Beam focusing characteristics of diffractive lenses with binary subwavelength structures

The diffractive optical elements with binary subwavelength structures have the ability for monolithic integration and can require only single step fabrication, but the subwavelength and aperiodic nature of the diffractive optical elements prevent the use of scalar diffraction theory and the use of coupled-wave theory. To overcome these limitations, we present the rigorous vector analysis and design of diffractive lenses that are finite in extent and have binary subwavelength structures by using a two-dimensional finite-difference time-domain method. By using these effective analysis tools, we analyze the focusing characteristics of continuous profile lenses and binary subwavelength diffractive lenses obtained by generalizing the design approach presented by Farn, for different incidence polarization waves (TE polarization and TM polarization) and for different f-numbers of lenses. The comparative results have shown that the focusing characteristics, including the focal shift, the focal depth, the focal spot size, and the diffractive efficiency, of binary subwavelength diffractive lenses are different from those of continuous profile lenses and are more sensitive to the polarization of incidence wave. (C) 2004 Elsevier B.V. All rights reserved.