Masaaki Okamoto

Head-mounted display using a holographic optical element

We will discuss the prototype of Head Mounted Display using Holographic Optical Element in this paper. It is obvious that a single HOE can record the multiple optical images by the characteristic in itself, that is angular selectivity and wavelength selectivity. Therefore, it is very easy to understand the HOE has the function which can separate the stereoscopic images onto the left and right eyes, like as the conventional HMD. In this report, we propose the prototype of HMD using a single HOE, and we will extract the problem in application of the real industrial field, especially manufacturing and designing. Consequently, we proved that the HMD using Lippmann hologram has the potentiality of miniaturization, lightening, wide field of vision. This HMD can be suitable in the Virtual Reality field. But it is necessary to adjust the pupil distance and the incident angle of conjugate beam precisely.

New approach to the real-time 3D display using a holographic optical element

A display system requiring no special glasses is a useful technology for 3D images. In this paper, two types of real- time 3D displays using a holographic screen instead of a lenticular screen are described. One is a stereoscopic 3D display system with viewing apertures such as conventional two-step holographic stereogram. The other is a stereoscopic 3D display system based on a reconstruction of parallax- rays. These systems consist of a liquid crystal device and a holographic screen formed on holographic optical elements. These systems can construct animated 3D images in real-time by updating LCD pixels.

Holographic stereovision system with multiple focuses

This report is concerned with a stereovision system using holographic optical element (HOE). The authors introduce a natural 3D display system that provides the observer the clear stereoscopic vision without glasses. Even though both eyes of the observer are arbitrary located at the focuses of the stereovision system, he can be satisfied to look at the suitable 3D images. It is important that the focuses are not restricted at the specific points but occupy more broad areas. Such a mechanism is realized by the method of exposing with the diffractive plate. Moreover the authors are interested in a deep stereovision system. The system with four focuses is described to provide the adequate focuses in the accordance with his distance from the object. This system has HOE of multiple focuses that makes two pairs of viewing points in the back and forth locations. In this system four original images are projected from the behind of the HOE. All images join at the HOE and advance for the schemed focuses.

Multiple illuminations method for rainbow hologram using an LCD projector

This report is concerned with several display systems for making 3D image fluctuate. These systems aim to reconstruct rainbow hologram images moved dynamically. The first method is using small motors for drifting an illumination and swinging a reflection mirror. The second method is using an electric fan for flapping a film hologram hung with rubber strings. The third method is using a liquid crystal display (LCD) projector controlled by a computer and a screen sized reflection panel composed of many small mirrors. In the last case, the small beam out of the LCD projector is reflected on a mirror of the reflection panel and illuminates the hologram panel. The hologram image generated by each small mirror has its particular property that is slightly different each other; shape, position and color. The highlight pattern of the beam projected on the reflection panel is moved by the computer program. When the pattern is fluctuated by the computer program, the position and color of the generated hologram image fluctuate accordingly.

Color multiplex imaging 3D display system using holographic optical element

The authors propose new 3D display system using Holographic Optical Element (HOE) without glasses. The proposed HOE is used as holographic screen in this system. The HOE of proposed method can reconstruct white light in white illumination light. Namely, this HOE can reconstruct color images. The HOE has diffraction efficiency issue. However, we solved this issue, because we considered the Bragg condition when we made the HOE.

Color control of hologram image using a single laser under the Bragg condition

A simple diffractive equation representing the Bragg condition is introduced from the pair of grating equations about thick hologram. Usually a color hologram is multiple exposured by 3 lasers; red, green, blue. Each fringe angle can be naturally equal to the others by adjusting 3 beams to the same direction. As the result every Bragg angle is the same value.

Computer-generated color holograms using RGB color filters

We have been making researches on 3D displays using computer-generated holograms (CGHs). We use an image setter with a resolution of 5080 dots per inch to record the binary CGH patterns. It is possible to reconstruct CGHs with light- emitting diodes or light bulbs which have small emitting segments. In the reconstruction with a light bulb, color- smeared images are observed due to the white light. In order to improve this dispersion, we considered a method to apply a color filter to the CGH. And, we propose a method to make computer-generated color hologram which can reconstruct color point light sources, by combining RGB color filters with the stripe CGHs corresponding to each color.

Fluctuation hologram with multiple images

This paper is concerned with illumination systems for fluctuating the images of rainbow holograms by an LCD projector and a wide mirror array. The authors introduce the early display systems developed for fluctuation holograms. These systems are not enough to fluctuate them arbitrarily because the locations or the angles of their light sources are fixed or cyclically varied. The authors developed an illumination system by which the observer can see the image of the hologram fluctuated like under the natural environment. An LCD projector and a lens-mirror array are used in the illumination system. The lens-mirror array is composed of about 400 small mirrors pasted over with thin concave lenses. The beam projected out of the LCD projector covers the lens-mirror array. The beam reflected by the lens-mirror array is centered for the hologram panel fixed above the LCD projector. When the highlight zone from the LCD projector is continuously moved on the lens-mirror array, the image of the hologram is smoothly fluctuated. In the case of a large holographic optical lens panel instead of the lens-mirror array, the illumination system becomes more simple. The time to adjust the position of the hologram and the angle of the holographic optical lens panel is extremely reduced. Although the bright area is limited around the zone of the mid height, the movement of the rainbow hologram becomes more natural. Next the authors prepared a multiple exposed hologram that was recorded multiple images like a stereogram. This case realized that the image of the hologram is fluctuated more complicatedly because the multiple images are reconstructed by the multiple illuminations.

Multi‐view display with hologram screen using three‐dimensional Bragg diffraction

Abstract Multi‐view function is important to three‐dimensional displays without dedicated glasses. It is the reason that the observers earnestly desire to change their positions freely. Multi‐viewing is also principal to the reality of three‐dimensional (3D) image displayed on the screen. The display of projection type has the advantage that the number of viewing points can be easily increased according to the number of projectors. The authors research on multi‐view projection display with hologram screen. Powerful directionality of the diffracted beam from hologram screen is required unlike two‐dimensional (2D) display. We developed a new method that all diffracted beams satisfied the same Bragg condition and became sufficiently bright to observe the 3D image under usual indoor light. The principle is based on the essential Bragg diffraction in the three‐dimensional space. Owing to such three‐dimensional Bragg diffraction we achieved an excellent hologram screen that could be multiple reconstructed in spite of single recording. This hologram screen is able to answer arbitrary numbers of viewing points within wide viewing zone. The distortion of 3D image becomes also sufficiently small with the method of dividing the cross angle between illumination and diffraction beam.

Hologram fluctuating in a kaleidoscope

This paper is concerned with the hologram fluctuating and spinning in a large kaleidoscope. The authors have been studying many display systems for fluctuating the image of rainbow holograms. In the prior systems the authors fluctuated holograms by using several assistant devices. In the new system holograms are fluctuated only by the intention and the operation of the observer. This simple system without surplus is one of the ideal fluctuation holograms. Two types of kaleidoscopes are introduced in this paper. The one is the prism kaleidoscope that has the popular shape made of three rectangles. It provides the observer many colorful reflected images of a rainbow hologram. The other is the pyramid kaleidoscope that has the unique shape made of three trapezoids. It provides the observer complicate and fantastic images of a rainbow hologram.