A spatial light modulator imaging system comprises an electrically addressed
spatial
light modulator (EASLM 4, 30) whose optical image output is projected onto
different areas of an optically addressed spatial light modulator (OASLM, 6,
8, 31) in a sequence. The OASLM carries electrodes which allow separate areas
to be selectively addressed by application of a voltage whilst receiving light
from the EASLM. The combined output from all areas of the OASLM forms a visible
image to an observer (11). When illuminated by coherent light the OASLM
may produce a holographic image, otherwise incoherent light is used to provide
a two dimensional image. The OASLM in one example contains a layer of nematic liquid
crystal material between two cell walls both treated with an alignment layer providing
low tilt surface alignment that is parallel in opposite direction; the product
of layer thickness d and material birefringence n approximately equals one
quarter of the wavelength of read light (12, 37). Other types of
nematic devices may also be used, with cell parameters arranged to give enhanced
diffraction efficiency.
