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Undersea Cable Repair Via 19th Century Tech
An anonymous reader writes to mention a story going across the wires about an old-fashioned way to fix a modern convenience. Taiwanese boaters are using simple hooks to fish up the fiber-optic cables damaged in an earthquake late last year. The outage that resulted kept millions of users offline in half a dozen countries around the Pacific rim. From the article: "They work 24 hours a day but the weather can hinder their progress. Walters said one ship is waiting for 30 to 40 mile-an-hour winds (48 to 64 kilometres- an-hour) to die down in the Bashi Channel. The winds have stirred up 10 to 12 metre waves ... After arriving at the scene they survey the ocean bottom to assess whether the contour has changed, and the degree of sediment movement. Then the traditional tools are brought out. A rope with a grapnel on the end is played out, down into the depths, and towed over the sea floor until tension registers on a graph on the ship, indicating contact has been made with the cable. Today's fibre optic cables are just 21 millimetres in diameter."
Disclaimer: I used to build the pump lasers for the submarine repeaters so I know something about this. I also have a fibre optics PhD and have made more fusion splices than I care to count.
OTDR only works if there are no isolators in the path. (Gizmos which let light pass in one direction only)
In some submarine cable designs at each repeater there is a return path (ie a fibre loops back) going back the way the light came. I seem to remember this being at an out of channel wavelength (so it passes through some wavelength dependent isolators). Anyway, once you know how many repeaters you do get light back from along this return path you know more about where the break is.
I was surprised by the comment about the cable thickness for working at 2.5 miles depth. The repeater chassis I've seen are steel, coffin sized, and the walls are 21mm thick.
I also have a feeling that todays technology is the same as that of 4 or 5 years ago. There hasn't been that much investment (or new jobs) in new submarine cable tech since the dot-com crash. Maybe it's picking up again now but it will take a while to get the momentum back that we had in the R&D team 6 years ago.