The invention relates to a coupling unit for optically coupling a multi-channel optical plug-in element to at least one opto-electronic converter of a multi-channel transmitter and/or receiver unit and to a method for inserting optical wave guides into said optical coupling unit. The coupling unit comprises a first coupling side for optical coupling to the multi-channel optical plug-in element, a second coupling side for optical coupling to the at least one opto-electronic converter and a plurality of receiving openings for optical wave guides; said openings being arranged on a plane, extending from the first coupling side to the second coupling side. According to the invention, the coupling unit is embodied in a single piece and the receiving openings extend at least partially inside the coupling unit. The optical wave guides are inserted into the single-piece coupling unit with the aid of an optical plug-in element. The receiving openings of the optical plug-in element are flush with the receiving elements of the coupling unit.