Optical Fibre Communication - May 2014

Electronics Engineering (Semester 7)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1(a) Compare dark current with optical current semiconductor.(5 marks) 1(b) Explain direct and indirect band gap Semiconductor.(5 marks) 1(c) What do you mean by optical wave guide? How it is different from Electrical Wave guide?(5 marks) 1(d) Explain Bandwidth distance product.(5 marks) 2(a) Derive the expression for numerical Aperture of a step index fiber.What will happen to numerical aperture cladding is removed?(5 marks) 2(b) Compare step index and graded index fiber.(5 marks) 2(c) What do you understand by intramodal dispersion.Derive the expression for material dispersion.(10 marks) 3(a) Explain the significance of V-number.derive the expression for number of guided modes in graded index fiber.(10 marks) 3(b) Explain Following terms:
Total internal reflection
Acceptance angle
Critical angle
Quantum efficiency
Responsivity.(5 marks) 3(c)
State the difference between LED and LASER(5 marks) 4(a) Explain Modified Chemical Vapour Deposition(MCVD)method of fiber fabrication?(10 marks) 4(b) Explain with neat sketches fiber splicing techniques.Enlist the desirable requirements of a good connector.(10 marks) 5(a)

A photodiode has a quantum efficiency 0f 65% when a photon of energy of( 1.5 ???10^{-19}J) are incident upon it.
At what wavelength is the photodiode operating.
Calculate the incident optical power to obtain photo current of 2.5μA when the photodiode is operating as shown above.

Write short Notes on: Any four

7 (a)

Linearly polorized modes