Do fibers have losses?
Everything in the universe is inefficient. It means that while a measured amount of something enters in a system, less comes out than initially went in. When you pour a liter of water in one end of a pipe, then you will always find less than a liter out of the other end. When you apply a voltage to the extreme of one wire, it doesn't matter how you do this, you will find a lesser value at the other end.
Fiber optics are no exception that the light entering one end encounters all types of obstacles and flaws, which are resulting in losses; from 2 to 10 percent for every running meter.