EE2021 Fibre Optics and Laser Instruments Anna University question bank | EE 2021 important 2 marks and 16 marks questions ...
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Fiber optics and laser instruments
2 mark questions
1. A silica optical fiber with a core diameter large enough to be considered by ray
theory analysis has a core refractive index of 1.5 and a cladding refractive index of
1.47. Determine the numerical aperture and acceptance angle in air for the fiber.
2. Mention the advantages and disadvantages of monomode fiber over multimode fiber.
3. What is intermodal dispersion? What is its cause?
4. Distinguish between intrinsic and extrinsic absorption.
5. Compare LED source and ILD source.
6. GaAs has a band gap energy of 1.43eV at 300K. Determine the wavelength above
which an intrinsic photodetector fabricated from this material will cease to operate.
7. Define the quantum efficiency and responsivity of a photodetector.
8. What is the fundamental parameter of a single mode fiber?
9. A step index fiber has a normalized frequency V= 26.6 at 1300nm wavelength. If the
core radius is 25μm, find the numerical aperture.
10. Mention the two causes of intramodal dispersion.
11. Define fiber loss.
12. Compare LED and LASER.
13. GaAs has a band gap energy of 1.43eV at 300K. What is meant by long wavelength
14. Commonly available single mode fibers have beat lengths in the range 10cm<Lp <2m.
What range of refractive index differences does this correspond to?(for λ=1300nm).
15. Define long wavelength cutoff of a photodiode.
16. What is meant by quantum limit?
17. It is desired to make a single-mode fiber at an operating wavelength = 1300nm with
ncore =1.505 and nclad =1.502. Find the Numerical Aperture and core radius.
18. Give the refractive index expression of a graded index fiber.
19. List the basic attenuation mechanisms in an optical fiber.
20. Define internal quantum efficiency of an LED.
21. List the important requirements of an optical receiver.
22. An APD generates a current of 100nA when the incident power is 5nW. The
operating wavelength is 1.5μm. Find its responsivity. If the quantum efficiency is 0.7,
find the multiplication factor.
23. Name few splicing methods in fiber optics.
24. What is meant by population inversion.
25. State the characteristics of laser.
26. What are the advantages of gas laser over the solid state laser?
27. What is meant by laser welding?
28. State the advantages of using Laser in Industry.
29. What is holography?
30. Mention the precautions to be followed while handling Lasers for clinical applications.
16 mark questions
UNIT I Optical Fibers and their properties
1. What are the different types of optical fibres and their characteristics.
2. Explain the various types of fibre optic losses in detail.
3. Explain the interferometric method of measurement of length by using an optical
4. Describe how the optical fibres are used for the measurement of pressure,
temperature, liquid level and strain.
5. Derive an expression for number of modes propagating in a graded index fibre from
the first principle.
6. a) Derive an expression for numerical aperture of a step Index fibre.
b) The relative index difference between the core axis and the cladding of a graded
index fibre is 0.7% when the refractive index at the core axis is 1.45. Estimate
values for the numerical aperture of the fibre along the axis when the index profile
is assumed to be triangular.
7. a)With the aid of diagrams discuss the various losses occurring in optical fibres.
b)A 6km optical link consists of multimode step index fibre 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 fibre output and the rms
pulse broadening due to intermodal dispersion on the link. Also derive the expression
involved in it.
8. a)What type of materials are used for optical sources. What are the advantages of
double hetero structure. Compare surface emitting and edge emitting LED
b)Derive an expression for the internal optical power level generated in LEDs.
9. a)Explain the operation of avalanche photodiode.
b)The quantum efficiency of a particular silicon RAPD is 80% for the detection of
radiation at a wavelength of 0.9μm, when the incident optical power is 0.5 μW. The
output current from the device after avalanche gain is 11 μA. Determine the
multiplication factor of the photodiode under these conditions.
10. What are fibre modes? Explain mode theory for optical fibres in detail.
11. Compare single mode fibers and Graded index fibres. Explain the requirements for
12.Discuss various kinds of losses that an optical signal might suffer while propagating
through fibre. Which is most important one? What is the effect of these losses on light
power and pulse shape?
13. What is mode coupling? Discuss pulse broadening in GI fibres.
14. With neat diagram explain the construction and working of high radiance surface
15. Discuss in detail fiber splicing and connectors. Explain the operating principles of
16. What is meant by ‘material dispersion’? Derive its expression.
17. Discuss the pulse broadening in Graded Index Fibers.
18. Discuss the mode theory of circular waveguide.
19. a) What is meant by heterojunction? Give example.
b) Derive the internal quantum efficiency of an LED.
20. a) Explain optical feedback and laser oscillation.
b) Derive the threshold condition for lasing.
21. Discuss the principle of operation of APD with neat circuit diagram. Also discuss the
requirements of photodetector.
22. a) Derive the wave equations for step-index fiber and explain.
b) A step-index fiber has a normalized frequency 26.6 at a 1300nm wavelength. If the
core radius is 25μm find the numerical aperture and mode volume.
c)What is meant by ‘weakly guiding approximatin’?
23.Discuss the major elements of an optical fiber transmission link.
24.a)Sketch the fundamental mode field in a curved optical waveguide and explain how
bending losses occur?
b)Find the radius of curvature at which the number of modes(in a bent fiber) decreases
by 50% in a graded index fiber.α=2, n2 =1.5, Δ =0.01, a= 25μm and λ=1.3μm.
c)What is meant by material Dispersion?
25. a)What is meant by waveguide dispersion? Derive the expression.
b) Discuss the design optimization of single mode fibers.
26. a)Draw a typical double-heterostructure light emitter and explain.
b)Draw the schematic of surface emitting and edge emitting LED and explain.
27. a)Derive the threshold condition for LASER.
b)Explain the laser action with neat diagrams.
c)A GaAs laser operating at 850nm has a 500μm length and a refractive index n=3.7.
What are the frequency and wavelength spacings?
28.a) Draw the structure of avalanche photodiode and electric fields in the depletion and
multiplication regions. Also explain the principle of operation of APD.
b)A given silicon avalanche photodiode has a quantum efficiency of 65% at a
wavelength of 900nm. If 0.5μW of optical power produces a multiplied
photocurrent of 10μA, find the multiplication factor M.
c) Explain the error sources in the optical receiver.
29. a)Draw the schematic diagram of a typical optical receiver and explain.
b) In InGaAs pin potodiode has the following parameters at a wavelength of 1300nm:
ID =4mA, η= 0.9, RL =1000Ω and the surface leakage current is negligible. The
incident optical power is 300nW(-35dBm) and the receiver bandwidth is 20MHz.
Find the various noise terms of the receiver.
30. Describe in detail any two techniques for achieving an expanded beam fiber
connector with a neat diagram.
31. Describe what is meant by the fusion splicing of optical fibers. Discuss the
advantages and drawbacks of this joining techniques.
32. Describe with the aid of the suitable diagram, three common techniques used for the
mechanical splicing of optical fibers.
33. Describe with the aid of suitable diagram a)the multimode fiber mechanical splice
b)a single mode fiber mechanical splice c) the multimode fiber splicing using a
silicon chip arrays.
34. Discuss the principle of operation of the two major categories of demountable optical
35. What are the common techniques for achieving a butt jointed fiber connector. Explain
any two types.
UNIT II Industrial Application of Optical Fibres
1. Explain the block diagram of basic optical fiber sensor system.
2. Explain the construction and working of
a) two arm single-mode fiber Interferometric sensor.
b) ring interferometer with multiturn fiber coil.
3. Explain any two types of intrinsic fiber sensor.
4. Explain the operation of
a)optical fluid level detector
b)optical reflective type displacement sensor.
c)Moire fringe modulator of displacement measurement.
5. Explain the operation of photoelastic pressure sensor with its structure and response
6. Explain the operation of fluorooptic temperature sensor.
7. Explain the operation and construction of Doppler velocimeter.
8. Explain the operation of optical Gyroscope.
9. Explain about the electric field sensor with neat diagram.
10. Explain about the magnetic field sensors with neat diagram.
11. Explain the block diagram of basic optical fiber sensor system.
12. Explain the block diagram and working principle of single mode optical fiber sensor
for current measurement.
13. Define modulation and its types. Compare the types and explain about figure of
14. Explain the principle and operation of electro optic modulator with a neat diagram.
15. Explain the principle and operation of magneto optic modulator with a neat diagram.
16. Explain the principle and operation of acousto optic modulator with a neat diagram.
UNIT III Laser Fundamentals
1. Explain briefly the three processes involved in the laser action. Describe for a Fabry
Perot resonator laser diode, modes and threshold conditions. Obtain its rate equations
for steady state output.
2. List the properties of lasers and how it fulfills the major requirements for an optical
3. Explain about the operation of a) Q switching b) mode hopping and mode drift c)
cavity damping in lasers
4. Derive Einstein relation for the rates of the three transition process of absorption,
spontaneous emission and simulated emission for two level atomic system.
5. Explain about a) population inversion b)optical feedback and laser oscillation.
6. Explain the construction and operation of ruby laser with a neat diagram.
7. Explain the construction and operation of gas laser with a neat diagram
8. Explain the construction and working of semiconductor laser with neat diagram.
UNIT IV Industrial application of Lasers
1. Explain how laser is used for the measurement of distance, velocity, current and
2. Explain how laser is used in material processing and also explain laser heating process
and laser trimming of material.
3. a) Explain about material processing using laser.
b) How the distance is measured by Michaelson interferometry using laser.
4. List industrial lasers and its application.
Explain about a)laser welding b) laser cutting c) laser drilling.
UNIT V Hologram and Medical Applications
1. Define Holography and explain recording and reconstruction of a hologram.
2. List the use of holography.
3. Explain about any three scientific applications of holography.
4. Describe the construction and reconstruction of hologram.
5. Explain about laser interaction with tissue.
6. Mention the advantages of laser surgery and photothermal application.
7. Explain about laser endoscope and explain about endoscope laser coagulation.
8. List and explain how lasers are used in nonlinear optics for basic sciences.
9. List all the applications of laser.
10.Describe any four medical applications of laser in detail.