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Optical Communication

Optical Communication. From Sound to Light and Back. Apparatus. Sound Waves. Longitudinal Waves. ٭ Longitudinal (Compression): ٭ Waves parallel to direction of travel. Credit: http://www.physicsclassroom.com. Wave Properties. ٭ Amplitude ٭ Frequency ٭ Wavelength ٭ Velocity.

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Optical Communication

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  1. Optical Communication From Sound to Light and Back

  2. Apparatus

  3. Sound Waves

  4. Longitudinal Waves ٭Longitudinal (Compression): ٭Waves parallel to direction of travel Credit: http://www.physicsclassroom.com

  5. Wave Properties ٭Amplitude ٭Frequency ٭Wavelength ٭Velocity

  6. Changing Wave Properties What happens when you change the pitch of the sound? Frequency is changed. How? What happens when you change the volume of the sound? Amplitude is changed. How?

  7. How does sound come from sound waves? ٭Air and other media have matter ٭Matter oscillates when waves pass through ٭Sound Pressure: ٭The deviation in equilibrium pressure caused by a sound wave

  8. How We Vocalize • Vocal Chords are infolded membranes stretched across larynx • Chords come close together, air pressure builds, pushes them apart • “Chopped” flow of air sustained • Steady oscillations create sound

  9. How the Ear Works Credit: http://magnatone.com/HEARIN-HEALTH.html

  10. The Light Transmitter ٭Sound waves enter microphone ٭Microphone is an electret ٭Contains permanently charged plate ٭Sound waves cause plate to vibrate ٭Electrical potential differences caused by vibrations ٭Voltage differences cause light in Light Emitting Diode (LED) to be modulated

  11. Modulation

  12. Fiber Optics ٭Cables made of thin glass or plastic strands ٭Not affected by electromagnetic interference ٭Propagate light over long distances with no energy loss (Total Internal Reflection)

  13. Snell’s Law ٭Describes relationship between angles of incidence and refraction between two different media ٭Media possess a Refractive Index (n) ٭Measures how much speed of light is slowed down by the medium ٭The more light is slowed, the higher its Refractive Index ٭Speed of light in a vacuum = 3 x 108 m/s ٭Refractive Index: n = 1 ٭Same as in air

  14. Refraction and Reflection = Angle of incidence = Angle of refraction Both angles are taken from normal

  15. Snell’s Law

  16. Total Internal Reflection ٭There is a special case of Snell’s Law ٭When going from high density to low density, there is a point after which all of the light is reflected ٭This point is the Critical Angle To Longitudinal Axis: To Normal:

  17. Critical Angle All of the light will be reflected when angle of incidence is greater than the critical angle

  18. Total Internal Reflection ٭Allows optical fibers to carry light very long distances without any loss of energy

  19. What’s Wrong Here??

  20. Critical angle was not exceeded every time

  21. Calculation ٭Find the critical angle to the longitudinal axis in a standard optical fiber. n of cladding = 1.343 n of core = 1.557

  22. Solution

  23. Receiver and Speaker • Photodarlington on receiver converts light energy back into electrical signals • Signals are amplified through circuitry

  24. Speaker * Speakers have both permanent magnets and electromagnets * Electromagnet Composed of magnetic metal wrapped in coil of wire Current runs through wire Creates magnetic field around metal

  25. Speakers • Both types of magnets have polar orientation • Electromagnets can change orientation • How? By changing direction of current Alternating Current (AC)

  26. Speakers • Amplifying circuitry switches electrical signals • Current constantly reversing • Polar orientation changes many times per second

  27. Speakers • Changing polar orientation changes interaction with permanent magnet • Electromagnet will move up and down as current alternates

  28. Speakers Movement of coil causes speaker cone to move up and down, creating longitudinal sound waves

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