Optical structure, optical navigation system, and method of estimating motion

An optical navigation system and method of estimating motion use an optical structure 210 configured to collimate light propagating along a first direction and to internally reflect the light off an output reflective surface 234 of the optical structure downward along a second direction perpendicular to the first direction toward a target surface 106. The optical structure is also configured to transmit the light reflected from the target surface through the output reflective surface toward an image sensor 212. This arrangement allows the navigation system to cope with a variation in height between the system and a surface 106 which may be caused for example by a transparent sheet 438 covering a work surface.