We developed an all-fiber component with a signal feedthrough capable of combining up to 6 fiber-coupled multi-mode pump sources to a maximum pump power of 400 W at efficiencies in the range of 89 to 95\%, providing the possibility of transmitting a high power signal in forward and in reverse direction. Hence, the fiber combiner can be implemented in al-most any fiber laser or amplifier architecture. The complete optical design of the combiner was developed based on ray tracing simulations and con-firmed by experimental results.