EI1001-dec 2009
Transcript of EI1001-dec 2009
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University Question Key- December 2009
Part-A
1. What is the principle used in the working of fibers as light guides?
Total internal reflection
The ray should travel from denser to rarer and the angle of incidence in the
denser medium should be greater than the critical angle of that medium.
2. Among the different fibers which has the least dispersion?
Single mode step index fiber.
Due to single mode propagation there is no multimode dispersion
Due to smaller core diameter and smallest refractive index profile, the value
of total dispersion is very small.
3. Why do we require modulation?
To get high the bit rate or bandwidth length product
To get the long distance communication
To improve S/N ratio at the receiver end
4. What are moire fringes?
Are the relatively thick lines produced when two patterns of thin lines overlap.
5. Define Q-Switching and mode locking.
Q-Switching- maintaining the population inversion to a very high value above
the threshold population inversion and simultaneously bringing down all the
atoms to undergo laser transition.
Mode locking- Due to broadened nature of laser cavity, a laser source can
support oscillations in many modes simultaneously. The number of modes
produced depends on the laser transition line width. If we mode lock the laser,
i.e., if we force all the modes to maintain the same relative phase to oneanother, the total irradiance got will be more.
6. What are the characteristics of laser?
High monochromacity
High intensity
High coherence
High directionality
7. What is meant by laser action? What are the conditions to achieve it?
Laser action the amplification of light by stimulated emission of radiation.
To get laser action There should be population inversion and stimulated
emission takes place.8. Mention the merits and demerits of laser welding.
Heat affected zone is very narrow.
High welding speed or cutting speed can be achieved.
There is minimum residual stress and distortion
The material processing can be done at room temperature
9. State the basic principle of holography.
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Process of image construction by recording and reconstruction of hologram
by means of interference techniques without the aid of lenses.
10. List any four medical applications of laser.
Gynecology
Oncology
Dermatology Thoracic surgery
Urology
Part B
11. a. i) Classify optical fibers based on the modes of propagation and refractive
index profile and discuss their properties.Based on refractive index profile
1. Step index fiber
a. single modeb. Multimode
2. Graded index fiber
ii) Discuss the different scattering losses in optical fibre at the operatingwavelength
b. i) Explain the different types of connectors and splicers.
ii) Give an account of the optical detector response time and its influence ondetector parameters
12. a. i) Explain any two fiber optic sensors.
ii) Give the principle and design of an optical modulatorb. i) Explain the mechanisms involved in interferometric method for the
measurement of length.
ii) How will you measure the pressure and temperature by using an optical
fibre