Abstract

Holographic optical interconnections have often been suggested for meeting the demanding requirements for high-density, independent weighted fan-out/fan-in interconnections imposed by advanced optical computing systems, such as neural networks. In this paper we consider the capabilities of a wide variety of previously proposed holographic interconnection schemes, as well as those of a recently proposed double angularly multiplexed incoherent/coherent architecture¹ to perform the desired interconnection functions. Based on numerical simulations that use the optical beam propagation method and on experimental verification of selected aspects, we present results that compare the degree of interchannel crosstalk, the independence and accuracy of weighted outputs, the throughput efficiency, and the practicality of real-time reconfigurability. We show that fan-out/fan-in interconnection systems with single-reference-beam multiplexing suffer from significant crosstalk that is caused by a k-vector degeneracy in the beams fanned in to a given output node. This beam-degeneracy crosstalk, which is distinct from the grating-degeneracy crosstalk discussed previously,² adversely affects the fidelity of the desired reconstructed weighted beams upon readout, even in the low-exposure (low-diffraction-efficiency) limit. We also verify, as is generally recognized, that fully coherent simultaneous recording introduces large weight distortions in the reconstructed output for both the coherent and incoherent readout cases. In comparison, however, we demonstrate that the double angularly multiplexed incoherent/coherent approach yields low weight distortion, allows simultaneous weight initiation and updates without coherent recording crosstalk effects, and permits incoherent summation at the output nodes with no incoherent fan-in loss.

© 1990 Optical Society of America