A planar integrated circuit includes a semiconductor substrate having a substrate surface and a trench in the substrate, a waveguide medium in the trench having a top surface and a light propagation axis, the trench having a sufficient depth for the waveguide medium to be at or below said substrate surface, and at least one Schottky barrier electrode formed on the top surface of said waveguide medium and defining a Schottky barrier detector consisting of the electrode and the portion of the waveguide medium underlying the Schottky barrier electrode, at least the underlying portion of the waveguide medium being a semiconductor and defining an electrode-semiconductor interface parallel to the light propagation axis so that light of a predetermined wavelength from said waveguide medium propagates along the interface as a plasmon-polariton wave.