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Posted Date: 18 Nov 2009 Posted By: ram Member Level: Gold
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2008 Biju Patnaik University of Technology B.Tech SIXTH SEMESTER EXAM-2008, FIBRE OPTIC INSTRUMENTATION Question paper
SIXTH SEMESTER EXAM-2008 CPEN 5304
FIBRE OPTIC INSTRUMENTATION
1.Answer the following questions. 2x10
(a). Define "Integral Power Efficiency" and "External Power Efficiency" of LED.
(b). Distinguish between "Spontaneous Emission" and "Stimulated Emission".
(c). Write the expression of the "Normalised Frequency”. What is the importance of this parameter ?
(d). Why the photo multiplier and pyro electric detectors are not suitable for optical fiber systems ? Mention a suitable photo detector for optical
fiber system, with reasons.
(e). Using Snell's law derive the expression of the "Angle of Acceptance" and "Numerical Aperture" of an optical fiber having refractive index of the core
and cladding n1 and n2 respectively.
(f). Define "Reflectivity" and "reflection coefficient" at the fiber core end-face.
(g). Write the expression of the maximum theoretical Optical Power coupling efficiency for a fiber of radius "a”, source radius "rs" and refractive index of
the core and cladding n1 and n2 respectively.
(h). What is the "Sagnac Effect" used in fiber Optic sensors ?
(i). Draw the schematic diagrams showing the measurement of longitudinal displacement, lateral displacement and angular displacement using intensity
modulated optical sensor.
(j). What do you mean by "Two Wavelength System" in fiber-optic measurement systems ?What is the importance of this ?
2.(a). Explain the basic principle of operation of LASER sources. 5
(b). describe the construction of Fabry Perot Resonator. What is the purpose of using this resonator in LASER sources ? 5
3.(a). Describe the construction and operation of PIN photo diode. 4
(b). Describe mathematically the characteristics of photo current resulting fro power Absorption by a photo detector. 2
(c). Define "quantum efficiency" in photo diode. 2
(d). How the "responsively" is related to "Quantum efficiency" ? 2
4.Describe in brief, how the "quantum noise" and "Dark current noise" are generated in photo detector current. Also derive the expression of "Total
Noise Current" and "single-to-Noise ratio". 10
5.(a). Explain the phenomenon of "multi path Time Dispersion". 2
(b). Derive the expression of Pulse Broadening per unit length of traversal of optical signals due to multi path Time-Description in a step index fiber. 5
(c). explain how the Multi-Path time Description is reduced using graded-index fiber. 3
6.(a). describe several possible lensing schemes for coupling improvement between an optical source and an optical fiber. 5
(b). Why "Non-Imaging Micro sphere" is used in optical power launching and coupling ? Show that the focal point of micro sphere can be located on its
surface with certain assumptions. 5
7.(a). Show mathematically the occurrence of constructive and destructive interface in an interferometer. 3
(b). Describe the construction, operation and application of Michelson Interferometer. 3
(c). describe how the modulation of wavelength by Transmission medium is achieved using 4
(i). Littrow Diffraction grating
(ii). Fresnel Zone Plate.
8.Write short notes on any two: 5x2
(a). reasons of optical attenuation due to Absorption, scattering and Fiber bending.
(b). Semiconductor optical amplifier.
(c). "Fiber Optic Bragg grating sensor" and also "Fiber-Optic Gyroscope".
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