Engineering chromatic response using cascaded metasurfaces

Abstract

To overcome the problem of a diffractive surface having a large, and often excessively large, amount of chromatic aberration, an optical system can use multiple cascaded or sequential diffractive surfaces that, combined, have a reduced amount of chromatic aberration. The optical system can be designed such that all rays traversing the optical system and passing through the diffractive surfaces have an equal optical path length. In the design process, the sets of rays are identified, and the designs of the diffractive surfaces are selected to produce the angular deviations to produce the identified ray paths. In one example, an achromatic lens formed as two annular optical surfaces can receive a collimated incident beam, redirect rays helically at the first surface toward the second surface, and redirect the rays at the second surface toward a focal point. The azimuthal redirection can decrease with increasing distance away from a central axis.