8th Sem Subject Ofc 3rd chapter notes by Lohith kumar 11GUEE6018
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This document discusses photonic sources such as light emitting diodes (LEDs) and laser diodes. It covers their basic structures and working principles, as well as key parameters like quantum efficiency, threshold calculations, modulation, and modes of operation. Some specific topics covered include double heterostructure LEDs and lasers, distributed feedback lasers, spontaneous vs stimulated emission, and comparisons between different laser structures and between lasers and LEDs. The document also contains 22 questions asking about structures, energy band diagrams, output power variations, single mode lasers, materials used, photodetector parameters, and calculations involving quantum efficiency, responsivity, and generated photocurrent.
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 ?