Breaking of inversion symmetry in 2-level binary, Fourier holograms

Methods of breaking inversion symmetry of images produced by 2-level, binary, phase holograms are considered which are of particular relevance to holograms produced by programmable devices. They are based on the use of the relationship which generalizes the method introduced by J.A. Davis et al. (1988) to enable intensity in the unwanted negative diffraction order spots to be located and spread in a controlled manner. Using this approach asymmetric spot arrays centred on the optic axis have been demonstrated, combined with high levels of suppression of both background and unwanted orders. Simply by relocating the image plane away from the Fourier plane the inversion symmetry is again removed by defocusing the negative diffraction orders. This method is explained using the general theory and it is also shown that adding a fixed phase mask can significantly reduce the background level. Experimental results for spot array without inversion symmetry are presented with uniformity of intensity of spots to within +or-6%, relative strength of unwanted spots of 3% and relative background strength below 2%.<
>