An apparatus includes an optical wave guide and a ferrule. The optical wave guide has a prespecified horizontal-positioning surface and a prespecified vertical-positioning surface. The ferrule is to precisely couple with the optical wave guide. The ferrule defines a first datum plane mating with the prespecified vertical-positioning surface of the optical wave guide to precisely mechanically vertically position the optical wave guide within the ferrule. The ferrule defines a second datum plane mating with the prespecified horizontal-positioning surface of the optical wave guide to precisely mechanically horizontally position the optical wave guide within the ferrule.