JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year OPTOELECTRONICS AND LASER INSTRUMENTATION Previous Question Paper (March - 2021 - R16)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Compare step index fiber and Graded index fiber.
Answer
| Feature | Step Index Fiber | Graded Index Fiber |
|---|---|---|
| Refractive Index Profile | Constant refractive index in the core (n1) | Refractive index decreases parabolically from the center |
| Pulse Dispersion | High (due to modal dispersion) | Low (due to self-focusing effect) |
| Bandwidth | Low | High |
| Core Diameter | Large (multimode) or Small (single-mode) | Generally medium |
| Signal Distortion | Significant due to different path lengths | Reduced due to varying speeds at different radial distances |
| Fabrication | Easier to manufacture | More complex to manufacture |
Define acceptance angle and Numerical aperture of Optical fiber and derive the relationship between acceptance angle and Numerical aperture.
Answer
The Acceptance Angle is the maximum angle at which light can enter the fiber core from the air and still be guided through the fiber via total internal reflection. The Numerical Aperture (NA) is a dimensionless measure of the light-gathering capacity of an optical fiber, defined as the sine of the acceptance angle.
Consider a fiber with core refractive index n1 and cladding refractive index n2, surrounded by air (n0 = 1). Let light enter the fiber at an angle θa (acceptance angle) and refract into the core at angle θr. By Snell's Law at the air-core interface:
At the core-cladding interface, the light must strike at an angle greater than the critical angle θc to undergo total internal reflection. If φ is the angle of incidence at the core-cladding interface, then φ = 90° - θr. For total internal reflection, sin(φ) ≥ n2 / n1. Since sin(φ) = cos(θr), we have:
Substituting sin(θr) = sin(θa) / n1 from the first equation:
Squaring both sides and simplifying:
Since NA = sin(θa), the relationship is:
Explain the following characteristics with respect to LASER: i) Stimulated emission ii) Population inversion
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Describe different Laser configurations.
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What are the types of optical Sources? And explain the principle of operation of LED diode.
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Compare electro-optic and Acousto-optic modulators.
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What is principle of interferometry and describe the working of velocimeter as interferometer.
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How can you measure the current using optical fibers? Explain.
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Describe the operation of basic holographic interferometers.
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Describe the Laser instruments used for plastic surgery.
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Describe the different kinds of dispersions happened in optical fibers.
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Compare CO2 laser and Argon-Ion Lasers.
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Compare PIN photo diode and Avalanche Photo diode.
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How can you measure the Liquid level using optical fibers? Explain.
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Classify the Gas lasers and explain the working principle of any one of them.
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How can you measure the distance using Lasers? Explain.
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