B.E. (Instrumentation & Control) FIBER OPTIC INSTRUMENTATION (Sem. – II) (2008 Pattern) (Elective – III)
Time :3 Hours] [Max. Marks :100
Instructions to the candidates :
1) Answer 3 questions from Section -1 and 3 questions from Section – II.
2) Answers to the two sections should be written in separate books.
3) Neat diagrams must be drawn wherever necessary.
4) Pigures to the right indicate full marks.
5) Use of logarithmic tables slide rule, Mollier charts, electronic pocket calculator and steam tables is necessary.
6) Assume suitable data, if necessary.
SECTION – I
QI) a) With a suitable ray diagram, explain ‘Total Internal Reflection’. How ‘Total Internal Reflection’ is achieved in an optical fiber? 
b) Explain with suitable diagrams (any two) : 
i) Acceptance angle.
ii) Numerical Aperture
iii) Skew rays.
Q2) a) An optical fiber has a numerical aperture of 0.25 and cladding refractive index of 1.555. Determine 
i) The acceptance angle for the fiber in water of refractive index of 1.33.
ii) The critical angle at the core-cladding interface.
b) Briefly indicate with the aid of suitable diagrams the difference between meridional and skew ray paths in step index fibers. 
c) With suitable diagram, explain Goos-Haenchen shift. 
Q3) a) What do you mean by signal degradation in an optical fiber? Discuss various signal degradation mechanisms in an optical fiber. 
b) Write a note on ‘Optical Time Domain Reflectometer’ (OTDR). Also describe the role of OTDR in distributed optical fiber sensing. 
Q4) a) Compare stimulated Brillouin and stimulated Raman scattering in optical fibers. 
b) Explain the reasons for pulse broadening in optical fiber. 
c) Differentiate between Microbending and Macrobending. Also explain what the critical bending radius for an optical fiber. 
Q5) a) What are the requirements for photo-detectors in an optical fiber? Enlist some photo-detectors, which are used in optical fiber. 
b) Compare PN diode with P-I-N photodiode. 
Q6) a) What is difference between splices and connectors. Describe any two types of splices in optical fibers with suitable diagrams. 
b) Discuss the principles of operation of the two major categories of demountable optical fiber connectors. Describe in detail a common technique for achieving a butt jointed fiber connector. 
SECTION – II
Q7) What are the advantages of Intensity Modulated Optical Sensors (IMOS)?
Describe following techniques of sensing which is based on intensity
modulation. Also enlist different parameters, which can be sensed by using
these techniques. 
a) Evanescent field
c) Encoding based position sensors.
Q8) a) What are the characteristics of light, which may be monitored in sensing applications? Describe one technique of sensing which is based on phase modulation. 
b) Write a note on ‘Encoding based position sensors’. 
Q9) a) What is ‘Optical Fiber Brag Grating’? Explain with suitable diagram working of ‘Optical Fiber Brag Grating’. 
b) Explain a fabrication technique of ‘Optical Fiber Brag Grating’. 
Q10)a) What do you understand by ‘Distributed Optical Fiber Sensing’? Enlist the advantages of Distributed Optical Fiber Sensing. 
b) Explain Distributed Optical Fiber Sensing for temperature monitoring. What are limitations of this type of sensing? 
Q11)a) What do you understand by ‘Integrated Optics Device’? What are advantages of Integrated Optical Devices over conventional optical devices? 
b) Explain with the aid of suitable diagrams, following integrated optical devices: 
i) Beam splitter
ii) Directional coupler
Q12) a) Sketch the major elements of a fiber amplifier and describe the operation of the device. Indicate the benefits of fiber amplifier technology in comparison with that associated with Silicon Laser Amplifiers (SLAs). 
b) What are the advantages of Optical Amplifiers over conventional electric amplifiers used in optical applications?