Skr Engineering College

SKR ENGINEERING COLLEGE DEPARTMENT OF ECE MODEL EXAM OPTICAL COMMUNICATION ( EC433 ) CLASS: IV ECE 1& 2 DATE: 14.10.06 SEM : VII DUR : 3 HRS Answer ALL questions. PART A – (10 x 2 = 20 marks) 1. A point of light is 12cm 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. Write the expression for the refractive index in GI fiber. 3. Write the expression of the effective number of modes that are guided by a curved multimode fiber of radius ‘a’. 4. What are the causes of absorption? 5. Distinguish between direct and indirect band gap material. 6. Define Responsivity. 7. A given APD has a quantum efficiency of 65% at a wavelength of 900nm. If 0.5µm of optical power produces a multiplied photo current of 10µA. Find the multiplication M. 8. What is meant by ‘bulk dark current’? 9. Write the concept of ‘soliton’. 10. An optical signal has lost of its power after traveling 3.5km of fiber. What is the loss in dB/km of this fiber? PART B – (5 x 16 = 80 marks) 11.(a) Discuss the mode theory for a circular waveguide. OR (b)(i) Discuss the propagation of modes in SM fiber.(8) (ii) Derive modal equation. (8) 12.(a) Discuss the pulse broadening in GI fiber. OR

(b)(i)What is mean by waveguide dispersion? Derive its expression for the same. (8) (ii) Explain about the PMD. (6) (iii) Discuss the mode coupling. (2) 13.(a)(i) What is meant by heterojunction? (2) (ii) Derive the external quantum efficiency and power of an LED. (14) OR (b)(i) Explain optical feedback and laser oscillation. (6) (ii) Explain the modes and threshold condition and derive. (10) 14.(a)(i) Discuss the requirements of an optical detector. (6) (ii) Explain the principle of Avalanche photodiode. (10) OR (b)An InGaAs pin photodiode has the following parameters at a wavelength of 1300nm: ID = 4 nA, η = 0.9, RL = 3000Ω and the surface leakage current is negligible. The incident optical power is 300 nW (-35dBm), and the receiver bandwidth is 20 MH Z. Find the various noise terms of the receiver. 15.(a)(i) Discuss the operational principle of WDM. (8) (ii) Explain about the connector return loss. (8) OR (b)(i) Explain the link power budget of a fiber optic point to point link.(6) (ii) Explain the rise time budget of a fiber optic point to point link. (10)

--------------ALL THE BEST-------------