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Comment by dustfinger | Hacker News Reader

> By shining a laser through the fiber optics, the scientists could detect vibrations from above ground thanks to the way the cable ever so slightly deformed.

> Civil engineers are already using DAS to study soil deformation, and biologists are even using offshore fiber optic cables to listen in on whales. (Sound propagates as a vibration, after all.) “It's just really exploding in terms of the applications,”

I wonder if ISPs are using residential fiber as an optical microphone [1] array to listen to their customers? If they are not, then I could see this as a future threat. I wonder how one might inexpensively insulate a fiber-optics cable to prevent unwanted eavesdropping.

[1] https://www.sciencedirect.com/science/article/abs/pii/092442...

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The real world answer is 99% of consumers carry a battery powered microphone and GPS beacon with remote telemetry, so there's no need.

Some also pay money to put internet connected microphones in their house.

I'm a layman network tech with no college degree and no grasp of physics beyond very-high level high school science, but I can almost guarantee getting voice audio from a fiber drop on a GPON network where the NID is outside or in the basement, and using the setup in the paper, is currently impossible. The paper you linked seems to require purpose-built hardware on either end of the fiber, and for the transmit strand to reflect into the receive strand, which is not at all how GPON works.

The paper I linked was also from March 1991. I imagine that the technology has changed since then. Here is another article on fiber optic microphones designed for operation in harsh environments [1]. It is from 1999.

[1] https://ui.adsabs.harvard.edu/abs/1999SPIE.3852..106K/abstra...

The abstract on that paper makes it seem like the study pertains to medical equipment, not telecommunications.

Photonics engineer here: DAS isn’t sensitive or spatially accurate enough to eavesdrop like that. Also, fibre is very rarely to the home. Normally it’s to a connection box just outside the property and then co-ax to the modem. Lastly, fibre telecoms uses lots of repeaters and switches that DAS can’t see past (needs optical line of sight).

Thank you for your insight, those are all great points. The fiber to my home physically runs through my home to a box that is located inside of my home. I didn't realize that most people have the box located outside of their home.

I've had fiber into an apartment and into my current home. I don't think it is that unusual.

At least in some European countries fiber goes to a GPON terminal in the apartment and then proceeds via Ethernet cable to the home router.

I'd guess the co-ax cable is probably a US-only practice.

Virgin Media (UK) use coax. There are some FTTP installs (with coax to the router), but most, as far as I'm aware, use coax for the last leg to the house and from the wall to the router.

I've just had BT FTTP installed, and have a fibre coming into the building. They use GPON. It's wired into a modem ("Optical Network Terminal") that Openreach provide, which then presents the connection via cat5. You then plug your router in, which then uses PPPoE to establish the connection.

I was speaking from a UK perspective which, as another commenter says, is mostly co-ax from a point on the pavement. 'Actual' FTTP is coming in now, like HyperOptic, starting with apartment blocks where they can get lots of customers per one new civil engineering job. Most consumer telecoms fibre networks in the UK were laid in the 90s and don't go right to the home.

If you're in the lucky situation of having true FTTP, then it's still very unlikely such fibre could be used as a 'microphone' because of the sensitivity and spatial resolution issues. It would also be pretty obvious it was being used because it would probably interfere unless they were very careful with bands. So don't worry, DAS isn't going to be used to listen to your voice. Much easier to do that with your phone!

By the same principle it should be possible to listen to reflections of the signal propagating in the Ethernet cable that external vibrations introduce. But I guess the noise in the cable is much greater and the frequency of the signal is like 6 order of magnitude smaller making this mostly theoretical.

In the US it’s not called fiber if there’s coaxial in the line. If that were true everybody with a cable modem would essentially have fiber.

> In the US it’s not called fiber if there’s coaxial in the line

My FIOS ONT has a coax out, so that's probably not entirely true.

Yeh that seems to basically be what we call fiber in the UK!

When I lived in Chattanooga back in 2011, the Electric Power Board offered fiber to the home with an offer of a Gigabyte up and down---hence the original use of Gig city for Chattanooga. I think this was even before Google showcased fiber to the home (was it in Oklahoma City at first? I don't recall)

We had to have a router with a fiber port to connect, then Ethernet via cat 5 or WiFi.

Any idea if the fiber being used for DAS is simultaneously capable of carrying data, or do they pick a strand that is unused?

There are a few different flavours of physics you can use for DAS, and they 'use up' different areas of the spectrum. As long as what you want to do for telecoms is using completely separate wavelengths (channels or bands) then yes you can do both. Most DAS providers and users prefer to just use un-used/dark fibres though as it avoids any headaches.

I have fiber to my home. It runs from the side of my house back to a box at the edge of the park down the street. Inside that box its combined with the feeds to all of my neighbors into a smaller number of runs back to the CO. On the side of my house is a steel utility box that contains an ONT which converts the signal into ethernet. The ethernet cable runs to the other end of my house where I have a router.

I guess theoretically it could sense when I operate the garage door and drive in and out, maybe if I take out the trash. But the fiber runs through conduit. And given they way the fibers are multiplexed down the street in practice its hard to infer much from that fiber.

Same here, the fiber gets to my home.

At least for me, my fiber install is fully inside my house.

My ONT (buried inside a BGW-320 that I can't bypass -_-) is fully inside as well. I think a lot of AT&T's setup is going this route as well from what I've read.

ISPs can’t get residential fiber to work in many cases, using it as a microphone is beyond mass capabilities.

Not to say that if the alphabet boys are interested in you they might do something similar (but in that cases there are likely cheaper methods).

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