Abstract

It has been recently predicted that high-efficiency diffractive optical elements can be fabricated as binary-phase-level surface-relief structures whose individual elements are smaller than the wavelength of light in the material.^1,2 Such a structure can be thought of as a surface layer of material whose effective index of refraction can be varied laterally by modulating the size and spacing of the individual features of the structure. This concept was recently demonstrated in metallic grating devices fabricated for long wavelengths (10.6 µm).³ Subwavelength diffractive structures have several advantages over conventional multiplex-phase-level diffractive optics formed by multiple lithography steps. Subwavelength diffractive structures can have very high efficiencies, form antireflection surfaces, incorporate polarization-dependent properties, and be fabricated in a single lithographic step. The major disadvantage is the difficulty of fabricating the small features required.

© 1995 Optical Society of America