High-power fiber amplifiers and lasers are based on rare earth doped, double-clad fibers. In principle, one can inject pump and signal light into such a fiber by appropriately focusing the light, onto a bare fiber end. Industrial laser however, are typically based on an all-fiber setup, where fiber-coupled pump laser diodes are directly connected to an active fiber via passive transport fibers, avoiding any air spaces in the beam path.The transport fibers (which are usually multimode fibers) then require special types of fiber couplers used for interfacing to the active fiber, these are also known as pump combiners. That approach allows for substantially better robustness and stability of the devices.