Submarine Cable Map • Hacker News Board

Re: Submarine Cable Map

#111

Post by hobbes » Wed, Feb 29, 2012, 2:08 PM UTC

mgkimsal wrote: post #109

Two random thoughts: 1. I'm always amazed that anchors can seemingly hit a cable at the bottom of the ocean floor. Given how hard it usually is for us to find anything on the ocean floor with any precision, we seem to be able to drop anchors and cut cables with surprising accuracy. 2. Do the cables have slack in them to account for continental drift? I don't know how much we drift, but I'd imagine over time the cable…

1. The beach, where my 5-year old paddles in the water, is also the ocean floor. Can get fairly shallow.

Re: Submarine Cable Map

#112

Post by maaku » Wed, Feb 29, 2012, 6:20 PM UTC

kijin wrote: post #77

maaku wrote: post #71

Earlier quoted context omitted.

Most cables don't run on the seabed.

Umm, then where do they run? They can't float in the middle of the water.

Uh, yeah they do. Often they hang from a buoy, floating in the middle of the water.

Re: Submarine Cable Map

#113

Post by Nrsolis » Wed, Feb 29, 2012, 10:30 PM UTC

saulrh wrote: post #74

Nrsolis wrote: post #72

Earlier quoted context omitted.

That's not strictly true. First, most EDFA (Erbium Doped Fiber Amplifiers) need power to operate since the lasers that perform the pumping action are local to the doped sections of fiber. Second, most submarine cables make extensive use of Raman amplification which leverages the transmission fiber as a gain medium via forward or backward pumping of lasers with frequencies chosen to produce Raman gain. In both cases,…

Huh, didn't know that. I stand corrected. That Raman amplification is nifty. :D

Raman amps are pretty cool but tricky. For one thing, the power required is pretty high. +1W dBm isn't uncommon for certain Raman amps. At those power levels, you need to be careful you dont cause burns to personel when they are working on the equipment.

The power to run the lasers is usually carried on conductors that are part of the cable itself. The voltages are somewhere in the several kilovolt range so laying submarine cable is also kinda like laying a high-volage transmission line across the ocean.

Re: Submarine Cable Map

#114

Post by tomkinstinch » Thu, Mar 01, 2012, 5:00 AM UTC

jleader wrote: post #82

tomkinstinch wrote: post #46

Earlier quoted context omitted.

They are "powered" by lasers themselves. No electronics involved; excess energy from a pumping laser boosts the intensity of the data laser, using sections of special doped fiber. http://en.m.wikipedia.org/wiki/Optical_amplifier#Doped_fiber...

That's very cool, but the "submarine communications cable" article I linked to above claims that the repeaters are powered by DC fed through a single conductor in the middle of the cable, though it doesn't cite a source for that information. I wouldn't be surprised if both methods have been used in different situations or at different times. Are you saying that there's an extra "pumping fiber" in the bundle, fed by a…

The DC may be likely for old-style repeaters, as Er-doped fiber amplifiers are (relatively) new.

It's my understanding that the pumping laser would be a different wavelength carried by the same fiber (just as a fiber can carry multiple data channels using different wavelengths in DWDM). The boost happens because of the special doped section.

Laser pumping is used extensively in laser physics, at places like the NIF: https://lasers.llnl.gov/about/nif/how_nif_works/injection_la...

The pumping laser essentially puts the doped medium in an energy condition where the data transmission can stimulate additional emission (similar to how lasers work in the first place). Few photons in, many out. The energy required to do so comes from the pumping laser.

http://en.wikipedia.org/wiki/Laser_pumping