Patent ID: 7701590

Claim:
Apparatus comprising: a first component that includes one or more films, at least one of the films having a laterally varying transmission property; the first component, in response to light that includes a shifting wavelength from a light source, transmitting the light and providing output light; and a second component that receives output light from the first component on a photosensitive surface, the output light provided in response to the shifting wavelength including a respective light spot on the photosensitive surface, the light spot shifting through a sequence of two or more positions on the photosensitive surface, each shift in light spot position being caused by a respective shift in the shifting wavelength; the second component including: circuitry that, in response to the light spot, provides a differential output resulting from one or more positions of the light spot on the photosensitive surface and uses the differential output to monitor the shifting wavelength.