An optical position sensing device for sensing a two-dimensional
displacement, comprising a first photosensor arranged parallel to a first
axis; a second photosensor arranged parallel to a second axis; wherein
the first and the second axis are at an angle with respect to each other;
and an encoding means which interferes with a path of light incident on
the photosensors such that a pattern consisting of light and shadow is
cast onto the photosensors, wherein the encoding means and the
photosensors are able to move with respect to each other, resulting in
modulation of light received by the photosensors, and are arranged in an
arrangement such that when the encoding means moves relatively in a
direction parallel to the first axis, the modulation of light received by
the second photosensor is larger than the modulation of light received by
the first photosensor; and when the encoding means moves relatively in a
direction parallel to the second axis, the modulation of light received
by the first photosensor is larger than the modulation of light received
by the second photosensor.