Turning optical fiber cable into microphone
Looking for stuff I found this post: http://blogs.wsj.com/tech-europe/2012/09/04/turning-a-fiber-optic-cable-into... Is internet cable in house a hot mic? Is it the end of the fiber, the field around the cable, or both? Thanks in advance :D
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.
On Thu, Jun 16, 2016 at 1:56 PM, This 1s
Looking for stuff I found this post:
http://blogs.wsj.com/tech-europe/2012/09/04/turning-a-fiber-optic-cable-into...
Is internet cable in house a hot mic?
Is it the end of the fiber, the field around the cable, or both?
Thanks in advance :D
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
From: Blake Hadley
On 6/16/16, jim bell
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... 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.
Jason McVetta: special equipment & dark fiber
grarpamp: morons with OTDR / DSP tech.
jim bell: light + reflection IR = FM-modulated signal.
Blake Hadley: send light down a cable, watch for vibrations of sound along the length of cable in the reflection
measurements can't be too far from target
Thanks! I wonder if my ISP are morons and how well they can clean up all the noise :P -- This1s
On Thu, Jun 16, 2016 at 10:56 AM, This 1s
Is internet cable in house a hot mic?
I doubt it. Sounds like this needs some pretty special equipment at the end of the fiber. Also not clear that it can be used concurrently with data transmission over the fiber. Could be that the company is lighting up unused fiber? Cheap way to get audio surveillance along a vast stretch of pipeline that happens to have some dark fiber sitting beside it.
participants (6)
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Blake Hadley -
grarpamp -
Jason McVetta -
jim bell -
Spencer -
This 1s