Abstract

A diffractive lens is a surface-relief structure made lithographically by exposing computer-generated zone plate patterns of clear and opaque rings in chromium masks into layers of photoresist and subsequently ion etching the substrate. A two-level or binary zone plate results from a single mask, while the use of two or more masks results in multilevel asymmetric profile zone plate ring structures. The equally spaced steps constitute a phase-quantized profile, and the magnitude of the step heights determines the spectral response. If the phase shifts due to the steps in a single zone sum to 2π, the diffracted spectrum is typically broadband and blazed, with most light being diffracted into a single order. The diffraction efficiency increases with the number of steps. If, on the other hand, the phase shift is 2π for each single step in the zone, the spectral response is typically narrowband, with an increase in the number of steps resulting in higher efficiency, but also causing the bandwidth to become narrower. Incident broadband radiation for this case can be divided into several high efficiency, narrowband, and nearly nonspectrally overlapping orders. These shallow surface-relief lenses can be readily replicated by nickel mastering and embossing into plastic.

© 1989 Optical Society of America