An optical interconnection structure between an optoelectric device and a single mode optical fiber for enlarging an alignment tolerance is provided. The optical interconnection structure is constituted by a microlensed optoelectric device and a graded index fiber ended single mode optical fiber. Light beams emitted from the optoelectric device are collimated by the microlens on the rear surface of a substrate or are enlarged in size by being focused or diverged. The extended output light travels a predetermined distance and then reaches the graded index fiber ended single mode optical fiber. When the length of the graded index optical fiber lens is appropriate, the incident extended beams are again focused by the lens, and thus enter into the single mode optical fiber while maintaining a great coupling efficiency. The optoelectric device and the microlens are integrated by the photolithography process, such that alignment with respect to all elements within a substrate is accomplished. Thus, there is no need to make optical alignment for each single element, resulting in the possibility of mass production. Since the graded index optical fiber lens and the single mode optical fiber have the same diameter and the same circular shape, so that they are easily aligned automatically and mechanically stable.