This invention relates to an optical device and system for producing a holographic optical element or digital hologram. Various techniques of producing digital holograms have been proposed. However, they tend to suffer from long exposure times, as well as problems associated with control of two or more independent beams of coherent light used to produce a hologram. Problems become even more acute as pixel size decreases. The present invention provides an optical device including: a beam deflector, adapted to deflect a collimated beam of coherent light to produce an incident beam; a beam splitter for producing first and second beams, said beams being displaced so that the angle of deflection of the first beam is the same but opposite to the angle of deflection of the second beam; and a combiner combines the first and second beams so as to produce an interference pattern at an output plane.