WO2001029835A1 - Apparatus for information retrieval from a multilayer fluorescent optical clear card - Google Patents

Abstract

Various embodiments of optical schemes permit page-by-page data retrieval from fluorescent multilayer optical cards. The integral optical unit for generation of reading radiation includes, depending on specific design, for instance a micro-miniaturized linear filament light bulb, one or a matrix of light-emitting or laser diodes, a wide optical waveguide or an optical strip waveguide array with a matrix of surface-embossed holograms on the bottom side and a matrix of collimating microoptics on the other side of said waveguides, as well as a matrix of electrooptical shutters based on liquid crystals and a second matrix of collimating optics generating one light beam in the location of the information page to be read.

Description

APPARATUS FOR INFORMATION RETRIEVAL FROM A MULTILAYER FLUORESCENT OPTICAL CLEAR CARD

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/159,543, filed October 15, 1999, whose disclosure is hereby incorporated in its entirety into the present disclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

This invention relates to an optical memory system for "page-by-page" retrieval of information and more particularly, to fluorescent multilayer read only memory (ROM) optical clear cards.

2. Description of the Prior Art.

Existing optical memory systems utilize two-dimensional data carriers with one or two information layers. Most of the previous technical solutions in optical data recording propose registration of the changes in reflected laser radiation intensity in local regions (pits) of the information layer. These changes could be a consequence of interference effects on the relief optical discs of CD or DVD ROM-type, burning of holes in the metal film, dye bleaching, local melting of polycarbonate in widely used CD-R systems, change of the reflection coefficient in phase-change systems, etc.

Three-dimensional, i.e. multilayer, optical storage systems provide a comparatively higher storage and recording capacity. However, this imposes specific limitations and requirements on the design and features of the optical information carrier, ways of data recording and reading, especially in the depth of the carrier.

In the reflection mode, each information layer of the multilayer optical information carrier shall have a partly reflective coating. Said coating reduces the intensity of both reading and reflected information beams because of passing through media to the given information layer and back to the receiver.

Besides, due to their coherent nature, both beams are subject difficult-to-estimate diffraction and interference distortions on fragments (pits and grooves) of the information layers on their way.

That is why multilayer fluorescent optical information carriers with fluorescent reading are preferable as they are free of partly reflective coatings. Diffraction and interference distortions in this case shall be much less due to non-coherent nature of fluorescent radiation, its longer wavelength as compared to the reading laser wavelength, and the transparency and homogeneity (similar refractive indices of different layers) of the optical media towards the incident laser and the fluorescent radiations. Thus, multilayer fluorescent carriers have some advantages over reflective optical memory.

The system based on an incoherent signal, such as fluorescence and/or luminescence, has twice as high spatial resolution as compared to coherent methods, such as reflection, absorption or refraction (see Wilson T., Shepard C. "Theory and Practice of Scanning Optical Microscopy", Academic Press, London, 1984). Using an incoherent signal the multilayer optical memory could lead to as high increase of information capacity as eight times. US patents NoNo 6,009,065 and 6,071 ,671 (V. Glushko and E. Levich) describe devices for bit-by-bit data reading from fluorescent multilayer optical discs.

SUMMARY

The subject of the present invention is different embodiments of a device for a bit-by-bit data retrieval from an FMLC when a source of reading radiation and a CCD camera are positioned on the same or different sides of an optical card.

Further, the subject of the present invention is a proposal on reducing strong spurious illumination of a photoreceiver from adjacent non-reading information layers of the FMC by using selective excitation, in particular reading by means of a focusing lens wherein the numerical aperture is larger than the numerical aperture of the objective lens, reading under a small angle relative to the plane of information layers or reading in a waveguide mode when intermediate transparent FMC layers serve as waveguides for the reading radiation. Further, the subject of the present invention is optimization of geometric size of pits in terms of gray levels in order to increase the FMC information capacity.

Furthermore, the subject of the present invention is a scanning system with sub-pixel resolution.

Further, the subject of the present invention is use of a dichroic mirror, two crossed polarizers located in the reading beam and in front of the CCD camera or Notch filters on the basis of cholesteric liquid crystals to separate the fluorescent signal from the reading signal.

Further, the subject of the present invention is execution of a system of autofocusing using a two-lens scheme wherein a possibility is provided for varying their mutual optical disposition or by means of their mechanical movement or using a liquid crystal optical path corrector.

Furthermore, the subject of the present invention is use of a liquid crystal varifocal lens in the optical autofocusing unit in place of an objective microlens movable by means of controllable electromagnetic actuator and use of photoanisotropic materials as photoorienting agents for liquid crystals.

Further, the subject of the present invention is various embodiments of integral optical schemes for page-by -page data retrieval from an FMLC. Said schemes include, depending on specific design, for instance a micro-miniaturized linear filament light bulb, one or a matrix of light-emitting or laser diodes, an optical waveguide or an optical waveguide array with a matrix of surface-embossed holograms, a matrix of colhmating microoptics and a matrix light- valve liquid crystal device the geometric size of which coincides with the size of the FMC.

The present invention relates to multilayer fluorescent read-only Memory (ROM) optical Clear Card. In the embodiment, the data are stored in a multilayer structure consisting of many optically thin information layers separated by isolating layers. Data bits are stored in information layers as individual marks with fluorescent material.

In the proposed invention, data are retrieved from the FMLC page by page using for instance a CCD camera at the rate of the order of 0.1 -0.001 frames per second. This enables utilization of luminophores with a long-life excitation state including phosphorescence of organic compounds, long-life luminescence of excimers and exciplexes. as well as luminescence of inorganic compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a simplified view of the fluorescent multilayer optical Clear Card as an embodiment of the present invention.

Figs. 2a and 2b present a schematic view of optical Clear Card reader embodiments. Fig. 3 demonstrates a liquid crystal varifocal lens.

Fig. 4 illustrates a focus change in the liquid crystal varifocal lens. Fig. 5 is a schematic view of an optical path corrector based on an liquid crystal cell.

Figs. 6a-6c illustrate variants of optical schemes of page-to-page data retrieval from a fluorescent multilayer optical Clear Card with selective excitation.

Fig. 7 is a schematic side view illustrating location of the main components of the apparatus for the Clear Card retrieval.

Fig. 8 is an optical scheme of an illuminator based on a microminiaturized filament light bulb and a waveguide based on the total internal reflection effect. Fig. 9 is a cross-section view of electrooptical shutters based on liquid crystals.

Fig. 10 is an upside view of electrooptical shutters.

Fig. 1 1 is another embodiment of the optical illumination system based on a light-emitting diode linear array and optical waveguide arrays. Fig. 12 is a cross section of waveguide arrays.

Fig. 13 is another embodiment of an optical reading system and light-valve device based on liquid crystals.

Fig. 14 is an optical reading system with one laser diode and adaptive liquid crystal phase plates. Figs. 15a-15c explain the principle of operation of a scanning system with subpixel resolution.

It should be understood that the figures are just schematic and not drawn to scale. In particular, certain dimensions, such as the thickness of layers, may be reduced. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will be explained below with reference to accompanying drawings.

Fig. 1 is a schematic view illustrating one of the variants of the structure of an optical fluorescent multilayer clear memory card (FMLC) 10 comprising as basic elements a thick substrate 11 as a rectangular parallelepiped, an optical fluorescent multilayer data carrier (FMC) 12 and a protective layer 20 to protect the optical recording medium from mechanical damage and aggressive media.

The substrate 1 1 is a nontransparent plastic plate used for mechanical fixing of FMC 12 thereon and installing the FMLC itself in the data retrieval device. In case the unit for reading radiation formation and the unit for fluorescent information signal recording are disposed on different sides of the FMLC. in the substrate 11 an insert 13 is provided which is made of an optically transparent material and located at the FMC 12 site. Openings 14 serve for precise installation of the FMLC in the data reader.

The FMC 12 is made as a multilayer structure wherein 0.1-1-μm thick fluorescent information-carrying layers 18 are separated by 10-70-μm thick polymer layers 19 which are transparent for reading and fluorescent radiations. To prevent spurious reflection on the boundary of layers 18 and 19, their refraction indices are preferably chosen equal for designated wavelengths.

Written information is stored as a multitude of pages 15 including a multitude of separate fluorescent information marks 17 (analogs of reflecting pits in known CD- or DVD-ROM memories) located along linear tracks 16. Along with information ROM layers, FMC can also include ROM address layers with control and display information designated in particular for positioning the reading head relative to the FMC.

A few pages located at different information layers above each other form a pile of pages or a data frame. From said frame information can be retrieved without mechanical movement of the reading head in the FMC plane by means of refocusing the objective lens from one page lying in one layer to another one lying in another layer. The FMC address layer serves for centering and is disposed as the first or the last one in the FMC thickness. Figs. 2a and 2b illustrate two variants of the system for data retrieval from FMLC Clear Card 101 with an information carrier based on fluorescent dye Oxazine 1. In the device shown in Fig. 2a an FMLC is used wherein information is recorded as pages with the field size of 300 x 300 μm and total working size of the reading field of 2 cm x 2 mm. The Clear Card is moved by means of a floppy disc driver. For data retrieval, a 20-mW diode laser 102 with the wavelength of 635 nm. The system of excitation radiation filtration is based on the use of dichroic mirrors 103 with reflection index <0.5% at the wavelength of 635 nm and >99% in the range of dye luminescence (640-680 nm). In addition, the lenses can have a coating reflecting 635- nm radiation and transmitting 640-680-nm one.

The image of an information page read off from a given FMC layer is generated in the CCD camera 104 by means of an aspherical lens 105 identical to the lens used in a compact disc driver (focus distance F = 4.5 mm, NA = 0.45) with magnification factor L=20. Refocusing from one information layer to another is done by moving the lens 105 using a controllable electromagnetic actuator 106. To prevent variation of the geometrical size of the image of the page being read off in the plane of the CCD camera while the lens 105 is moving, a two-lens system of autofocusing is provided. The first, aspherical lens is designated to transmit image to infinity. The second lens 107 (shown by a dotted line in Fig. 2a) has focus distance F_C=T-F. i.e. magnification of the optical system is defined by the focus distance ratio of the lenses used. The optical system is computed such that the image of the information page located in the focal plane of the first lens is transmitted to the focal plane of the second lens. Refocusing from one page of the multilayer data carrier is done by moving the short-focus lens. In doing so, changing the distance between the lenses does nit lead to changes in the magnification factor of the system on the whole.

In the proposed information carrier a possibility is provided for changing the image scale with magnification (10 x, and 30 x) by means of varying data recording density to enable image transmitting in relations 1 pit in 1 pixel, 1 pit on 4 pixels and 1 pit in 9 pixels. To ensure different magnification a possibility is provided of replacement the correcting lens (if necessary) and installation of the CCD camera in three fixed positions relative to the Clear Card.

The information read off by the CCD camera (ASCII-encoded text) is stored in the computer memory, processed in the real time mode (the image is identified and converted to digital data) and displayed. There are two alternative systems for autofocusing and auto framing, namely: autofocusing generated directly by a signal from the CCD camera or by a signal from an extra tracking system from a photodiode 108 disposed in front of the CCD camera behind a partly transparent (transmission not more than 10%) rotating mirror 103.

The diode laser can be replaced by a light-emitting diode (LED) radiating in the same spectral range (maximum 635 nm with the band half-width of 20-30 nm). The LED radiation is incoherent enabling a more uniform illumination of the information page. The LED has a simpler feed control circuit and is relatively simply switched to pulsed glow operation allowing reduction in the light load on the information layer.

However, commercially available standard LEDs have too high radiation divergence. Nevertheless, the optical correction system permits achievement of final illumination divergence of as low as 3°. The optical system of the reader illustrated in Fig. 2b generally differs from the scheme shown in Fig. 2a in that the source of the reading radiation and the CCD camera are on the same side of the FMLC 101. In this case, the short-focus lens is used both for image transmission and for reading radiation focusing.

As an optical device for separation of fluorescent information signal from reading laser radiation (Figs. 2a and 2b) in place of dichroic mirrors there can be used two crossed polarizers, one of them disposed in the reading beam, the other in front of the CCD camera. The necessary condition in this case is isotropy of molecules in FMC information pits to ensure isotropy of luminescence even under the action of polarized reading radiation. Then the reading flux incident on the CCD camera will be virtually completely absorbed by the analyzer. Nonpolarized fluorescent radiation, partly attenuated, will pass through the analyzer and be recorded by the CCD camera. It is also possible to use the available (in front of the CCD camera) electrically restructured reflecting spectral filters like Notch ones based on cholesteric liquid crystals. Such filters ensure a good filtration of radiation within the spectrum. An alternative variant of the system for autofocusing and refocusing from information layer to another is illustrated in Fig. 3. This embodiment requires no mechanical motion of the microobjective lens 105 (Figs. 2a and 2b) by means of controllable electromagnetic actuator 106. For this purpose liquid crystal (LC) varifocal lenses 1 10 are applied. The focal length of the LC varifocal lens 110 can be electrically varied by changing the LC refractive index by means of the focus error signal 1 1 1 of the autofocusing device. As a result, the parallel incident (reading) light beam 1 12 is refracted to a converging beam 1 13 and focused on different information layers 1 14 of FMC 12 (Fig. 1). To make such a device operable, a polarizer (not shown in Fig. 3) is placed in the reading beam in front of the lens 1 10.

The operation speed of such a device can be of the order of 60- 100 Hz, which is sufficient for FMC page-by-page reading using a CCD camera.

Fig. 4 illustrates a cross section of said lens. It is made as an electrically controllable LC cell 120 comprising substrates 121 with transparent electrodes 122 and an LC medium in-between said substrates.

A focusing optical element 124, such as the microrelief Fresnel lens, is applied onto one of the electrodes 122. Instead of the Fresnel lens, a conventional microobjective lens can be used, as well as a micro-relief computer or holographic diffraction element, etc.

It is well known, that focal length of lens, radii of both surfaces R and R? and a refractive index n of LC lens can be expressed as:

l/F = (n-l)(l/Rι -l/R₂),

which means that a focal length of the LC varifocal lens can be changed by changing its refractive index n. For this purpose, the LC molecules 125 of the varifocal lens should be planarly oriented while the reading beam should be polarized. The polarization vector of the reading radiation should be parallel to LC director N. In this case the refraction index of the LC varifocal lens varies from the value of ri_e for an unusual beam in the absence of electric field to the value of no on application of the electric field.

To obtain an LC varifocal lens with a high optical quality the LC molecules 125 should be properly oriented.

Inadequate orientation results in occurrence of scattered radiation on defective surfaces and volumes. This can lead to higher noise level at data reading. Traditional methods for generation of orienting coatings 126 by applying polymer layers onto the LC lens electrodes with subsequent mechanical rubbing in this case are inapplicable in principle since the optical element of the LC lens (Fresnel lens) has a microrelief. Because one of the inner sides of the LC cell has a microrelief, in this invention we used the so-called special Photo Anisotropic Materials (PAMs) as an orienting agent 126. For said PAMs there can be used polyvinylcinnamate and derivatives thereof, photosensitive polyimide and derivatives thereof, photosensitive LC polymers, azo dyes etc.

When irradiated by polarized light in their own absorption band, said PAMs become capable of orientating liquid crystals without applying a conventional procedure of mechanical rubbing of the orienting layer. This precludes mechanical damage of the microrelief surface of the focusing element and ensures a high optical quality of orientation of the LC layer 123. The orientation directions of the LC and polarization vector coincide. The focal distance 127 of the LC varifocal lens 120 is changed by application of voltage U from the focus error signal 1 1 1 to the electrodes 122.

In order not to use the two-lens system for generation of an image necessary for maintaining the system's magnification intact on the whole (Figs. 2a and 2b, items 106 and 107), in the FMLC reader instead of the lens 107 we installed an extra element to compensate for the variation of the optical path length. Said extra element is an LC cell 130 consisting of substrates 131, transparent electrodes 132 and an LC layer between them (Fig. 5). To gain a high quality of the LC cell 130, in the present invention the LC is oriented using photoorienting agents 133 based on photoanisotropic materials.

Driving voltage 134 determining orientation of the LC layer 135 and consequently the magnitude of phase delay variation is the focus error signal 11 1 fed to the electrodes 132 of the cell 130. Depending on the requisite size of phase delay, the LC cell can be either one- or multisectional.

In addition, the LC cell 130 and LC varifocal lens 120 can be made as one unit wherein part 127 of the LC varifocal lens 120 will play the role of the LC varifocal lens, while the remaining part 128 thereof will play the role of the optical compensator 130.

Depending on concrete realization of the FMLC reader optical scheme, different combinations of microlenses. or LC varifocal lens and optical compensator are possible.

The fluorescence of non-reading layers leads to a strong parasitic signal and hence deterioration of contrast and contamination of the information signal by noise. To avoid these undesirable effects we suggest selective excitation. The straightforward solution of the problem is provided by excitation through the focusing lens with the numerical aperture more than the numerical aperture of the objective lens (see Fig. 6a). As a result, the focusing angle of exciting beam is more than the angle of collection of fluorescence and only part of the excited regions of the non- reading layers contribute to the angle of collection of fluorescence.

Another solution for reduction of the parasite signal is excitation at a small angle relative to the plane of information layers (Fig. 6b). For this geometry, the excited regions of the non-reading layers are shifted relative to the reading area to the right or to the left side. Thus, the fluorescence from the non-reading layers does not contribute to the spherical angle of collection of information signal.

Another solution is provided by a multilayer waveguide system, in which every information layer is located on the internal surface of a certain waveguide layer

(see Fig. 6c). When the light is focused into this waveguide layer, it excites the fluorescent layer without exciting any nonreading layers. For the case of coherent scattering at the frequency of exciting light the multi-waveguide system was developed in NTT (Shogo Yagi et al. "Multilayered Waveguide Holographic Memory Card." Joint International Symposium on Optical Memory and Optical Data

Storage 1999, July, Koloa, Hawaii, Technical Digest). The main advantage of the fluorescent system is that the light emitted from a certain information layer at the wavelength of fluorescence does not interact with fluorescent pits in the nonreading information layers. The phenomenon of waveguiding needs difference of the refractive index at the boundary of the waveguide layer. Generally, this planar multilayer structure could lead to aberration and parasite interference. Fortunately, the waveguides with thickness of about several tenths of a micron need very small difference of refractive index. To illustrate this property we consider the example of propagation of TEMoo mode in the planar waveguide with a rectangular profile. The electric field is written in the form

Eι =E, e' ^λ sin(qz), for |z|<h/2

|

-II.1II ⁼ E₂.₃ e ιk\ -ιg|z for |z|>h/2

Where k² + q² =ειω²/c², k² + g² = ε₂ω²/c² and the transverse projection of the wave vector fulfills the quantization condition -q/V[q² - (ε,-ε₂)ω²/c²] = tng(qh/2) The first solution for q is localized near the singular value

qh=π. Combining these relationships we get estimation for the difference of the refractive index n, - n₂ =V(ει-ε₂)/2(nι+n₂) = [π/(khV2(nι+n₂))]²

Substitution in the last expression of the values of parameters k = 2π/λ , λ = 0.64 μ, h = 50 μ, nι~n =1.6 gives ni - n -10 . This estimation shows that the formation of the waveguide with a comparatively large aperture of several tenths of a micron needs very small difference of the refractive index, which cannot disturb the imaging of information in the direction perpendicular to the waveguide plane.

The availability in the waveguide channel of the layer with a fluorescent dye leads to additional losses of the waveguide. The concentration of the dye, which is acceptable for the reading of the fluorescent signal, can lead to significant absorption of exciting light. However, if the thickness of the fluorescent layer is very small in comparison with the cross section of the waveguide, the effective losses are moderate. Let us consider a numerical example. For typical cross section of dye absorption of about σ =10^'16 cm², concentration c ~ 10^"3mol/l, the effective area occupied by pits 10%, the thickness of the pit 0.5 μ and thickness of the waveguide 50 μ, the effective length of waveguide losses is of about l_eff —10 cm, which is quite acceptable. Fig. 7 illustrates another optical scheme of the FMLC reader. In this scheme, the unit for generation of reading radiation 146 and the unit for information (fluorescent) signal recording 145 are disposed on different sides of the FMLC 144. The reading radiation unit 146 comprises an illuminator 141, electrooptical shutter array 143 and collimated optics (not shown in Fig. 7) which forms the array of strongly collimated light beams 142 directed substantially perpendicular up to the input side of the electrooptical shutter array 143. The number, geometric size and spatial position of collimated light beams 142 and of electrooptical shutters 143 correspond to the number, geometric size and spatial position of information frames formed in the FMLC 144.

At the stage of reading the mutual disposition of individual elements of the unit 146 and the FMLC 144 itself remains intact.

For reading of information pages the information recording unit 145 moves together with the autofocusing device (not shown in Fig. 7).

As a photoreceiver in the unit 145 there can be used a CCD camera or an array of light-sensitive elements. In the latter case, their number and geometric position should correspond to the number and mutual location of information pits in the frames of the FMLC 144.

Fig. 8 illustrates one of the embodiments of the illuminator 141. It comprises a micro-miniaturized linear filament light bulb 151, a reflecting mirror 153 and a waveguide 152 based on a local break of total internal reflection. Whenever necessary, to optimize the input mode of reading radiation 154 in the waveguide 152, a coupler, for instance a cylindrical lens (not shown in Fig. 8) can be installed between the waveguide and the radiation source 151. The waveguide 152 can be from 50 to 1000 μm thick. Said waveguide is made of optically pure polymer or glass.

Radiation from the source 151 is fed to the waveguide 152 and propagating there 154 it undergoes total internal reflection. On the opposite side said radiation reflects from an opaque mirror 160 and comes back 155. To generate a multitude of collimated beams on the top and bottom surfaces of the waveguide, special defects are made that destroy the total internal reflection at the boundary. In particular, on the bottom side micro-relief surface embossed holograms 156 are formed. To enhance the effect they are covered with a coat of Al 161. Radiation 157 diffracted on said holograms is channeled to the other transparent side where by means of collimated optics 158 it is converted to a multitude of collimated beams 159. Their spatial „_ΛO„ PCT/USOO/28108

WO 01/29835

position corresponds to the spatial position of the frames in the optical storage medium 12 on the FMLC 10.

Figs. 9 and 10 illustrate a cross section and an upside view of the electrooptical shutters 143 based on liquid crystals. Said device is designated for selection of the requisite collimated beam out of the total multitude of beams 142 generated by means of the optical device 141. Each shutter works in individual and separately controllable region of an LC panel. In the absence of voltage on the shutter electrodes there is no transmission and the reading beam does not pass through this element of the array of electrooptical shutters. On application of voltage the reading beam passes through the bleached element on the selected frame of the FMC. The wanted page is chosen in the frame by means of refocusing of the reading head on the requisite information layer of the FMC.

Fig. 9 illustrates a cross section of the electrooptical shutters 143 including substrates 161 with transparent electrodes 165 and 166, polarizers 164, orienting agents 163 and a nematic liquid crystal 162 in-between them.

As can be seen from Fig. 10, the electrooptic shutter 143 looks like a matrix light- valve shutter having two systems of strip orthogonal transparent electrodes 165 and 166. When the vertical 166 and horizontal 165 electrodes, the so called columns and lines, cross, they form discrete elements (LC cells) 174 all together making a rectangular raster identical to the spatial distribution of the information frames 15 in the optical storage medium 12 of the FMLC 10 (Fig. 1). To prevent spurious illumination of the frame to be read, the space between LC cells is filled with photomasks absorbing the reading radiation (not shown in Fig. 10). For colhmating the output reading radiation, an array of microlenses 167 can be formed on the surface of the substrate 161 facing the FMLC 10. Location of the microlenses matches that of the LC cells.

Bleaching of the requisite element (shutter) of said raster is carried out by supplying driving voltage 172, 171 on coordinates X and Y from a control unit 173. Operation of the control unit 173 is adequately synchronized with the movement and focusing of the unit for recording information signal 145. In known LC displays, film polarizers based on iodine-died polyvinylalcohol are used. These very thick (more than 40 μm) polarizers are placed on external sides of substrates of LC displays.

In the present invention, super-thin (of the order of one μm) polarizers are utilized. They are disposed inside the LC device.

This kind of disposition makes the device more compact and allows formation of collimated beams of reading radiation 142.

The super-thin polarizers in the present invention are made from lyotropic liquid crystals manifesting their liquid crystalline properties within a certain range of concentrations of anisotropic organic compounds in a solution. Water is generally used as a solvent.

The absorption spectrum of lyotropic LCs depends on the chemical composition of compounds used and can be selected according to the wavelength of the source of reading radiation used.

The super-thin polarizers based on lyotropic LCs can be made by several different methods.

Some amount of lyotropic LC is applied onto the surface of substrate 161 with electrode 165 and a paste-like film is formed by means of a doctor blade. The LC molecule orientation coincides with the direction of doctor blade movement. Following evaporation of the solvent, on the surface of the substrate 161 there results a 1-2 -micron solid film of anisotropic organic compound. The resulting film possesses a strong absorption dichroism and can be used as a super-thin polarizer.

Another method involves precoating of the substrate 161 with a polymer solution, for example polyvinyl alcohol or polyimide. Upon drying, the resulting film is mechanically rubbed, whereupon a solution of lyotropic LC is applied thereon.

In this case the rubbed film is an orienting agent of the lyotropic LC. Then the procedure of forming a super-thin polarizer is repeated as in the first method. Polarizers 164 can be also placed between the substrate 161 and electrode 165. As in the case of the LC varifocal lens and compensating LC cell, the high optical quality of the LC electrooptical shutter was ensured by application of a PAM photoaligning layer.

The illuminator 141 and electrooptic shutter device 143 can be combined in a single unit. To this end, the latter is provided directly on the illuminator 141. In this case the substrate 161 is removed, while elements 165, 164 and 163 are consecutively provided on collimated optics 158.

Fig. 1 1 illustrates another optical scheme of an illuminator of the reading radiation unit 146 for the FMLC reader. This scheme also comprises a radiation source 181. coupler 183. waveguide 182, reflecting mirror 184. micro-relief surface embossed holograms 193 (Fig. 12) and collimated optics 186. Said scheme differs from the one shown in Fig. 8 in the use of a linear array of laser diodes (LD) or light emitting diodes (L D) in place of a linear filament light bulb. In addition, the waveguide is made as optical waveguide gratings 185. The cross section of said waveguide is shown in Fig. 12. It includes a monolithic layer 191 with refractive index n₂ and immersed therein strip waveguides 192 with refractive index nι>n . The thickness of the strip waveguide 192 can be much lower (2-10 μm) than that of the waveguide 152 (50 -1000 μm). The number of LEDs or LDs and strip waveguides is equal to the number of information frames on one FMC coordinate. Radiation from each LD 181 is channeled to proper strip waveguides 192 by means of coupler 183.

The availability of a multitude of independent of each other combinations

"radiation source - strip waveguide" allows independent generation of a linear array of reading optical beams in each such strip. The wanted frame is selected in this strip waveguide by bleaching the element of the array of electrooptical shutters (see Figs. 9 and 10) matching this frame.

Fig. 13 schematically illustrates another arrangement of the LD structure, strip waveguides and array of LC electrooptical shutters. Complete illuminator 141 of the unit for generation of reading radiation 146 consists of a linear array of such structures.

Said structure, as distinct from the, one in Fig. 8, ensures generation of only one collimated beam in each strip waveguide in a specified region of the optical storage medium 12 of FMLC 10. The device includes an LD 201 serving as a source of reading radiation 202 and a coupler 203 enabling efficient input of reading radiation 202 in a waveguide

204. a linear polarizer 205. a mirror 2017 to ensure reverting of radiation 202 into the waveguide 204. On the top surface of the waveguide 204 an LC light-valve shutter 206 is installed.

The matrix light-valve shutter 206 includes two arrays of orthogonal transparent electrodes 207 (165. 166 in Figs. 9, 10) and orienting layers 208 separated by a microporous plate 209. The micropores of the plate 209 are filled with liquid crystal 2010.

Directly on the upper electrode 207 there is a layer 207 with collimated optics

201 1. All this is made optically integral and mounted on a substrate 2012.

Said device operates as follows. Reading radiation 202 polarized by means of polarizer 205 is channeled to the strip waveguide 204 as TE mode with polarization vector orthogonal to the incidence plane. Refractive indices of the waveguide 204 n_w, porous plate 209 n_p, LC 2010 (in the absence of driving voltage 2013) n_e and substrate 2012 n_s are chosen such that the polarized reading radiation (TE mode) is propagated in the strip waveguide 204 without losses being subjected to full inner reflection. In this case an LC with negative dielectric anisotropy is used in which the conventional refractive index no > n_e and the condition n_u > n_p. n_e n_s is met.

With the availability of driving voltage 2013 on the designated element of the matrix LC shutter, the refractive index of the LC material for the TE waveguide mode in a specified spatial microregion (the area where the wanted frame is located) is increased up to the value of n₀. This leads to destruction of full inner reflection for the optical reading radiation in the given microregion. As a result, the reading radiation 2015 locally propagates in the micropore of the medium 209 filled with LC 2010 and is fed to the corresponding frame of the FMC 2014 by means of the element 2016 of the collimated optics 201 1.

The size of micropores and their spatial arrangement match the size and spatial arrangement of frames in the FMC. In this case n_p < no The principle of operation of the device will not change significantly provided a continuous LC layer (free of microporous medium) is used. In Fig. 14 there is a schematic upside view of a two-dimensional unit for generation of reading radiation 146 wherein the structural arrangement of the strip waveguides and array of LC electrooptical shutters is identical to the one shown in Fig. 13 but each separate collimated reading beam is generated in any designated two- dimensional region of the optical storage medium 12 of the FMLC 10 using only one LD. The unit is made optically integral.

Said unit comprises a source of reading radiation (LD) 21 1. coupler 212, polarizer 213. unit of polarization selection of reading beams 214, a system of strip waveguides 215 and LC electrooptic shutters (not shown in Fig. 14) made, for instance, as in Figs. 9 or 13.

The polarization selection unit 214 in its turn includes a system of thin film polarization-sensitive beam splitters 216 transmitting light radiation 217 with polarization TE and reflecting radiation with polarization TM as well as a system of electrically controllable by control unit 218 thin film polarization rotators 219 of reading radiation 217 responsible for TE-TM or TM-TE polarization transformation.

Said device operates as follows.

Reading radiation 217 from LD 211 by means of coupler 212 is channeled into the polarization selection unit 214. Before that the reading radiation passes through polarizer 213 and becomes linearly polarized. Then radiation 217 by means of unit 214 is channeled into one of designated strip waveguides 215. For this purpose, all polarization rotators 219 located in front of the designated strip waveguide ensure TE polarization to the reading radiation 217 that passes through said polarization rotators. As a result, the radiation 217 passes through polarization sensitive beam splitters 216 free of losses. The polarization rotator positioned in front of the designated beam splitter transforms polarization of the reading beam from TE to TM. Then the beam splitter 216 located behind said polarization rotator reflects the beam in the designated strip waveguide, for example 220.

The radiation from this strip waveguide is withdrawn according to the scheme given in Fig. 13. Consequently, the application of the control system 218 allows an independent input of reading radiation in any strip waveguide (reading beams 220 to 223).

Said device enables random sampling of one of the frames across the entire surface of the optical storage medium 12 of the FMC 10 using one source of reading radiation.

As thin film polarization-sensitive beam splitters 216 can be chosen deposited multi-layer dielectric stacks.

Electrically controllable polarization rotators 219 can be produced on the basis of nematic or ferroelectric LC layers.

The production process for said and other devices described above is fully consistent with the state-of-the-art process for production of integral fiber-optical and microelectronic devices.

It is extremely desirable that the optical surfaces between the waveguides and the liquid crystal be carefully treated .

First, surface effects and the quality of the alignment of the crystals within one micron of the interface determine the degree of Rayleigh scattering near the interface due to dielectric inhomogeneities which should be small comparatively to the wavelength.

Such scattering in the "off or "dark" state of a cell must be minimized and will be the major factor in determining of the image contrast ratio.

Second, the degree to which this surface can be prealigned will strongly affect the withdrawal of radiation from strip waveguides in the full inner reflection mode.

The use of photoalignments instead of conventionally applied in the LC displays mechanically rubbed orienting agents allows one to obtain layers with an ideally smooth surface free of any microscratches (inevitable at rubbing). This ensures a higher degree of orientation of LC materials and improves optical characteristics of such devices through reducing light scattering. Photoaligners can be applied using such procedures as spin-coating, thermal vacuum spraying, Langmuir-Blodgett method, etc.

In the latter case, the layer thickness may constitute one monolayer (10-20 A).

We suggest a system with sub-pixel resolution. The scanning system is suggested to resolve the image of several pits projected onto one pixel. The sub -pixel resolution is possible because the boundary of an individual pixel is much narrower than its size. If the typical size of a pixel is about 10 microns, the width of the boundary is about 0.25 micron and depends on the accuracy of photolithographic technique. When the CCD matrix scans an image plane, the images of individual pits cross the boundary of pixels. The differential signal from each pixel provides information about the individual pit crossing the boundary. However, certain boundaries may be crossed by several pits having different gray levels. To simplify the process of data extracting, the following features of the optical storage system are desired: a) The distance between pits is uniform and is more than the size of pits. For example, if the size of a pit is 0.5 micron or less, the distance between pits centers is of 1 micron. b) The piezoelectric or electromagnetic step motors capable of making step-like motion in the XY-plane with sub-micron accuracy of about 1-2 ms allowing the use of CCD cameras with frame rate 25-60 fps. d) The range of step-like motion is equal (or more) to the size of the pixel. e) The size of the non-active zone between pixels must be much less than the pixel size.

Below a simple algorithm for data retrieving is suggested.

In the optimal geometry the size of pixel corresponds to an integer number of the columns and rows (see Fig. 15a). It is obtained by properly chosen magnification. The length of one step must be equal to the maximal size of pit. Possible steps are depicted in Figs. 15a and 15b as a grid.

The signal from an individual pit located at the upper right corner is measured in the following sequence of steps. Let us consider a pixel in which pits are located in the vicinity of the upper border of the pixel (see Fig. 15b). The first step down leads to the negative differential signal from the pixel because the upper row of pits moves away. The difference between the initial signal E₀ and the signal after the first step Ei gives the integral signal of the upper array

Next step to the left side gives the integral intensity without the upper row and the right column. The next step gives the initial integral intensity of the pixel without the right column. The difference between the last two measurements gives the integral signal of the upper array without one pit from the upper right corner. Thus, the signal from this pit is equal to

The case considered above refers to the second row of pixels in Fig. 15a. All other rows of pixels in Fig. 15a have the upper array empty. The pixels in these rows have a common feature: the difference E₀ - Ei is negative or equal to zero. This is an unambiguous sign that the position in the upper right corner is empty and can be used in the image processing program.

Upon completing the sequence of measurements described above the procedure is repeated again and again until all pits from the upper row of each pixel are read off in a parallel way. Then the CCD matrix is shifted down by one step and the procedure is repeated for the second row and then for the next one until the moment when all rows are read off.

The suggested algorithm works as well in the case when part of pits is located on the boundary between different pixels. In this case each part of the crossed pit is read off separately and the following image analysis can identify it as one pit.

If the signal from each pit projected onto certain pixel deviates from the average value (average over certain pixel) by not more than 100/N %, where N is the effective number of pit images crossing the pixel boundary simultaneously, then the signal from each individual pit can be extracted by a single measurement.

The described above sub-pixel shift algorithm is only one of the variety of algorithms to solve the problem. In the above scanning algorithm, we utilize the back pixel boundary, therefore the differential signal is negative. As an example of an alternative algorithm, we use the front boundary of a pixel with a positive differential signal. The sequence of steps is presented in Fig. 15c. The shift to the left side leads to the crossing of the last right column of pit of the adjacent left pixel and the differential signal gives

The next shift down crosses the upper row of the low adjacent pixels. And the final shift allows calculation of the intensity of the pit located in the upper right comer of the adjacent pixel along the diagonal

In =Eo + E₃ - E₂ - Eι. By using more sophisticated image processing algorithms it is possible to perform step shifts along to the diagonals of the pixels or realize the rotate steps or steps in the magnification. Each of these scanning sequences is one of possible realization of the invented state of the art. In the other embodiment, the step motors drive the objective lens. The images of pits are shifted relative to the fixed CCD matrix.

The suggested method of sub-pixel resolution is also applicable to the fluorescent multilayer optical card, in which information is stored in the form of plurality of pages consisting of individual pits. In addition to the algorithm of the described above mechanisms here it is possible to move the optical card relative to the CCD matrix. The range of integral shift must be of about the size of pixel.

While various preferred embodiments have been set forth above in detail, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, recitation of dimensions, wavelengths, materials, or the like should be construed as illustrative rather than limiting. Therefore, the present invention should be construed as limited only by the appended claims.

Claims

What is claimed is:

l.An apparatus for page-by-page retrieving of data from a fluorescent multilayer optical card having a plurality of data surfaces in which the data are written in pages, the apparatus comprising:

- a card holder;

an electromagnetic radiation source for producing an electromagnetic reading beam ;

a focus device for focusing the electromagnetic radiation beam onto a selected one of the plurality of data surfaces to illuminate one of said pages;

- an optical system for projecting an image of the plane illuminated by the focus device onto a detector plane;

an optical detector, located at the detector plane, for the retrieval of information fluorescence produced from the page illuminated by the focus device to produce an output signal representing the data in the page;

- a moving device for moving the card relative to the reading beam;

- a device for controlling the moving device for rough and precise positioning of the card.

2. The apparatus of Claim 1, wherein the reading beam has a wavelength of 635 nm.

3. The apparatus of claim 2, wherein the optical detector registers fluorescent radiation in the range of 640-680 nm.

4. The apparatus of claim 1, further comprising spectrum filters for separating the reading beam from the image of the plane.

5. The apparatus of claim 4, wherein the spectrum filters comprise dichroic mirrors.

6. The apparatus of claim 4, wherein the spectrum filters comprise notch filters.

7. The apparatus of claim 6, wherein the notch filters are based on cholesteric liquid crystals.

8. The apparatus of claim 4, wherein the spectrum filters comprise crossed polarizers.

9. The apparatus of claim 1 , wherein the optical system comprises an autofocusing system.

10. The apparatus of claim 9, wherein the autofocusing system comprises two lenses which are movable relative to each other.

1 1. The apparatus of claim 9. wherein said autofocusing system comprises an electrically controllable liquid crystal varifocal lens having transparent conductive layers and a microrelief focus device on one of the transparent conductive layers.

12. The apparatus of claim 1, wherein the output signal represents the data stored in several gray levels or colors.

13. The apparatus of claim 1 , wherein the reading beam has a wavelength which exceeds a lateral pit dimension of the card.

14. The apparatus of claim 1. wherein the moving device and the device for rough and precise positioning move the card to achieve a sub shift smaller than a pixel size of the detector, and wherein the output signal comprises electric signals from each pixel whose differences are used for reading the data.

15. The apparatus of claim 1. wherein the moving device comprises an electromagnetic mover which drives the optical system parallel to the detector plane.

16. The apparatus of claim 15, wherein the electromagnetic mover moves the optical system in increments equal to a pit dimension of the card.

17. The apparatus of claim 16, wherein said increments are realized in one direction if one gray level is used for encoding or are realized in two or more directions if several gray levels are used for encoding.

18. The apparatus of claim 1 , wherein the focus device has a numerical aperture which is greater than a numerical aperture of the optical system.

19. The apparatus of claim 1 , wherein:

the card comprises an intermediate transparent layer; and

the focus device focuses the reading beam onto the intermediate transparent layer for waveguide illumination of the page.

20. An apparatus for reproducing information from a fluorescent multilayer optical card which includes a substrate, a fluorescent three-dimensional optical storage medium, and a protective layer, the card having the information written in multiple pages, the apparatus comprising:

(a) a unit for generation of reading radiation, the unit comprising:

(i) an illuminator for emitting reading radiation to induce fluorescence in the card in which the card emits fluorescent radiation;

(ii) a waveguide with a local break of total internal reflection and which has a blind mirror at an end opposite to the illuminator, local microrelief surface embossed holograms on a bottom side and collimated optics (lenslets) on a top side of the waveguide, for directing the reading radiation to the card;

(iii) a coupler for coupling the reading radiation from the illuminator into the waveguide;

(iv) a matrix of shutters for selecting a portion of the fluorescent radiation from one of the pages; and

(v) colhmating microoptics for focusing the reading radiation from the waveguide into a plurality of beams for illuminating the pages;

(b) an optical autofocusing device and a unit for page-by-page reproduction of the information from the fluorescent radiation, the unit comprising a camera, wherein the optical autofocusing device and the camera are disposed on a side of optical card opposite to the waveguide, and wherein during reading the autofocusing device and the camera move jointly relative to the waveguide and the card, while the waveguide and the card are stable relative to each other.

21. The apparatus of claim 20, wherein the shutters comprise photoaligners.

22. The apparatus of claim 20, wherein the shutters ensure transmission of only one designated reading beam from the waveguide to a corresponding page of the card.

23. The apparatus of claim 20, wherein the shutters are installed directly on the collimated optics of the waveguide.

24. The apparatus of claim 20, wherein the illuminator comprises a plurality of laser diodes equal in number to a plurality of said pages along a single direction of the card.

25. The apparatus of claim 20, wherein the waveguide is made as a plurality of strip optical waveguide.

26. The apparatus of claim 25, wherein each strip waveguide independently forms a one-dimensional array of collimated light beams directed substantially to a one- dimensional array of liquid crystal shutters equal in number to the number of strip waveguides.

27. The apparatus of claim 20, wherein:

the illuminator comprises a one-dimensional array of laser diodes with polarizers the number of which is equal to the number of information pages along one coordinate of the optical card;

the waveguide comprises strip optical waveguide gratings with matching elements the number of which is equal to the number of laser diodes in the one- dimensional array and which have a blind mirror on the opposite side and a system of microrelief holograms on the bottom side;

the matrix of shutters comprises electrooptical shutters based on a liquid crystal with negative dielectric anisotropy installed directly on the upper surface of the strip optical waveguide gratings, which include two arrays of orthogonally disposed transparent electrodes with photoaligners separated by a porous plate with liquid crystal material in the pores, with the size and spatial arrangement of the pores corresponding to the size and spatial arrangement of the frames in the optical card; and

the colhmating microoptics are disposed between the liquid crystal shutters and the fluorescent data carrier.

28. The apparatus of claim 27. wherein the following correlation is met between the refraction indices of waveguide material n_w, porous plate n_p, liquid crystal n_e , and substrate n_s: n_w> n_p,n_e ,n_s; n_p>n_s

29. The apparatus of claim 27, wherein each strip waveguide together with the liquid crystal shutter ensures generation of only one reading beam from the illuminator to a corresponding page of the optical card.

30. The apparatus of claim 20, wherein:

the illuminator comprises a laser diode with a polarizer;

the waveguide comprises an array of strip waveguides, the number of which is equal to the number of frames along one coordinate of the optical card; and

the matrix comprises liquid crystal shutters and a unit for polarization selection of reading beams comprising a system of thin film polarization-sensitive beam splitters based on deposited multi-layer dielectric mirrors and a system of electrically controllable polarization rotators (TE-TM or TM-TE modes) of reading radiation based on nematic or ferroelectric liquid crystals, the number of which is equal to the number of strip waveguides along one coordinate, as well as a control system ensuring an independent input of reading radiation only in one of the strip waveguides.

31. The apparatus of claim 30. wherein the liquid crystal shutters are installed directly on the upper surface of the strip waveguide array.

32. The apparatus of claim 30, wherein the colhmating microoptics are disposed at least partially between the liquid crystal shutters and the strip waveguide array. The apparatus of claim 25, wherein one laser diode is responsible for generation of a single collimated beam for reading of any page in the card.