Eun-Seok Kim

Dynamic characteristics using dark reaction in photopolymer

The diffraction efficiencies of DuPonts photopolymer OmniDexR 706 holographic recording material are measured for exposures, incident angles, diffusion-time delays and exposure times. As attaching the material on a glass or plastic plate, unwanted secondary gratings are induced, which make the diffraction efficiencies much lower than expected. In order to eliminate this phenomenon, we change the incident angle between the object beam and the reference beam. Since the polymerization and the photospeed of photopolymers are 1000 times slower than silver halide materials, holograms can be influenced with many kinds of parameter. It was examined the static characteristics and the dynamic characteristics that are related with an exposure time and a diffusion-time delay using the dark reaction of monomer in polymerization. Applying the dynamic characteristics, the diffraction efficiencies of this material were stabilized. As a result, the best condition is achieved when the total input power is 8 mW [exposure energy is 200 (mJ/cm2) in our experiment] and the diffusion-time delay is from one to three minute.

Holographic optical element for head-mounted display application using photopolymer

In this paper an application of the Holographic Optical Element (HOE) which is designed by using the photopolymer is proposed. Using the HOE to replace two optic elements of the conventional HMD is possible to reduce the volume and weight. In order to implement the proposed system, we analyze the optical characteristics of the photopolymer and confirm the optimum recording condition of the HOE. The proposed system is verified experimentally.

Holographic stereograms using new geometrical sampling method

Sampling method for making 3D animation using computer animation data is presented. Computer animation data has 3D information and displayed with 2D images on the screen or CRT. We divide these 3D animation data into several aspect of views (2D images) and synthesize onto holographic film. After chemical processing we can see 3D images the same as what they have when they are made. Also, using the TFT LCD (liquid crystal device), holographic stereograms can be made easily. In this paper, geometrical method is used in order to easily calculate the sampling angles and TFT LCD to display the 2D images. Experimental results show that this method is very tolerable to be shown with 17 degree for several people. In addition, with these series of stereograms and holographic screen, the 3D movie will be possible.

Diffraction efficiency stablilization in reflection-type photopolymer

The polarization properties of the reflection-type holographic recording material, DuPont photopolymer OmniDexTM 706, have been studied. Depending on the position of photopolymer-Mylar assembly, linearly polarized laser beam alters its polarization state about 40%. Due to the birefringence of Mylar substrate, this phenomenon has been occurred very randomly through a wide range and affected in diffraction efficiencies. In the case of reflection-type hologram, the directions of two beams incident onto the recording materials are not same, the change of the polarization states cause the weak fringe visibility. As a result, reflection holograms have shown low diffraction efficiencies and unstable characteristics.

Analysis of polarization characteristics of reflection-type photopolymer for stabilization

Some polarization properties of reflection-type photopolymer are investigated. The Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. The extinction ration is of the order of 1 to 3.7 for the tested samples. Polarization effects are found to change over different regions of each sample by approximately 10 to 50%. The Mylar substrate alone was found to distort the incoming polarization to a comparable degree. By aligning the position of the photopolymer to have the maximum amount of light passed through the analyzer, it is possible to make stabilized gratings with uniform diffraction efficiencies.

Dynamic characteristics analysis of a reflection type photopolymer

Refractive-index changes in photopolymers are caused by exposure-related polymerization as well as by consequential diffusion of monomers. The authors perform experiments using the following procedures: The experiments are performed with equal input intensities of 1 mW for the two beams whose diameter is 1 cm. As a first step, the diffraction efficiency as a function of the exposure energy is measured. Also, the dependence of the incident angles is measured. One beam is fixed at 0/spl deg/ to the normal of the surface of the recording material and the angle of the other beam is changed. The diffraction efficiency curve as a function of the incident angle is determined.

Enlargement of holographic stereograms for an architectural perspective presentation

As the interest of holographic stereogram in the 3D displays is increased, the application of this technique has been suggested in several fields. Especially, in architecture, 3D birds-eye view can be replaced instead of building models. In this paper, the possibility of application is proposed and demonstrated it in architectural perspective presentation. Using computer graphics, we can create an object that has 3D information, but it is only 2D when projected on a screen or CRT. Dividing these computer- generated graphic objects into several views aspects (2D images) and then synthesize them onto holographic film. A geometrical method is used to calculate sampling angles, and a TFT LCD is used to display the 2D images. Using a big size of collimating mirror and films, we made a holographic stereogram, which is 600 X 400 mm2.

Holographic stereogram using a geometric method for computer-generated images

To realize the cyber space that exists only in the computer, a geometric method for a holographic stereogram is proposed. In the calculation of the binocular parallax angle, some additional distance that is not real is considered. Considering the magnification of the projected images, the binocular parallax angle is calculated and horizontalparallax- only (HOP) holograms are made. This method is applicable to both flat and cylindrical stereograms.

New approach to the sampling of holographic stereograms

Simpler and easier sampling method which is one of the most important parameter required for making holographic stereograms is presented to reconstruct the images from transfer hologram. Instead of fringe-by-fringe sampling method which is difficult to apply in recording holographic stereograms, a new geometrical method is proposed for easier calculation of the sampling numbers. When the slit size is fixed under human pupil size, one can see the full 2D image through a slit. Dividing the distance between the two pupils by slit size, it determines the sampling numbers which are needed for recording. The angle difference of the real object becomes a binocular parallax. And the series of these 2D images are recorded on the master hologram. After processing, it transfers to transfer hologram. As a result, two images which exactly correspond to the places of viewers eyes can be seen simultaneously. Because the object is taken at different angle and these two images are observed simultaneously, it makes us feel as a real object.