Resolution limits from charge transport in optically addressed spatial light modulators

Spatial resolution of optically addressed spatial light modulators (OASLMS) is degraded by several different transfer processes in these devices. We have developed a general transient charge transport model to calculate and simulate the resolution limits of OASLMs due to the following charge spreading mechanisms during the transfer process in which the input image is converted into a particular charge distribution in the photosensor layer. (i) The effect of charge drift in the photosensor bulk on resolution increases with the thickness of the photosensor and the light-modulating layers. It also increases with the total amount of photogenerated charge collected at the interface. (ii) The effect of charge diffusion in the photosensor bulk on resolution is largely independent of the carrier mobility in the semiconductor photosensor. In most cases the corresponding spatial frequency fsoa is proportional to md,, where d,, is the photosensor thickness and V,, is the voltage drop in that layer. To have high-sensitivity OASLMs the transit time of charge carriers from the photosensor bulk to the interface must be much shorter than the recombination lifetime. (iii) The effects that charge drift, diffusion, and trapping at the photosensor-light-modulating layer interface have on resolution depend strongly on the interface properties. Decreasing the mobility or the trapping time of charge carriers at the interface can dramatically improve the resolution of OASLMs. The resolution ranges from 3 to 875 line pairs/mm for respective diffusion lengths of 10 to 0.1 ,um at the interface. The combined effect on resolution from each of the charge spreading and other discussed.