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lasers
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by Mesousa_san
on 2006-12-12 23:02:30
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does any one actually know how you can transfer data through lasers and send it to a speaker (like a cd player or a coax cable for a surround sound system) or any cd-rom/dvd-rom?  |
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Re: lasers
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by
on 2006-12-12 23:34:45 (edited 2006-12-12 23:34:56)
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its called fiber optics 
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Re: lasers
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i think mesousa san may be looking for a bit more detail - like how are lasers used to send modulated signals along an optical fiber. i haven't studied lasers to deeply. as i understand it, since lasers have a fixed frequency or group of frequencies in which they operate, laser communications operate using one of the many variations of pulse width modulation. in other words, the laser is turned on and off very rapidly with the shortest possible pulse being just a single wave. pulse width modulation can be used for both analog and digital signals (for example, fm radio is an analog variant of pulse width modulation) but digital signals are the ones generally encoded with lasers. while it is possible to send optical signals directly to your speakers over optical fibers (the riaa would love thant since it would make analog audio signals extremely hard to record), it's impractical. aside from needing entirely separate digal-to-analog decoders in every loudspeaker, the original digital signal would still have to pass through a "de-multiplexor" to separate out each of the individual channels. if you're going to go through the trouble of designing a component to separate out the individual channels and then apply any desired surround sound effects, you might as well put them into the analog domain at the same time. interestingly, audiophiles don't seem to like using optical fiber in their audio systems very much. the bandwidth advantage of optical fiber is trivial with most digital audio signals, and while optical fiber is resistant to electrical interference, modulating and demodulating the lasers adds an additional layer of jitter or digital noise on top of that introduced by the analog-to-digital and digital-to-analog conversions. the best applications for optical fiber are in either extremely noisy electrical environments, or for very high bandwidth (such as high definition video). i don't know about suitability over long distances. i think optical, twisted pair, and coax all need repeaters over long distances. |
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Re: lasers
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The way data is read/written to a cd is different. A laser scans the disk as it rotates. There are many invisible (to the human eye) pits in the disk. The laser interprets the pits and flat surfaces as data to be read. A CD or DVD written using a home burner doesn't actually make the pits in the CD-r, but rather scorches the surface instead, creating a readable surface. A CD-r can only be written over once. A CD-rw has a special "dye" that can be written over multiple times, though storage is evetually lost as the dye is modified multiple times and becomes unreadable.
>,>; Did I just say that...?
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Re: lasers
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same as the admin.  |
