Addressing a matrix-type liquid crystal cell

Optical modulator apparatus comprising a matrix-type liquid crystal cell and an addressing signal generator for addressing said cell, the cell including liquid crystal material which is electrically settable to first and second stable optical states, and comprising a plurality of pixels which are defined by areas of overlap between members of a first set of electrodes on one side of the material and members of a second set of electrodes, which cross the first set, on the other side of the material, the addressing signal generator having outputs coupled to the first and second sets of electrodes and being contructed to address the pixels in lines by each time (a) applying an erase signal having a given polarity to the corresponding electrode of the first set while applying at least one charge-balanced bipolar data signal to each electrode of the second set, thereby setting any pixel of the line which is not already in the first state to that state, and (b) subsequently applying a strobe signal having an opposite polarity to said given polarity to the corresponding electrode of the first set while applying a charge-balanced bipolar data signal to each electrode of the second set, thereby selectively setting to the second state any pixel of the line for which the data signal applied to the corresponding electrode of the second set has a given form, characterised in that the generator is constructed so that when said data signal has said given form it comprises first, second and third successive portions in which it has said given polarity, said opposite polarity and said given polarity respectively, the amplitude of the second portion being less than the amplitude of the strobe signal, the end of the first portion coinciding with or occurring before the start of the strobe signal, the end of the second portion occurring after the start of the strobe signal, and the start of the third portion occurring before the end of the strobe signal.