An optical communication system comprising first and second planar substrates and an alignment assembly. The first substrate of a semiconductor material, is located on a planar surface of a sub-mount and having a planar first edge. The second substrate of a different second material, is located on said planar surface of said sub-mount and having a planar second edge. The alignment assembly is located on said sub-mount, said alignment assembly including rigid standoff structures configured to fixedly vertically align said first and second edges above said sub-mount such that each optical output of one of said lasers is vertically aligned with the end of one of said light-guiding structures.