The invention pertains to an optical connector assembly having an alignment mechanism for coupling two single-lens, multi-fiber optical connectors together. Particularly, each connector comprising a single lens through which the light from multiple fibers is expanded/focused for coupling to corresponding fibers in a mating connector. In one aspect of the invention, the alignment mechanism includes mating features extending from the fronts of the lenses having substantially longitudinal surfaces that meet and contact each other when the two connectors are coupled together in only one or a limited number of rotational orientations relative to each other to as to properly rotationally align the multiple fibers in the two mating connectors. This mechanism also helps align the two connectors with the optical axes of their lenses parallel to each other. In another aspect of the invention to even more effectively align the two connectors with their optical axes parallel to each other, the connector assembly includes an alignment sleeve into which the front of each lens extends when mated, an inner diametrical surface of the alignment sleeve contacting an outer diametrical surface of each of the two lenses over a substantial longitudinal portion of each lens. The alignment sleeve may, for instance, be a resilient split sleeve that expands radially to accept the lenses.