Punjab Technical University 2005 M.Tech Electronics and Communication Engineering OPTICAL CUMMUNICATIONSYSTEMS ECE 506/507 - Question Paper

OPTICAL CUMMUNICATIONSYSTEMS ECE 506/507 2nd/3rd Sem. May 2k5

Max Marks 100

Note: Attempt any 5 ques.. All ques. carry equal marks.


1. Starting from Maxwell’s equations, derive TE, TM and hybrid node solutions of step index fiber.

2. (a) Prove that three dB optical bandwidth of an LED is related to the three dB electrical bandwidth by relation f3dB (optical) = v3 f3dB (electrical).
(b) A 250 micrometer long InGaAsP laser has an internal loss of 40 cm-1. It operates in a single mode with modal index 3.3 and the group index 3.4. compute the photon life time. What is the threshold value of electron population? presume that the gain varies as G = GN (N-N0) with GN= six x 10-3 s-1 and N0=1 x 108.

3. (a) define different noise mechanisms in a photodiode and derive an expression for he signal to noise ratio for the case of a direct detection using a photodiode.

(b) An APD generates a current of 100 nA when the incident power is five nW. The operating wavelength is 1.5 micrometer. obtain the responsivity. If the quantum efficiency is 0.7, obtain the multiplication factor.

4. (a) discuss the mechanism of amplification in EDFA with a suitable energy level diagram.

(b) An optical amplifier is operating at 1.3 micrometer wavelength with input power of 0.5 milliwatt and noise figure of four dB. What is the receiver bandwidth if the SNR at the output is 30 dB?

5. (a) discuss optical equalizing filters in detail.

(b) The pre-chir technique is used for dispersion compensation in a 10 Gb/sec light wave system operating at 1.55 micrometer and transmitting the one bit as chirped Gaussian pulses of 40ps width (FWHM). Pulse broadening up to 50% can e tolerated. What is the optimum value f chirp parameter C, and how far can the signal be transmitted with this optimum value? Use D = 17 ps/(km-nm).

6. (a) A Fabry – Perot filter of length L has equal reflectivities R for the 2 mirrors. Derive an expression for the transmission spectrum T(v) considering multiple round trips inside the cavity containing air. Use it to show that the fineness is provided by F = pi vR /(1-R)

(b) The C and L spectral cover a wavelength range from 1.51 to 1.61 micrometer. How many channels can be transmitted through WDM when the channel spacing is 25 GHz? What is the effective bit rate-distance product when a WDM signal covering the 2 bands using 10 Gb/s channels is transmitted over 2000 km.

7. (a) Verify numerically by propagating a fundamental soliton over 100 dispersions lengths that the shape of the soliton does not change on propagation.

(b) To what bit rate is the soliton communication system operating at 1.55 micrometer is limited for amplifier spacing of 50 km. (given q0=6).

8. Write short notes on the following:
(a) WDM soliton systems.
(b) WDM system performance problems.

Earning:   Approval pending.