Patent ID: 8867872

Claim:
An optical apparatus comprising: a waveguide substrate; a set of one or more optical waveguide layers on the substrate; source, primary, and secondary optical waveguides formed in one or more of the optical waveguide layers, each of the optical waveguides being arranged to substantially confine in two transverse dimensions a corresponding guided optical mode; a light source that emits an optical signal and is arranged to launch a portion of the optical signal to propagate along the source waveguide as a source optical signal in the corresponding guided optical mode; a first optical waveguide tap formed in one or more of the optical waveguide layers and arranged to direct a primary fraction of the source optical signal to propagate along the primary waveguide as a primary optical signal and to direct a secondary fraction of the source optical signal to propagate along the secondary waveguide as a secondary optical signal; and one or more light traps formed in the optical waveguide layers, each light trap comprising one or more lateral surfaces of the optical waveguide layers and a substantially opaque coating on the lateral surfaces, wherein: the lateral surfaces of each light trap are arranged to define a corresponding spiral region of the optical waveguide layers, which region includes an open mouth and closed end of the light trap; the secondary waveguide is arranged so that the secondary optical signal propagates to an end of the secondary waveguide and emerges from the secondary waveguide to propagate as a stray optical signal in one or more of the optical waveguide layers without confinement by any of the optical waveguides in the corresponding guided optical modes; and the secondary waveguide and the light trap are arranged on the waveguide substrate so that the stray optical signal propagates into the open mouth of the optical trap without confinement by any of the optical waveguides in the corresponding guided optical modes.