Optical source LED by sufiyan a khan

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  1. 1. OPTICAL SOURCE By Prof.Sufiyan A. Khan ACET, ETC Nagpur
  2. 2. What Are LEDs? LED is an acronym for Light Emitting Diode Instead of a filament they use a semiconductor diode which emits narrow- spectrum light. Depending on the composition & condition of the semiconducting material used (Silicone, germanium), they come in either Infrared for sensing heat, Visible for every day use, or Near-Ultraviolet for spotting stains at a crime-scene. An LED consists of a chip of semiconducting material that has been doped with impurities in order to create a p-n junction. A p-n junction is basically a junction between an anode and a cathode. Current flows easily from the p-side to the n-side, but never in the reverse order. The wavelength and color of the LED depends on the band-gap energy of the materials forming the p-n junction.
  3. 3. Where do we see LEDs? Everywhere!!
  4. 4. Current uses of LEDs Status indicators on all sorts of equipment: your cell phone, computer, monitor, stereo Traffic lights Architectural lighting Exit signs Motorcycle and bicycle lights Railroad crossing signals Flashlights Emergency vehicle lighting Message displays at airports, railways, bus stations, trams, trolleys and ferries Military and Tactical missions utilize red and/or yellow lights to retain night vision. Movement sensors LCD backlighting in televisions Christmas Lights Lanterns
  5. 5. LEDs Vs. Incandescents Incandescent Positives Cheap to manufacture & buy Easier to come by Generally stronger light output Better for seeing through Fog and Smoke Negatives VERY breakable Horrible patterns in light Hot burning Heavy on battery consumption Short lifespan Yellowish color filters out anything with yellow in it, IE: White looks yellow, yellow doesnt show, red looks brown, green looks black. LED Positives Virtually indestructible 100,000 hour lifespan Low energy consumption Symmetrical beam with little-to-no artifacts Cheap to manufacture Available in a multitude of colors without requiring a filter. Pure white light means no color will be filtered out. Low functioning temperature Negatives Less potential output (for now) Slightly more expensive to purchase
  6. 6. Potential uses in the future LEDs are already being used in tail-lights for cars, and some companies like Lexus are experimenting with LED headlights Home lighting: Imagine a light-bulb with 100,000 constant hours of use. In other words: 100,000 hours/24 hours a day = 4,166 days 4,166 days/365 days a year = 11.4 years. Not only will the light bulb last for 11.4 years, but it will also require much less current than a traditional light-bulb. If one LED-light bulb requires half the energy of one Incandescent light-bulb, we may not have to suffer through rolling blackouts ever again! LEDs are already getting brighter. Here is an example of one of the most recent LEDs to hit the market titled the Luxeon Rebel. It is both twice as bright, and uses half the current of its predecessor of only 2 years. Technology will eventually dictate that LEDs are the light source of the future.
  7. 7. How will this affect the business world? With the horizons of LED technology broadening, many light manufacturers are putting their top scientists to work: Maglite, for instance, always made Incandescent lights, but have recently begun creating drop-in LED modules for their incandescent torches. If one car company comes out with LED headlights that manage to function at a higher efficiency and also increase output, it is inevitable that all other car companies will follow. Nobody likes a burnt out headlight! Energy is an expensive commodity! The more money we can save on energy, the more money we can spend on more important business aspects. One office building that solely uses LED bulbs could save thousands a year in Energy use alone. When the sun explodes we wont be able to make anymore energy and we will have to rely on LEDs and their efficiency to find food in the pitch black. Impact of LEDs on the world of Business
  8. 8. Light Emitting Diode: LED
  9. 9. What is an LED? Light-emitting diode Semiconductor Has polarity
  10. 10. LED: How It Works When current flows across a diode Negative electrons move one way and positive holes move the other way
  11. 11. LED: How It Works The wholes exist at a lower energy level than the free electrons Therefore when a free electrons falls it losses energy
  12. 12. LED: How It Works This energy is emitted in a form of a photon, which causes light The color of the light is determined by the fall of the electron and hence energy level of the photon
  13. 13. Inside a Light Emitting Diode 1. Transparent Plastic Case 2. Terminal Pins 3. Diode
  14. 14. LIGHT EMISSION / DETECTION 14 Transmission channel Tx E O Rx O E ReceiverConverterTransmitter Converter The principle of an optical communication system
  15. 15. Wavelength range of optical transmission 15 Wavelength [nm] Frequency [Hz]2x1014 3x1014 5x1014 1x1015 Infrared range Visible range Ultraviolet range Fiber optic transmission range Glass Plastic 850 -1630 nm 520-850 nm 1800 1600 1400 1200 1000 800 600 400 200
  16. 16. From electricity to light 16 Conversion from electricity to light is achieved by a electronic : LED (light emitting diode) VCSEL (Vertical Cavity Surface Emitting Laser) LASERS FP (Fabry - Perot) That: changes modulated electrical signal in light modulated signal inject light into fiber media
  17. 17. Light emitters characteristics Main characteristics for transmission purposes: 1 Central wavelength (850/1300/1550) 2 Spectrum width (at power) 3 Power 4 Modulation frequency (consequence of slope) 1 Wavelength nm Power dB 3 2Power/2 4
  18. 18. Spectrum of a LASER or LED source 18 +5 to -10dBm LASER 1-5nm LED Density -15 to -25 dBm 60-100nm Different frequency = different wavelength = different colors
  19. 19. Power 19 Is the level of light intensity available for transmission Average power is the mean value of the power during modulation Power available for transmission is also function of: Fiber core size Numerical aperture Light entrance cone N.A. (Numerical Aperture)
  20. 20. Modulated frequency 20 Is the rate at which transmission changes intensity (logical 0 to 1) Rate is function of time Time is function of slope Slope is characteristic of emitter (technology) LED functions at lower frequency (longer time) LASERS at higher (shorter time) TIME influences modal bandwidth
  21. 21. Emitters comparison 21 Type Cost Wavelength (nm) Spectral width (nm) Modulated frequency Power (dBm) Usage LED $ 850-900 1250-1350 30-60 < 150 < 200 MHz - 10 to -30 F.O. systems Short Wavelength Lasers $$ 780 4 1GHz +1 to -5 CD Fiber Ch. VCSEL $$ 850 1300 1 to 6 5GHz +1 to -3 F.O. Giga speed Lasers $$$ 1300 1550 1 to 6 5GHz +1 to -3 F.O. SM
  22. 22. Emitter characteristics transmission related effects 22 LED VCSEL LASER Over Filled Launch (OFL) Restricted Mode Launch (RMF) Restricted Mode Launch (RMF) Emitters inject light into fiber under different conditions (emitter physical characteristic). Modes travel consequently Power is distributed consequently
  23. 23. Semiconductor Sources for Optical Communications
  24. 24. Considerations with Optical Sources Physical dimensions to suit the fiber Narrow radiation pattern (beam width) Linearity (output light power proportional to driving current)
  25. 25. Considerations with Optical Sources Ability to be directly modulated by varying driving current Fast response time (wide band) Adequate output power into the fiber
  26. 26. Considerations Narrow spectral width (or line width) Stability and efficiency Driving circuit issues Reliability and cost
  27. 27. Semiconductor Light Sources A PN junction (that consists of direct band gap semiconductor materials) acts as the active or recombination region. When the PN junction is forward biased, electrons and holes recombine either radiatively (emitting photons) or non- radiatively (emitting heat). This is simple LED operation. In a LASER, the photon is further processed in a resonance cavity to achieve a coherent, highly directional optical beam with narrow linewidth.
  28. 28. LED vs. laser spectral width Single-frequency laser (


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