Yasuo Yamagishi

A Nematic-Cholesteric Bistable Liquid Crystal Display For Projectors

An electrically writable bistable liquid crystal projection display has been developed. This projection display uses the bistable effect of nematic-cholesteric liquid crystal phase transition under an electric field. The nematic-cholesteric liquid crystal has some advantages in application for a projection display. These are a bright screen with no need for polarizers, a high information content, thanks to the bistable memory effect, a compact system written by only electric field, and a low cost projection system using a simple matrix panel. The newly developed liquid crystal projector has 640x400 pixels, and has good contrast under the bright ambient light of a normal office environment. It takes 1.6 seconds to write all the pixels and 100 milliseconds to type in a 16x16-dot letter. It operates satisfactorily between 5 to 45 T. Use of the nematic-cholesteric liquid crystal results in the total size of the projection system to that of a portable overhead projector. Writing by an electric field makes it quite easy to connect with floppy disk systems, key boards and communication equipment systems.

A multicolour projection display using nematic-cholesteric liquid crystal

A multicolour projection display with a bright screen and large information capacity has been developed using nematic-cholesteric (NC) liquid crystals (LCs). Through investigation of light scattering in the focal-conic state of the LC layer, the authors found that the transmittance depends on the light wavelength, because of diffraction scattering, and that the colour of light transmitted through the layer can be controlled by the birefringence and the thickness of the LC layer. A 640-*400-pixel multicolour projection display was fabricated using a two-layered LC panel, each layer passing green and red light under the focal-conic state. The Munsell chroma value was 6 for both of the projected colours. The projector also provides excellent white and black, because of the high transmittance of the nematic state and the subtractive mixture of complementary colours.<<ETX>>

A multicolor projection display using nematic-cholesteric liquid crystal

A multicolor projection display with a bright screen and high information content using nematic-cholesteric (NC) liquid crystals is discussed. Through investigation of light scattering in the focal-conic state of the NC liquid-crystal layer, it was found that the transmittance depends on the light wavelength due to diffraction scattering and that the color of light transmitted through the layer can be controlled by the birefringence and the thickness of the liquid-crystal layer. A 640*400 pixel multicolor projection display was fabricated using a two-layered liquid-crystal panel, each layer passing green and red light under the focal-conic state. The Munsell chroma value was six for both the projected colors. The projector provides excellent white and black because of the high transmittance of the nematic state and the subtractive mixture of complementary colors. >

Holographic Recording Material Containing Poly-N-vinylcarbazole

A volume phase holographic recording material with high diffraction efficiency and high durability against humidity has been developed. The holographic material consists of Poly-N-vinylcarbazole (PVCz) as a base polymer, camphorquinone as an initiator and thioflavine-T as a sensitizer. This film is sensitive to argon ion laser light, and exposure energy of 500 mJ/cm2 is required to realize high diffraction efficiency. After recording a latent image of a fringe pattern by exposure, a hologram was developed by swelling and shrinking of the film with two sorts of solvent. The thickness of the hologram could be reduced to 2.5 μm, because the PVCz hologram has a large amplitude of the refractive index modulation related with the crystallinity modulation. The high diffraction efficiency coupled with the thin layer made an incident light angle wide enough to maintain a high diffraction efficiency around the Bragg angle.

New developing process for PVCz holograms

The authors investigate a developing process for volume holograms consisting of poly-N- vinylcarbazole (PVCz), and achieve a new process that enables high diffraction efficiency, large holograms and uniform quality. Conventionally PVCz holograms are developed by two sequential dipping processes: first into good solvent, then into poor solvent. When a swollen PVCz film is dipped into poor solvent, PVCz molecules precipitate into small grains, and micro-gaps between grains are formed corresponding to the degree of swelling. As the result of the difference in swelling between highly exposed and low exposed areas, refractive index modulation appears. In this process, it is difficult to obtain a large hologram, because the upper area dries more than the lower area when the swollen film is carried to poor solvent. Based on the investigation above, the authors found a new process where the holograms are developed by a single dipping process into a mixture of volatile good solvent and nonvolatile poor solvent. The hologram film swells with the mixture, and is then carried out slowly from the tub. The solvent mixture in the film becomes poor solvent, rich and small grains are formed, because a good solvent evaporates more quickly than a poor solvent. With this new process all areas of a hologram plate can be developed under same conditions, so large holograms with uniform quality become possible.