Data input device and method for detecting an off-surface condition by a laser speckle size characteristic

摘要

A data input device for use with a tracking surface having light-scattering properties with respect to the device is disclosed. The device comprises a coherent light source for projecting a coherent light beam onto the tracking surface. The tracking surface scatters the coherent light beam striking the tracking surface. The device further comprises a detector associated with the coherent light source for detecting at least a portion of the scattered light. The detected portion of the scattered light comprising a speckle pattern. The device further comprises a controller configured to respond to the detected speckle pattern and operate the device in one of a tracking mode and a non-tracking mode, depending upon a speckle size characteristic of the detected speckle pattern as determined by the controller.