Patent ID: 7465917

Claim:
An encoder comprising: a code scale having a plurality of tracks thereon, wherein each track comprises a plurality of alternating luminescent and absorptive stripes, wherein the luminescent stripes of each track generate light in a unique band of wavelengths corresponding to that track, wherein the unique band of wavelengths corresponding to that track is different from another band of wavelengths corresponding to an adjacent track; an illumination system to illuminate the tracks, wherein said illumination system emits light to excite the luminescent stripes of a particular track which emit light in a band of wavelengths corresponding to the particular track; and a plurality of photodetectors, each photodetector to receive light from a corresponding one of the tracks and to generate a signal indicative of a quantity of light received from that track, each photodetector being limited to detecting light in a band of wavelengths corresponding to that track.