Browsing by Subject "Light Field Synthesis"

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Open Access
Signal processing based solutions for holographic displays that use binary spatial light modulators
(2012) Ulusoy, Erdem
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
Open Access
Three-dimensional monochromatic light field synthesis with a deflectable mirror array device
(SPIE, 2006) Ulusoy, Erdem; Uzunov, V.; Onural, Levent; Özaktaş, Haldun M.; Gotchev, A.
We investigated the problem of complex scalar monochromatic light field synthesis with a deflectable mirror array device (DMAD). First, an analysis of the diffraction field produced by the device upon certain configurations is given assuming Fresnel diffraction. Specifically, we derived expressions for the diffraction field given the parameters of the illumination wave and the tilt angles of the mirrors. The results of the analysis are used in later stages of the work to compute the samples of light fields produced by mirrors at certain points in space. Second, the light field synthesis problem is formulated as a linear constrained optimization problem assuming that mirrors of the DMAD can be tilted among a finite number of different tilt angles. The formulation is initially developed in the analog domain. Transformation to digital domain is carried out assuming that desired fields are originating from spatially bounded objects. In particular, we arrived at a Dp = b type of problem with some constraints on p, where D and b are known, and p will be solved for and will determine the configuration of the device. This final form is directly amenable to digital processing. Finally, we adapt and apply matching pursuit and simulated annealing algorithms to this digital problem. Simulations are carried out to illustrate the results. Simulated annealing performs successful synthesis when supplied with good initial conditions. However, we should come up with systematic approaches for providing good initial conditions to the algorithm. We do not have an appropriate strategy currently. Our results also suggest that simulated annealing achieves better results than MP. However, if only a part of the mirrors can be used, and the rest can be turned off, the performance of MP is acceptable and it turns out to be stable for different types of fields.