Patent ID: 7113255

Claim:
An arrangement comprising: a first set of grating patches arranged on a first side of a lens, said first set including a first grating patch and a second grating patch; and a second set of grating patches arranged on a second side of the lens, said second side being substantially optically opposite the first side, said second set including a third grating patch and a fourth grating patch, wherein at least one of the first and second sets is moveable with respect to the other, wherein in a first configuration of the arrangement the first and third grating patches are optically aligned so that light emitted from the first grating patch passes through the third grating patch, wherein in a second configuration of the arrangement the second and fourth grating patches are optically aligned so that light emitted from the second grating patch passes through the fourth grating patch, and wherein the first and second set of grating Patches are arranged with respect to each other so as to preclude the first and second configurations from occurring at a same time.