An arrangement for producing binary, phase or intensity, spatial light modulation uses a controllable two state ferroelectric liquid crystal spatial light modulator (10) (FLC SLM) which can alter the polarisation of input light in one of two ways depending on the state of the SLM (10). The SLM (10) is placed before a retardation plate (15) and a mirror (18). When used in this arrangement the efficiency of the modulation is enhanced by a factor of two for small switching angles o of the FLC SLM (10) when compared with the same SLM (10) used in a conventional transmission mode.
