ABSTRACT

Planar arrays of diffractive micro-optics lie at the centre of a quiet revolution in optical system design. Microscopic relief structures incised into the surface of flat or curved substrates form the basis of novel optical elements that, individually or collectively, steer, concentrate, multiplex, image, or otherwise transform an incident wavefront (Stone and Thompson, 1991; Cole and Pittman, 1993; and others). These diffractive optical elements (DOEs) modulate the phasefront according to instructions encoded in the continuous or stepped surface-relief profile. The principal technique for manufacturing phase-only computer-generated DOEs with a stepped surface-relief profile has been named binary optics technology. The name reflects the inherent binary coding of both the phase quantization and the process sequence. Binary optics technology exploits the flexibility and precision of VLSI (very large-scale integration) circuit processing techniques and computer-aided design (CAD) tools to fabricate diffractive micro-optics in virtually any dielectric, metallic or semiconductor substrate (Veldkamp and Swanson, 1983; Swanson, 1989). It offers new opportunities in design optimization by providing a universal method to fabricate DOEs such as multifocal or bichromatic lenses, generalized phase plates, and space variant arrays, that would be difficult or even impossible to make by standard holographic methods (Leger et al., 1988a, 1988b; Goltsos and Holz, 1990; Stern et al., 1991b; Leger and Goltsos, 1992). To obtain high-quality optics, however, the lithography and substrate patterning techniques developed for semiconductor processing must be adapted to meet the specific and distinct demands of optical structure fabrication (Stern et al., 1991a, 1992). Coupling these processing techniques with recent advances in the replication of microstructures holds great promise for the low-cost production of diffractive micro-optics (Gale et al., 1993; Shvartsmann, 1993).