Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-04-20
2004-01-27
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S690000, C430S270140, C430S270180
Reexamination Certificate
active
06682799
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the field of media for WORM optical discs with fluorescent reading, providing high capacity optical memory, including 3-dimensional optical memory systems.
BACKGROUND OF THE INVENTION
Recently WORM optical memory devices have experienced great evolution, providing recording of data with the possibility of its immediate reading. This feature—data recording in a real-time regime—is significant for various applications of optical recording in memory devices, especially for computer systems. For this field duplication of data is not so essential.
All WORM optical media of practical interest is based on a photo thermal principle of recording [1]. The data on such media is recorded by scanning the recording layer with the focused laser beam. The laser power is absorbed by the active medium of the layer and transformed into thermal energy, causing its physical and chemical changes, which can be optically registered at reading. Photochemical effects can also be used, i.e., optically detected changes in the state of medium, caused by direct interaction of photons with this medium. The efforts are made to use photosensitive medium for photochemical recording on WORM discs. Hence, until now there was no practical application for WORM discs with a photon mechanism of recording. The reason can be the non threshold nature of photochemical recording on the contrary to photo thermal recording at the same laser for recording and reading (with different laser power). Therefore, the photochemical recording cannot provide the necessary stability of medium characteristics at multiple reading. According to the mechanisms of thermally induced effects, the photo thermal recording on WORM optical medium with practical applications can be divided in two parts: ablative, providing optically registered geometric changes in the thin active layer during its melting, evaporation or chemical transformations, and with phase change, which does not provide geometric changing of the active layer, otherwise changing its optical constants, that causes optical contrast, which is usually not high for these materials.
Among various types of medium for ablative recording, WORM optical discs with thin (10-100 nm) layers of organic dyes with or without dye-in-polymer are of special interest. Layers of organic dyes provide a range of sufficient advantages in comparison to metal or half-metal layers, used in WORM discs with ablative recording. Such advantages are the following: dyes may have a stronger selective absorption on the recording laser wavelength; dye layers are more sensitive to the laser radiation because of their small thermal conductivity and low temperature of melting or decomposition. That provides a higher recording capacity; dye layers provide a higher stability at higher humidity. Medium based on layers has better signal-to-noise ratios, because of the lack of noise, provided by amorphous layers. The procedure of coating the layers in the centrifuge makes this method more simple and cheap than vacuum deposition used for obtaining metal and half-metal layers on WORM discs.
The existing WORM optical discs based on organic dyes have a capacity up to 3.5 GB. For the WORM discs with one recording layer said optical memory capacity is the utmost or, at least for the diode laser with 780-830 nm wavelengths. Future increasing the capacity for WORM discs is possible with the use of three-dimensional optical memory carriers with multilayer data recording and fluorescent reading [2,3]. Fluorescent reading offers a range of sufficient advantages in comparison to reading, based on the changes in the reflection ratio, even in the single-layer systems. One of the advantages is the reduced tolerance for the sizes of recorded pits in comparison to the existing WORM discs. For example, changing the size on a hundred nm does not influence the reading from a fluorescent disc, while it totally eliminates the signal from reflective discs. Another advantage is the reduced sensitivity of fluorescent discs to changing the slope up to one grad that is absolutely intolerable for reflective discs. Nevertheless, the basic advantage of fluorescent reading is its most fitness for three-dimensional optical memory carriers, i.e., multilayer discs.
The use of layers of organic dyes with ablative recording in such medium is not possible due to owing to the following reasons: Reading is performed by laser beam, scanning the change of the reflection in the pre-irradiated spots. In the multilayer system, this method causes a strong fall of the reading quality, becoming dramatic for systems with more than four active layers. Changes in the geometrical structure of the layer under the heat influence during recording, such as: burning out of holes, creation of bubbles, change of surface texture, etc. are also unsuitable for multilayer medium, as it causes dispersion of the reading beam, hence abruptly lowering the detection quality. The dye concentration in the recording layer of the existing WORM discs is the utmost (up to 99%). In this case, the dye fluorescence is usually suppressed because of high concentration. In the thin dye layers (10-100 nm) of the existing WORM discs, the local heating of the medium at recording can reach 700° C. Such high temperature makes it difficult to avoid changing the geometrical structure of the layer. Increasing the thickness of the dye layer up to 200 nm and more by using polymer dye at preserving the surface concentration of dye, leads to lowering the local heating temperature and allows to prevent the layer deformation. It also provides the appearance and growth of the dye fluorescence due to lowering the concentration suppression effect. However at all the same conditions the layer sensitivity to laser radiation is dramatically lowering, that leads to drop of recording speed and density.
Thus, all the known materials, used for single-layer optical WORM discs with reflective reading, as well as photo thermal recording methods cannot be used for multilayer optical WORM discs with fluorescent reading. Comparatively, thick layers (200 nm and more), containing fluorescent dyes, are also not likely suitable for multilayer medium creation without use of special ways and additives, providing an increase in recording speed and density.
SUMMARY OF THE INVENTION
Considering the above-stated, the purpose of this invention is to obtain a high-sensitive dye-in-polymer (DIP) medium for fluorescent WORM discs, providing high rates and density of photo thermal recording. The other purpose of the present invention is to provide a DIP medium with high sensitivity to the recording laser radiation in visual and infrared ranges. It is a further object of the invention to provide a DIP medium for single and multilayer materials with high optical memory capacity, high resolution and high darkness and radiation stability. In accordance with the object of the invention, the DIP medium is comprised of a fluorescent dye, capable to absorb the recording laser radiation and transform the absorbed light power into the heat, and nitrocellulose, capable to generate decomposition products under heating. According to the other purpose of the present invention, the above-stated DIP media contains a fluorescent dye, which generates non fluorescent dimers with sandwich structure, capable to absorb the recording laser radiation and transform it into heat, and nitrocellulose, capable to generate decomposition products under heating. According to the future purpose of the present invention, the above-mentioned nitrocellulose decomposition products cause the distinguishing of fluorescence or discoloring of the fluorescent dye, thus making the recording. If the recording laser radiation is absorbed by the monomer form of fluorescent dye, the same laser can be used for reading and recording (i.e., 650 nm, but with different power pulse). If the recording laser radiation is absorbed by the dimer form of fluorescent dye, the recording laser has a shorter wavelength (i.e., 635 n
Alperovich Mark
Khaikin Arkady
Levich Eugene
Zuhl Irene
Blank Rome LLP
Mulvaney Elizabeth
Valdas Ltd. (A British Virgin Island Corp.)
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