WO2003001516A1 - Fluorescent-liquid crystal optical memory and recording/reading system thereof - Google Patents

Abstract

A multilayer fluorescent information carrier (300) having a plurality of data layers (302), each of the data layers (302) comprises a thin controllable liquid crystal cell composed of two electrodes (303) and at least one orientation film (304 or 305) and information is recorded thereon in the form of orientation capability which is spatially modulated over its surface with respective to a liquid crystal composition and when playing back, it allows for partial or complete elimination of the fluorescent cross-talk from the adjacent data films.

Description

FLUORESCENT-LIQUID CRYSTAL OPTICAL MEMORY AND RECORDING/READING SYSTEM THEREOF

BACKGROUND OF THE INVENTION

Field of the invention

This invention relates to optical memory systems for "pit-by-pit" or "page-by-page" information recording and information reading, and more specifically, to a multilayer optical memory system ROM, WORM, RW or their mixed types with fluorescent information playback.

Description of the Prior Art

The existing optical memory systems utilize three-dimensional information carriers with one or two data layers. Most of the previous technical solutions in optical data recording teach the recording of changes in the reflected laser radiation intensity in local regions (pits) of the data layer. These changes could be a consequence of the interference effect on the relief optical discs of CD or DVD read-only memory (ROM-type), burning of holes in a metal film, dye bleaching, local melting of polycarbonate in widely used CD- write once many (WORM) systems, a change in the reflection coefficient in phase-change rewritable (RW) systems, etc. [Bouwhuis G. et al., Principle of Optical Disc Systems - Philips Research Laboratories, Eindhoven, Adam Hilger Ltd., Bristol and Boston]. In these carriers, in order to increase the recording density, such methods as the use of radiation sources operating at shorter wavelengths in combination with high-NA objective lenses are used [I. Ichimura et al., SPIE, 3864, 228)], and a reduced track pitch, and increased groove depth in a land groove recording type optical disk (S. Morita et al., SPIE, 3109, 167] are also used. For high-density data storage, new media and methods for information playback are used [T. Vo-Diny et al., SPIE 3401 , 284], as well as pit-depth modulation (S. Spielman et al., SPIE, 3109, 98], as well as and optical disks having square data pits arranged in symmetrical patterns (Satoh et al., US Patent No. 5,572,508]. According to US Patents 4,634,850 and 4,786,792 (Drexler Technology Corp.), the data density is increased, and, at the same time, the errors are minimized by using a "quad-density" or "micro-chessboard" format of digital optical data which is read by a CCD photo detector array to quadruple the amount of digital data that can be stored optically on a motion picture film (or optical memory cards).

The density of recording of information in excess of a few terabits per one cubic centimeter can be achieved by using three-dimensional (monolithic) photosensitive media, which exhibits various photo physical or photochemical non-linear effects with the two-photon absorption. The most optimum recording and playback mode in such three-dimensional WORM or RW information carriers is the cooperative two-photon absorption by the photosensitive components and by the products of the photo reaction through an intermediate virtual level similarly to the case of the photochromic [D. Parthnopoulos et al., Science, 1989, 245, 843] or photo bleaching materials or the recording of changes in the index of refraction as is the case with the photorefractive crystals [Y. Kawata et al., Opt. Lett., 1998, 23, 756] and photopolymers [R. Borisov et al., Appl. Phys., 1998, B67, 1].

This recording and playback mode allows, in principle, for local recording of information in the form of pits (analogs of the data pits in conventional reflecting CDs or DVD-ROMs) having altered optical properties within the space of the information media.

However, the practical implementation of this concept is extremely difficult at the present time because of high cost and large size of femto- second laser radiation sources that are required for such recording and extremely low photosensitivity of the media. The latter is generally caused by extremely small cross-sectional areas of the two-photon absorption of photosensitive substances that have been known so far.

The use of multilayer optical information carriers is more justifiable from the technical point of view. However, they also impose certain limitations and create additional problems both for the design and properties of the information media proper and for information playback methods and devices (and also for recording in the case of WORM and RW optical memory) especially in the areas deep within the media.

In the reflection mode, every data layer of the multilayer optical information carrier shall have a partly reflective coating. It reduces the intensity of both the information playback beams and the information recording beams as they pass through the media to arrive at a given data layer and back to the receiver.

In addition, because of their coherent nature, both beams are exposed to diffraction and interference distortions on the fragments (pits and grooves) of the data layer on their way, which are hard to estimate.

This is why the multilayer fluorescent optical carriers with fluorescent reading are preferable since they are free from partly reflective coatings. Diffraction and interference distortions in this case are be much lower because of the non-coherent nature of fluorescent radiation, its longer wavelength in comparison to the playback laser wavelength, and transparence and homogeneity (similar refractive indexes of different layers) of the optical media towards the incident laser and fluorescent radiation. Therefore, the multilayer fluorescent carrier has certain advantages in comparison to the reflective optical memory. US Patent 4,202,491 discloses the use of a fluorescent ink layer on which data spots emit infrared radiation.

JP Patent 63,195,838 teaches a WORM disk with the fluorescent playback method, wherein the data layer is applied to the mat surface of the substrate. The strong light diffusion of the recording and playback radiation completely rules out the possibility of creating multilayer information structures based on this concept. This possibility of providing multilayer optical disks has been realized by using fluorescent compositions disclosed in US Patents 6,027,855 and 5,945,252 and also in EP 00963571 A1.

US patents 6,009,065 and 6,071 ,671 to V. Glushko and E. Levich disclose bit-by-bit information playback devices for multilayer fluorescent optical disks. At the present time, the general requirement for all types of multilayer fluorescent information carriers (optical disks and cards) is the provision of carriers with the maximum possible volume and density of recorded information and with the maximum possible playback speed at high signal-to- noise ratio. This requirement is met through minimizing the dimensions of the data pits, raising the density of recording within each individual data layer, increasing the number of the data layers, and using the playback radiation at a shorter wavelength. The maximum possible power of the fluorescent data signal is indispensable to achieve high playback speed. The actual recording density, as well as the other above-mentioned parameters of the optical recording process, depend not only on the wavelength of the recording radiation, but also on the properties of the actual recording media that is used, as well as on data input/output methods that are used in optical memory devices. In the case of the multilayer fluorescent media, similarly to any other three-dimensional media, additional requirements are imposed upon the media and the data input/output methods. More specifically, the recording radiation should be absorbed only in a predetermined local micro area of the space within the three-dimensional media, or it should have a threshold effect based on the intensity of the recording radiation and/or playback radiation. Otherwise, the recording of a data bit deep inside the recording media will be accompanied by changes in the optical properties along the whole path of the recording beam through the media.

In addition, there are specific differences between the forming of the modes of information playback from the carriers made as optical disks and cards with the one-photon absorption of the playback radiation by fluorescent molecules.

Figures 1 and 2 show two possible options for playback from a multilayer information media (10 (20)), wherein data layers 11 (21 ) are separated by polymer layers 12 (22) that are transparent for playback radiation 17 (23) and for fluorescent radiation 24 and 25. The disk systems generally use the bit-by-bit information playback with a sharply focused laser beam 23 (Figure 2).

The presence of the spatial filtering during the acquisition of the fluorescent radiation 24 from data pits 26 by a photo receiver allows for obtaining low cross talk between the layers which is caused by the excitation of fluorescence 25 in the adjacent data layers through which the playback radiation passes. Therefore, when such information carriers are used, low contrast is acceptable (the ratio of the difference between the intensities of fluorescence 24 in the area of location of the data pit 26 IA (pit) and the intensity of fluorescence 25 of the background IA (noise) to their sum K = (In (pit) -I_fi (noise)) / (IA (pit) + l_fl (noise))); K =1/2- 1/3 of a signal recorded from each individual data layer.

It should be noted that the spatially spaced data layers 21 may be continuous. The fluorescent substance fills both the micro recesses (data pits) 26 and the space 27 between them.

This arrangement allows for the use of conventional injection/compression molding processes or 2P-process based on photo polymerizable compositions from relief carrier master disks (originals), with subsequent application of the data layers 21 by spin-coating, roller coating, or dip-coating.

The multilayer fluorescent information carriers in the form of optical cards allow for multiple-channel (page-by-page) playback with a CCD camera of entire pages 14 of information consisting of several thousand pits 16. It should be noted that the spatial filtering of the image of the page 14 is rather difficult, and the cross talk between the layers caused by fluorescence 25 from the adjacent data layers result in a material reduction in contrast at the photo receiver. For this reason, when an optical card is used, it is imperative to obtain high contrast (K of about 1.0) within each layer. To achieve the contrast level that is so high, it is desirable to form the data layers 11 as islets (an island-like structure), and only the data pits should be filled with the fluorescent substance. This structure of the data layers calls for a rather complex manufacturing process. Moreover, since the surface area occupied by the fluorescent data pits within the layer is about fifty percent of the total area layer, the intensity of the data signal that comes from this layer to the photo receiver even with this filling ratio amounts only to 1/N-th part of the intensity of the whole fluorescent flux that comes to the photo receiver when the multilayer carrier is read, wherein N is the number of the data layers in the carrier.

The present invention provides several versions of a new structure of a multilayer fluorescent information carrier of the ROM-, WORM-, or RW-type and methods for information recording to, and reading from the information carrier, which assure the electrical control of the absorption and emissions capacity of the fluorescent molecules dissolved in a liquid crystal matrix. This, in turn, allows for realizing partial or complete elimination of fluorescent cross talk from the adjacent data layers during playback both in the "pit-by-pit" mode and in the "page-by-page" mode. This also offers the opportunity of the electrical control of the fluorescence intensity of the data signal and for a reduction in the spacing between the layers, which allows for increasing the number of the data layers in the carrier, while at the same time reducing the effect of the aberration distortions during the playback. In addition, the invention broadens the capabilities of using various, not only non-linear, but also linear photochemical and photo physical mechanisms of single or repeated information recording and allows the same radiation source to be used for recording information to, and for reading information from such carrier.

Other features and advantages of the present invention will become apparent from the following detailed description of the concepts of the recording, playback, and rewriting of information in the information carrier according to the invention with reference to the accompanying drawings and some examples illustrating the invention.

SUMMARY OF THE INVENTION

A multilayer combined fluorescent - liquid crystal optical information carrier, having a plurality of data layers located in parallel planes, said plurality of the data layers being positioned on a common substrate and separated from each other by transparent intermediate layers, each of said plurality of the data layers being in turn made as a multiple-component structure in the form of a thin electrically controlled liquid crystal cell composed of two identical optically transparent electrodes made as continuous layers or as a system of two mutually orthogonal strips with at least one orientation film applied thereto, which are separated from each other by spacers, the space between layers being filled with a guest-host liquid crystal composition in which the host is composed of photochemically stable anisotropically absorbing fluorescent substances.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically shows the page-by-page playback of information from a multilayer fluorescent information carrier having a fluorescent background defined by the data layers that are not to be read.

Figure 2 schematically shows the bit-by-bit playback of information from a multilayer fluorescent information carrier having a fluorescent background defined by the data layers that are not to be read out.

Figure 3 schematically shows a cross-sectional view of a generalized version of the structure of a multilayer combined information carrier of the liquid crystal - fluorescent dye type.

Figure 4 schematically shows a data layer having transparent electrodes made as mutually orthogonal strips.

Figure 5 shows an alignment and switching configuration of a fluorescent liquid crystal data layer.

Figure 6 is a top view and a cross-sectional view of a single data layer in the absence and in the presence of voltage on the electrodes, respectively.

Figures 7 a, b show various embodiments of recording layers with patterned orientation surfaces and methods for reading the fluorescent signal therefrom. Figures 8 a, b, c show various embodiments of the structure of a combined data layer of the ROM-, WORM-, or RW-type.

Figures 9 a, b show schematic top views of a track in an optical card and optical disk before (a) and after (b) writing by beam incidence, respectively.

Figure 10 shows a typical behavior of the kinetic curves of induction, erasure, and dark relaxation of the optical anisotropy in photo anisotropic materials based on photochemically stable anisotropically absorbing substances. The up (T) and down (I) arrows show the moments of activation and deactivation of the photoactive radiation. Symbols A → B and B - A depict the moments of switchover of the state of polarization of the photoactive radiation to the orthogonal state. The signs "0", "1", and "-1" show the initial state and two photo-induced thermodynamically stable states, respectively. Figure 11 schematically shows an embodiment of a device for the bit- by-bit recording of information on a multilayer combined fluorescent - liquid crystal optical carrier, which assures the real-time bit-by-bit check and correction of the information recording quality.

Figure 12 shows an embodiment of a device for the page-by-page check of the quality of the recorded recording layer of a multilayer combined fluorescent - liquid crystal optical carrier.

It should be noted that the drawings given herein are neither to scale, nor do they show proportions of individual components, and they are given only to facilitate the understanding of the structure and concept of the functioning of the multilayer fluorescent information carrier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of the present invention will be given below with reference to the accompanying drawings. Figure 3 schematically shows a cross-sectional view of a generalized version of the structure of a combined multilayer fluorescent information carrier 300 (double-layer to simplify the explanation of the functioning concept), based on an electrically controlled guest-host liquid crystal system.

The information carrier 300 has as its basic components a substrate 301 and a plurality of data layers 302 which, unlike prior art fluorescent data layers disclosed e.g., in US Patents 6,009,065, 6,071 ,671 , WO 99/24527, and others, are also, made as a multilayer structure rather than a single-layer structure, and this structure is generally made as thin electrically controlled liquid crystal cells (LCC) composed of two identical optically transparent electrodes 303 with orientation films 304 and 305 applied thereto, which are separated by spacers 306. The space between the orientation films, which is defined by the spacers 306, is filled with a guest-host liquid crystal composition (LC) 307. Host substances 308 are photochemically stable anisotropically absorbing fluorescent substances 308.

Such photochemically stable anisotropically absorbing fluorescent substances fluorescing in a preset spectral area are selected from among the substances which are well soluble in liquid crystal compositions and which have high quantum efficiency of fluorescence whose molecules have a stiff rod-shaped or disc-shaped configuration and whose long-wave absorption oscillator extends along their longer axis (such as stilbenes) or transversally to this axis (such as tetracene, pentacene and other polyacenes).

These fluorescent substances are selected for the purposes of the present invention from photochemically stable compounds that belong to aromatic hydrocarbons and their derivatives such as polycyclic condensed aromatic hydrocarbons and their derivatives, hydrocarbons having an arylethylene group and an arylacetylene group and their derivatives (1 ,2- diarylethylenes, diarylpolyenes, functionally substituted stilbene and 1,4- distyrylbenzene, etc.), polyphenyl hydrocarbons; compounds having five- member heterocycles (furans, thiophenes, pyrroles, and their derivatives, etc.) and six-member heterocycles having one or two nitrogen or oxygen atoms, etc.; compounds having a carbonyl group (coumarins and carbostyryls, anthrone and aromatic acid derivatives, substituted oxazol-5-one, indigoids, and thioindigoids, quinones, etc.); compounds based on naphthalic acid; as well as complex organometal ligands and organic dyes selected from the group of xanthene, acridine, oxazine, azine, perylene, terylene, vialanthrone, cyanine, phthalocyanine, porphyrines, etc.

The liquid crystal and the dye are mixed in a molar ratio between 1 :0.01 and 1 :0.8. The liquid crystals can be selected from smectic or cholesteric liquid crystals or their mixtures, but it is most preferred to use nematic liquid crystals or their mixtures with other liquid crystals. The data layers 302 are separated from each other by intermediate layers 309 from a few microns to hundreds of microns thick, which have high optical quality and which are transparent for the recording radiation, playback radiation, data (fluorescent) radiation, as well as erasing radiation. A protective layer 310 is used to protect the optical information media against mechanical damage and harmful effects of aggressive factors. To rule out the spurious influence of light reflection, light diffusion, and light diffraction from out-of-focus layers, the refractive indexes of all the data layers, intermediate layers, and protective layers, as well as of the guest-host LC composition 307 in the homeotropic or planar modes of information recording and/or playback depending on the nature of the composition at specified radiation wavelengths are chosen to be as close as possible to each other. If required, the data layer 302 can be made as a multilayer antireflection interference coating for specified wavelengths. For that purpose, additional layers may be integrated in the data layer (not shown in Figure 3).

The data layers and the intermediate layers are integrated into the integral multilayer carrier 300 by using photo hardening or thermal hardening adhesives 311.

A controller 312 is used for exercising individual electrical control of the orientation of LC molecules in the composition 307, hence the control of the fluorescent host molecules 308 included in the makeup of this composition with the use of a power supply 313. The controller 312 and the power supply 313 are outside the multilayer carrier 303, and they are located in a self- contained information recording and/or playback device (not shown in Figure 3). The optically transparent electrodes 303 can be made as transparent electrode layers that are normally used in the manufacture of LC displays, which are based on metal oxides such as indium tin oxide (ITO), indium oxide, tin oxide, and the like, which are approximately 0.001 μm thick. They can be made as continuous films 303, or, to save energy in general when recording to, and reading or erasing information from the carrier, they could be in the form of mutually orthogonal strips 41 , 42 (Figure 4). In the latter case, each of the liquid crystal cells functions as an array of optoelectric shutters, which controls the value of the transmission coefficient in the spectral area of fluorescence excitation of the host substance 308 during the recording, playback, or erasure of information in a predetermined area (on a predetermined page) 43 of one of the data layers 302 of the multilayer carrier 300, as well as the magnitude of its fluorescence. The electrodes 303 are applied to both sides of glass or polymeric intermediate layers 309 (e.g., Mylar [DuPont], polycarbonate, epoxy resins, photosensitive resins, photopolymerizable composites, and the like), which preferably have isotropic optical properties.

To form the directionally orientation film 304, which is uniform over the surface, orientation films that are normally utilized in the manufacture of liquid crystal displays can be used, e.g., those described in [P. Chatelain, Bull. Sc. franc. Miner, 66, 105 (1943)], produced by the unidirectional mechanical rubbing of polymeric films such as polyamide films that are less than one micron thick applied to one of the transparent electrodes 303 (Figure 3) or to one of the electrodes 41 or 42 (Figure 4). This method is hardly suitable, or even unfit for use when the intermediate layers 309 are very thin (approximately 10 μm or thinner), or when the intermediate layers have surface relief. In this case, other non- contact known methods for imparting a planar orientation to the liquid crystal layers can be used, e.g., oblique sputtering of certain transparent substances [J. L. Janning, Appl. Phys. Lett. 21 , 173 (1972)], or multimolecular Langmuir films [E. Guyon, Vac. Sci. Technol. 10, 681 (1973)].

For the purposes of the present invention, we used a process for orienting liquid crystals discovered by one of the present inventors [V. Kozenkov et al. 11 USSR Conference "Optic Liquid Crystals", Krasnoyarsk, 1990, p. 30 (in Russian]. This process makes use of so called photoanisotropic materials, i.e., initially isotropic photosensitive materials in which the optical anisotropy is induced under the effect of a directional optical radiation, which is even non-polarized.

This anisotropy is a consequence of formation of the anisotropy of the molecular orientation distribution not only within the body, but also on the surface of the remaining initial anisotropic molecules and newly formed anisotropic products of photochemical reactions. In this case, the direction of the prevailing orientation of the permanent dipole moments of the remaining initial molecules is in the plane of the material in the event of the normal incidence of the activating radiation upon the photoanisotropic material and, as a rule, in the orthogonal relation to the vector of the electric field of the activating radiation. As a result of this orientation, the orientation-wise anisotropic ensemble of the initial anisotropic molecules that are on the surface, which make part of the photoanisotropic material and their anisotropic photo products, acquires the ability to orient liquid crystal molecules in the planar and directional manner in accordance with the direction of the prevailing orientation of the surface molecules of the photoanisotropic material.

According to the present invention, the layers based on such materials can be applied by spin coating and dip coating, by using Langmuir-Blodgett method, or by thermal sputtering in vacuum, and the non-contact, non- mechanical optical method of imparting the orienting capacity to the layers can be used for super-thin intermediate layers 309 or layers with microrelief by treating one of the surfaces.

When such liquid crystal cells are used in the data layers 302, the orientation film 304 may be dispensed with.

According to the invention, orientation films 305 provided on the opposed transparent electrode 303 (Figure 3) or on the electrode 42 (Figure

4), in addition to the orientation function, also function as the recording layers.

They can also be made either based on the mechanically rubbed polymeric layers, as obliquely sputtered films, or as Langmuir-Blodgett films (for ROM- type information carriers), or by using the above-described photoaligners from photoanisotropic materials (for ROM-, WORM-, or RW-type carriers).

In the latter case, after the recording, they comprise a plurality of individual data carrying micro areas or data marks or pits (analogs of the reflecting pits in known CD-ROM or DVD-ROM systems) 314 against background areas 315, which differ from each other by the surface molecular ordering, hence, the aligning capacity with respect to the electrically controlled layers of the guest - host liquid crystal composition 307 both on their outer surfaces 316 and 317 and within the body of the liquid crystal layer 307, respectively. Simultaneously with the electrically controlled alignment of the liquid crystal molecules, the anisotropic host fluorescent molecules 308 dissolved in the liquid crystal, which absorb the playback radiation, are also aligned under the electric control. Depending on the presence or absence of voltage at the electrodes 303 or 41 and 42, the absorption coefficient and the fluorescence intensity of the data layers 302 will change.

The use of photoanisotropic materials as the photoalignment layers has a number of advantage over contact or non-contact, always non-optical methods for orientation of liquid crystal molecules. These advantages are as follows: simplicity of the formation of the photopatteming orientation surfaces with a predetermined three-dimensional configuration of the aligning capacity of this surface; enhanced orientation of the liquid crystal molecules on the surface in terms of optical quality, and possibility of controlling the energy of cohesion of the liquid crystal molecules to the surface molecules of the orientation film.

The latter advantage is very important because when the surface density of information recording is high in the data layer 302, the thickness of the liquid crystal layer 307 should be commensurable with the size of the data spot that is recorded in the recording layer 305. For example, when the spot is about 0.4 μm in size, the liquid crystal layer should also be approximately 0.1 to 0.4 μm thick. At the same time, it is known that with the realistic values of the electric fields, the electric realignment of molecules, e.g., of a nematic liquid crystal cannot be obtained within an area in the direct contact with the interphase surface, is about 0.01 μm thick or which has a thickness of a few molecular layers. It will be apparent that by controlling the energy to which the photoanisotropic material is exposed, not only the axis of the directional planar orientation of the liquid crystal can be imparted, but the amount of energy of cohesion of its molecules to the surface molecules of the photoaligner could also be controlled, and their optoelectric behavior could be influenced.

Therefore, the layers 304 (if they are physically present) in the electrically controlled multiple-component structure of the data layer 302 perform their conventional function of the orientation films, and the orientation films 305 also simultaneously function directly as the recording layer of the ROM-, WORM-, and RW-type. In this case, a latent image of the data pits is formed in them as variations in the orientation properties with respect to the liquid crystal molecules, which are modulated over its surface. This latent image can be optically read out (visualized) if required with high intensity of fluorescence by using the electrically controlled guest-host liquid crystal cell of the data later 302 of which the orientation and recording film 305 makes part and in which the anisotropically absorbing fluorescent molecules are used as the host 308.

The combined multilayer fluorescent optical information carriers according to the invention can be in the form of CD read only memory or DVD read only memory (ROM), write one read many memory (WORM), rewritable (RW) memory, or their mixed types in a variety of optical disks, cards, or tapes. The geometry of the bidimenesional spatial distribution of the data pits in such carriers may be represented both as straight-line, spiral-shaped, or annular tracks in which the data flow is recorded using a 14-bit channel modulation EFM (eight-to fourteen modulation) code, which is widely used nowadays, and as four adjacent bytes recorded by ETT (eight-to-ten) method of bidimenesional information encoding over the surface of orientation and recording films 305. The intensity of fluorescence can be controlled by changing the orientation of, e.g., the longer axes of the light-emitting dichroic molecules 308 with respect to the direction of the playback radiation, which excites fluorescence. Dichroism of the absorption of the fluorescent substance 308 results in the fact that the light that is emitted by this substance has the maximum intensity with such arrangement of its molecule that corresponds to the maximum absorption of the playback radiation. By varying the direction of orientation of the liquid crystal matrix 307 using the electric field of the controller 312, the amount of absorption of the playback radiation by the fluorescent molecules 308 can be controlled to control the intensity of the fluorescent data light emitted by the molecules. With the infinite variation of the magnitude of the electric field, it possible to vary the intensity of fluorescent radiation if required without changing the intensity of the playback radiation itself. The optical memory system according to the invention can be formed, e.g., based of the electrostatic deformation of homeotropic textures of nematics 501 with the negative dielectric anisotropy or unidirectional homogeneous (planar) textures of nematics 502 with the positive dielectric anisotropy. These deformations are accompanied by a respective change in orientation of molecules of dichroic fluorescent substances 503 dissolved in a nematics matrix 504 (Figureδa).

The nematic liquid crystals, e.g., having the positive dielectric anisotropy, function as matrices that align the elongated dichroic molecules of the substances 508 to extend in parallel with each other and with the molecules 502 of the liquid crystal layer proper. A change in orientation of the liquid crystal matrix in the electric field also causes a change in orientation of the dichroic substance 503, hence a change in the absorption capacity (theoretically down to zero) and a change in the fluorescent capacity (also theoretically down to zero) of the thin guest - host liquid crystal layer 504 with respect to a playback (or recording) radiation as well as erasing radiation 505.

For example, in order for the dichroic molecules 503 to align orderly in parallel with the plane of the electrodes 303 in the absence of voltage (V = 0), a directional planar texture is formed in a nematic specimen 502 having the positive dielectric anisotropy, and the dichroic molecules 503 are chosen in such a manner as to have the maximum absorption., e.g., at the wavelength of the playback radiation (Figure 5 b, Curve 1), hence to have the maximum fluorescent capacity in reading (Figure 5b, Curve 1¹). The nematic 502 with the positive anisotropy, which is chosen for the memory matrix, yields a homeotropic texture under the effect of the electric field V = V-i, and the molecules of the dichroic substance 503 are aligned at right angles with respect to the direction of the electric vector of the light wave (polarized or not), and they transmit this light substantially completely (absorption at the playback radiation wavelength, hence the fluorescent capacity substantially disappears) (Figure 5b, Curves 2 and 2¹, respectively).

It should be noted that the absence of the fluorescent background 506 from all out-of-focus layers other than the layer that is being played back allows the fluorescent cross talk from such layers to be eliminated, thus improving the signal-to-noise ratio during the playback. The reduction of the absorption capacity of the layer 504 substantially to zero also allows the same radiation sources to be used for recording, playback (and erasing) of information in the WORM or RW mode.

From the point of view of energy saving in the playback device, the option using the nematic liquid crystals with the negative dielectric anisotropy is more advantageous because there is no absorption of the playback radiation, hence no fluorescence in all data layers 302 when there is no voltage at the electrodes 303. The control voltage should only be applied to the electrodes 303 (or to certain stripes of the electrodes 41 and 42) when a preset data layer 302 or a preset data page in this layer is read.

Still another advantage of the multiple-component structure of the fluorescent data layer 302 according to the invention over prior art single-layer fluorescent data structures is that the recording layer 305, which in this system is also a photopatteming orientation film with respect to the guest - host liquid crystal composition 307, may be as thin as required, and it can be built as a monolayer having a thickness of ten Angstroms. The absorption capacity of this layer will also be low, and the intensity of the recording, playback, or erasing radiation will remain practically unchanged upon passage of the radiation through this multilayer media. In addition, the possibility of electric control of the absorption capacity of the anisotropic fluorescent molecules allows for the recording, playback, and erasing of information on the WORM- or RW-type carriers using a radiation source with the same wavelength, provided the condition of complete or partial mutual overlap of the absorption spectra of this photosensitive orientation recording layer 305 and the anisotropically absorbing fluorescent substance 308 is met. Moreover, the range of various, not only non-linear, but also linear photochemical and photomechanical mechanisms for a single and repeated recording information on the carriers is extended.

It should be noted that a decrease in the thickness of such photosensitive recording layer 305 down to a monolayer molecule thickness does not cause any decrease in its photosensitivity during the recording and in the magnitude of the data (fluorescent) signal during the playback as is the case with conventional single-layer recording structures. This can be explained by the fact that information that is thus recorded is usefully stored only in the form of a change in the orientation properties on the surface 316 of the recording layer 305, and the amplification of the data signal in reading is assured by means of the electrically controlled guest - host liquid crystal layer 307 with the fluorescent molecules 308, and this amplification does not depend on the thickness of the recording layer 305, and it is only determined by the thickness of the liquid crystal layer 307 and concentration of the fluorescent substance 308 in this layer. The change in the volumetric properties within the data pit 314 is not used in the playback method according to the invention. Moreover, it is desirable that the pit thickness be kept as small as possible to rule out the spurious effect of diffraction of the recording and/or playback radiation at the data pits of the out-of-focus layers.

To illustrate the principle behind operation of the above-described information carrier, Figures 6a, b schematically show a top view (Figure 6a) and a cross-sectional view (Figure 6b) of one such multiple-component data layer 302 for the information carrier 300 according to the invention, e.g., of the WORM- or RW-type in the absence of the control voltage V (V = 0) at the electrodes 303 and in the presence of this voltage (V = V-i). As shown by arrows 601 and 602 in Figure 6a, the orientation directions on the surfaces 316 and 317 of the data pit 314 and background area 315, respectively, of the optically formed photopatteming recording and orientation film 305 extend, e.g., at an angle of 90° with respect to each other, and an orientation direction 603 on the surface of the homogeneous layer 304 runs in parallel with the orientation direction in the area where the data pit of the layer 305 is located.

The spatial three-dimensional pattern of the guest - host liquid crystal layer 307 has an optical patterning form, in which liquid crystal molecules 604 and fluorescent molecules 605 in an area 608 located opposite to the surface 316 of the data pit 606 are aligned in parallel with the orientation direction 601 , which is in the plane of the drawing. An area 607 that is located in front of the background surface 317 is in the form of a twisted nematic in which the liquid crystal molecules 604 with the fluorescent molecules 605 on the surface of the layer 304 are oriented in the plane of the drawing, and they have an orthogonal orientation on the opposite side. In other words, in the event of the twist effect, the directions of the planar orientation of the nematic liquid crystal molecules on the opposed electrodes are at right angles with respect to each other. In the playback mode, this multilayer structure of the data layer 302 is exposed without voltage application (V = 0) on the side of the recording layer 305, e.g. to a radiation 610, which is, e.g., linearly polarized by means of a polarizer 609 with polarization 611 in the plane of the drawing. The playback radiation is absorbed, hence it will be re-radiated (612) by the molecules 605 of the fluorescent substance only in the areas where the liquid crystal composition 608 is located in front of the surface 316 of the data pits 314, whereas the areas of the liquid crystal composition that are located opposite to the background surfaces 317 will be transparent for the playback radiation with this polarization of the playback radiation. Visually, a fluorescent pattern of the data pits is observed against a non-fluorescent background. The fluorescent radiation will be also polarized. This allows for partially getting rid off the background exposure from an extraneous radiation by using an additional polarizer positioned in front of the photo receiver (not shown in Figure 6).

When the direction of the polarization plane of the playback radiation is changed to the orthogonal direction, the negative playback mode is possible, i.e., with the luminous background with non-fluorescing data pits.

To eliminate the fluorescent cross talk from the rest of the layers during the playback, voltage should be applied to them as shown in Figure 6b. As a result, all liquid crystal molecules 614 of the matrix and the fluorescent molecules 613 within the liquid crystal matrix are aligned at right angles with respect to the electrodes, and the out-of-focus layers become fully transparent for the playback radiation.

When liquid crystal materials with the negative dielectric anisotropy are used, the fluorescent substances in the absence of voltage are aligned in a direction orthogonal with respect to the electrodes, and they do not absorb the playback radiation incident in the direction that is orthogonal to the layer. In the playback mode, voltage is applied to the selected data layer, and, as a result, the liquid crystal layer 307 with molecules of the fluorescent substance 308 acquires a patterning form with the planar directional orientation in accordance with the information that has been recorded in the recording and orientation film 305.

Figure 7 shows as an example a few options of the formation of the recording and orientation films 305 based on photoanisotropic materials with information recorded in the form of patterning orientation surfaces and respective types of the fluorescent signal, which is read out by using the conventional intensity-based technique with various states of polarization of the playback radiation. In doing this, similarly to a conventional fluorescent information display method such as those described in [US Patents 6,009,065 and 6,071 ,671 to Glushko and Levich], the fact of the presence or absence of a data pit in a given local micro area of the carrier is detected quantitatively based on the difference between the intensities of fluorescence at points where the data pits and background are located. In Figure 7a, data pits 701 and background areas 702 have surfaces with directions of the orientation capacity 703 and 704 that are orthogonal to each other. This arrangement of the patterned recording layers 305 assures the maximum contrast of K = 1 (positive or negative) when reading with a linearly polarized radiation (705 or 706), but a non-polarized radiation (707) cannot be used for this purpose because contrast in this case drops to zero when the conventional intensity-based playback technique is used.

This disadvantage is eliminated when the method for reading information according to the invention is used, in which the detected signal does not represent a difference in intensity, but rather the fact of the presence or absence of the anisotropy properties in the fluorescent signal when a polarized or non-polarized playback radiation is absorbed, or the difference in the direction of the optical axis of anisotropy thereof.

In effect, fluorescence of the anisotropically absorbing molecules is also anisotropic. Therefore, in the case of the spatial orientation configuration shown in Figure 7a, the fluorescent radiation, which carries information, will be polarized not only when the playback is carried out by using the linearly polarized radiation 705 or 706, but also by using the non-polarized radiation 707. It should be noted that in the latter case, the polarization vectors of the fluorescent emission for the areas where the data pit 701 and background area 702 are located will be orthogonal to each other, and their identification can be easily done, e.g., by using a polarizer positioned in front of the photo receiving elements of the playback device.

Figure 7b shows another potential configuration in which the background areas 708 do not possess orientation properties 709, and the surface of data pits 710 assures a directional planar orientation 711. In this case, when the conventional intensity-based playback technique is used, a polarized radiation 714 and a non-polarized radiation 712 can be used with a contrast of a magnitude K = 1/3, and a polarized radiation 713 assures a contrast K = -1 when the intensity of the fluorescent signal l_fl becomes two times as low as its upper limit value. When the polarized playback radiation 713 or 714 is used, polarization of the luminescent signal can be detected, e.g., by means of an optical system including a modulator for rotating the polarization plane of the playback radiation and a photo receiver, which photoelectrically detects the AC component of the electric signal obtained from the fluorescent radiation at two times the frequency of rotation of the polarization vector of the playback radiation. The intensity of fluorescence from the background area 709 that contains randomly oriented fluorescent molecules will not change, and the DC component of the electric signal that has been formed by this radiation will be cut off.

When the non-polarized playback radiation 712 is used, the polarized fluorescence is emitted only by the data pits 711 , and its presence can also be detected, e.g., by providing an additional polarizer in front of the photo receiver. The single-photon playback, based on both intensity and polarization, allows both bit-by-bit and page-by-page playback.

The multiple-component structure of the fluorescent data layers according to the invention with the use of the photoanisotropic materials for forming on their basis the orientation and recording films and the guest - host liquid crystal compositions with the anisotropically absorbing photochemically stable fluorescent substances as the guest allow for creating optical carries of the ROM-, WORM, or RW-type. In addition, the multiple-component data layers of the ROM-type can be made also with the use of orientation films that have been normally used in liquid crystal displays. Figure 8a shows an embodiment of a ROM-type data layer 810 in which a spacer 811 is provided between separation layers 812 having uniform thickness having transparent electrodes 813 and layers 814 which cause uniform directional orientation. The spacer 811 in this embodiment not only assures the required thickness of the guest - host liquid crystal layer with fluorescent molecules 815 in the data pits 816. It also functions as a ROM- type data layer. The spacer has a spatial patterned form, and it can be made of photosensitive acrylic resin or positive or negative photoresist. The information recorded in the spacer can be formed by conventional contact or projection photolithography methods, by the electrophotography, or by scanning modulated laser radiation over the photosensitive surface with subsequent developing. Photoaligners 813 can be made either as photoaligners based on photoanisotropic materials or as conventional liquid crystal photoaligners. According to the invention, one or even both photoaligners 813 can be present in the system shown in Fig. 8a.

Figure 8b shows another embodiment of a multiple-component structure of a fluorescent data layer 820 of the ROM-type in which separation layers 821 with the data surface in the form of microrelief 822 and a planar surface 823 are made similarly to the reflecting CD or DVD optical disks, e.g., by using the injection/ compression molding technologies or the 2P-process based on photopolymerizable compositions. Transparent electrodes 824 are sputtered to both sides of the separation layer 821, and orientation coatings 825 and 826 are applied on top of them. To protect the data layer 826 against potential damage and to impart orientation properties thereto, the optical method based on photoanisotropic materials was used. Data pits 827 were filled with a guest - host liquid crystal composition 828 containing a fluorescent substance. Similarly to the previous embodiment, at least one of the orientation films 825 or 826 could be dispensed with.

Figure 8c shows one of the structures of a WORM-type or RW-type data layer 830 according to the invention, wherein separation layers 831 having a planar surface 832 and a surface 833 with straight-line, concentric, or spiral-shaped tracks or channels 834 are made using the injection /compression method technologies or the 2-P-process based on photopolymerizable compositions. The size and shape of the tracks are chosen based on the orientation properties of the guest - host liquid crystal 835 with fluorescent molecules 836 and on the desired tracking mode. Transparent electrodes 837 are applied to both sides of the separation layer 833. In the event the liquid crystal layer 835 has a small thickness (less than one micron), an orientation film 838 can be dispensed with, and an orientation film 840 is made of photoanisotropic materials. When the same radiation source is used for information recording or erasing, these steps are carried out in the mode of the homeotropic orientation of the guest - host composition 839 in all data layers located upstream of the preset layer and also in the preset layer, and when the playback is carried out, these steps occur in all layers but the layer that is being read, in which the liquid crystal composition has the planar orientation.

Figure 9a, shows a top view of the orientation and recording film 305 of the multiple-component structure of the data layer 302 of the WORM- or RW-type, which is generally shown in Figure 3, before (Figure 9a) and after (Figure 9b) the recording of information in the layer. Tracks 911 (921) for information carriers that are made as an optical card 910 (or optical disk 920), are formed directly in an orientation and recording film 912 (922), which is made of the photoanisotropic material. This layer 912 (922), which also functions as a photopattemed photoalignment layer for the guest - host liquid crystal composition with photochemically stable anisotropically absorbing fluorescent molecules in the multiple-component data layer 302, has background areas 913 (923), e.g., with a randomly oriented molecular ensemble 914 (924) and straight-line tracks 911 (for the optical cards 910) or spiral-shaped tracks 921 (for the optical disks 920) with prevailingly directionally oriented molecular ensembles 915 (925). The direction of the prevailing orientation of these molecular ensembles (as shown by arrows in Figure 9) can run at a certain angle Ψ with respect to the track, e.g., as is the case for the straight-line tracks 911 of the optical card 910, or they can run along (or transversally), e.g., as is the case for the concentric tracks 921 of the optical disk 920.

This structure of the surface of the orientation and recording photosensitive layer 912 (922), which is spatially modulated in terms of the orderly arranged molecular orientation, is formed by exposing this layer with the initially disorderly arranged molecular orientation 914 (924) first to a focused linearly polarized radiation (not shown in Figure 9) scanning the surface, which is absorbed by the photoanisotropic material, before making the multilayer information carrier 300. The projection or contact photo printing, which is widely used in photolithography, can be used with polarized radiation through metal-clad positive phototemplates with transparent tracks. To obtain a structure with disorderly oriented tracks 911 (921) against an orderly background 913 (923), negative phototemplates should be used.

Using the orientation and recording films prepared as described above, which are applied to one side of the intermediate layer 309 with the electrode 303, the multilayer combined fluorescent - liquid crystal optical carriers are then formed. As mentioned above, in the mode of information recording on one of the recording layers of such multilayer carrier, the required absorbing capacity of all its multiple-component data layers 302 is preliminarily controlled by applying voltage to them from the external controller 312.

Subsequently, a recording beam (not shown in Figure 9), e.g., in conducting the bit-by-bit information recording is focused on a spot 916 or 917 (926 or 927) in the area where the track 911 (921 ) is located, and it is partly absorbed by the recording media 912 (922) made of the photoanisotropic material. As a result of occurrence of certain photo physical, photochemical, or photo thermal processes, the initial molecular ordering within the body, and more importantly on the surface in the exposed area 916 or 917 (926 or 927) changes, which is accompanied by a change in its aligning capacity with respect to the guest - host liquid crystal later 307.

These changes depend on the type of the photoanisotropic material used and on parameters of the recording pulse (the time-dependent and spatial distribution of the intensity and energy level in the pulse, the pulse duration, the state of polarization and orientation of the polarization vector of the recording radiation with respect to orientation of the molecular ensemble 915 in the spot 916 or 917 (926 or 927). They can manifest themselves either as a change (or formation in the case of a negative) in direction of the spatial orientation of the surface molecules 918 (928), e.g., to the orthogonal orientation in the micro area 916 (926) or as their complete misalignment 919 (929) in the micro area 917 (927) for a positive case given in Figure 9. The orientation of the liquid crystal layer 307, which is in direct contact with these modified surfaces 918, 919, 928, and 929, will change accordingly.

The first recording option is used for the photoanisotropic materials with the photochemical and photo physical mechanisms of recording with polarized radiation with the polarization vector directed, e.g., in the orthogonal relation to the initial orientation of the molecular arrangement 916 (926) in the tracks 911 (921).

The second option makes use of the photo thermal recording mechanism, wherein the micro area 917 (927) is melted, with subsequent loss of the directional orientation of the molecules (919, 929) in the area upon cooling.

The data pits that are recorded in this manner can be read in the modes illustrated in Figures 6 and 7 using either a source of radiation having a different wavelength, which is absorbed by the fluorescent molecules of the liquid crystal composition, or the same radiation source that was used for recording, but with a lower intensity.

It should be noted that the representation of the oscillators of absorption of anisotropically absorbing molecules as the linear oscillators may not be realistic enough for some of them. For this reason, even with their perfect homeotropic orientation, such molecules will partly absorb the playback radiation. In addition, as mentioned above, the subsurface areas of, e.g., nematic liquid crystals, hence the fluorescent molecules that are dissolved in them, which are in direct contact with the interphase surface of the orientation and recording film 912 (922), are not fully realigned under the effect of the electric field.

All these factors may result in incomplete suppression of the fluorescent background from the out-of-focus layers. In order to completely eliminate the background, according to the invention, the direction of the prevailing orientation of the molecular ensemble 915 (925) with respect to the tracks 911 (912) of each of the recording layers 912 (922) of the multilayer information carrier 300 is also marked (encoded) with its own value of the angle Ψ, which is used at the playback step for additional polarization detection (decoding) of the anisotropic (partially polarized) fluorescent radiation of the layer that is being read from among the rest of the out-of-focus layers.

The distinguishing feature of all photoanisotropic materials is their inherent reversibility regardless a specific photochemical or photo physical mechanism by which their optical anisotropy, hence their orientation capacity with respect to liquid crystals is imparted. It should be noted that the optical anisotropy, as well as their orientation capacity, i.e., the information recorded in the recording photoanisotropic layer can be locally erased either optically or photometrically. The complete erasure of the recorded information in such recording layer can be done by purely thermal means, by heating the entire layer.

The information can be restored (or overwritten) with the same orientation or with a changed orientation of the optical path of the induced anisotropy with the polarized initial optical radiation with the same or with a changed orientation of its polarization vector. However, the number or cycles of such reversibility depends on a specific mechanism that is used for forming the optical anisotropy in these materials.

According to the invention, the photoanisotropic materials that are based on irreversible monomolecular photochemical reactions or bimolecular phototopochemical reactions can be used for the WORM-type information carriers. The examples of the latter are materials based on low-molecular or high-molecular photosensitive substances, e.g., selected from the class of derivatives of diacetylenes such as Langmuir films or sputtered films of nonacosadein-10,12-carboxylic acid [Kozenkov V., et al., POVERKHNOST.

Fizika, khimiya, mekhanika, 2, 129, 1989] or polyvinylcynnamate [Kozenkov

V., et ai.]. However, their reversibility is low, and it is limited by the number of photosensitive molecules that are photochemically expended upon each cycle. For this reason, such materials could be used according to the invention as the recording media of the WORM-type, provided the rotational mobility of their molecules is eliminated. It should be noted that the low reversibility of the photo-induced anisotropy in these materials can be used for correction of information being recorded directly during the recording or after the recording has been completed. The majority of photochromic materials also has the effect of the photo- induced optical anisotropy. However, they are poorly suited for the purposes of the invention because of their reversed dark relaxation and quite a high quantum efficiency of the irreversible photo destruction of photochromic molecules in the initial state and/or in the photo-induced state. The photoanisotropic materials based on photochemically stable anisotropically absorbing non-fluorescent substances are the most promising materials for use according to the invention. Unlike the materials that exhibit the photo-induced optical anisotropy as a result of occurrence of various reversible or irreversible photochemical reactions (Weigert's effect), the optical anisotropy in these materials is formed as a result of a photo physical process of the orientation-wise ordering of the molecules when polarized or even non-polarized but directional radiation is absorbed without any chemical or conformational changes in their molecular structure.

It should be noted that the anisotropic photochemically stable and non- fluorescent molecules are prevailingly oriented either in a plane orthogonal with respect to the vector of the electric field of the light wave or in the direction of propagation of this vector for non-polarized radiation. Being photochemically stable, these materials assure not only the correction of the information that is being recorded, but also a substantially unlimited number of cycles of recording - erasing - rewriting of information on such materials. The information can be stored for many years.

In addition, these materials allow for practically non-destructive playback.

Moreover, according to the invention, all steps of recording, erasing, and rewriting of information in such media can be conducted using the same radiation source by changing its parameters (time-dependent, energy, and polarization characteristics of light pulses). These materials may be used as the ROM-type, WORM-type, or RW-type carriers. It is the most promising to use them as multilayer combination carriers, containing simultaneously the recording layers of the ROM-type, WORM-type, and RW-type, which can be made of the photoanisotropic material of the same or different component makeup. This approach can substantially facilitate the process of manufacture of such combination multilayer carriers and extend their functional range.

The photochemically stable anisotropically absorbing non-fluorescent substances, which are used in such photoanisotropic materials, can be inserted on the molecular level in polymeric matrixes, or they can be used as an integral film of such mono-substance with a small quantity of special doping additives, e.g., the additives that improve the film-forming capacity.

To illustrate these capabilities, Figure 10 shows typical kinetic curves of induction and dark relaxation of the optical anisotropy (birefringence) in such photoanisotropic material having the form of a mono-substance film exposed to polarized radiation at the various steps of induction or erasure.

As can be seen in Figure 10, the material is isotropic in its initial thermodynamically stable state. This state could be characterized as a state corresponding to logical "0." During the recording of information in the process of exposure to radiation, the optical anisotropy is induced in the material, which reaches asymptotically a photostationary value (Curve 1). With short time (low energy) exposure levels, the dark relaxation process occurs (Curve 2), which results in complete or partial decrease in the induced anisotropy to a certain stationary value, which increases with an increase in the energy to which the layer is exposed. This decrease is a consequence of the Brownian rotational molecular diffusion, which causes a random disarray in the orientation of the photochemically stable molecules. However, as the exposure energy increases, the rate of dark relaxation slows down to a complete extinctions (Curve 3).

Moreover, with the exposure rates that are high enough (of the order of 0.1 to 1 nJ/μ²), turning off the activating radiation results even in further self- ordering of the molecules in the layer (Curve 4) to achieve a new thermodynamically stable state. The rate of this "upward dark relaxation" increases when the layer is heated. This highly oriented state can be regarded as a state corresponding to logical "1." This state remains stable to temperatures close to the melting point of the photoanisotropic material.

The maximum achievable values of the photo-induced optical anisotropy in such media are close to respective values in liquid crystals. Thus, the parameter of orientation order S

S = (DH - DI) / (DII + 2D L) (1 ) and the birefringence value Δn

Δn = nι- nn (2) reach the values of about 0.8 and 0.3, respectively, wherein n-n and = ni and Dn and D are the values of the refraction index and optical density of the material for components of the polarization vector of the measuring radiation that are parallel and perpendicular with respect the polarization vector of the activating radiation, respectively. We have found that the photo-induced state (including the orientation- wise ordered state of the surface molecules) in such materials can be maintained for at least 10 years.

The fluorescent playback of the information that has been recorded in this manner can be done by using the modes shown in Figures 6 and 7. It should be noted that a short time or low-intensity level exposure of this orientation-wise ordered layer to the same non-polarized or circularly polarized radiation source causes its partial disordering (Curve 5), which is accompanied by partial degradation of its orientation properties with respect to liquid crystals. The same result is obtained when the direction of polarization of the playback radiation is changed to the orthogonal direction. However, when this radiation is turned off, the photo-induced thermodynamically stable state is again restored (Curve 4¹), and the orientation capacity with respect to liquid crystals is also restored. This property of the photoanisotropic materials based on photochemically stable anisotropically absorbing non-fluorescent substances allows for practically non-destructive playback of information recorded in the multiple-component fluorescent data carrier structures according to the invention using the above- described materials as the orientation and recording film. It should be added that the relationship between of the sign and rate of dark relaxation (Curve 2, Curve 4, and Curve 4¹) allows the "background" induction of the optical anisotropy in the out-of-focus layers to be eliminated because spontaneous "erasure" occurs when energy that has been absorbed is low (see Curve 2 in Figure 10).

The recorded information can be erased in the same mode as the one used for playback, but the erasing radiation should have higher energy. In doing this, either complete dark (photothermal) molecular misalignment (and the loss of the orientation capacity with respect to liquid crystals) in the micro area that is being erased (Curve 6) is possible as a result of local melting of the layer with its subsequent cooling, or re-alignment to the orthogonal orientation (Curve 6¹) may occur (a change in the spatial direction of the orientation capacity with respect to liquid crystals) when radiation is used that is polarized in the orthogonal direction.

It should be noted that in the latter case, when the exposure energy is commensurable with the exposure energy that was used for recording, still another thermodynamically stable oriented state (up to temperatures below the melting point of the layer), high and orthogonal with respect to the initial state, which can be regarded as logical one with the minus sine, "-1", is obtained. It should be added that a new recording can be done actually simultaneously with the erasing.

The rewriting mode can be similar to the initial recording mode (Curve 7).

According to the invention, all recording and erasing steps in a predetermined photosensitive orientation and recording film are carried out either by applying voltage to all out-of-focus layers that are located upstream of this layer including this layer itself (for liquid crystal composition having the positive dielectric anisotropy) or by applying voltage to this layer only (for liquid crystal compositions with the negative dielectric anisotropy). Accordingly, the information playback is carried out either by applying voltage to all data layers but the one that is being read in the former case or by applying voltage only to the layer that is being read in the former case.

According to the invention, the spatial changes in the anisotropic optical properties of such dual-function orientation and recording film 912 (922) are not used for playback. However, they could be used as mentioned above for quality control and for correction of the information that is being recorded or that has been recorded in such media both in real time and after the full recording is completed. These steps are carried out by adjusting the time-dependent and/or spatial magnitude and distribution of intensity and energy of radiation in the recording pulse, by adjusting the state of polarization of the recording radiation, or by providing necessary alignment of the optical system of the recording device.

As a matter of fact, the photo-induced anisotropy in the photoanisotropic materials emerges directly during the exposure to radiation because the time of occurrence of the photoaligning and photochemical processes in the materials does not exceed hundredths of a microsecond. The resulting birefringence is induced also in the area of their transparence, i.e., outside the spectral area of photosensitivity of the recording layers.

All the above allows for non-destructive check of the information that is being recorded by using non-photoactive radiation, e.g., from a He-Ne (λ = 632.8 nm) laser or a semiconductor (λ « 700 NM) laser in real time or after complete recording of information.

In the exposure phase, e.g., with exposure to polarized photoactive radiation, precursors of data pits, which become fluorescent during the playback, emerge in the layer 912 (922) in the form of a latent local molecular ordering on the surface and in the form of a three-dimensional anisotropic phase (birefringent) spatially modulated pattern against the isotropic background. Because of a small thickness of the layer, the degrees of molecular alignment within the body and on the surface of the layer 912 (922) are in a on-to-one relation to each other.

The recording quality can be checked by using non-photoactive polarized radiation by converting the latent three-dimensional phase image of the precursors of the above-mentioned pits into the spatially intensity amplitude modulated pattern by using a polarizer/ analyzer positioned between the recording layer that is being exposed and a photodetector.

The three-dimensional distribution of intensity of the playback radiation (l(x,y)) that has passed through the latent image of the precursors of the pits that are being formed and through the analyzer is determined by the value of birefringence that was induced during the recording: l(x,y) = lo x Sin² (πΔn(x,y)dλ) = Const x [Δn(x,y) (3) wherein: Δn(x,y) = ψ[H(x,y)] is the three-dimensional distribution of birefringence induced in the precursor of the pit that is being formed under the effect of the activating radiation having the spatial energy distribution H(x,y); d is the thickness of the recording layer; λ is the wavelength of the playback radiation; lo is the intensity of the playback radiation incident upon the information carrier;

Const = lo x (πd/λ²), and

X, Y are the spatial coordinates in the plane of the recording layer.

It is assumed that the optical axes of the polarizer and analyzer are orthogonal and that the optical axis of birefringence induced in the recording layer extends at angle the of 45° with respect to these axes.

For the sake of simplicity, it is assumed in (3) that because of a small thickness of the recording layer, absorption at the wavelength of the photoactivating radiation in this layer is small, the intensity of radiation in depth Z of the layer, hence birefringence are uniform, and the phase lag value φ (φ = (πΔn(x,y)dλ) is small.

Figures 11 and 12 schematically show two embodiments of an information recording system using the method for checking and for correcting the quality of the latent image of the data pits in the layer according to the invention. The embodiment shown in Figure 11 assures the check and correction of the bit-by-bit recording by providing for the bit-by-bit playback of the latent image of the information that is being recorded using the DRAW technique (direct reading after write) in real time. During the recording, a modulator 1103 modulates a laser beam 1101 , which is polarized in a polarizer 1102 with a recording signal 1104. A modulated recording beam 1105 is focused by an objective lens 1106 on a recording layer 1107 of a multilayer carrier 1108. The device uses the beam sweep method, and each element (pit) is exposed individually. The method does not require the use of phototemplates. To obtain a preset information pattern, a beam sweep programming device is used.

Precursors of the fluorescent data pits are formed in the layer 912 (922), in the exposed micro areas as a birefringent spatially modulated pattern against the isotropic background. The birefringence value and its spatial distribution in the latent image (the spatial precursor technique) depends on the magnitude and spatial distribution of energy of the recording pulse. The latter depends on the modulating code 1104 and on the quality of the focusing optics 1106.

The latent image of these phase precursors of the data pits is read bit- by-bit in real time by using a focused non-photoactive laser radiation 1110

(e.g., from a He-Ne laser 1109 with a wavelength of 632.8 nm). For that purpose, the playback beam 1110 is converted by means of a polarizer 1111 into a linearly polarized beam 1112 and, after passing through a dichroic mirror 1113, it is focused by an objective lens 1116 on the area on which the recording beam 1105 is focused in the recording layer 1107. After passing through the micro area of this layer that contains the latent anisotropic image of the precursor of the fluorescent pit, which has been recorded there, the linearly polarized playback beam 1112 is converted into an elliptically polarized beam 1114, which partly passes through an analyzer 1115. The objective lens 116 projects the visualized image of this precursor of the fluorescent pit on a photoelectric detector 1117, and an electric signal from the detector is sent to computer processing and is then transmitted to the control unit of the exposure device (not shown in Figure 11 ). Therefore, method for precision real time measurement of parameters of the latent image of precursors of the fluorescent data pits that are being formed allows for a feedback by adjusting the power and polarization of the recording radiation, the exposure time, and correction of the quality of the intensity profile in the exposure beam by adjusting the focusing of the objective lens 1106.

Figure 12 shows another embodiment of the method according to the invention in which a CCD camera 1119 is used as the photodetector 1117. This provides the opportunity of selective and, if required, complete check of the quality of the spatial topology of the latent images of the precursors of the fluorescent data pits in the recording layer of a multilayer carrier 1120 after the recording has been completed. The reading system shown in Figure 12 is similar to that shown in Figure 11 , and it also has the polarizer 1111 and the analyzer 1115, and the objective lens 1116 reads the entire latent image of the recording layer all at once, which is projected by the objective lens 1116 on the plane in which the CCD camera 1119 is located. This opportunity to analyze the latent images allows for optimizing the conditions under which the recording layers are formed, e.g., the ROM-type layers in combination multilayer information carriers. The invention will now be illustrated by the following examples of the component makeup and structure of the guest - host fluorescent liquid crystal of the data layer.

The construction of the fluorescent data layer according to the invention in the form of a multiple-component structure which is a thin liquid crystal cell having at least one initial patterning orientation film (for ROM-type systems) or photoanisotropic photosensitive orientation film (for WORM-type or RW-type systems) allows its functions to be shared among various spaced elements.

When recording in the case of WORM-type or RW-type systems, this function applies to one of the orientation films which simultaneously functions as a recording layer, in which information is recorded in the form of the orientation capacity with respect to the liquid crystal layer, which is spatially modulated over its surface, i.e., a photo patterning or photo aligning layer is formed.

In the playback mode, this function applies to the guest - host liquid crystal matrix containing the anisotropically absorbing photochemically stable fluorescent substances, which are used as the host regardless of the carrier type (ROM, WORM, or RW).

This separation of functions during information recording and playback in the combined fluorescent - liquid crystal information carriers of the WORM- type or RW-type substantially eases up the requirements for the fluorescent compositions for such structures. The use of the photochemically stable fluorescent substances in such systems resolves such problems as, e.g., dark storage of conventional fluorescent data layers of WORM-type photosensitive systems, which are based on bimolecular photochemical reactions with substances that are fluorescent substances or that yield fluorescent photoproducts. This is due to the possibility of occurrence of dark thermochemical or diffusion processes in such substances, which cause fogging formed from the fluorescent molecules and which form a background fluorescent radiation during playback or cause a decrease in intensity of the fluorescent signal because of the dark decomposition of the initial fluorescent dye.

As mentioned above, the disadvantages of RW-type photosensitive systems based on the photochromic reactions is the presence of the reversed dark processes and the low number of recording - erasing - recording cycles because of the photodestruction of the photochromic molecules. Therefore, the invention provides a new structure for a multilayer combined fluorescent - liquid crystal optical memory system of ROM-, WORM, or RW-type and methods for information recording to, and playback from the structure, which assures electrical control of the absorption and emission capacity of the fluorescent molecules that are dissolved in the liquid- crystal matrix of the data layers. This, in turn, allows for partial or complete elimination of the fluorescent cross talk from the adjacent data layers during the playback in both pit-by-pit mode and page-by-page mode. Additionally, an opportunity is provided to electrically control (with infinite control is necessary) the intensity of the data signal with the same intensity of the playback radiation. The reduction or complete elimination of the fluorescent cross talk allows for a reduction in spacing between the layers, thus assuring an increase in the light gathering from the playback fluorescent radiation, simplification of the design of the playback head because of the smaller effect of spurious distortions, as well as an increase in the possible number of data layers in the carrier. In addition, the invention extends the capabilities of use of various, not only non-linear, but also linear photochemical or photo physical mechanisms of single or repeated information recording and allows the same radiation source to be used for recording, playback, and erasure of information in such carrier.

The use of the photoanisotropic materials based on photochemically stable anisotropically absorbing non-fluorescent substances as the recording media, which combine in themselves the function of the photo patterning and photo aligning layers allows a rewritable multilayer memory system with the fluorescent information playback to be realized.

The examples described above are only given to illustrate the new structure of a multilayer combined fluorescent - liquid crystal optical memory system and method for information recording to, and playback from this structure, and they cannot limit the scope of the attached claims.

Claims

What is claimed is:

1. A multilayer combined fluorescent - liquid crystal optical information carrier, comprising: - a plurality of data layers positioned in parallel planes;

- said plurality of data layers being provided on a common substrate and separated from each other by transparent intermediate layers;

- each of said plurality of data layers being in turn made as a multiple-component structure comprising a thin electrically controlled liquid crystal cell, which consists of two identical optically transparent electrodes made as continuous layers or as two mutually orthogonal strips having at least one orientation film applied thereto and separated from each other by spacers, the space between the layers being filled with a guest - host liquid crystal composition in which the host substances comprise photochemically stable anisotropically absorbing fluorescent substance

2. The information carrier of claim 1 , wherein the optically transparent electrodes are applied on both sides to glass or polymeric preferably optically transparent intermediate layers designed in a general case for the recording, playback, fluorescent, and erasing radiation, at least one side of which has a smooth surface and the other side can have a plurality of tracks for recording and tracking in the form of tiny recesses (grooves) extending along a straight line or along a spiral.

3. The information carrier of claim 1 , wherein the refraction indexes of all data layers and intermediate layers, as well as of the guest - host liquid crystal composition in the homeotropic state (or in the planar state, depending on nature of the composition or information recording and/or playback mode) are identical or close to each other at the wavelengths of the recording radiation, fluorescent (data) radiation, and excitation (playback) radiation, as well as erasing radiation.

4. The information carrier of claim 1 , wherein the data layer comprises a multilayer interference antireflection filter for the wavelengths of the recording radiation, fluorescent (data) radiation, and excitation (playback) radiation, as well as erasing radiation.

5. The information carrier of claim 1 , wherein the thickness of the liquid crystal layer is of a value commensurable with the minimum size of a data pit formed therein.

6. The information carrier of claim 1 , wherein the photochemically stable anisotropically absorbing substances, which are fluorescent in a predetermined spectral area, are selected from substances that are well soluble in liquid crystal compositions and that have high fluorescence quantum efficiency, whose molecules has a stiff rod-like or disk-like shape and whose long-wave absorption oscillator extends along their axis or transversally thereof.

7. The information carrier of claims 1 and 6, wherein the fluorescent substances are selected from photochemically stable substances belonging to the group of aromatic hydrocarbons and their derivatives such as polycyclic condensed aromatic hydrocarbons and their derivatives having an arylethylene group and an arylacetylene group and their derivatives (1 ,2-diarylethylenes, diarylpolyenes, functionally substituted stilbene and 1 ,4-distyrylbenzene, etc.), polyphenyl hydrocarbons; compounds having five-member heterocycles (furans, thiophenes, pyrroles, and their derivatives, etc.) and six-member heterocycles having one or two nitrogen or oxygen atoms, etc.; compounds having a carbonyl group (coumarins and carbostyryls, anthrone and aromatic acid derivatives, substituted oxazol-5-one, indigoids, and thioindigoids, quinones, etc.); compounds based on naphthalic acid; as well as complex organometal ligands and organic dyes selected from the group of xanthene, acridine, oxazine, azine, perylene, terylene, vialanthrone, cyanine, phthalocyanine, porphyrines, etc.

8. The information carrier of claim 1 , wherein the liquid crystals comprise nematic, smectic, or cholesteric liquid crystals or their mixtures with others.

9. The information carrier of claim 1 , wherein the liquid crystal and the fluorescent substance are mixed in a molar ratio between 1 :0.01 and

1 :0.8.

10. The information carrier of claim 1 , wherein the photochemically stable anisotropically absorbing and fluorescent substances are covalently bonded to the molecules of a substance that exhibits liquid- crystal properties.

11. The information carrier of claim 1 , wherein the photochemically stable anisotropically absorbing and fluorescent substances comprise liquid crystal substances proper that are capable of fluorescing under the action of radiation absorbed thereby.

12. The information carrier of claim 1, wherein the at least one orientation film comprises layers obtained by one of the methods of unidirectional mechanical rubbing of polymeric films, Langmuir-Blodgett method, or the oblique sputtering method, as well as by the method of non-contact photoalignment with the use of the photoanisotropic materials.

13. The information carrier of claim 1 , wherein the spacer positioned between the separation layers, which are smooth on both sides and have uniform thickness, has a spatially patterned configuration and assures not only the required thickness of the guest - host liquid crystal composition, but simultaneously functions as the data layer of the ROM-type.

14. The information carrier of claims 1 and 13, wherein the spatially patterned spacer is made, e.g., of a photosensitive polymer, a positive or negative photoresist by the lithographic method or by the laser scanning method.

15. The information carrier of claims 1 and 13, wherein the spatially patterned spacer, which simultaneously functions as the data layer of the ROM-type, is formed, e.g., by the injection-compression molding technologies or the 2P-process based on a polymerizable composition directly on one of the sides of the separation layer.

16. The information carrier of claims 13 and 15, wherein one or both orientation films are not used.

17. The information carrier of claim 1 , wherein one of the orientation films simultaneously functions as a photosensitive recording layer of the ROM-type, WORM-type, or RW-type, which is made of the photoanisotropic material that is non-soluble in the guest - host liquid crystal compositions, and which contains after recording thereon a plurality of data micro areas (data pits), which are different from the background areas by their prevailing direction of surface molecular ordering, hence, by the orientation capacity with respect to the electrically controlled layer of the guest - host liquid crystal composition with host fluorescent molecules.

18. The information carrier of claims 1 and 17, wherein the minimum thickness of the photosensitive orientation and recording film can be a single monomolecular layer.

19. The information carrier of claim 1 , wherein tracking areas for guiding beams for recording or erasing are formed directly in the photosensitive orientation and recording film, which is made of the photoanisotropic material, the directions of the prevailing molecular orientation ordering on the surface of the layer in the area in which the tracks are located and in the background area being different, and each of the recording layers of the multilayer information carrier is marked (encoded) with its individual set of values of the angles that characterize the directions of the prevailing orientation of the surface molecular ensembles in straight-line or spiral-shaped tracks (or in the background areas) with respect the tracks proper.

20. The information carrier of claims 1 and 17, wherein the magnitude of energy of cohesion of the liquid crystal molecules to the surface molecules of the photosensitive orientation and recording film is controlled by the magnitude of energy of its exposure to the recording polarization radiation.

21. The information carrier of claim 1 , wherein the photosensitive orientation and recording film of the WORM-type is made of the photoanisotropic materials based on monomolecular reversible photoreactions or bimolecular phototopochemical reactions, e.g., of the type of diacetylene derivatives or polyvinylcynnamates.

22. The information carrier of claim 1 , wherein the data layers may comprise CD- or DVD-read only memory (ROM), write once read many (WORM), rewritable (RW) or their mixed types in a variety of optical disks, cards, or tapes, and the photosensitive orientation and recording films of the ROM-, WORM, or RW-type for combination multilayer carriers integrating different memory types at a time may be made of a photoanisotropic material of a different or of the same component makeup based on photochemically stable anisotropically absorbing and non-fluorescent substances.

23. The information carrier of claims 1 and 22, wherein the photochemically stable anisotropically absorbing and non-fluorescent substances are added to a polymeric matrix, or they comprise an integral; film of this mono-substance with a small quantity of process additives, which, e.g., improve the film forming properties.

24. The information carrier of claims 1 and 22, wherein the function of the data layer in the data layer comprising a multiple-component structure in the form of a thin electrically controlled liquid crystal cell having at least one orientation film, is shared among various spaced elements, the function applying, during the information recording, to the orientation film, which simultaneously functions as the photosensitive recording layer based on the photoanisotropic material in which information is recorded in the form of orientation capacity with respect to the guest - host liquid crystal composition with fluorescent molecules, which is spatially modulated over its surface, and this function applying, during playback, to the guest - host liquid crystal matrix proper containing the photochemically stable anisotropically absorbing fluorescent molecules whose absorbing and emitting capacity is controlled by applying an external electric field to the electrodes of this liquid crystal cell.

25. A system for information recording to, playback and erasing from a fluorescent multilayer information carrier, said system comprising: a multilayer combined fluorescent - liquid crystal optical information carrier comprising a plurality of data layers made as a multiple-component structure, which is in the form of a thin electrically controlled liquid crystal cell composed of two identical optically transparent electrodes made as continuous layers or as a system of two mutually orthogonal strips, having at least one orientation films applied thereto and separated from each other by spacers, the space between the layers being filled with a guest - host liquid crystal composition in which the host comprises photochemically stable anisotropically absorbing fluorescent substances; electromagnetic radiation sources with wavelengths for the optical or thermooptical recording, for optical playback, and optical or thermooptical erasing of information stored on the carrier; an optical polarization device for imparting predetermined polarization characteristics to the recording, playback, and erasing radiation; - an optical device for imparting a predetermined spatial configuration to the beams of the electromagnetic recording, playback, and erasing radiation for operation in the pit-by-pit mode or page-by-page mode; a photo receiver device for the pit-by-pit or page-by-page photoelectric detection of intensity of the playback data fluorescent radiation and/or its polarization characteristics (the degree of polarization and the direction of the prevailing orientation of the partially polarized radiation), with subsequent conversion thereof into electric data signals; an optoelectronic device for checking and correcting the quality of information that is being recorded with the formation of a feedback signal with an adjustment of the recording mode in real time or after the full recording has been completed; a device for applying voltage to any predetermined pair of the continuous or strip electrodes for controlling the absorption and fluorescence capacity of the guest - host liquid crystal composition located therebetween.

26. The system of claim 23, wherein the absorption spectra of the photosensitive orientation and recording film, which is made of the photoanisotropic material, and of the fluorescent substance of the multilayer information carrier overlap each other partially or completely.

27. The system of claims 25 and 26, wherein a radiation source having the same wavelength but different time-dependent, energy, and polarization parameters of its optical radiation is used for the recording, playback, erasing, and correcting the quality of the recorded information on the multilayer optical WORM-type or RW-type information carriers.

28. A method for recording, playback, erasing, or correction of the quality of the information that is being recorded in a multilayer combined fluorescent - liquid crystal optical information carrier of the WORM-type or RW-type of claim 27, wherein the recording, correction of the quality of information, or erasing of information in a predetermined data layer is carried out by applying control voltage to the electrodes of all liquid crystal cells of the multiple-component data layers that are located between the radiation source and this layer including the electrodes of the layer itself for initially planar oriented guest - host compositions based on liquid crystals with the positive dielectric anisotropy or without voltage application for initially homeotropically oriented compositions based on liquid crystals with the negative dielectric anisotropy, and wherein playback is carried out by applying voltage to all data layers of the carrier but the layer that is being played back for the former case and only to the layer that is being played back for latter case.

29. A method for recording information to a multilayer combined fluorescent - liquid crystal optical information carrier, the method comprising the steps of: exposing a photosensitive orientation and recording film of a predetermined data layer, which has initially orientation-wise disorderly molecular structure, with polarized radiation which is absorbed by this layer for forming tracks directly in this layer in the form of a molecular ensemble prevailingly directionally oriented at a predetermined angle in the plane of the layer different from the direction of the prevailing orientation of the molecular ensemble outside the tracks (background areas) and subsequently exposing this photosensitive layer to the data radiation, which is also absorbed by this layer and which has polarization characteristics (the direction of the polarization vector) different from those used for the primary exposure.

30. The method of claim 29, wherein the tracks are formed in the photosensitive layers before making the multilayer combined fluorescent - liquid crystal optical information carrier with the use of these layers.

31. The method of claims 29 and 30, wherein the primary polarization exposure is carried out to a radiation that is focused and scanned over the surface of the photosensitive layer or by using the projection or contact photolithography technique.

32. The method of claim 29, wherein the direction of prevailing orientation of molecules in the area in which the data pits recorded in the photosensitive layer are located and, respectively, the direction of a potential prevailing orientation of the liquid crystal molecules thereby is determined by the direction of the polarization vector of the recording radiation and is different from the orientation of the surface molecules on the track outside the pits and in the background areas, and the magnitude of energy W of cohesion of this molecules to the liquid crystal molecules is determined by the recording exposure energy.

33. The recording method of claim 29, wherein the directions of the prevailing molecular orientation ordering on the surface of the photosensitive layer in the area in which the tracks and data pits are located and in the background area are different from each other, each of the photosensitive orientation and recording films of the multilayer information carrier being marked (encoded) with its own individual set of values of the angles of prevailing orientation of the surface molecular ensembles in the straight-line and spiral-shaped tracks, data pits and background areas which is used at the playback step for additional polarization detection (decoding) of the anisotropic (partially polarized) fluorescent radiation of the layers that is played back from also partially polarized fluorescent radiation from all the rest of the out-of-focus data layers.

34. The recording method of claims 28 and 29, wherein the quality of the recording is checked by using non-photoactive polarized radiation by converting a latent phase (birefringent) image of the precursors of the data pits formed within the body of the photosensitive orientation and recording film into a spatially intensity amplitude modulated pattern by means of a polarizer/ analyzer positioned between the recording layer that is being exposed and a photo receiver that is positioned on the opposite side from the playback radiation source.

35. The recording method of claims 28 and 29, wherein the check and correction of the quality of information that is being recorded in the bit- by-bit mode is carried out by playing back in the bit-by-bit mode, synchronously with the recording, a latent image of the information that is being recorded using the DRAW (direct read after write) technique in real time and by using the resulting data for forming a feedback signal for adjusting the power and polarization stage of the recording radiation, its wavefront (spatial distribution of intensity in the exposure beam), and the focusing of the objective lens.

36. The recording method of claims 28 and 29, wherein the quality is checked after the recording is completed in the page-by-page mode using a CCD camera as the photo receiver.

37. A method for playing back information of claim 28.

38. The method for playing back information of claim 28, wherein the fact of the presence or absence of a data pit in a given micro area is detected quantitatively by the difference between the intensity of fluorescence at points where the data pits are located and in the background during absorption of polarized or non-polarized playback radiation with power that is lower than that used for recording.

39. The method for playing back information of claim 28, wherein the fact of the presence or absence of a data pit in a given micro area is the fact of the presence or absence of the optical anisotropy properties

(the degree of polarization and/or the direction of the prevailing orientation of the partially polarized radiation) in the fluorescent signal or the fact of the presence or absence of differences between the directions of prevailing orientation of this partially polarized radiation in a given micro area from the background areas during absorption of polarized or non-polarized playback radiation.