5-optoelectronics

5-optoelectronics - Optoelectronics Photons Meet Electrons...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
Optoelectronics: Photons Meet Electrons Prof. Greg Kovacs Department of Electrical Engineering Stanford University
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EE122, Stanford University, Prof. Greg Kovacs 2
Background image of page 2
EE122, Stanford University, Prof. Greg Kovacs 3 Overview of Optoelectronics Light emission: Incandescent lamps Light emitting diodes Laser diodes Vacuum fluorescent devices Plasma devices Gas lasers Electroluminescent devices Light detection: Photoconductors Solar cells Photodiodes Phototransistors Integrated photodetector chips
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EE122, Stanford University, Prof. Greg Kovacs 4 Lamps - Properties and Uses Incandescent lamps - the most common type used around the house - rely on heating up a thin wire (usually tungsten) to white heat. The resistance of the wire increases with temperature (as do the resistances of most materials) so that it doesn’t have “thermal runaway.” As seen in the original Hewlett-Packard Wein bridge oscillator, a light bulb can be used as a regulator for power or amplitude.
Background image of page 4
EE122, Stanford University, Prof. Greg Kovacs 5 LEDs - Overview Light emitting diodes, or LEDs, are inexpensive, solid-state light emitters. With improved new technologies, they are bright enough that they can be used for illumination (e.g., flashlights) with very little power. They do no emit heat, resist shocks, and last for tens of thousands of hours. They are increasingly being used for traffic signals (red now, yellow and green coming).
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EE122, Stanford University, Prof. Greg Kovacs 6 LEDs - Displays + Annunciators
Background image of page 6
EE122, Stanford University, Prof. Greg Kovacs 7 LED Mechanisms - Nerd Stuff When a forward bias is applied to an LED, electrons acquire enough energy to cross from the n+ through the depletion region to recombine in the p+ region (similar for holes leaving the valence band). Photons are emitted with no phase relationship to each other (incoherent). Very bright LEDs are now commonplace (>3 cd). Direct bandgap, large quantum efficiency (>80%). Typical materials: GaP, GaAs, GaAsP, SiC, etc. p+ n+ Large Numbers of Electrons Large Numbers of Holes h ν Transitions on the n+ side are non-radiative. Electron Injection
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EE122, Stanford University, Prof. Greg Kovacs 8 CATHODE (-) ANODE (+) Bond Wire Epoxy Lens Metal Lead-Frame LED Die
Background image of page 8
EE122, Stanford University, Prof. Greg Kovacs 9 LEDs - Proper Use If driving from a voltage source, should limit current using a series resistor. Need to know the forward voltage of the LED to calculate the resistor’s value. Determine the LED forward voltage, select the current you want (usually not more than 20 mA) and compute R LED . I f V f I MAX = V SUPPLY R I = 0 When all voltage is dropped across the diode R LED = V SUPPLY - V fLED I LED
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EE122, Stanford University, Prof. Greg Kovacs 10
Background image of page 10
EE122, Stanford University, Prof. Greg Kovacs 11 Visualizing Infrared Emitters Infrared-emitting LEDs can be visualized using a CCD camera (such as a camcorder) because silicon detectors are
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/21/2010 for the course EE 5581 taught by Professor Moon,j during the Spring '08 term at Minnesota.

Page1 / 62

5-optoelectronics - Optoelectronics Photons Meet Electrons...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online