Optical Line-Out Red Light?

Discussion in 'Mac Pro' started by hidea, Feb 2, 2007.

  1. hidea macrumors regular

    Joined:
    May 10, 2006
    #1
    I have a question,

    why is there a red light lit on the optical out port at the back of my mac pro?
     
  2. Erasmus macrumors 68030

    Erasmus

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    #2
    Now I'm done chuckling,

    Optical (as pointed out before) is relating to the use of light. That means there is no electricity coming out of the port. Very short light pulses, generated I imagine by a laser, or maybe some kind of LED, are transmitted down an optical fibre from the computer to whatever it's plugged into. The audio signal is encoded in these light pulses, just like they would be if electricity was used instead.

    Of course, if you're wondering why the light's on when you (I'm guessing) don't have anything plugged into it, I can only guess it's making sure it knows the second you do plug something in, or making sure whatever you plug into it knows that it now has to take orders from the new big boss ;)
     
  3. Erasmus macrumors 68030

    Erasmus

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    #3
    Hmmm... I seem to remember there were a lot more posts in this thread last time I was here...

    Question on similar topic... Do fibre channel network cards (Those things that you can get for the Mac Pro) glow when they don't have anything plugged in, and if so, are they red, or multi-spectrum white?
     
  4. EricNau Moderator emeritus

    EricNau

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    Apr 27, 2005
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    San Francisco, CA
    #4
    Yes, there were. :confused:

    I believe they use a laser, although I can't remember if it's visible or not.
     
  5. pseudobrit macrumors 68040

    pseudobrit

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    #5
    It's an LED. More here:

    http://en.wikipedia.org/wiki/TOSlink

    edit: the LED being illuminated is its normal status (check the back of just about anything with an optical digital out port). As soon as it's connected to a source waiting for signal it will deliver data.
     
  6. pseudobrit macrumors 68040

    pseudobrit

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    #6
    It's infrared (1300 or 1550nm for SMF), so it's not visible.
     
  7. Erasmus macrumors 68030

    Erasmus

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    #7
    Cheers for the info. A bit wierd that it would be infra red, considering the massive bandwidth advantages of being red, blue, or even multi-spectral.
     
  8. Cybix macrumors 6502a

    Cybix

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  9. apple_iBoy macrumors 6502a

    Joined:
    Oct 28, 2003
    Location:
    Philadelphia, PA
    #9
    On a related note, how about that optical line-in? I tried hooking it up to my cable box's optical line out, hoping I'd be able to record myself some cool tunes from MHD. Just got gibberish though.
     
  10. orangezorki macrumors 6502a

    Joined:
    Aug 30, 2006
    #10
    If it's coming from a cable box, would it be encrypted?

    David.
     
  11. Sdashiki macrumors 68040

    Sdashiki

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    Location:
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    #11
    but i dont think this has anything to do with bandwith in that sense.

    because isnt the optical just doing what a CD laser does?

    reads pits and smooths as 0s and 1s.

    so, couldnt the optical just be on for 1 and off for 0? with some sort of timing scheme to count the amount of 0s or 1s that are in a row?
     
  12. dkoralek macrumors 6502

    dkoralek

    Joined:
    Sep 12, 2006
    #12
    I don't think that there is any encryption on audio (super audio cds, though do require that you have six-channel input, iirc).

    cheers.
     
  13. Erasmus macrumors 68030

    Erasmus

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    #13
    The point is how fast you can switch the laser on and off. When the light pulses start getting anywhere near the size of the wavelength of the light being used to transmit the signal, wierd stuff starts happening, which ends up screwing with your signal. This means the amount of data you can transfer per second is proportional to the frequency of the light you are transmitting it with. That means if you use a blue laser, you can probably pump about twice as much information down an optical fibre than you can with an infra red laser.

    If you have an infra red laser, a red laser, a yellow, blue, purple, etc. all travelling down the one fibre, you can separate them (or combine them at the beginning) using glass prisms, and easily boost the amount of data you can send down one piece of optical fibre enormously. This is of course because you can break up data into streams, and use each colour to send different lots of data down the fibre simultaneously.

    The frequency of light is so high that even infra red light should be capable of transferring huge amounts of data per second, but the point is it does have a limit. That limit could be as high as TBps, but if you want to push that, for example networking really fast computers (like 8 core Mac Pros) then even that limit might be pushed. OK, maybe not, but it won't last forever, and a new standard will have to be developed. With a bit of luck, it will use *insane physics alert!* supercontinuum generation in short pieces of PCF to create very spectrally broad light pulses that are still very short in time. This would enable huge amounts of data to be transmitted as even a full octave of light frequencies can be used to transfer data simultaneously. *end of insane physics!*

    So, yeah. I think I've made my point. Infra red obviously works today, but it won't in the near future. Think that the soon to be released ATI/AMD R600 GPUs will most likely have bandwidth requirements of over 150 Gbps.
     

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