SRM University 2007 B.Tech Electronics and Communications Engineering Bank : Microwave and Optical Communications - Question Paper

7. What is LASER? define its properties.
8. What are the direct-band gap and indirect band gap materials?
9. What are light source materials?
10. Define responsivity?
11. What is meant by impact ionization in APD?
12. What do you mean by avalanche effect?
13. What are the conditions needed to achieve high signal to Noise ratio in a photodiode?
14. What are PIN Photodiodes?
15. What are the avalanche photodiode?
16. What do you mean by diffusion length?
17. What are RAPD?
18. Describe reach through structure.
19. State the threshold condition for LASER Oscillation.
20. An engineer has 2 Ga1-x Alx As LEDS 1 has a bandgap energy of 1.54ev and other has x = 0.015 a) obtain the aluminum mole fraction x and the emission wavelength for the 1st LED b) obtain the bandgap energy and the emission wavelength of the other LED.
21. Give the principle of phtotodetection.
22. Compare PIN and APD device.
23. Explain the phenomenon of optical pumping?
24. GaAs has Bandgap energy of 1.43eV at 3000 K. Determine the wavelength above which the photodetector fabricated from this material cease to operate.

Part-B
1. Draw the structure of Edge-Emitting LED and discuss the operation.
2. Derive Einstein relationship and Threshold condition for Lasing action.
3. Sketch the structure of SLED and discuss its working principle.
4. Sketch the structure of LASER and discuss its working principle.
5. Explain in detail the Laser Diode structures and its Radiation trend.
6. With a neat sketch discuss the principle and operation of PIN Photodiode.
7. With a neat sketch discuss the principle and operation of Avalanche photodiode.
8. Discuss in detail the effect of the different noise mechanism in a photodetector and its signal to noise ratio.

Unit V – Optical Link, Coupling and Splicing
Part-A
1. What is WDM and draw a typical WDM network?
2. List a few of the principle requirements of a good connector design.
3. How do you analyse the performance of an optical link.
4. Define ‘Excess Loss’ and ‘Insertion Loss’.
5. Define Coupling Efficiency.
6. Distinguish ranging from a splice and a connector.
7. Draw a sketch of simplex point to point link.
8. Name and sketch any 2 splicing techniques.
9. What for splicing is used?
10. How to connect optical fibres?
11. Is WDM efficient for multiwave length scheme?
12. A coupler has an excess loss of 1dB and 1:1 splitting ratio. How much of the input power reaches the 2 output terminals.
13. Define Channel Width.
14. What is the Crosstalk of a WDM System.
15. List the steps involved in splicing procedure.
16. What is a connector?
Part-B
1. a) discuss in detail the rise time budget of a fibre optic point to point link
b) A fiber link includes five splices at 0.02dB/splice, 4 connectors at 0.2dB/ connector transmitter power at -10dBm, receiver sensitivity of -25dBM. What length of this link will be allowed if a SM fiber with attenuation of 0.3dB/km is used and the needed power margin is 3dB?

2. Discuss the operational principles of WDM highlighting its key features.
3. Write notes on i) Mechanical Splicing ii) Fiber Connectors.
4. What are the parameters needed for analyzing point to point link? discuss them in detail.
5. Discuss on different splicing techniques.
6. a) For a point to point link explain the link power budget.
b) A 90 Mb/s NRZ data transmission system uses a GaAlAs Laser diode having 1nm spectral width. The risetime of the laser transmitter output is 2ns. The Transmission distance is seven Km over a graded index fiber having a 800 MHz Km bandwidth distance product. If the receiver bandwidth is 90MHz and the mode mixing factor q=0.7. provided D(?)=2ps / km-ns. What is the system rise time?

7. a) discuss in detail the rise time budget of a fiber optic point-to-point link.
b) An optical fiber link is designed to operate eight Km length of the link without a repeater. The rise time of various individual components are
The rise time of LED source = 5ns
The rise time of p-in photodector = 8ns
Rise time due to modal dispersion = 5ns /km
Rise time due to material dispersion= 1ns/km

compute the system rise time and maximum bit rate that can be achieved in the link using (i) RZ format (ii) NRZ format.

Earning:   Approval pending.