Abstract

Free space optical interconnects can provide the fast, highly parallel data channels needed for interwafer communication. High quality optical elements enable the use of high density source/detector arrays. We have fabricated and tested multilevel reflective gratings in Si. Four-level gratings give single order efficiencies of 75%, close to the theoretical maximum of 81%. We present the theoretical and experimental performance of reflective off-axis binary optical elements, and a scenario for the integration of these devices into current hybrid wafer-scale computers. Half- and quarter-wavelength constant phase surfaces are computed and then approximated by short line segments which form polygons. We discuss the methods of dealing with patterning curved grating structures using what are inherently rectilinear lithography tools. We also discuss the sensitivity to overlay misalignment between the phase surfaces and other unavoidable fabrication errors. Measured radiation patterns for fabricated binary-optic reflective focusing gratings are compared with the calculated patterns. Possible integration into current hybrid-scale packaging schemes are discussed.

© 1991 Optical Society of America