The present invention relates to a spatial light modulator used for an optical computing system or display, which comprises a photoconductive layer having a rectification function for receiving incident lights to generate charges, an electrode for accumulating the charges and a ferroelectric liquid crystal layer for modulating the incident light according to bias voltage change with the accumulated charges, wherein the ferroelectric liquid crystal layer is arranged between a pair of alignment layers made of polyimide represented by the general formula (I); ##STR1## wherein n is 2 or more, X is S, Se or Te, Y is an aromatic group or a substituted aromatic group, and Z is a group containing an aromatic group. In the spatial light modulator, any charges are not accumulated on the alignment layer with the driving time and thus a bistable memory condition can be realized.