Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1998-10-05
2001-12-11
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299010, C349S002000, C349S128000, C349S191000, C349S196000, C430S270110
Reexamination Certificate
active
06329026
ABSTRACT:
TECHNICAL FIELD
This invention relates to novel chirooptical systems and displays using novel chirooptical medias. Specifically this invention relates to liquid crystal optical storage devices and systems.
BACKGROUND ART
For storage of data, materials and devices with reversible optical storage capability are needed. Optical storage can be applied in optical computers, storage systems for audio and video informations.
There are many types of optical storage devices, which can be written in only once (write-once-read-many systems=WORM systems), using irreversible processes for storage. However they were not applicable for storage systems for computers and, find only limited application in audio and video informations because of their non-reversible properties.
For many purposes more advantageous are devices, which can be written in multifold (erasable-direct-read-after-write systems=EDRAW systems) by use of reversible storage processes. For this purpose a survey about materials for optical data storage has been presented by M. Emmelius, G. Pawlowsky and H. W. Vollmann, Angew. Chem. Intern. Ed. 28, 1445 (1989). However because all available media for optical data storage have some shortcomings like storage density, storage rate, reversibility, long time stability, the search for new optical storage materials and devices is quite actual.
Devices of this kind typically consist of a layer of liquid crystal material, contained between two glass slides. By irradiation with light of different wavelengths, devices containing azo compounds change from the nematic to the isotropic state and reverse (for example, D. Demus, G. Pelzl, F. Kuschel DD WP 134 279).
Especially liquid crystalline polymers containing azo groups have been proposed for such devices (H. Finkelmann, W. Meier and H. Scheuermann, in: Liquid Crystals. Applications and Uses, ed. by B. Bahadur, World Scientific Singapore 1992, vol. 3, p. 345-370).
The proposed azo compounds have the disadvantage, that the intensity and time of irradiation are quite high, because a large amount of the azo compound has to be transformed to the corresponding isomer. Therefore the switching times are extremely large.
Also thermo-optical liquid crystal devices have been proposed, based on thermally induced texture change of cholesteric phases (S. Kobayashi and A. Mochizuki, in: Liquid Crystals. Applications and Uses, ed. by B. Bahadur, World Scientific, Singapore 1992, vol. 3, p. 291-293) or smectic A phases (D. Coates, in: Liquid Crystals. Applications and Uses, ed. by B. Bahadur, World Scientific, Singapore 1990, vol. 1, p. 275-303).
Thermo-electrooptic displays use the combined effect of heat and electric fields, in glass forming low-molecular glass forming liquid crystals (D. Demus and G. Pelzl, DD WP 242 624 A1) resp. polymer glass forming liquid crystals (H. Finkelmann, W. Meier and H. Scheuermann, in: Liquid Crystals. Applications and Uses, ed. by B. Bahadur, World Scientific, Singapore 1992, vol. 3, p. 345-370). However thermo-optical devices generally need a quite large energy for locally heating up the liquid crystal material.
M. Zhang and G. B. Schuster, J. Phys. Chem. 96, 3063-3067 (1992) reported about the photoracemization of chiral binaphthyl derivatives, converting the cholesteric mixture to nematic mixture. Because the reaction is irreversible, the change from nematic to cholesteric is impossible and the material cannot be used for repeated data storage.
Holographic technology has been investigated for reversible data storage systems. Several kind of materials have been investigated toward this application. There are three types of materials, inorganic metal compounds, photorefractive polymers and polymer liquid crystals, have been reported. However they all have disadvantages.
For materials of optical data storage, photorefractive crystals like lithium niobate (LiNbO
3
), barium titanate (BaTiO
3
) and bismuth silicon oxide (Bi
12
SiO
20
), have been proposed and studied for 25 years. However because they are difficult and expensive to grow, and their properties cannot easily be modified, they have not become commercially feasible.
Variety of photorefractive polymer and polymer liquid crystals have also been proposed (K. Yoshinaga et al., Japanese Patent Kokai 2-280116, T. Todorov et al., Applied Optics, 23 (23), 4309 (1984), M. Eich et al., Makromol. Chem., Rapid Commun., 8, 59 and 467 (1987)). It was recognized that the photorefractive effect enable them to store 100 or more complete image or holograms, each containing 1 million bits of imformations. They can be easily produced so that they have a big economic advantage. They, however, have significant disadvantages. The speed with which they respond to light is quite slow compared with semiconductors. And most of the existing polymers require that an electric field be applied to orient the non-liner optical chromophores so that the material becomes electro optically active.
Novel data storage systems, devices and materials which are easy to produce, and have advanced properties, such as low viscosity facilitating quick response, large capacity of data storage, reversible and stable with reading and writing informations, have been desired. The aim of this invention is to overcome the above mentioned disadvantages of the previous technologies and providing novel data storage systems, devices and materials having above mentioned desired properties.
DISCLOSURE OF INVENTION
By our continuous efforts, it has been found, that using mixtures of suitable chiral materials (chiral dopants) with nematic liquid crystals, by irradiation with light of two different wavelengths the chirality of the mixture can be reversibly switched between two stable states of different chirality, corresponding to two states of different optical properties, useful for storage of information.
By using two states having different optical properties that are induced by the different chiral pitch lengths, large number of informations can be stored in the liquid crystal mixtures. The system is reversible and by irradiation with light having two different wavelengths reading and writing data can be repeated. The two states are chemically and phsically stable and except the switchings the optical properties of the two states never change.
The system, specifically devices, consist of nematic liquid crystal cells comprising chiral nematic liquid crystals inbetween two glass or plastic plates. The information storage can be done within nematic temperature ranges.
Because the invented data storage system uses nematic liquid crystals as the data storage materials, the viscosity of the materials is relatively low, which facilitate very quick response against light irradiation.
These attractive properties can be induced by the combination of nematic liquid crystals, chiral dopants, nematic liquid crystal cells and light irradiation, which is novel strategy that has never been proposed before.
More specific description is as follows. For example, for materials showing irradiation induced switching between two states of different chirality, the form “A” can be switched to another form “B” by irradiation with light of wavelength “C” nm, the reverse switching occurs with light of another wavelength “D” nm. The switching between the two forms does not need to be completed. The two states consist of mixtures of both isomers, however, differing in their chirality.
The chiral compounds and mixtures of both are dissolved in liquid crystal materials, usually multicomponent mixtures, giving cholesteric liquid crystalline media (chiral nematic mixture).
The cholesteric medium exhibits strong optical activity, this is turning of the plane of linearly polarized light. This material is preferably inserted between two substrate planes, e.g., glass or plastic plates, forming a hybrid cell. In the hybrid cell the two substrate planes are arranged in such a manner that the liquid crystal molecules on one plane are parallel, with or without a tilt angle, on the other plane perpendicular to the substrate planes as shown in F
Demus Dietrich
Miyazawa Kazutoshi
Takeuchi Hiroyuki
Tarao Ryokichi
Chisso Corporation
McDermott & Will & Emery
Wu Shean C.
LandOfFree
Compositions containing chiral compounds and nematic liquid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compositions containing chiral compounds and nematic liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compositions containing chiral compounds and nematic liquid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2588184