Analysis of charge-controlled gray scale in ferroelectric liquid crystal optically addressed spatial light modulator

In an optically addressed spatial light modulator (OASLM) with ferroelectric liquid crystal (FLC) and p-i-n photodiode hydrogenated amorphous Si (a-Si:H), the gray scale characteristics can be explained by the charge-control principle; the amount of charge supplied from the a-Si:H photodiode determines the FLC polarization state between the bistable states. We construct an equivalent circuit model based on this principle, formulate the operation of the OASLM, and show that this theory agrees with various experimental results. We also show that the OASLM gray scale is realized not by FLC multidomain switching, but by uniform director rotation between bistable states.