Browsing by Subject "Holography."
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Item Open Access Computation of holographic patterns between tilted planes(Bilkent University, 2004) Esmer, Gökhan BoraHolography is a three-dimensional visualization method. This method depends on duplication of information-carrying optical waves which come from a threedimensional environment in the absence of the original source. Computation of the diffraction pattern due to an object is the most important process in digital holography. The diffraction pattern due to an object can be calculated by using several methods. Two models are generated and they are based directly on Rayleigh-Sommerfeld diffraction integral; there is no need for Fresnel or Fraunhofer approximations. The generated models are used to calculate scalar optical diffraction between tilted planes for monochromatic light. First model we generate is called pointwise model. The model provides calculation of the diffraction pattern on an observation plane by superposition of the diffraction patterns of the point light sources that made up the object on a input plane. However, it is a time consuming process. Second model is named plane wave spectrum model and it is much more faster than the pointwise model. The performances of the presented models are examined under several scenarios.Item Open Access Improving the resolution of diffraction patterns from many low resolution recordings(Bilkent University, 2010) Yücesoy, VeyselHolography attempts to record and reconstruct wave fields. The resolution limitation of the recording equipments causes some problems in the reconstruction process. An automatic method for the registration and stitching of low resolution diffraction patterns to form a higher resolution one is proposed. There is no prior knowledge about the 3D position of the object in the recordings and it is assumed that there is only one particle in the object field. The method uses Wigner transform, Canny edge detection and Hough transform to register the patterns, and some additional iterative methods depending on the local variance of the reconstructed patterns to stitch them. The performance of the overall system is evaluated against object radius, noise in the original pattern, recording noise and presence of multiple particles in the object field by computer simulations.Item Open Access A method for extracting object related information from in-line holograms using Wigner distribution(Bilkent University, 1990) Özgen, Mehmet TankutIn this thesis, a method based on Wigner distribution is developed to find the three-dimensional coordinates of particles directly from their in-line hologram without reconstruction. If a one-dimensional discrete hologram signed is subtracted from unity and the discrete-time Wigner distribution of the resulting signal is computed then a two-dimensional real sequence is obtained which can be displayed as an image carrying coordinate information about the objects encoded in the hologram. In order to analyze three-dimensional object distributions, the idea described above is adapted to the case of twodimensional holograms in the following way. A two-dimensional hologrcim is digitized in an image processing system, then, one of its rows or columns is selected and a DC level shift is given to thcit row or column. The discrete-time Wigner distribution of the resulting one-dimensional signal is computed and displayed as a two-dimensional image. If this is done for a sufficient number of rows and columns of the hologram then a set of images is obtained which contaixas the total information about the coordinates of particles encoded in the hologram.Item Open Access Signal processing based solutions for holographic displays that use binary spatial light modulators(Bilkent University, 2012) Ulusoy, ErdemHolography 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 designsItem Open Access Simulation of a holographic 3-D television display(Bilkent University, 1990) Bozdağı, GözdeThe theory and the computer simulations of an acousto-optical holographic 3-D television display are presented in this dissertation. The technique used is based on the reproduction of the desired pattern, in our case the hologram, using traveling surface waves. The crystal that will be used as the medium of display is assumed to have a number of electrodes attached to it on one side. If signals are applied to all of the electrodes, propagating waves from the electrodes will superpose to form a time-varying surface field pattern on the crystal. It is possible to find out the signals to be applied to the electrodes through an inversion relationship from the original holographic pattern. The proposed method is simpler and more efficient than the methods available in the literature and it solves the display resolution problem completely.Item Open Access Simulation of an FPGA implementation of holographic video generation in real time(Bilkent University, 2010) Yılmaz, Timur EyüpHolography is a promising method for three-dimensional vision. Different research efforts are being spent to improve generation of holograms and image reconstruction from holograms. A computer generated hologram can be a precise method of generating a real like video in the future. RayleighSommerfeld diffraction method and Fresnel-Kirchhoff diffraction formula are two algorithms suitable for FPGA implementation of hologram calculation. Simulator image reconstructions and optical image reconstructions with spatial light modulator using the generated holograms are compared and it is seen that they are quite similar. A field programmable gate array (FPGA) implementation of real time holographic video generation based on Rayleigh-Sommerfeld formulation is simulated. FPGA implementation is tested and verified by a computer simulator. An FPGA board capable of capturing video input and giving video output for spatial light modulator (SLM) is chosen as the implementation platform for simulations. A small size hologram calculator can be implemented on the FPGA board. A custom board for specific hologram calculation algorithm can be designed to increase the performance. Pipelined architecture and SDRAM memories can be used to increase the performance.Item Open Access Three-dimensional holographic video display systems using multiple spatial light modulators(Bilkent University, 2011) Yaraş, FahriSpatial light modulators (SLMs) are commonly used in electro-holographic display systems. Liquid crystal on silicon, liquid crystal, mirror-based, acousto-optic and optically addressed devices are some of the SLM types. Most of the SLMs are digitally driven and pixelated; therefore, they are easy to use. We use phase-only SLMs in our experiments. Resolution and size of currently available SLMs are inadequate for satisfactory holographic reconstructions. Space-bandwidth product (SBP) is a good metric for the quality assessments. High SBP is needed when lateral or rotational motion is allowed for the observer. In our experiments 2D images whose sizes are even larger than the SLM size are reconstructed using single SLM holographic displays. Volume reconstructions are also obtained by using such displays. Either LED or laser illumination is used in our experiments. After the experiments with the single SLM holographic displays, some laboratory prototypes of multiple SLM holographic systems are designed and implemented. In a real-time color holographic display system, three SLMs are used for red, blue and green channels. GPU acceleration is also used to achieve video rates. Beam-splitters and micro-stages are used for the alignments in all multiple SLM designs. In another multiple SLM configuration, SLMs are tiled side by side to form a three by two matrix to increase both vertical and horizontal field of view. Larger field of view gives flexibility to the observer to move and rotate around the reconstructed images of objects. To further increase the field of view, SLMs are tiled in a circular configuration. A single large beamsplitter is used to tile the SLMs side by side without any gap. A cone mirror is used to direct incoming light toward all SLMs. Compared to planar configuration, circularly configured multiple SLMs increase the field of view, significantly. With the help of such configurations holographic videos of ghost-like 3D objects can be observed binocularly. Experimental results are satisfactory.