Phase masks are used to eliminate the Fourier-plane hotspot that otherwise degrades holographic data storage
performance. In order to eliminate the cost, bulk, and precision alignment difficulties of inserting a discrete phase mask
into an optical system we have designed phase masks integrated directly into the structure of a spatial light modulator
used as the storage system's write head. A micron-thick ferroelectric liquid crystal film is confined between the surface
of a VLSI integrated circuit and a window containing planarized relief structures on its inward-facing surface. This
arrangement avoids depth-of-field problems encountered by designs that place the phase mask on the outer surface of the
window. Any of a variety of phase mask designs can be implemented in this fashion. An alternative architecture in
which pixel surfaces of the CMOS VLSI backplane are etched to differing heights is also investigated.
Barriers to commercialization of optical correlators include the complexity and cost of their manufacture, their large size compared to typical electronic processors, and the cost of their components. Using sub-micron CMOS VLSI fabrication processes it is possible to build the two SLMs and photodetector array of a Vander Lugt correlator on a single silicon die. The correlator's lenses can be fabricated on a single piece of glass using diffractive optics technology and then attached to the CMOS die to form a monolithic assembly. This approach greatly reduces the mechanical degrees of freedom that must be controlled by the correlator's housing thus lowering cost, reducing size, and improving reliability. Here we report on the design and performance of a prototype.
Due to advances in spatial light modulator technology and high-speed imagers, optical correlators are becoming viable for a variety of high-speed image processing applications. However, conventional approaches to assembling correlators produce systems which are costly to manufacture, and which are too large for some uses. We are investigating approaches to the construction of compact, highly integrated correlators that combine ferroelectric liquid-crystal-on- VLSI spatial light modulators, a CMOS imager, and diffractive optical elements.
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