Improved reconstruction quality of holographic projections by controlling the individual pixel shape

Diffractive optical elements (DOE) are widely used to project defined intensity patterns, e.g. in security or display applications. The main advantage of using DOEs is their small size and flatness. It is well known that the quality of the projected pattern is proportional to the number of pixels in the hologram plane. However, the achievable size of an individual pixel is limited by the manufacturing process. This reduces the number of pixels per area, thus limiting the quality of the projection. We introduce an approach to calculate computer generated holograms which overcomes this limitation by incorporating the shape of each individual pixel. The method entails the calculation of a high-resolution hologram with subsequent subsampling and first order local Taylor series expansion to determine the slopes of the pixels. We show that our approach reduces the overall error by a factor of approximately 8 as compared to subsampled holograms with constant pixel shape.