Abstract

Multi-level binary diffrac­tive optical elements are of increasing importance in an expanding variety of engineering applications. Virtually all previous work on the analysis and design of binary diffractive elements has been for diffraction of infinite plane waves rather than the practical case of finite bounded-profile beams. Only diffraction of Gaussian beams by thick holographic gratings has been previously investigated. In this work the diffraction of finite beams by multi-level binary gratings is analyzed in detail by using the rigorous coupled-wave approach. The analysis applies to any finite beam that is spatially slowly varying on the scale of the wavelength of light. Detailed diffraction characteristics for the important case of Gaussian beams are presented. The diffraction efficiency of these gratings and the profiles of the transmitted and diffracted beams are calculated as a function of the grating depth, grating spacing, light wavelength, and Gaussian beam waist. It is shown that if the beam waist is more than 10 times the grating period, the diffraction efficiency follows very closely to the plane-wave diffraction efficiency with no significant distortion of the profiles of the diffracted beams. The conditions for plane-wave-like diffraction behavior (with finite profile) are determined.

© 1992 Optical Society of America