An optical apparatus comprises an optical device formed on a device substrate, a first optical waveguide formed on the substrate or on the optical device, and a second, mechanically discrete optical waveguide assembled with the device substrate, optical device, or first optical waveguide. The first optical waveguide is arranged for transferring an optical signal between the optical device and the first optical waveguide. The first and second optical waveguides are arranged, when the second optical waveguide is assembled with the device substrate, optical device, or first optical waveguide, for transferring the optical signal therebetween via optical transverse coupling.