Fiber manufacturers have to keep in mind the use of CWDM and DWDM(multiple light wavelengths over a single strand of fiber) when constructing fiber cables. They can’t have lightwaves “bouncing around” inside fiber and have it work.
There always is, though. There is no such thing as a perfect fiber, or connector or splice. All induce some loss into the system. This loss is measurable and determines the distance between repeaters, among other things.
With this solar power application, though, it might be desirable to scatter the light inside the fiber.....