An output/input coupler for multi-mode glass fibers characterized by a substrate and a main line having a square cross section disposed on the substrate and having at least one branch line extending on said substrate therefrom with the branch line having a rectangular cross section smaller than the cross section of the main line and having one surface coplanar with the surface of the main line. The branch line may have the same thickness as the main line with a reduced width or may have both a reduced thickness and width. In one embodiment, the branch line extends as an arc and may terminate in an end line which has a square cross section equal to the cross section of the main line and extends at an angle to the main line. In another embodiment, the branch line extends rectilinearly and may terminate in an end line which extends parallel to the main line and has a square cross section equal to the square cross section of the main line. The coupler may be formed by stamping the coupler from a sheet of material or by using a photolithographic process to form the coupler from a layer of photosensitive material. If the coupler has branch lines with a thickness less than the thickness of the main line, the photolithographic process includes developing a first layer or foil of photosensitive material to form part of the main line and the branch line and then developing a second applied layer to produce the remaining portion of the main line.