KEYWORDS: Holograms, Holographic displays, Spatial light modulators, RGB color model, Near eye displays, 3D image reconstruction, Multiplexing, Light sources and illumination, Lenses, 3D displays
Near-eye displays (NED) are devices that are intended to project three dimensional images with wide-angle view. However, at present most of the 3D displays are based on stereoscopic principle, which does not satisfy the required parameters of human vision. This limitation can be overcome by implementing digital holograms within the NED. This is because a digital hologram contains the whole wavefront information of the scene. Thus, a holographic NED (HNED) is capable to reconstruct any three-dimensional scene while matching all the physiological cues of human vision. Nevertheless, truly immersion experience in HNED requires wide angle view and full colour reconstruction as well. In this work, we study HNED for pupil and non-pupil configuration that reconstructs large 3D colour scenes. The colour reconstruction is made by using RGB illumination and time multiplexing. Numerical analysis is carried out to test the FOV and the quality of reconstructions. Moreover, experimental colour reconstructions are made by employing laser for the pupil configuration and LED for non-pupil configuration. This is done to compare reconstruction quality and FOV of the displayed 3D scene.
Methods for manipulating the geometry of 3D image by linear transforming of hologram data are very efficient. Such techniques are desirable also for wide-angle viewing holographic display. Especially when there is no direct access to the reconstructed image due to lack of numerical hologram reconstruction techniques. Hence, methods based on directly manipulating the holographic image cannot be applied. In this paper, we investigate theoretically, numerically, and experimentally the image manipulations based on hologram stretching for the case of wide-angle near eye holographic display. We show that for wide-angle display the significant Petzval curvature and astigmatism errors are obtained in image reconstruction. Finally, applicability of the investigated image manipulation methods is shown with experiments of hologram reconstructions in a wide-angle holographic display.
In this paper, a color holographic imaging solution using tabletop holographic display and synthetic aperture Fourier capture system is discussed. As a display, we utilize a tabletop prototype, which is based on temporal multiplexing method and two parabolic mirrors from our previous work. In order to provide the same perspective effect as looking at an object on a table, the wavefield of the tabletop display propagates from the hologram plane to a viewing window at 45° angle. A color capture system is implemented by optical path modification of synthetic aperture Fourier capture system using two tilting mirrors to record the same perspective view of the object as the display. The numerical processing path for three channel color hologram solution is presented including compensation of lateral RGB dimensions, propagation with sampling compensation, and binarization. To evaluate the proposed method, numerical and optical reconstructions are presented in the experimental results.
KEYWORDS: Holograms, Digital micromirror devices, Digital holography, Holography, Multiplexing, Binary data, 3D image reconstruction, LED displays, Speckle
In the paper we investigate hologram binarization method through time multiplexing based on histogram. In the proposed approach input object is divided into N components with equal total intensity distributions. Next, propagation and binarization procedure is employed for each component separately. Presented method is matched to DMD application since it modulates the input light simply by reflection. In the computer simulations the quality of the reconstructed holograms with the proposed method is compared with that of the threshold method for different reconstruction distances. Additionally, efficiency of the technique is verified experimentally during optical reconstructions performed in the holographic display with DMD and LED illumination.
KEYWORDS: Holography, Spatial light modulators, Holograms, LED displays, Digital holography, RGB color model, 3D image reconstruction, Light emitting diodes, Multiplexing
The digital holography and holographic display constitute the best framework of 3D imaging as they aim to recreate the complete optical field emitted by a recorded scene. In this paper, we present two techniques of Fourier holographic imaging of real world objects. The first solution is an end-to-end full color Fourier holographic imaging approach, which involves standard RGB holographic recording an LED-driven viewing window display. It gives possibility of almost undistorted orthoscopic reconstruction of large real objects. Second architecture uses the same digital holographic content and horizontal parallax rainbow holographic display, which has reduced space bandwidth product requirements.
The rainbow hologram provides observation of the reconstructed object with different spectra over different viewing position. Recently, we’ve proposed a concept of digital rainbow holographic display using diffraction grating and white LED lighting source. In the technique, the slit is implemented numerically by reducing the frequency of the hologram, while the rainbow effect is realized by dispersion of white light source on the diffraction grating. Phase only SLM with 4F imaging system is used for implementation of complex wave fields. For classical rainbow hologram, image blur is known to be very important key point regarding holographic image quality. In this paper, we analyze image blur and visual perception for digital rainbow holographic display. The quality of reconstructed rainbow holograms is investigated under varying viewing conditions regarding visual perception and depth resolution. In experiments, the visual properties of the digital rainbow hologram are analyzed using optical reconstructions for the hologram of 3D and 2D objects of different depth.
KEYWORDS: Data compression, Optical design, Binary data, Holography, Digital micromirror devices, Light emitting diodes, LED displays, 3D displays, Holograms, Spatial light modulators, Multiplexing, Imaging systems, RGB color model
In the paper we investigate the possibility of color reconstructions of holograms with a single DMD and incoherent LED source illumination. Holographic display is built with 4F imaging system centering reconstruction volume around the DMD surface. The display design employs complex coding scheme, which allows reconstructing complex wave from a binary hologram. In order to improve the quality of reconstructed holograms time multiplexing method is used. During the optical reconstructions we analyze quality of reconstructed holograms with incoherent RGB light sources as a function of reconstruction distance, present the possibility of 3D hologram reconstruction, and investigate temporal coherence effects in holographic display with the DMD.
In this work we present holographic display that uses LED sources illumination and have enlarged viewing angle. In this holographic display design we employ phase only SLM because it allows to obtain reconstructions of high quality. Our setup realizes complex coding scheme and allows to reconstruct complex holographic images. Thus reconstruction of inplane holograms is possible. Holograms displayed on SLM are computer generated. For enlargement of angular field of view we use three spatially separated illumination sources and time multiplexing technique. In experimental part, where we display computer generated holograms, we show that it is possible to obtain holographic reconstructions of 3D object with extended viewing angle.
In presented paper we study the influence of spatial and temporal coherence of light source on resolution and depth of focus of holographic reconstructions. Presented holographic display setup uses phase - only spatial light modulator and realizes complex coding shame which allows to reconstruct objects in volume centered around plane of the modulator. In simulations we implement partially coherent reconstructions of complex hologram theory. It allows to investigate quality of holographic reconstructions for various degree of illuminating light coherence. During experimental tests we validate simulation results. We show that the influence of spatial coherence effect of light source on resolution of reconstructed objects is stronger than that of temporal coherence. Moreover we prove that it is possible to obtain high quality holographic reconstructions for large size source and wide spectrum for objects having large depths.
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