Patent ID: 7324086

Claim:
A data input device for use with a tracking surface, said tracking surface having light-scattering properties with respect to said device, said device comprising: a single laser having a cavity from which a light beam is projected, said laser being configured to project the light beam onto said tracking surface, at least a portion of the light beam striking said tracking surface reflecting back into the cavity of said laser, said light beam being subsequently projected and thereby altering at least one characteristic of the light beam projected by the laser, wherein said subsequently projected light beam is reflected from a reference surface acting as a field stop for limiting direct detection of light reflected from the tracking surface prior to said detecting; a detector associated with the laser for detecting said altered characteristic of the light beam projected by the laser; and a controller responsive to the detector for determining the relative distance between said device and said tracking surface as a function of the altered characteristic of the subsequently projected light beam detected by the detector.