A process comprising: (a) applying a stop etch mask to a substrate, the mask defining the location on the substrate of a groove for receiving a waveguide and one or more fiducials for positioning the optical device on the substrate relative to the waveguide; and (b) etching the substrate to define the fiducials and the groove, the groove being dimensioned to receive at least a portion of a waveguide and the fiducials enabling the optical device to be positioned on the substrate such that it is optically aligned with the waveguide.