This is so neat! Few questions though, if anyone can answer:
1) The cable still looks pretty thin, is it being housed in some sort of protective layer/tube before it is laid? Seems like an anchor snag could easily break that line. If that happens, is it possible to 'patch' a fiber cable?
2) Once it nears the coast, how deep is the line being buried?
3) This may be a dumb question (I'm no engineer), but does the light travel from the source all the way to end without any "relay" mechanism?
4) How much bandwidth can travel through one of these lines?
1) The fibre pairs are housed in multiple layers of armor to protect against the elements, supply power to inline amplifiers and -most notably- provide the structural strength needed to survive being deployed. Outside diameter is still less than one inch, though.
2) Depends, but a metre or two (tops!) would be the right ballpark.
3) Not a dumb question; while loss in fibre optic cable is very low, repeaters are installed at regular intervals along the cable. they are powered by high-voltage DC supplied through the cable armor. The ocean acts as the return path.
3) is wrong. The amplifiers are powered by DC, but one side of the fiber provides positive voltage and the other negative - the ocean is not a part of the circuit.
I was under the impression that cable systems are best understood as constant-current systems. As a side effect of this, they can withstand a power failure at either end, in which case the ground path is part of the circuit. (Essentially "single rail" operation.)
If nothing else, both ends still share a common ground reference, yeah?
-You are right; I just looked it up. I guess (not that it makes much of a difference!) I picked this up from a book on earlier days of submarine cables.
>"3) Not a dumb question; while loss in fibre optic cable is very low, repeaters are installed at regular intervals along the cable. they are powered by high-voltage DC supplied through the cable armor. The ocean acts as the return path."
That's incorrect, amplification is done via Erbium doping, it is part of the core of the cable. There are no external repeaters.
So to clear this up a bit.
EDFAs (which are the in-line amplifiers which use erbium doping) work by having a section of a fiber doped with erbium ions. Only the part which is going to amplify the signal is doped, the rest of the fiber is supposed to be as clean as it gets.
Those erbium ions get shot with a laser (that's the part that needs power from the shore) and get excited. The source signal then hits the ions, which then emit more photons of the same exact properties, but just way more of them - therefore the amplification part.
Continue 80km down the line, and the same thing has to happen again, as enough light has been attenuated.
I mostly work with land systems, where the EDFAs are pieces of equipment completely separated from the fiber - you get a normal strand of fiber dug into the ground, and once you want to amplify it, you've got to plug it into an EDFA line card with the erbium-doped fiber already contained in it.
In the sea, those systems are way more integrated and the fiber is usually spliced right into the amplifier.
I might be able to dig up a card tomorrow if you're curious as to how the system looks.
1: I think they don't put that thin cable on the seafloor, they are bunched together, in a much bigger cable with a lot of stuff around it [0] to protect it.
About the patching, they say that in the article: they sometimes cut the cable (in case of a bad weather) and attach it to a buoy. So they can "patch it" ;)
1) The fiber is pretty thin, but there are several fibers combined in one transoceanic cable, see here https://en.wikipedia.org/wiki/Submarine_communications_cable. They don't patch them, but splice the fibers. Patching introduces a little loss, so it should be avoided.
2) Not sure how deep they are buried, but I think to remember that the shore end of a submarine cable is better protected than the part in the deep ocean. Due to more ship traffic at the coast etc.
3) Good question. The loss of an optical fiber is roughly 0.2 dB/km. Across the ocean the optical signal must be amplified several times (every 80-100km). Nowadays the amplification is all optical (EDFA or Raman). Before there were electrical regeneration schemes. Check out the history of the field, it's is quite interesting [1].
4) Not sure how much data such a cable can carry, since it depends on how many fibers are deployed within. However, there are multiple interesting things to look into here. In research labs, people are investigating multicore/multimode fibers (space division multiplexing) [2], these fiber have incredible capacity. Personally, I think the most interesting metric is the spectral efficiency, so how much data can be transmitted per second per Herz. Such a metric is independent of multiplexing schemes over space/wavelength/time, and improvements have to come from better devices, signal processing or signal shaping methods [3]. Another mind-blowing area is using the nonlinear Fourier transform for better signaling methods [4].
Feel free to ask more questions :)
and checkout the two biggest conferences for more in depth info.
With a degree in Optical Communications, are you trying to go into Optical Engineering or pursue further education in academia? How is the salary for the engineer compared to software?
I received my PhD in December, so I already pursued further education. My masters was in telecommunications, starting my PhD with a background in signal processing/information theory rather than optics/physics. All the master students I supervised either had similar background like me or an optics/physics background. That said, optical communications combines multiple disciplines, which makes it so fascinating, and I think that a PhD is inevitable if you want to pursue a career here. There are so many steps to understand to get from bits to electrical signal to optical signal and all the way back to bits. I don't think a masters degree can cover all of it in depth. Further, a PhD is in particular helpful due to the conferences where all the big players are looking out to hire you, or where one meets senior researchers for potential postdoc positions.
Salary-wise it's difficult for me to answer, as most of the big industry players are in the US or Canada, but I'm in Europe. From hearsay a fresh PhD with reasonable publication list will get around 10k per month in the bay area. However, glassdoor might give you a better idea. Look for companies like: Infinera/ciena/acacia communications/juniper/mellanox/finisar/keysight...
After my PhD, I probably could have pursued a postdoc somewhere in Europe, but I decided to leave academia. I wanted to stay in Copenhagen and therefore had to change my field of work and will be working for a hearing aid company in their signal processing department.
Make window fullscreen, press Windows-G on a Windows 10 computer with halfway good graphics card. Pump it into VLC and crop away the stuff you don't want ... and profit? :-)
That animated image is made up of a canvas background of the world and an SVG foreground of the cables. Both are created using js from downloaded json data, ne_110m.json and fusion-cables-2019-02-27-simplified.json. Quite tough to get that into something that's not using pixel graphics and self-contained (aka only displaying the stuff in the page).
I'm on an iPad at the moment so I can't give you a direct link to any videos, but search for Hibernia Atlantic on Youtube. They have some short videos showing how the cables are laid, repaired, and so on.
1) The cable still looks pretty thin, is it being housed in some sort of protective layer/tube before it is laid? Seems like an anchor snag could easily break that line. If that happens, is it possible to 'patch' a fiber cable?
2) Once it nears the coast, how deep is the line being buried?
3) This may be a dumb question (I'm no engineer), but does the light travel from the source all the way to end without any "relay" mechanism?
4) How much bandwidth can travel through one of these lines?