transmission is not used in the environment

prone to _____________radiations7. FDM utilizes bandwidth more economically than______

8. The numerical aperture of skew rays is _______________-than meridional ray.9. The relative refractive index of optical fiber is given as ____________