In a previous paper, we described an optical interconnection system in which two arrays of mutually coherent sources are used for the recording of holographic gratings that form weighted interconnection between another source array and a detector array. Mutually coherent source arrays are required for the writing of holographic gratings. The generation of coherent diffracted light beams from a single laser source using programmable SLMs is an attractive and simple method. Two-dimensional surface-emitting laser arrays can be used to readout the written holograms but not for recording them, as individual lasers have yet to be made mutually coherent. There are numerous other applications for programmable source arrays. They could for example drive optically pumped surface-emitting laser diode arrays or optically controlled smart pixels of a spatial light modulator. Their potential use in three- dimensional display systems and in wavelength division multiplexing applications is also being studied. Each of the modulators described in this paper has programmable features suitable for a variety of applications. Four methods to generate programmable coherent source arrays using addressable liquid crystal spatial light modulators and two-dimensional arrays of Fresnel lenses that produce multiple diffracted light beams are described in this paper. These include an optically addressed light modulator, a matrix-addressed pixellated (television) display with thin-film transistors, and two modulators fabricated at Bellcore that are electrically addressed through specially designed electrode patterns. Implementations with binary-amplitude and binary-phase Fresnel lenses are discussed identifying programmable features and resolution limits of each type of modulator.
A photorefractive interconnect system with coherently erasable synapses (PISCES) is described. Comparing holographic erasure by intensity and phase modulation of the writing beams, we find that the timeaverage technique is most amenable to system implementation. Calculations derived from a simple model of diffraction show that it is possible to find configurations that maximize the interconnection capacity. The PISCES includes Fresnel zone plates for spot array generation, amplitude and phase spatial light modulators based on liquid crystal technology,
and detector arrays, in addition to the photorefractive crystal. Alternatives for each of these elements are described.