Abstract

The concept of using holograms in optical processing and computing has been found in a variety of areas such as optical interconnects [1], optical associative memory [2] and optical computing systems [3]. In conventional holography, holographic optical elements (HOEs) are generally located in three-dimensional free space (see Figure 1(a)). This type of 3-D free-space holograms has important limitations. First, alignment problems are critical. If the sources and detectors are not in exact 3-D alignment with the holographic elements, performance suffers possibly to the point where the system becomes inoperative. Second, and more importantly, conventional 3-D Bragg holographic elements have low angular and wavelength selectivity (i.e., multiplexing) due to the limited hologram thickness (t ~ 20μm, for dichromated gelatin). Although multifacet holograms [4] are proposed, to improve performance, they suffer from diffraction-limited because of the small facet apertures.

© 1989 Optical Society of America