PARISUTHAM INSTITUTE OF TECHNOLOGY & SCIENCE
DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING
SUBJECT CODE & NAME: EC2402/ OPTICAL COMMUNICATION AND NETWORKING
CLASS: IV YEAR / VII SEM
Unit-1
Part-A
1. A point source of light is 12 cm below the surface of a large body of water (n = 1.33). What is the
radius of the largest circle on the water surface through which the light can emerge?
2. Consider a parabolic index waveguide with n1 =1.75, n2 = 1.677 and core radius
25 micro meter. Calculate the numerical aperture at the axis and at a point 20
micro meter from the axis.
3. Define numerical aperture of a step index fiber.
4. Define mode-field diameter.
5. Commonly available single mode fibers have beat lengths in the range 10 cm < Lp <2 m . What
range of refractive index differences does this correspond to? (for wavelength = 1300 nm)
6. Define mode field diameter.
7. What is the fundamental parameter of a single mode fiber?
8. A step index fiber has a normalized frequency V = 26.6 at 1300 nm wavelength.
If the core radius is 25 pm, find the numerical aperture.
9. What are the limitations of optical fiber communication systems?
10. What is meant by mode coupling?
11. What is V number of a fiber?
12. Differentiate between single-mode fiber and multi-mode fiber.
13. Why step index single mode fiber preferred for long distance communication?
14. What are the advantages of graded index fiber?
Part-B
1.
2.
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8.
Discuss the signal distortion in single mode fibers
Discuss pulse broadening in graded index fibers with necessary equations
Discuss the propagation modes in single -mode fibers.
Discuss the structure of graded index fiber
What is meant by 'material dispersion'? Derive its expression
Discuss the pulse broadening in graded index fibers
What are fiber modes? Explain mode theory for optical fibers in detail.
Compare Single mode fibers and Graded index fibers. Explain the requirements for fiber
materials.
9. What is mode coupling? Discuss pulse broadening in Gl fibers.
Unit-2
Part-A
1. Write the expression for the effective number of modes guided by a curved multimode fiber of radius
'a'.
2. Define normalized propagation constant.
3. Give expression for the effective number of modes guided by a curved multimode fiber.
4. What are the causes of absorption?
5. Find the coupling loss for two fibers having core refractive index profiles alpha E = 2.0 and alpha R =
1.5.
6. Mention the two causes of intra-modal dispersion.
7. Define fiber loss.
8. What is meant by Fresnel reflection?
9. What is meant by attenuation coefficient of a fiber?
10. What are the factors that cause Rayleigh scattering in optical fibers?
11. What is meant by dispersion in optical fiber?
12. What are the ways to reduce macrobending losses?
13. Define – Group Velocity Dispersion
14. What is polarization?
15. What is fiber birefringence?
16. What is polarization mode dispersion ( PMD)?
Part – B
1. Discuss various kinds of losses that an optical signal might suffer while propagating through fiber,
which is most important one? What is the effect of these losses on light power and pulse shape?
2. Explain Non-linear scattering loss and fiber bend loss with neat diagram and expressions.
3. Explain material dispersion in optical fiber
4. Explain mechanical splices with neat diagram.
5. Write a neat note on fiber alignment and joint loss.
6. What is meant by material dispersion? Derive the expression for pulse broadening due to material
dispersion.
7. Describe the various types of fiber connectors and couplers.
8. Derive expressions for material dispersion and waveguide dispersion and explain them.
9. With diagram, explain intra and intermodal dispersion.
10. An LED operating at 850 nm has a spectral width of 45 nm. What is the pulse spreading in ns/km due
to material dispersion? What is the pulse spreading when a laser diode having a 2 nm spectral width is
used? The material dispersion is 90 ps/nm km.
11. Describe the linear and non-linear scattering losses in optical fibers.
Unit-3
Part-A
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16.
Draw the three key transition process involved in laser action
Write the concept of indirect band gap semiconductor materials
What is meant by hetero junction?
What is meant by indirect band gap semi conductor material?
Give example for direct and indirect semiconductor materials
Calculate the ratio of stimulated emission rate to the spontaneous emission rate for a lamp operating
at a temperature of 100 K. Assume average operating wavelength is 0.5 micro meter.
Compare LED and LASER.
What is meant by population inversion?
What are the advantages of LED?
Define – Quantum Efficiency of a photo detector
In a 100ns pulse, 6 *106 photons at wavelength of 1300nm fall on an In GaAs photo-detector on the
average, 5.4 *106 electron-hole pairs are generated. Find the quantum efficiency.
What is the principle of operation of LASER?
When an LED has 2V applied to its terminals, it draws 100mA and produce 2mW of optical power.
Determine conversion efficiency of the LED from electrical to optical power.
Distinguish between direct and indirect band-gap materials
Define – Responsivity of a photo detector
Why is silicon not used to fabricate LED or LASER diode?
Part – B
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8.
Draw the structure of edge emitting and surface emitting LEDs and explain.
Explain any two injection laser structures with neat diagrams.
Draw and compare the construction and characteristics of PIN and Avalanche photo diode.
Compare LED with a laser diode.
With the help of a neat diagram explain the construction and working of a surface emitting LED.
Explain the structure of and working of Silicon APD.
Define S/N ratio of a photodetector. What conditions should be met to achieve a high SNR?
Draw and explain the structure of Fabry-Perot resonator cavity for a laser diode. Derive laser diode
rate equations.
9. Briefly explain the different noise sources of a photo detector.
10. Define Internal quantum Efficiency of a LED. Derive the expression for the same.
11. Describe the operation of an injection laser.
Unit – 4
Part – A
1.
2.
3.
Define Quantum limit.
What are the error sources of receiver?
A digital fiber optic link operating at 1310 nm, requires a maximum BER of 10 -8. Calculate the
required average photons per pulse.
4. Why silicon is preferred to make fiber optical receivers?
5. Define – Modal Noise and Mode Partition Noise.
6. What are the methods used to measure fiber refractive index profile?
7. What is dark current?
8. State the significance of maintaining the fiber outer diameter constant.
9. What is reflection noise?
10. List the advantages of preamplifiers.
Part – B
1.
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Draw and explain the operation of high impedance FET and BJT amplifiers.
Explain the following measurements
a) Attenuation measurement using cut-back techniques.
b) Frequency domain measurement of fiber dispersion.
What are the various types of preamplifiers available for optical networks? Explain any three of
them with circuit diagrams.
Write detailed notes on the following.
a) Fiber refractive index profile measurement
b) Fiber cut-off wavelength measurement
With suitable diagram, explain optical receiver operation and its performance.
Describe the dispersion and numerical aperture measurements of a fiber.
Explain the measurement technique used in the case of
(i) Numerical aperture
(ii) Refractive index profile
(iii) Fiber cut-off wave length
(iv) Fiber diameter.
Explain the insertion- loss method used for attenuation measurement.
Unit-5
Part – A
1.
2.
What are the three topologies used for fiber optical network?
Calculate the number of independent signals that can be sent on a single fiber in the 1525 – 1565 nm
bands. Assume the spectral spacing as per ITU – T recommendation G.692.
3. Define – WDM
4. What are the advantages of WDM?
5. What are the drawbacks of broadcast and select networks for wide area network applications?
6. What is EDFA?
7. What is chirping?
8. What are the advantages of using soliton signals through fiber?
9. What are solitons?
10. What is SONET / SDH?
11. Give the important features of time-slotted optical TDM network.
12. Distinguish between fundamental and higher order soliton.
Part – B
1.
Explain the principle of solitons and discuss the soliton parameters with suitable expressions and
diagrams.
2. Write short not on Optical CDMA.
3. Write short note on WDM and EDFA system performance.
4. Explain the layered architecture of SONET/SDH with neat diagrams.
5. What are the non-linear effects of network performance? Explain them briefly.
6. Explain SONET layers and frame structures with diagram.
7. Write short notes on Wavelength Routed Networks.
8. Discuss the concepts of Media Access Control protocols in Broadcast and select networks.
9. What is a broadcast and select multihop network? Explain.
10. Write short notes on Ultra high capacity networks.