On 6/16/16, jim bell <[email protected]> wrote: > Presumably, the light (probably actually the IR, or infrared) leaves the end > of the fiber, and then reflects off a (very nearby, say 10 micron away) > flat, ultra-thin membrane (perpendicular to the fiber) which has been coated > to make it optically reflective. The resulting reflection re-enters the > fiber, and returns to the source. The light source (presumably a laser) > is then optically-mixed with the reflection IR, and this results in an > FM-modulated signal. Jim Bell
> The way they describe it, they send light down a cable, then watch for the > reflection to come back to them. > The reflection should look the same with every single pulse of light, unless > something affects it, which in this case would be the vibrations of sound. > So it should pick up sound along the entire length of cable, which would > return a lot of ambient noise if you're trying to hear inside someone's > house from all the way back at a utility company. > I don't know how good their audio filtering abilities are, but it seems like > wherever you take measurements can't be too far from what you want to hear. > Looking for stuff I found this post: > http://blogs.wsj.com/tech-europe/2012/09/04/turning-a-fiber-optic-cable-into-a-microphone/ > Is internet cable in house a hot mic?Is it the end of the fiber, the field > around the cable, or both? Without searching for their mentioned acronym and tech, and since any moron can setup what amounts to a $100 optical audio bounce off a glass window pane, be it a tiny polished fiber end or bedroom window... given the frequency limit, distances, and going more exotic, I was thinking audio / groundwave causing lateral physical stress upon the fiber inducing lensing effects possibly detectable by insane OTDR / DSP tech. Then again, I'm insane.
