Patent ID: 7976208

Claim:
A flat light guide ( 1 ) comprising: a first face and second face acting as input and output parts ( 2 , 3 a ) of the light guide, the first face ( 2 ) being small in relation to the total width of the light guide, the second face being formed by a tapered sheet ( 3 ) configured to taper down in thickness along the direction of travel of light that is input at the first face; an input slab ( 4 ) adjoining the tapered sheet and configured to cause light from a point of input at the first face to fan-out through the input slab to a thick end of the tapered sheet; wherein the light guide is configured to have optical properties such that the angle at which a ray is injected into the first face determines the position at which it leaves the second face ( 3 a ), or the position at which the ray enters the second face determines the angle at which the ray leaves the first face; in which the optical profile of the light guide is polar-symmetric about the first face ( 2 ), so that rays travelling along the light guide follow the local direction of taper.