Abstract: A first out-coupled light spot is produced on a first detector surface, from a first region of varying refractive index formed in an optical waveguide. A second out-coupled light spot is produced on a second detector surface different than the first, from a second region of varying refractive index formed in the waveguide. The light spots are produced in response to a forward propagating communications signal in the waveguide. A signal from the first surface is compared to a signal from the second surface, and this comparison is used to discriminate between a wavelength shift and a change in power in the communication signal. Other embodiments are also described and claimed.

Abstract: A refractive index grating is formed in an optical waveguide. A detector has an incident light surface that is oriented at about a right angle to a longitudinal axis of the waveguide. The surface is positioned upstream of the grating and outside of the waveguide to receive reflected light from the grating. An index matching material fills essentially the entirety of the light path for the reflected light, from an outside surface of the waveguide to the detector's incident light surface. Other embodiments are also described and claimed.