Data input device for tracking and detecting lift-off from a tracking surface by a reflected laser speckle pattern

摘要

A data input device for use with an optically rough tracking surface comprising a coherent light source projecting a coherent light beam and an optic positioned in the coherent light beam. The optic alters a wavefront profile of the coherent light beam so that the coherent light beam has a substantially constant phase relative to a plane perpendicular to the beam at a tracking distance from the optic. The coherent light beam is projected onto the tracking surface to reflect a substantially stable speckle pattern. A controller responsive to a detector correlates the substantially stable speckle pattern to track relative movement between the coherent light beam and the tracking surface. The controller suspends tracking of relative movement between the coherent light beam and the tracking surface when the detector detects a boiling speckle pattern.