A method of controlling the switching of an optically addressable spatial
light modulator (OASLM), to a first surface of which a write light signal
is applied and to a second surface of which a read light signal is
applied. The method comprises applying a bipolar switching waveform to
control electrodes of the (OASLM) during each write cycle such that the
leading pulse of the waveform applies a voltage across the (OASLM) which
is in the photosensitive direction and the trailing pulse applies a
voltage which is not in the photosensitive direction.