A data input device for use with a tracking surface, said tracking surface having light-scattering properties, said device comprising: a substantially coherent light source for projecting a substantially coherent light beam onto said tracking surface during operation, said tracking surface adapted to scatter the substantially coherent light beam striking said tracking surface; a first optic for guiding the projected substantially coherent light beam toward the tracking surface, said tracking surface scattering the substantially coherent light beam when the substantially coherent light beam strikes the tracking surface, said first optic comprising, a first boundary facing said substantially coherent light source, and a second boundary opposite the first boundary and configured to face said tracking surface; a detector for detecting at least a portion of the substantially coherent light beam scattered by the tracking surface, said detected portion comprising a speckle pattern; said first optic being arranged between said detector and said tracking surface during operation such that the tracking surface is spaced from the second boundary by a distance sufficient to inhibit any substantial retro-reflection of the substantially coherent light beam striking the second boundary from striking the detector; a second optic for collecting at least a portion of the scattered light beam and altering a wavefront profile of the collected scattered light beam so that the collected scattered light beam has a substantially constant phase relative to the plane of the detector, such that the detector detects a substantially stable speckle pattern from the collected scattered light beam; and a controller responsive to the output of the detector for operating the device in a tracking mode by utilizing the detected speckle pattern to track relative movement between the device and the tracking surface. a substantially coherent light source for projecting a substantially coherent light beam onto said tracking surface during operation, said tracking surface adapted to scatter the substantially coherent light beam striking said tracking surface; a first optic for guiding the projected substantially coherent light beam toward the tracking surface, said tracking surface scattering the substantially coherent light beam when the substantially coherent light beam strikes the tracking surface, said first optic comprising, a first boundary facing said substantially coherent light source, and a second boundary opposite the first boundary and configured to face said tracking surface; a first boundary facing said substantially coherent light source, and a second boundary opposite the first boundary and configured to face said tracking surface; a detector for detecting at least a portion of the substantially coherent light beam scattered by the tracking surface, said detected portion comprising a speckle pattern; said first optic being arranged between said detector and said tracking surface during operation such that the tracking surface is spaced from the second boundary by a distance sufficient to inhibit any substantial retro-reflection of the substantially coherent light beam striking the second boundary from striking the detector; a second optic for collecting at least a portion of the scattered light beam and altering a wavefront profile of the collected scattered light beam so that the collected scattered light beam has a substantially constant phase relative to the plane of the detector, such that the detector detects a substantially stable speckle pattern from the collected scattered light beam; and a controller responsive to the output of the detector for operating the device in a tracking mode by utilizing the detected speckle pattern to track relative movement between the device and the tracking surface.