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Video over laser

Discussion in 'LEDs and Optoelectronics' started by bigkim100, Jul 27, 2020.

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  1. bigkim100


    Apr 17, 2013
    I would like to send video over a short length (12 inches).
    Is there any way to do this inexpensively?
    I was thinking of using the laser/receiver units of a dvd p[layer, but then I thought that the DVD player may not respond without seeing an actual dvd, and its regional data in its proper place.
    Any ideas?
  2. kpatz


    Feb 24, 2014
    What's the purpose? Can't you use WiFi or Bluetooth?
    bigkim100 likes this.
  3. Nanren888


    Nov 8, 2015
    Free space optical. Google it. Unlikely to get anything under any cost that is sensible for a 300mm link.
    Interesting distance :)

    Definitely worth considering other means?
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Laser in free space? Sounds possibly dangerous, even at low power. You will need to set up measures to ensure no one can look into the beam and possibly damage his/her eyes.
    Definitely worth considering less dangerous alteratives.
  5. bigkim100


    Apr 17, 2013
    To wrap up all your replies, I do have laser goggles, this is an experiment where I cannot use wi fi, or BluTooth, and I can use a ultra-bright LED instead of a laser.
  6. bertus

    bertus Moderator

    Nov 8, 2019
    hevans1944 likes this.
  7. bigkim100


    Apr 17, 2013
    Ok, so I figured out a way to do this, with my own tiny little brain.
    There are composite audio video in composite A/V output units transmission over Fibre Optic sold for security purposes. Hopefully this will work.
  8. Nanren888


    Nov 8, 2015
    Keep the fibre, too.
    The unit will expect that most of the emitted light from the source gets into the fibre and that most of that will come out the other end and reach the sensor.
  9. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Yes, maybe. No, probably. The correct answer depends on the nature of your "video," which you have not bothered to describe.

    My television set has a provision to input "composite video," also known as NTSC video, using a shielded coaxial cable. Typical cable lengths are on the order of one meter or less, usually between a VCR or DVD player and the television set. This is analog video, which is pretty much obsolete today, but if this is the kind of "video" you are asking about, then the answer is definitely "Yes."

    "Video" can be analog or digital. The video information that can be extracted from a DVD is digital in nature, but this video information is not displayable as an image without further digital processing. DVD video is encoded as a serial bit-stream of data, represented as microscopic "pits" on the reflective back surface of the DVD platter. Illuminated by a laser diode, and reflected from the back surface of the DVD platter onto a photo-diode detector, "reading" these "pits" as digital data requires a critical optical alignment. There is a servomechanism within the DVD player that is responsible for positioning the laser diode such that the focus of the beam is optimum for producing a usable digital signal from the photo-diode. The range of motion of this focusing servomechanism is on the order of a few millimeters, about the thickness of a typical DVD platter.

    This is a really bad idea. The DVD player uses a CW (continuous wave) diode laser that focuses to a very small area to allow reflections of the digitally encoded "pits" of video and audio information to be "read" by a photo-diode. The focal length of the laser lens is very short, unsuitable for transmission over distances much more than the thickness of a DVD platter without additional optics. Plus, you have to figure out how to modulate the CW laser beam with your "video" signal and then demodulate the received light beam to recover your "video" signal. That's a lot of trouble just to "send video over a short length..."

    Sure. With a beam expander and perhaps a spatial filter, plus a means of modulating the laser diode with whatever your "video" source is, it is possible that you could transmit a video signal "over a short length (12 inches)" with acceptable fidelity. Depending on laser power, modulation method, and optics on both the transmitter and receiver end, you might be able to reach longer distances, perhaps several feet... or several miles if an unobstructed line-of-sight path exists. This has all been done by amateurs with varying degrees of success. Go visit the Ronja project page that @bertus linked to in post #6 to get some idea of how it is done.

    Ripping apart a DVD player (not necessarily a Blu-Ray player) to salvage and re-purpose the laser diode and photo-diode optics could allow you to build what you want: a device to send video over a short length. You will have to insert a lens with a short focal length after the laser diode to expand its beam to a practical collimated beam diameter, maybe a quarter inch or thereabouts. Most folks use a low-power microscope objective lens for this purpose. A relatively simple convex focusing lens can be used in front of the photo-diode. Once you have the optics aligned and working, all you have do is design a modulator for the laser diode and a de-modulator for the photo-diode. Put this all together for a field trial and... voila! Bob's your uncle. If you can't perform all these tasks, then the answer to your question is probably "No." But good luck on your journey of discovery! And remember to have FUN!
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