An optical apparatus comprising an optical device having an optical input-output face, at least two planar waveguide arms being located on a substrate, an optical splitter being located on the substrate, and, an optical grating coupler being located on the substrate. The optical splitter has an optical input and a plurality of optical outputs, each optical output being optically connected to a corresponding one of the planar waveguide arms. The optical grating coupler is connected to receive light from each planar waveguide arm and form diffraction pattern therefrom such that a principal maximum of one of the diffraction patterns overlaps with a principal maximum of another of the diffraction patterns on the optical input-output face of the optical device, the principal maxima of the one and another of the diffraction patterns being directed in different directions.