Byung-Chul Cho

Implementation of Multiview 3D Display System using Volume Holographic Optical Element

Generally, the autostereoscopic 3D displays provide the viewer with a truly 3D image without the need of any special glasses. In this paper, a new multiview autostereoscopic 3D display system using a photopolymer-based VHOE is proposed. The proposed system utilizes a time-multiplexed scheme where a series of views of a scene are displayed sequentially on a high-speed SLM and the VHOE acting as an optical directional modulator is synchronized with the image repetition rate to project each image to a spatially different zone in front of the screen. The VHOE is made by recording angularly different multiple interference patterns in the photopolymer hologram, and it can used to diffract the incident light to the spatially different positions by simply controlling the angles of the reference beam. In this paper, Dupont photopolymer is used for implementing the VHOE device and its physical properties such as sensitivity, diffraction efficiency for the optimal recording of diffraction gratings are measured. From some experimental results on the optical characteristics of the Dupont photopolymer-based VHOE, a possibility of implementation of the time-sequential multiview 3D display system using the VHOE is also suggested.

Performance analysis of phase-code multiplexed holographic memory

For analysis of effective phase-code multiplexing in a holographic memory system four types of phase code are generated and used as a reference beam. In computer simulations the size of the address beam is fixed at 32 x 32 pixels, and 0%, 5%, 10%, 15%, 20%, and 25% phase-error rates in a pixel are purposely added to the real phase values for consideration of the nonlinear phase-modulation characteristics of a practical spatial light modulator. Cross talk and signal-to-noise ratios (SNRs) are comparatively analyzed for these phase codes by calculation of the autocorrelation and the cross correlation. The pseudorandom code (PSR) has the lowest cross-correlation mean value of 0.067 among the four types of phase code, which means that the SNR of the PSR is higher than with other phase codes. Also, the standard deviation of the PSR, indicating the degree of recalled data degradation, has the lowest value, at 0.0113.

Performance analysis of photopolymer-based VHOE for time-sequential multiview 3D display system

In this paper, optical characteristics of the photopolymer-based VHOE for a new time-multiplexed multiview autostereoscopic 3D display system is analyzed. The photopolymer-based VHOE is recently, proposed as a optical directional modulator for projecting the time-multiplexed multiview stereo images to the spatially different directions. Since the VHOE is made by multiplexed recording of the multiple directional gratings in a photopolymer material, the resolution and parallax number of the VHOE-based 3D display system can be limited by the photopolymers physical and optical properties, in general. Accordingly, to make the photopolymer-based VHOE to be applicable for a multiview autostereoscopic 3D display system, it is required to have some important properties such as low distortion, uniform intensity & high diffraction efficiency of the diffracted light beams, etc. In this paper, the optical and physical characteristics of the Du-Pont photopolymer-based VHOE such as the degree of distortion & uniformity of the light beam diffracted from the VHOE, its photosensivity and diffraction efficiency are measured and discussed.

Multiview autostereoscopic 3D display system using volume holographic optical element

In this paper, a new multiview autostereoscopic display system using the volume holographic optical element (VHOE) is proposed. The VHOE is used for projecting the multiview images to the spatially different directions sequencially in time and it can be made from volume holographic recording materials. In this paper, Dupont photopolymer is used for VHOE materials and measured its physical properties such as sensitivity, diffraction efficiency for the optimal recording of diffraction gratings. In addition, from analyzing the dynamical aspects of optical characteristics for the photopolymer-based VHOE with coversheet, it is more useful for the practical implementation of the VHOE-based multiview 3D display system. By analyzing the basic and dynamic characteristics of Dupont photopolymer through some experiments, the feasibility for the implementation of VHOE-based multiview autostereoscopic display system is suggested.

Optical memory using programmable pseudorandom codes

For analysis of an effective phase code multiplexing in a holographic memory system, the Hadamard matrix (HAM) and the pseudorandom phase code (PRC) are generated and used as a reference beam. In computer simulations, the size of the address beam is fixed to 32 X 32 pixels, and 0%, 5%, 10%, 15%, 20%, or 25% phase error rate in a pixel is purposely added to the real phase values in order to consider the nonlinear phase modulation characteristics of the practical spatial-light modulator. Crosstalks and signal-to-noise ratios (SNRs) are comparatively analyzed for these two phase codes by calculating the auto- and cross-correlation. The cross-correlation mean values of the PRC and the HAM are 0.067 and 0.139, respectively, which means that the SNR of the PRC is higher than the HAM.

Phase-Error Considerations for the Practical Phase Code Multiplexed Holographic Memory

For analysis of an effective phase code multiplexing in a holographic memory system, the Hadamard matrix (HAM) and the pseudorandom phase code (PRC) are generated and used as a reference beam. In computer simulations, the size of the address beam is fixed to 32×32 pixels, and 0%, 5%, 10%, 15%, 20%, or 25% phase error rate in a pixel is purposely added to the real phase values in order to consider the nonlinear phase modulation characteristics of the practical spatial-light modulator (SLM). Crosstalks and signal-to-noise ratios (SNRs) are comparatively analyzed for these two phase codes by calculating the auto- and cross-correlation. The cross-correlation mean values of the PRC and the HAM are 0.067 and 0.139, respectively, which means that the SNR of the PRC is higher than the HAM.

Implementation of design simulator for integral photography-based 3D imaging and display system

The 3D imaging and display system based-on the integral photography(IP) method has been actively researched. But, It is a little bit difficult to implement the IP-based 3D display system to have the satisfiable 3D image resolution by using the conventional optical devices. Besides, it has some problems of limited viewing angle and observation distance. Accordingly, to alleviate these kind of problems, some sort of the design simulator for implementing the practical IP-based 3D display system is needed, in which the system parameters of the conventional optical devices can be optimized for given environments. Therefore, in this paper, the design simulator for the IP-based 3D display system is implemented by using the various display and design parameters through Visual C ++ program in GUI(graphic user interface) environment. From the analysis of relationship between the design and display parameters by using the implemented design simulator, the optimized design parameters for the cases of the various conditions can be derived. From some computer simulation, it is suggested that the optimum design parameters for any kind of given situations can be derived by using the IP-based 3D display design simulator.

Analysis of optical characteristics of photopolymer-based VHOE for multiview autostereoscopic 3D display system

Generally, an autostereoscopic display presents a 3D image to a viewer without the need for glasses or other encumbering viewing aids. In this paper, we propose a new autostereoscopic 3D video display system which allows viewers to observe 3D images in the same range of viewing angle. In this system, a photopolymer-based VHOE is made from volume holographic recording materials and it is used for projecting a multiview images to the spatially different directions sequentially in time. Since this technique is based on the VHOE made from the photorefractive photopolymer instead of the conventional parallax barrier or lenticular sheet, the resolution and parallax number of the proposed VHOE-based 3D display system are limited by the photopolymers physical and optical properties. To make the photopolymer to be applicable for a multiview autostereoscopic 3D display system, the photopolymer must be capable of achieving some properties such as a low distortion of the diffracted light beam, high diffraction efficiency, and uniform intensities of the reconstructed diffracted lights from the fully recorded diffraction gratings. In this paper, the optical and physical characteristics of the DuPont HRF photopolymer-based VHOE such as a distortion of displayed image, uniformity of the diffracted light intensity, photosensitivity and diffraction efficiency are measured and discussed.

Rotation-angularly multiplexed holographic memory system using moving window and double-focusing lens

A new rotation-angularly multiplexed holographic memory system by using moving window and double-focusing lens (DFL) is proposed, in which crosstalk due to two neighboring moving window rows in the vertical direction of the conventional moving window (MW) holographic memory system can be overcome. That is to say, in the proposed method, crosstalk in the vertical direction can be eliminated by combined use of the DFL, which has periodical curvature of radius R1 and R2 with different focal lengths F1 and F2, respective, and moving windows on the LCD spatial light modulator. Light beams form curvature of radius R1 and R2 parts of double-focusing lens are focused at F1 and F2 locations, respectively, to occur different reference wave vectors Kr and Kr. By such shift multiplexing effect, crosstalks due to two neighboring MW rows in the vertical direction on the reconstruction can be eliminated. By combining the proposed multiplexing method with rotating disc-type photopolymer, it is possible to achieve the high- density storage capacity compared with the conventional holograph memory system and its feasibility is demonstrated through optical experiments.

Performance Analysis of Complex Phase-Code for Volume Hologram Multiplexing

In this paper, performance of the complex phase code (CPC) which is recently proposed as a practical phase encoding method for volume hologram multiplexing is analyzed in detail. This new CPC has been known to have not only random and orthogonal properties but also the potential to generate a relatively large number of address beams in a holographic memory. For performance analysis of the CPC in a holographic memory system, four types of phase code, the new CPC, as well as the conventional pure random code (PR), random code with equality (RCE), WHM (Walsh Hadamard Matrix), are generated and used as the address beam. In computer simulations, the size of the address beam is fixed at 32 x 32 pixels and 0%-25% phase-error ratio in a pixel are intentionally added to the ideal phase values to consider the nonlinear phase-modulation characteristics of the practical spatial light modulator. From comparative analysis of crosstalks and signal-to-noise ratios for these phase codes by calculating auto-correlation and cross-correlation, it is found that the new CPC have the lowest cross-correlation mean value of 0.021, the lowest standard deviation of 0.0113 and the highest SNR of 26.9 among the four types of phase code. In addition, from the calculation of the number of all possible address beams for these four types of phase code as the size of the address beam is fixed to 32 x 32 pixels, the CPC is found to have 6.334 x 10 4 9 address beams, which are relatively higher number than that of the conventional phase codes.