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Sending Information By Laser

  1. Jan 7, 2010 #1
    Is it possible to send information by laser? If so, how much faster is this than radio signal?
  2. jcsd
  3. Jan 7, 2010 #2


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    That is what the fiber optic networks are.
    Same speed 299,792,458 metres per second.
  4. Jan 8, 2010 #3
    I dont know what you mean by faster but if you mean speed well they are both electromagnetic waves so they both travel at the speed of light (speed indicated above^) if you mean faster as in more information? well it could go either way, just depends on what kind of technology you are using as a reciever for each one
  5. Jan 8, 2010 #4


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    Just to split hairs, the speed of light in a fibre is 299,792,458 /1.48 (m/s) so rather slower than a radio signal.
  6. Jan 8, 2010 #5
    The speed of light in an optical fibre cable would be a lot slower than in a vacuum. The refractive index of the fibre is around 1.5
  7. Jan 8, 2010 #6


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    Not faster, but a lot more efficient. A radio signal sends a wave out in all directions, and some tiny amount of that radio energy happens to intersect with the antennas of the people who are trying to receive. A laser can be pointed directly at the receiver, and a much greater fraction of the original power of the signal would reach the receiver.
  8. Jan 8, 2010 #7
    Laser signals have been sent to the Moon at the speed of light, and reflected back to Earth by a retroreflector (corner cube) at the speed of light for doing laser-ranging studies.
    Bob S
  9. Jan 8, 2010 #8
    Some SETI types would suggest we'd send data to an advanced, interrstellar species by means of a laserbeam....
  10. Jan 8, 2010 #9


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  11. Jan 9, 2010 #10
    In terms of information rate, optical transmission is capable of being faster, because the carrier frequency is very much higher than for radio. The wavelengths commonly used for fibre optics are around 2*1014Hz, whereas ordinary radio only goes up to a few * 109Hz, or maybe a couple of orders higher for extreme microwave.

    Things get really exciting in optical fibres when multiple carriers are used, 100 or so, each carrying 10Gbit/s or more. This makes it practical to have cables running at Tib/s rates.
  12. Jan 9, 2010 #11


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    But the limit is how quickly you can modulate the signal and how much bandwidth your detector has.
    OC-48 is the most common at 2.5GHz. You can go faster than this but the fiber dispersion reduces the range very quickly as bandwidth increases - the hardware also gets very expensive.
    DWDM lets you put 128 or mode signals at slightly different colors down the same fibre (equivalent to different TV channels) but they are so close together in the optical that you can generally reuse the same fibre - boosting it's capacity by 128x
  13. Jan 10, 2010 #12
    Yes, dispersion is a key limiting factor - its management is a serious problem. The detail of this is not my subject, but currently mature technology uses a mix of fibre types with opposing dispersion. As I understand it, it is actually better to allow the signals to become dispersed along the line, until just before reaching the detector, when full compensation is applied.

    Despite this difficulty, for Submarine cables, products using 10Gbit/s modulation per wavelength on a 100-plus wavelength DWDM have been in commercial production for a few years. The multiplexed signals are transmitted using Optical Amplifiers spaced every 100km or so along cables spanning transoceanic distances.

    Just in case you think that this is all a fisherman's tale, try looking this up:
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