There's no way you're getting through that without it being service affecting. Even once you get through the layers of protective sheathing, and around the copper power lines that provide power to the undersea amps, you're suggesting that they fully remove the reflective sheathing to bend the fiber and tap off light? That is absolutely ludicrous. The process would introduce much more span attenuation than splicing in a 50/50 fiber tap (which is 3db).
Are you doing this to every fiber in the bundle, you'll need at least two tapped to get bi-directional communication. It's simply unfeasible.
The NSA loves when people think this thought.
At some point the signal must
a) be converted from electrical to optical
b) be boosted down the wire
c) be converted from optical to electrical
Easiest solution? Tap in at A, B or C.
Who's going to notice that your repeater at the bottom of the ocean actually has a NSA listener plugged into its debug socket?