Free Space Optical using LED as opposed to Laser

Discussion in 'The Projects Forum' started by lozza3951, Jan 15, 2015.

  1. lozza3951

    Thread Starter New Member

    Jan 15, 2015
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    Hi all,

    I am looking for some technical assistance with a current project I have been tasked with.

    The project requires the construction of a working Free Space Optical (FSO) link. Although exact distances have not been stated as yet, it is hoped to achieve somewhere in the region of 500m to 1km. Most traditional FSO systems utilise a Laser as the light source but I have been tasked with experimenting with the use of high powered LEDs.

    The end system needs to be required to transmit/receive data bi-directionally at low speeds of around 1Mbps.

    Does anyone have any knowledge or experience in designing circuits that may be possible of achieving this? I have looked at the RONJA systems online but they seem to be very complex and manpower intensive.

    Any help is massively appreciated!!

    Lauren
     
  2. MikeML

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    Last edited: Jan 15, 2015
    Bernard likes this.
  3. lozza3951

    Thread Starter New Member

    Jan 15, 2015
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    Thanks very much Mike.

    If anyone else would like to add further information I am very appreciative!
     
  4. crutschow

    Expert

    Mar 14, 2008
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    A LED would be difficult to use for this task since it doesn't put out a narrow coherent beam of light that a laser does, so it's difficult to focus the light into the narrow beam required to transmit long distances. It likely will require much more power than a laser system.
    Good luck.
     
  5. MikeML

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    However, as Clint shows in this article, the LED is much better at carrying modulation than is a laser because of scintillation. That might not matter in space.
     
  6. wayneh

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    My first boss taught us to always ask, "Why?" It seems an obvious question here: Why deviate from proven technology?
     
  7. MikeML

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    I just answered this:
    "However, as Clint shows in this article, the LED is much better at carrying modulation than is a laser because of scintillation."
     
  8. alfacliff

    Well-Known Member

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    at a ham club meeting about 7 years ago, some guys were demonstrating leght beam communications using led's with telescopes, worked pretty well.
     
  9. wayneh

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    I'm curious why the OP is looking at this. Maybe someone else read Clint's article as well.
     
  10. lozza3951

    Thread Starter New Member

    Jan 15, 2015
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    I have asked that question to the project proposer and they have their own reasons behind using LEDs as opposed to Laser so unfortunately this is a must for this project.

    Had a meeting with them today and we are now looking at just a basic one way working system with a simple transmitter at one end of the link and a receiver at the other.

    Also we are playing around with the idea of implementing the modulation/demodulation part of the system using FPGA's as opposed to PCB's and component level electronics. There is quite a healthy budget available for the project so we are not restricted on what products we can buy.

    The basic system block diagram at the minute is looking something along the lines of:

    Transmitter
    I/O Device (Probably TCP/UDP) >>> FPGA BOARD (To modulate the data and drive a high current to the LED) >>> LED ARRAY >>> FRESNEL LENS ------ free space

    Receiver

    free space >>> SPOTTING SCOPE >>> PHOTOSENSOR/PHOTODIODE >>> FPGA BOARD (To de-modulate the data) >>> I/O Device (TCP/UDP)

    Now i am sure it is probably far more complex than I am making out but this is just an initial idea. Thankfully we have until April to deliver the project so i have plenty of time for learning!!

    Lauren
     
  11. bertus

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  12. wayneh

    Expert

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    And they won't share their reasoning with you? Hmmm...that would drive me nuts, to have hidden objectives.
     
  13. lozza3951

    Thread Starter New Member

    Jan 15, 2015
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    I think they just want to try something different. I know LEDs do have some advantages over Lasers and vice versa.
     
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