Binary optics from a raytracing point of view

Surfaces which achieve optical power from prescribed surface relief profiles (called kinoforms) have been generally described in the literature1-3 as diffraction devices, probably because of their similarity to holograms. The design and evaluation of these lenses are performed by either modeling the surface as a very high index lens4,5 or by using a raytrace code to define an arbitrary phase surface expressed as a polynomial. These methods do not utilize the full aberration correction capability of the relief profile when it is defined from a zonal raytrace refraction design. For example, the optimum relief profile for a kinoform surface2 focussing collimated light is a conic with conic coefficient of -n2 and with a different curvature in each Fresnel zone. Such a surface has discontinuous slopes at the zone boundaries even before the surface is given the two pi phase jumps. The above methods of design do not provide for discontinuous slopes.