Smart-pixel spatial light modulator for incorporation in an optoelectronic neural network

We present the design, fabrication, and testing of a novel liquid-crystal-on-silicon optically addressed spatial light modulator for use as a weight matrix in an ART-1 optoelectronic neural processor. Each pixel in the 50 x 83 element array occupies 75 microm x 75 microm and consists of a photodetector, a threshold circuit, a 1-bit (flip-flop) memory element, and a liquid-crystal modulating mirror. The array is designed to switch all the pixels initially to the ON state. Subsequently each pixel is independently switched to the OFF state if a superthreshold amount of light falls upon the pixel's photodetector. The device has a contrast ratio of 20:1, a switch-on time (10-90% rise time) of 500 micros, and a switch-off time of ~500 micros (depending on the externally set threshold). Measured device uniformities and interpixel coupling are also described.