An optical apparatus comprises: a waveguide substrate; three planar optical waveguides formed on the substrate, each comprising a transmission core and cladding; a laser positioned to launch its optical output to propagate along the first waveguide; a photodetector positioned to receive an optical signal propagating along the second waveguide; and means formed on the substrate for i) transferring a first fraction of laser optical output propagating along the first waveguide to the second waveguide, and ii) transferring a second fraction of the laser optical output propagating along the first waveguide to the third waveguide. The transferring means may comprise: i) a pair of parallel spaced-apart tap core segments; ii) a branched splitter core; or iii) a lateral splitter core.