8th Sem Subject Ofc 3rd chapter notes by Lohith kumar 11GUEE6018

1. Part A | 3rd chapter question |:
Photonic Sources: Semi conduction materialfor photo devices, LEDs
structure, Operation quantum efficiency and power. Modulation of an LED
, Laser diodes, Laser diode modes and Threshold calculations, structures
quantum efficiency , resonant frequencies single mode lasers, Modulation
of laser diodes.
1. For a typical GA AIAs double hetero structure LED dram the following
and explain
 Cross section view of the structure
 Energy bank diagram
 The variation of the refractive index
2. Dram the variation of the optical output power with the change in drive
current for LED and Laser sources. Briefly explain the graph?
3. What is single mode laser ? Discuss.
4. Which semiconductor material is used for fabrication a light source?
Why so
5. Explain the working of Distributed – Bragg Reflector (DBR) laser?
6. Explain the structure and working principle of a typical GaAIAs double
–hetero structure LED?
7.With the help of schematic representation of a pin photodiode ckt ,
explain its operation?
8.For a Photodector define the discuss the following ?
 Quantum efficiency
 Responsively

2. 9. Define Multiplication – M calculate same give that quantum efficiency of
the avalanche photodiode is 60% , wavelength is 900nm, 0.4µwoptical
power produces a multiplied photocurrent of 15µA.
10. Explain the phenomenon of population inversion in case of two level
atomic structure ?
11. what are the various laser diode structures ? With a neat diagrams
explain any two of them.
12.The radiative and non radiative recombination life time of the minority
carriers in the active region of a double hetrojunction LED are 60ns and
100ns respectively. Determine the total carried recombination lifetime and
the power internally generated within the device when the peak emission
wavelength is 0.87 µM at a drive current of 40µA.
13. Why silicon is not used to fabricate a photo source ? Explain ?
14. With the Help of Energy bank diagrams differentiate spontaneous
emission from stimulated emission.
15. With the help of figure, explain distributed feedback
(DFB)semiconductor Laser?
16. Compare Laser lightsource with LED lightsource?
17. Bring out the differences between ‘ Fabry – Perot Resonator Laser’and
the ‘Distributed –Feedback LASER ‘
18. Radiative and Non radiative recombination times of LED are 20ns and
80ns respectively. The drive currentis 30mA.Find the internal power level.
If the refractive index of the lightsource material is 3.7, Find the power
emitted from the device.
19. Explain the principle operation of PIN photo detector using energy
diagram?

3. 20. Define quantum efficiency of a photo detector. Deduce an expression
for the same?
21. What is responsively R of photo detector? How is related to quantum
efficiency?
22. Photos of the energy 1.53*10-9 j are incidenton a Pd which has a value
of R+0.65A/W. calculate the photo generated currentif the optical power
level is 10µm. if the quantum efficiency for the PD is 90%, whatis the value
of the wavelength ofthe lightfalling of the diode ?