Anna University Chennai 2005 B.E Electronics

B.E./B.TECH.DEGREE exam APRIL/MAY 2005
VII -SEMESTER
OPTICAL COMMUNICATION


TIME :3 hrs
MAX MARKS :100


PART -A (10 X two = 20 MARKS)

1. describe numerical aperture of a step index fiber

2. describe mode-field diameter

3. provide expression for the effective number of modes guided by a curved multimode fiber

4. elaborate the causes of absorption?

5. What is meant by hetero junction?

6. What is meant by indirect band gap semi conductor material?

7. describe responsivity

8. A provided APD has a quantum efficiency of 65 % at a wavelength of 90 nm . If 0.5 micro watt of optical power produces a multiplied photocurrent of 10 micro Ampere , obtain the multiplication M

9. What is meant by solitron?

10 What is meant by modal noise?

PART-B (5 X 16 = 80)

11(I) explain the propagation modes in single -mode fiber

(ii) explain the structure of graded index fiber

12(a) (i) What is meant by material dispersion?

(ii) Derive an expression for material dispersion

(iii) Derive the expression for wave guide dispersion
OR
(b) explain the pulse broadening in graded index fibers

13(a) Draw the structure of edge emitting and surface emitting LEDs and discuss
OR
(b) explain the laser diode structures and radiation trends

14(a) An InGaAs pin photodiode has the subsequent parameters at a wavelength of 1300 nm : I D = four nA, ? = 0.9, RL = 1000 ohms and the surface leakage current is negligible. The incident optical power is 300 nw (- 35 dBm), and the receiver bandwidth is 20 MHz . obtain the different noise terms of the receiver
OR
(b) explain the performance of digital receiver by defining the probability of fault

15 (a) (i) explain the operational principles of WDM

(ii) define the key features of WDM
OR
(b) discuss the rise-time budget of a fiber –optic point – to – point link

Earning:   Approval pending.