Standard, non-patterned optically addressed spatial light modulators (OASLMs), comprising an a-Si:H photodiode and a ferroelectric liquid crystal (FLC), have a fixed write-light intensity threshold when driven at a particular frequency. We present a patterned OASLM in which the threshold may be varied. The structure and operation of this device is significantly different from the standard OASL.M. While the square-wave drive for the non-patterned OASLM provides a time-varying voltage for the device, the thresholding OASLM uses a dc drive, with
spatiallyseparated bias voltages. By varying the voltage applied to a patterned metal layer between the a-Si:H and FLC, we achieved dynamic thresholding over one decade of write-light intensity. Fabricated devices have response times as low as 200 μsec, and contrast ratios as high as 50:1.