The reconstructed image from digital holography are laden with many distortions. The main cause of these distortions is known as the finite size of pixels in the display panel/chip. Due to this finite size, the starting position of the reconstructed rays in each pixel can be any place in the pixel. Hence the starting position can be different from the recording beam position which is usually considered as the center of each pixel. This difference makes that the reconstructed rays are no longer the phase conjugated rays of their corresponding recording rays. The reconstructed rays are somewhat distorted in their wavefronts. To estimate these wavefront distortions, a Shack-Hartmann wavefront sensor is used in the pathway of the reconstructed beam. The phase distribution obtained with the sensor reveal that the distortion is more for the bigger pixel size and for the images with more reconstructed image points as expected. This result indicates that the sensor is a reasonable method of estimating the distortions in the reconstructed image. The same sensor is also used to estimate the functional performance of holographic optical elements for image projection.
Generally in electronic holographic display systems, coherent light sources are used to reconstruct holograms. The random distribution of phase profile of an object image causes unwanted dark and bright spots to degrade reconstructed hologram images. In addition, a periodic structure of available spatial light modulators such as liquid crystal on silicon devices and digital micro-mirror devices generates various diffractive signals when they are illuminated by coherent light sources. Consequently, it is necessary to select a proper signal band in spatial frequency domain by effectively filtering out unwanted signals. In this paper, the speckle pattern in a table-top holographic display system is measured and the method for reducing the speckle patterns is to be shown.
We have designed and successfully implemented 360-degree viewable holographic display prototype systems. Core idea of the system design lies in the exploitation of fast operating speed of DMD for binary amplitude modulation of light field, being distributed to more than 1,000 viewpoints along the 360 degree viewing circumference. Slanted downward viewing angle and 360 degree viewable 3-dimensional(3D) image over the center of tabletop display is achieved by specially designed optics. As a result, solid-looking 3D moving color images of larger than 3 inches are rendered and observed by several viewers at the same time from different viewing positions. We have implemented and experimented several variations of the system. They are tiling of SLM modules(2x2 tiling with 4 DMDs for mono-color display and 1x2 tiling with 6 DMDs for color display), using different SLMs(DMD of pixel pitch 13.68μm and resolution 1,024x768, DMD of pixel pitch 10.8μm and resolution 1,920x1,200), and applying different structure of image floating optics((1)double parabolic mirrors, (2)one parabolic mirror and one beam splitter, (3)two spherical and one flat mirror). We report the result of various display system implementations based on several combinations of above-mentioned design options.
Space bandwidth product (SBP) is one of the most significant limitation for displaying the digital holographic display. Due to the SBP problem, the size and viewing angle of displayed holograms cannot be enlarged simultaneously. To overcome the SBP problem, holographic projection system has been researched. It uses a field lens to converge diffracted light from a spatial light modulator (SLM) into a viewing window, where the observer can see whole hologram image displayed on the SLM. However, it has a problem that the viewing distance between the display and observer cannot be controlled and fixed on the viewing window plane. We propose a method to control the position of viewing window formation in the holographic projection system by using an electrically focus tunable lens. We added the focus tunable lens in the holographic projection system, and the position of the viewing window can be controlled by its lens power variation. The principle of controlling viewing window in the proposed system is described, and the relationship among the optical power of focus tunable lens, location and size of the viewing window is analyzed. A computer generated hologram encoding based on Fresnel diffraction theory is developed to generate hologram contents for the proposed system with consideration of varying optical power of the focus tunable lens. Test-bed is built to verify the feasibility of the proposed method, and the experimental results confirm that the proposed method can effectively control the viewing window position of the holographic projection system.
In this paper, we use an optical method for the implementation of spatially-tiled digital micro-mirror devices (DMDs) to expand space bandwidth product in general digital holographic display systems. In concatenating more than two spatial light modulators (SLMs) optically, there may exist both phase discontinuity and amplitude mismatching of hologram images emanating from two adjacent SLMs. To observe and estimate those properties in digital holographic display systems, we adopt quantitative phase imaging technique based on transport of intensity equation.
We present an extended viewing angle holographic three-dimensional display system using optical fiber arrays backlight and a pupil-tracking technique. One of the limitations in implementing a wide viewing-angle holographic three dimensional display is the restrictive space-bandwidth product of the spatial light modulator. In our proposed method, the optical fiber arrays backlight with pupil-tracking system enables to enlarge the static viewing angle of the holographic reconstruction using only one spatial light modulator.
Sub-hologram based holographic display method is one of the most practical approaches for realizing big size
holographic display. However, this method needs highly accurate face and eye tracking function in real-time to enable
precise steering of backlight and generation of corresponding sub-hologram for each video frame. We theoretically
estimated several parameters, such as accuracy, speed and distance from an observer, required for the eye tracking
function and developed an eye tracking system whose objective is accurate and fast 3D positioning of left and right
pupils of an observer. Experimental results show that the system obtains accurate 3D pupil positions with an error less
than 3 mm at 30 frames per second under disturbing conditions such as more than 2m distance and an observer wearing
glasses. Therefore, our implementation could be sufficiently applied to the sub-hologram based display system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.