Patent ID: 8120762

Claim:
An apparatus, comprising: a light guide having a first surface, an opposing second surface, and a slanted facet located at a corner of the light guide, said slanted facet extending at least from the first surface toward the second surface; and an optical sensing module located at the slanted facet, wherein the light guide comprises a diffractive element on the second surface, the diffractive element comprising a plurality of curved fringes arranged such that when a light beam is directed from a location on the first surface toward the second surface at a predefined direction, the light beam is diffracted toward the first surface by the diffractive element and guided by the light guide toward the slanted facet, and then exits through the slanted facet as an exit light beam toward the optical sensing module at an exiting angle, the exiting angle indicative of a distance between said location and a reference point at said corner.