Lecture19

Below threshold the diode is led above threshold the

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Unformatted text preview: er diode. Below threshold, the diode is LED. Above threshold, the population is inverted and the light output increases rapidly. light output increases rapidly. population is inverted Georgia Tech Georgia Tech ECE 3080 - Dr.-AlanAlan Doolitt ECE 3080 Dr. Doolittle EE 332 Spring 2013 Semiconductor LaserLED vs LASER? Semiconductor •Light Emitting Diode •Light is mostly monochromatic (narrow energy spread comparable to the distribution of electrons/hole populations in the band edges) •Light is from spontaneous emission (random events in time and thus phase). •Light diverges significantly •LASER •Light is essentially single wavelength (highly monochromatic) •Light is from “stimulated emission” (timed to be in phase with other photons •Light has significantly lower divergence (Semiconductor versions have more than gas lasers though). Georgia Tech ECEEE 332 Alan Doolittle 3080 - Dr. Spring 2013 (through Stimulated emission) (through Stimulated emission) to to Using Mirrors and OpticalLight” “Amplify the Gain “Amplify the Light” The ends of the chip form partially reflective mirrors, which allows the photons to be reflected back and forth and thus be exposed to gain for a longer period of time. The ends of the chip form partially reflective mirrors, which allows the photons to be reflected back and forth and thus be exposed to gain for a longer period of time. Georgia Tech Georgia Tech ECE 3080 - Dr. Alan Doolittle ECE 3080 - Dr. Alan Doo EE 332 Spring 2013 Cavity Modes used in Wavelength Cavity Modes used in Wavelength Selection Selection Cavity Modes Used in Wavelength Selection Wavelengths that are integer multiples of half the cavity’s length can resonate, interfering constructively. Wavelengths that are integer multiples of half the cavity’s length can resonate, interfering constructively. Other wavelengths die out eventually. Other wavelengths die out eventually. Georgia Tech Georgia Tech ECE 3080 - Dr. Alan Doolittle ECE 3080 - Dr. Alan Doolitt EE 332 Spring 2013 Cavity Modes used in Wavelength Selection Cavity Modes Used Selection in Wavelength Sele...
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This document was uploaded on 02/18/2014.

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