Roar of cicadas was so loud, it was picked up by fiber-optic cables

Brood X made itself known in a way that could change how we monitor insect populations.

See full article...

 

[tonylurker]

"“We use them just to transmit the data—zeros and ones—but we can do much more,” says Ozharar. “That’s why fiber sensing will become more and more important, and more widely used, in the near future.”"

Question is what changes will need to be made in this fiber that both preserves it's original function and the additional functionality?

No changes need to be made to the fiber for it to work. Now if you want to optimize sensitivity, you can come up with changes to the fiber that will get you a few dB. There is also the question of whether you need a dark fiber, or whether this will work alongside other fibers in a WDM link. Or, more specifically, how well this will work in a WDM link when kept to a power low enough not to interfere with the other channels, or what changes to optical filtering would be necessary to make sure it all works together properly.

 

[tonylurker]

Is it just me or did this article arbitrarily decide to call OTDRs "interrogators"? Are they using some novel new device for DAS?

While there are several ways to do DAS, what is being described in the article is similar to an OTDR, but quite different. In an OTDR you send a broadband pulse of light down the fiber and look at the intensity of the return. With an OTDR, all you see is the Rayleigh scattered light and large scale effects like a source of loss, or a reflection from a break or connector. In an OTDR based DAS, you send a pulse from a narrow linewidth laser and use coherence effects of the return light to detect changes in the fiber. because the light in pulse has a long coherence length, you get interference between the light scattered back from different sections of the fiber that arrive at the detector at the same time. In addition, the phase of the returned light will change from pulse to pulse as the fiber is stretched or bent.

There are many ways to use this technique to detect vibrations and sound. The most basic version of this would be to send the light down, measure the optical intensity of the reflected light from each pulse, and just rely on the fact that as the fiber is stretched or bent, the coherent interference of the light returning from that area of the fiber will change, so the intensity will change from pulse to pulse. For a more complicated and sensitive version, you would use some form of coherent detection to detect the change in intensity and phase of the reflected light. There are dozens of these systems out there being produced by multiple groups for commercial and research purposes (perimeter defense, pipeline protection, "smart infrastructure", etc.). For a while the Oil and Gas industry was putting big money into this for their applications, but I don't know if they still are.

edit: by dozens of these systems, I mean versions/brands. There are probably hundreds (or more) of these systems on fences, pipelines, or just in labs. (The commercial ones for fences and pipelines can be rather expensive (few hundred thousand $), the no frills systems are closer in price to a modes luxury car).

 

[tonylurker]

Laying fiber alongside all the highways and streets isn't a bad idea, though.

I mean, it should be easy to determine the difference in local vibrations between "no traffic," "normal traffic," and "a bunch of people sitting in one place with engines idling." That could pinpoint the location of traffic jams and accidents on a continuous basis. Local emergency services could be notified of at least some accidents automatically, without waiting on someone to report them. The same thing goes for mobile map apps routing around traffic jams.

Even better, the info could be used to adjust timing and synchronization of traffic signals depending on how heavy traffic is, so you don't back traffic up as much during rush hour, but you don't have to wait forever to cross the main streets during off-peak traffic.

Most fiber runs along streets already (or railroads or some other existing right-of-way). Groups have written papers talking about using this technology on existing fibers for similar purposes. I'm pretty sure I saw a Princeton-NEC-Verizon talk about an experiment doing this in some urban area at a fiber optics conference I went to in the pre-COVID days. I did a search and here it is.