An optical coupler converts a light distribution from a light source into a small angle distribution that extends over a volume larger than the variations in the alignment of an optical fiber. In one embodiment, a diffractive or hybrid diffractive/refractive bifocal lens forms first and second images of the light source respectively in first and second image planes. An input face of the optical fiber is between the first and second image planes and receives light diverging from the first image plane and light converging toward the second image plane. The net optical power coupling into the fiber is uniform over a large range of fiber positions and provides the optical coupler with a relaxed tolerance for misalignment of the fiber or the light source. The relaxed alignment tolerance facilitates low cost manufacture of multi-channel optical transmitters using single-mode optical fibers.