December 17, 2011

OPTICAL COMMUNICATIONS JNTU previous years question papers

OPTICAL COMMUNICATIONS JNTU previous years question papers

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

 1. (a) Describe the basic block diagram of a optical communication system and explain how it differs from conventional co-axial cable communication system.
(b) Determine the normalized frequency at 0.82 µm for a step index fiber having 25 µm core radius, n1 = 1.48 and n2 = 1.46. How many modes propagate in this fiber at 0.82 µm? What percentage of optical fiber power flows in cladding? [8+8]

2. (a) Discuss different mechanisums causing scattering losses in SiO2 fiber as a function of operating wavelengths.
(b) A K2O - SiO2 glass core optical fiber has an attenuation resulting from rayleigh scattering of 0.46 dB Km-1 at a wavelength of 1 µm. The glass has an estimated fictive temperature of 758 K, isothermal compressibility of 8.4 × 10-11 m2N-1 and a photo elastic coefficient of 0.245. Determine the refractive index of glass core. [8+8]

3. Define and distinguish between the different types of signal distortion in optical fibers. [16]

4. (a) Two multimode step index fibers have NAs of 0.2 and 0.4 respectively and both have the same core refractive index which is 1.48. Estimate the insertion loss at a joint in each fiber caused by a 50 angular misalignment of the fiber core axes. It may be assumed that the medium between the fibers in air.
(b) Explain the intrinsic coupling losses at fiber joint due to mismatch of core diameter, NA and refractive index profile difference. [8+8]

5. Write short notes on the following:
(a) Power coupling from a vertical Cavity Surface Emitting Laser (VCSEL) diode to a single mode fiber.
(b) Radiation patterns in axial and vertical planes from surface emitting LED and edge emitting LED. [8+8]

6. (a) Define sensitivity and Bit Error Rate (BER) with reference to a fiber optic receiver.
(b) Describe the dependency of BER on Signal-to-Noise Ratio at the output of a receiver.
(c) Express Noise due to photocurrent generation process as an equation. Describe the significance of such noise on overall SNR of the receiver. [4+4+8]

7. (a) Discuss the effect of mode mixing factor on modal dispersion for calculating the maximum allowable transmission data rate in a fiber optic link.
(b) The rise times for various components of intensity modulated fiber optic link are listed below. Determine if these specifications support a 5 Km repeaterless fiber optic link with 6 MHz optical bandwidth: [8+8]
Risetime of LED transmitter electronics = 10ns Inter modal dispersion induced = 8ns/Km
Intra modal dispersion induced = 2ns/Km
Risetime of Detector and receiver electronics = 3ns

8. (a) Describe the principle of wavelength division Multiplexing for optical communication links.
(b) Describe the method of implementation of wavelength division multiplexing in full duplex optical communication links.
(c) Describe briefly the necessity and procedure of Line coding in optical links.



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