Prototype 3-D optoelectronic neural system

We report the implementation of a prototype 3-D optoelectronic neural system that combines free-space optical interconnects with silicon-VLSI-based hybrid optoelectronic circuits. The prototype system consists of a 16-pixel input, 4-neuron hidden and a single-neuron output layer, where the denser input-to-hidden layer connections are optical. The input layer uses PLZT light modulators to generate optical outputs which are distributed to an optoelectronic analog neural network chip through space invariant holographic optical interconnects. Optical interconnections provide fan-out with negligible delay and allow the use of compact, purely on-chip electronic H-tree fan-in structures. The scalable prototype system achieves 8-bit electronic fan-in precision and a maximum speed of 640 million interconnections per second. The system was tested using synaptic weights learned off-system and applied to a simple line recognition task.