1. COMMUNICATION ENG. PROF. A.M.ALLAM
TUT-4
OPTICAL SOURCES
LECTURES

2. COMMUNICATION ENG. PROF. A.M.ALLAM
1-An injection laser has a GaAs active region with bandgap energy of 1.43
eV. Estimate the wavelength of optical emission from the device
2- Assume that the optical power from a LED varies with modulation
frequency according to this relation:
Show that the 3-dB-optic and detected-electrical bandwidths are related by
LECTURES

3. 3-The relation of optical power to current for an LED is given by P = 0.02 i.
The maximum allowed power is 10 mW. The LED has a dc bias current
and a 1MHz ac current applied.
(a) Sketch the power-current curve
(b) If the peak signal power is 2mW and the peak total power is 10 mW,
compute the total peak current, the dc current, the average power,
and the modulation index (peak signal power/average power).
(c) Repeat if the modulation index is 100% (and so the peak signal
power is no longer 2 mW).
(d) Let the dc current be 50 mA and the peak ac current be 75 mA. Plot
the output power versus time for two cycles of the ac signal.
4-Describe with the aid of suitable diagram the mechanism giving the emission
of light from an LED. Discuss the effects of this mechanism on the
properties of the LED in relation to its use as optical sources for
communication

4. COMMUNICATION ENG. PROF. A.M.ALLAM
5-Briefly outline the advantage and drawbacks of the LED in comparison
with the injection laser for use as a source in optical fiber communication.
LECTURES