Fig. 1a illustrates the standard operation of an optical mouse for opaque object sensing. A light emitting diode
(LED) illuminates the surface at an angle. A lens is used to image the surface of the mouse pad onto a CMOS sensor
located in the camera chip. The off-axis illumination by the LED helps to put the tiny textures on the surface in sharp
contrast. The CMOS sensor typically comprises 18 by 18 pixels (324 pixels in total). The mouse works by comparing
the images of the surface that are refreshed approximately every 1500th of a second. This allows any object movement
in the x, y and z axis to be sensed. In the modified setup shown in Fig. 1b, the illumination of the LED is disabled.
In its place, a laser illuminates a ground glass that is placed after it such that a speckled wavefront is produced. This is
duly recorded on the CMOS sensor. As a lens is located in front of the CMOS sensor, the speckle pattern recorded is
subjective as opposed to objective [15]. Movements of the ground glass in the x and y axis should then permit registration by the optical mouse.