Signal processing based solutions for holographic displays that use binary spatial light modulators

Abstract

Holography is a promising method to realize satisfactory quality threedimensional (3D) video displays. Spatial light modulators (SLM) are used in holographic video displays. Usually SLMs with higher dynamic ranges are preferred. But currently existing multilevel SLMs have important drawbacks. Some of the associated problems can be avoided by using binary SLMs, if their low dynamic range is compensated for by using appropriate signal processing techniques. In the first solution, the complex-valued gray level SLM patterns that synthesize light fields specified in the non-far-field range are halftoned into binary SLM patterns by solving two decoupled real-valued constrained halftoning problems. As the synthesis region, a sufficiently small sub-region of the central diffraction order region of the SLM is chosen such that the halftoning error is acceptable. The light fields are synthesized merely after free space propagation from the SLM plane and no other complicated optical setups are needed. In this respect, the theory of halftoning for ordinary real-valued gray scale images is extended to complex-valued holograms. Simulation results indicate that light fields that are given either on a plane or within a volume can be successfully synthesized by our approach. In the second solution, a new full complex-valued combined SLM is effectively created by forming a properly weighted superposition of a number of binary SLMs where the superposition weights can be complex-valued. The method is a generalization of the well known concepts of bit plane decomposition and representation for ordinary images and actually involves a trade-off between dynamic range and pixel count. The coverage of the complex plane by the complex values that can be generated is much more satisfactory than that is achieved by those methods available in the literature. The design is also easy to customize for any operation wavelength. As a result, we show that binary SLMs, with their robust nature, can be used for holographic video display designs