Just thinking out loud here and I apologize as this is not my field of engineering (Civil Engineers build targets), but I would think that you would need to lay the fiber bundle in a small, highly reflective tray similar to a oversize rain gutter so that you can focus the light on to the fiber array.
But I am sure they already thought of this...
I don’t think a fiber accepts much light in from the sides. Fibers are designed to take light from the ends and shoot it down the length.
Going in from the side with a trough reflector, you would not need the FO, but you could do it with a wire or pipe (for cooling).