Masachika Watanabe

Color reflection holography using four recording wavelengths

We present a theoretical analysis of color reflection holography using four recording wavelengths. The color reproduction of the hologram is discussed using the 1976 CIE chromaticity diagram. The optimum combination of the four wavelengths which minimizes the distance between the reconstructed image and the object points is calculated using nonlinear least square method. It is found that the extremely good color reproduction can be achieved by four- wavelength recording. We also analyze the color reproduction for the four practical laser wavelengths. The optimum choice of the wavelengths and the attainable color reproduction are discussed.

Mass-produced color graphic arts holograms

We have been developing various types of holograms. In this paper mass-produced color graphic arts holograms are discussed. The TRUE IMAGETM hologram, as it is known in Japan, is a volume-type hologram which diffracts selected wavelengths of the ambient light to selected desired angles. When replicating the TRUE IMAGETM, three lasers are used simultaneously or independently. There are four beneficial characteristics of the TRUE IMAGETM hologram; (1) Repeatable mass product techniques and few defects: a direct lamination method has been developed. (2) Looking bright and clear under fluorescent light: specially designed masters and replication conditions allows TRUE IMAGETM holograms to be seen under fluorescent light. (3) Stable chromaticities: expressing full color by developing objects, paints, mastering process and replication process. (4) Good environmental stability: use of effective adhesive films. In this paper, the first characteristic is mainly discussed.

The evaluation of speckle contrast with variable speckle generator

— While laser projection has many advantages, there is a problem with speckle patterns generated as a result of interference of the laser beam and results in bad effects to observers. In 2010, a variable speckle generator, which produces an angular shift of incident light to the screen and generates variable speckle patterns, was suggested. In this study, the performance of a variable speckle generator by using a volume phase holographic beam shaper and scanning mirror was investigated in detail by evaluating both the objective and subjective speckle contrast. The morphology of the speckle pattern was also investigated when the variable speckle generator was activated. With a scanning VPH beam shaper, the objective speckle was effectively reduced because each point of the VPH beam shaper generated different speckle patterns and coherency among each pattern disappeared by using the scan process. On the other hand, subjective speckle was also dramatically reduced by changing the incident angle on the screen, which resulted in generating variable subjective speckle. It was also shown that the speckle reduction rate by using a variable speckle generator did not depend on the coherent length of a laser by evaluating the normalized speckle contrast against the angular shift on the screen.

Mastering process for color graphic arts holograms

We have been developing holograms and holography technology for more than two decades for various applications. Embossed-type holograms manufactured by NDP are commercially available and are used widely in Japan. Currently, we are developing volume-type holograms. Some holographic optical elements (HOEs) and color graphic-arts are ready for commercialization. We are studying color holograms are ready for commercialization. We are studying color holograms as the next generation of volume-type holograms. At the previous SPIE meeting, we reported on the process for mass producing full-color Loppmann holograms and the adhesive film employed. This paper concerns the mastering process. It should be simple so as to be suitable for mass production, and a hologram copied from a master should have limited viewing range so as to provide greater brightness. To obtain a brighter hologram with the desired viewing angle, we employ a new modified Denishuku method for mastering. In this study, the relationship between the incident angles used for mastering and for copying was examined, and a new way of limiting the viewing area was devised. Through a combination of our mastering, replication and adhesive technologies, we have succeeded in mass production full- color holograms for the first time in the world. This has enabled DNP to develop commercial-level color graphic-arts holograms, some of which are widely available in the marketplace.

Computer simulation of reconstructed image for Computer-Generated Holograms

This report presents the results of computer simulation images for image-type Computer-Generated Holograms (CGHs) observable under white light fabricated with an electron beam lithography system. The simulated image is obtained by calculating wavelength and intensity of diffracted light traveling toward the viewing point from the CGH. Wavelength and intensity of the diffracted light are calculated using FFT image generated from interference fringe data. Parallax image of CGH corresponding to the viewing point can be easily obtained using this simulation method. Simulated image from interference fringe data was compared with reconstructed image of real CGH with an Electron Beam (EB) lithography system. According to the result, the simulated image resembled the reconstructed image of the CGH closely in shape, parallax, coloring and shade. And, in accordance with the shape of the light sources the simulated images which were changed in chroma saturation and blur by using two kinds of simulations: the several light sources method and smoothing method. In addition, as the applications of the CGH, full-color CGH and CGH with multiple images were simulated. The result was that the simulated images of those CGHs closely resembled the reconstructed image of real CGHs.

32.1: Laser Projection System with Variable Speckle Generator

Laser projector with variable speckle generator was introduced, which image of micro display was projected on screen. Variable speckle generator utilizing holographic beam shaper and scanning mirror made angular shift of incident light and generated numerical speckle pattern in a short time. Speckle contrast of 0.03 was achieved.

Holographic polymer dispersed liquid crystal system utilizing the co-polymerizations with siloxane compounds and polypropylene glycol derivatives

Holographic polymer dispersed liquid crystal (HPDLC) has a feature that can control diffraction of light by applying electric field. HPDLC can be used for optical elements such as an optical switch, or a polarized beam splitter etc. One of the reactive systems for making HPDLC is well known photopolymerization-induced phase separation (PIPS). The performance of HPDLC by PIPS is dependent on distribution of oriented liquid crystal (LC) molecules, or size and shape of LC droplets. These are controlled by chemical structure or functional group of polymer matrix. In this report, Organic-inorganic hybrid materials having sensitivity at 532 nm were synthesized. Polymer matrix was formed with co-polymerization of siloxane-containing materials and poly (propylene glycol) derivatives functionalized with methacrylate groups. Siloxane chain was introduced in polymer matrix to encourage phase separation of LC and stabilize grating structure. In addition, poly (propylene glycol) derivatives were designed to control polymerization rate and extent of phase separation of LC. The characterization of HPDLC was evaluated in terms of diffraction efficiency, contrast between diffraction and transparency modes by applying voltage, and switch speed. As a result, the separation ratio of p-polarized light and s-polarized light was 100:1. The value of ▵n was 0.075, and the index matching of both polymer-rich layer and LC-rich layer was completed at voltage of 17V/μm.

Development of peripheral materials for color graphic arts holograms

Dai Nippon Printing is the first company in the world to succeed in the mass production of full-color 3D Lippmann type holograms, which are marketed under the name of TRUE IMAGETM. TRUE IMAGETM labels consist of a panchromatic photopolymer material and pressure-sensitive adhesives (PSAs). This new medium is expected to have wide application in various fields, such as publishing, labels for authentication, and so on. For commercial use, TRUE IMAGETM labels require high-quality PSAs. In this study, two new PSAs and a new layer structure were developed. One PSA provides TRUE IMAGETM labels with good environmental stability, and the other adjusts the playback wavelengths. These two PSAs together with a new layer structure have enabled the development of a new type of TRUE IMAGETM label for security applications.

Depth Perception with See-Through Holographic Display

The depth perception of three-dimensional images was evaluated with see-through holographic display. In our experimental conditions, the influence of visual angle of the image is greater than that of accommodation in the depth perception.

Quality evaluation of Lippmann-type hologram using CGH

Dai Nippon Printing Co., Ltd. (DNP, Tokyo, Japan) has succeeded in recording Lippmann holograms with an image of Computer-Generated Holograms (CGHs). As Lippmann holograms are usually made by real three-dimensional object, design variation of the objects are restricted by the possibility of manufacturing the object. On the other hand, as CGHs are made by computer graphics (CG), many different kinds of virtual images can be built into holographic images. Also, it has very fine resolution because it is made by the Electron-Beam lithography system. By incorporating the image expression of the CGH into Lippmann hologram, we have developed a new hologram combining both CGHs and the Lippmann holograms.