A device includes three elements fabricated on a common substrate. The first element includes an active waveguide structure having at least three sub-layers supporting a first optical mode. The second element has a passive waveguide structure supporting a second optical mode, and the third element, butt-coupled to the first element, has an intermediate waveguide structure supporting intermediate optical modes. One sub-layer in the active waveguide structure includes an n-contact layer, another sub-layer includes a p-contact layer, and a third sub-layer includes an active region. A tapered waveguide structure in at least one of the second and third elements facilitates efficient adiabatic transformation between the second optical mode and an intermediate optical mode. No adiabatic transformation occurs between that intermediate optical mode and the first optical mode. Mutual alignments of the three elements are defined using lithographic alignment marks that facilitate precise alignment between layers formed fabrication of the elements.