No, it is not recommended to mate a high-power optical fiber with a low-power one. Low-power fibers are not designed to support hundreds of watts and are generally smaller than high-power optical fibers. The modal mismatch between the two cables will give rise to substantial energy loss localized at the ends of the fibers. This results in the heating and sometimes even the burning out of the fiber outputs. It is also not recommended to use a mating sleeve as that increases the risk of damaging the fibers.