Abstract: An optical apparatus comprises: source, primary, and secondary waveguides formed in waveguide layers on a substrate; a light source; and an optical waveguide tap. The light source launches a source optical signal along the source waveguide. The tap divides the source optical signal into a primary optical signal in the primary waveguide and a secondary optical signal in the secondary waveguide. The secondary optical signal emerges from the secondary waveguide to exit the waveguide layers at the substrate edge or to propagate within the waveguide layers as a stray optical signal without confinement by any waveguide. The stray optical signal propagates thusly unconfined into the open mouth of an optical trap that comprises one or more lateral surfaces formed in the waveguide layers and an opaque coating on the lateral surfaces, and comprises a spiral region of the optical waveguide layers with an open mouth and closed end.