Abstract

The problem of generating binary phase relief structures with a phase delay of π radians appears in the context of enhancing the diffraction efficiency of (conventionally binary-amplitude) image display holograms, matched filters, computer-generated holographic memories and interferograms, but it is especially severe in fabricating Fourier-domain optical interconnects. Two major types of phase error are of concern here. Incorrect absolute value of the phase delay (phase mismatch) results in excessive brightness of the undiffracted field component, which is always disturbing and implies a reduction of light efficiency into the desired wavefront. The variation of the phase delay over the hologram surface (phase non-uniformity) causes distortions in the diffracted wavefield and consequently reconstruction errors in the image. Other problems in accurate phase profile generation with conventional techniques such as ion-beam and plasma etching include the tilt of the edges of etched features and scattering from small-scale surface roughness. These factors effectively prevent the full utilization of the accuracy of the advanced lithographic patterning techniques. In this paper we investigate a novel method of generating binary-phase wavefields. Our method only requires a metal on glass binary-amplitude computer hologram with the structure corresponding to that of the desired wavefield (and, in practise, a right angle prism). Use is made of a combination of phase delays that occur in total internal reflection and in reflection from a glass-metal interface. Our initial experiments show that a significant increase in the diffraction efficiency of binary-phase grating beam splitters (by about a factor of four) is achievable.

© 1989 Optical Society of America