How do we repair a broken submarine fiber cable?

On April 22, 2017, one segment of Asia-Pacific Cable Network 2 (APCN2) that serves Taiwan’s major Internet connectivity with Japan, Europe, and America, was broken. According to some news sources, it might take one month just to fix this outage. I live in Taiwan, and I do feel the Internet speed became slow after this outage. I was wondering how could the repairing take one month.

I want to know how to repair a broken submarine fiber cable. I searched on Google and I found this video. This video was created and published by TE SubCom. I summarize the key steps mentioned in this video, and I also added some of my own notes all in this post. I hope this post together with the original video would help you to understand the repairing operation as well.

How could the submarine fiber cable break in the first place?

Other than uncontrollable natural events such as earthquakes, most of the incidents are caused by human. For example, a towed fishing net might tangle with the cable and snap it. Sometimes biting the cable by sea animals might also damage it.

How to locate the broken spot?

In fact, we can use Optical Time-domain Reflectometer (OTDR) to measure the cable length to the broken spot from a known location first, and then determine this spot according to the cable run map.

Repairing steps in this video

1. Cutting grapnel deployed on seabed to cut target cable. (0:23)
2. Holding grapnel deployed on seabed for recovery of cable end. (0:37)
3. Cable end recovered to cable repair ship. (0:50)
4. Buoy launch to mark end of cable. (0:56) I call it End A.
5. Holding grapnel deployed to recover second cable end. I call it End B. (1:42)
6. Cable end is recovered and brought to shipboard jointing shop. (2:02)
7. Initial splice - spare cable is spliced to recovered cable end. (2:11)
   
   I believe in this step we must also examine the recovered cable end and cut remove the damaged portions of the cable. Here I call the new End B as End B’. After this step, End B’ is sliced with one end of the spare cable.
   
8. Millenia Cable Joint Assembly. (2:53) I believe this is a special hardware to protect the cable joint.
9. Cable joint and spare cable are deployed as repair ship moves to recover cable buoy. (3:07)
10. Cable repair ship is positioned to recover buoy and first cable end. That is, End A. (3:16)
11. Cable ship using dynamic positioning to maneuver. I believe this is to ensure the cable slack. (3:31)
12. Final cable splice - First cable end is spliced to the end of the spare cable. That is, End A is sliced to the other end of the spare cable. (4:32)
13. Millenia Cable Joint Assembly. (4:42)
14. Final splice deployment. (4:53)
15. Repair complete - Final splice released. (5:07)

One more thing…

We need special repair ships first before we can do anything to repair the broken cable. However, few such ships are standing by around the globe. It would take days or even weeks just to move one such ship to the location of repair.

We must always include backup paths of cables when we design a submarine fiber cable system. This is what I learned first.

Second, we also know that the spliced fiber would add up attenuation to the signal strength. When we have done enough number of repairing and slicing operations on the fiber, the whole fiber would become unusable and thus be at the end of its life.

That is, any submarine fiber cables have a limited lifetime. We must be prepared to replace the whole fiber cable when it is out of its lifetime.