A coupling unit includes a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides. One or more grooves are provided at the attachment area. Each groove is configured to receive an optical waveguide and defined by a bottom surface, a first region, a second region, and an opening. The first region is defined between the bottom surface and the second region. The first region in cross section has substantially parallel sidewalls separated by a spacing. The second region is disposed between the first region and the opening. A width of the opening is greater than the spacing.