Browsing by Subject "Digital Holography"

Now showing 1 - 3 of 3

Open Access
Computation of holographic patterns between tilted planes
(2004) Esmer, Gökhan Bora
Holography 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.
Open Access
Improving the resolution of diffraction patterns from many low resolution recordings
(2010) Yücesoy, Veysel
Holography 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.
Open Access
Three-dimensional holographic video display systems using multiple spatial light modulators
(2011) Yaraş, Fahri
Spatial 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.