WO1999062070A1

WO1999062070A1 - Method and apparatus for three-dimensional storage of data

Info

Publication number: WO1999062070A1
Application number: PCT/HU1999/000042
Authority: WO
Inventors: Béla MEDVEY
Original assignee: Medvey Bela
Priority date: 1998-05-28
Filing date: 1999-05-26
Publication date: 1999-12-02
Also published as: AU4158999A; HU9801249D0

Abstract

The invention relates to a method for three-dimensional storage of data. The method uses a three-dimensional storage medium (2), which can be switched between two stable states by physical excitation. The switching between the states is controlled by controlling the duration and/or the intensity and/or the wavelength of the excitation. The readout of data is effected by detecting the momentary state of the storage medium (2) within a memory cell (3). According to the invention, during writing a selected memory cell (3ijk) is subjected to excitation with at least three directed and concentrated energy beams (4) from at least three directions. The memory cell (3ijk) is positioned in the crossing point of the three energy beams (4). The intensity and/or duration and/or wavelength of the illumination is determined such, that through simultaneous excitation by two energy beams (4) the switching threshold between the states is not reached in any memory cell (3) of the storage medium, while through simultaneous excitation by at least three energy beams (4) the switching threshold is surpassed in any memory cell (3). The invention also relates to an apparatus for performing the method.

Description

METHOD AND APPARATUS FOR THREE-DIMENSIONAL STORAGE OF

DATA

Technical Field

The invention relates to a method for three-dimensional storage of data, including writing and reading of data, using a three-dimensional storage medium. The storage medium can be switched between two stable states by illumination. The switching between the states of the storage medium is controlled by controlling the duration and/or the intensity and/or the wavelength of the illumination.

10

Background Art

Methods for storing data in an optical storage medium are known in the art. The documents US 5,346,789, US 5,618,654 and further US 5,228,001 teach the use of bacteriorhodopsin in a thin layer or film. In these known methods the

15 bacteriorhodopsin protein is used as a bistable medium. Bacteriorhodopsin is an optical storage material, which comprises helical polymers, and where these polymers constitute a membrane structure, the latter comprising the so-called retinal chromophore molecules. The chromophore absorbs light on certain wavelengths, and beside its ground state, it is able to convert into an other stable state. The z • molecule may be switched back into the ground state with light having a certain wavelength. E. g. the molecule changes its absorption spectrum, i. e. its colour by irradiation with light, e. g. from lilac to yellow, and remains in this state for a longer period of time. With other words, the states are distinguished by the colour of light which they absorb and which they transmit. A reverse switching into the ground

25 state may only be done by illumination with a certain light intensity and wavelength.

The greatest disadvantage of the known solutions is the limited storage capacity of the thin film storage devices. The use of thin films is necessary for the readout of the data, because the known systems allow the readout of one information layer 30 only. Such an optical system for the writing and readout of data from a storage layer containing bacteriorhodopsin is disclosed in the document US 5,228,001. One of the disclosed optical systems comprises two laser light sources, which are imaged on the storage layer via optical switches. One of the lasers is a green laser, the other laser is a red laser. The bits of the storage layer are arranged along the X and Y coordinates of the layer. The writing of the bits is effected by an appropriate switching of the optical switch and by controlling the intensity of the laser light falling upon the layer. The readout is done with the help of a photo-detector.

It is an object of the present invention to improve the known storage methods in a manner, that allows the utilisation of a three-dimensional storage volume instead of

^• n a two-dimensional one, and thereby increases the storage capacity. Further it is an object of the invention to eliminate the disadvantages of the known solution, ensuring a simple and fast readout system.

Summary of the Invention

15 The objects of the invention are achieved with a method using a three-dimensional storage medium, which can be switched between two stable states by physical excitation, and where the switching between the states of the storage medium is controlled by controlling the duration and/or the intensity and/or the wavelength of the excitation, and where the writing of the data is effected by switching to a 0 predeteraiined state within predetermined memory cells of the storage medium, and where the readout of data is effected by detecting the momentary state of the storage medium within predetermined memory cells. According to the invention, during writing into the three-dimensional storage medium a memory cell is subjected to excitation with at least three directed and concentrated energy beams from at least 5 three directions, so that a memory cell is positioned in the crossing point of the three energy beams, and where the intensity and/or duration and/or wavelength of the illumination is determined such, that through simultaneous excitation by two energy beams the switching threshold between the states is not reached in any memory cell of the storage medium, while through simultaneous excitation by at least three 0 energy beams the switching threshold is surpassed in any memory cell. According to an further aspect, bacteriorhodopsin is used as storage medium.

Preferably, the illumination is performed from perpendicular directions. Alternatively, the illuminating beams are translated parallel.

The method of the invention may be applied for manufacturing of three-dimensional displays, if materials with fluorescent, luminescent or phosphorescent properties are used, and where the readout of a memory cell is effected by detecting the fluorescence, luminescence or phosphorescence. In this case the fluorescence, luminescence or phosphorescence may be detected with the naked eyes.

It is also suggested to store an analogue value by controlling the intensity and/or duration and/or beam diameter of the illumination.

For the application of a three-dimensional display it is suggested to use a transparent (translucent) storage medium.

In an especially advantageous embodiment, it is foreseen to illuminate a memory cell during readout of the data from that memory cell with light beams with different intensities and/or wavelengths and/or duration of illumination according to the light necessary for switching between the states. Thereby the switching during the illumination is detected, and the momentary state of the memory cell is determined from the coincidence of the switching with the illumination having appropriate intensity and/or wavelength and/or duration. In order to maintain the original state of the cell it is foreseen to store the state of a memory cell after detecting the momentary state of that cell, and to reset the state of that cell according to the stored state.

According to an other aspect of the invention, there is proposed an apparatus for three-dimensional storage of data, particularly for the implementation of the method according to the invention. The proposed apparatus comprises a three-dimensional optical storage medium divided into several memory cells, where an optical property of the storage medium may be switched by illumination between at least two stable states, and where the switching between the states is controlled by controlling the duration and/or the intensity and/or the wavelength of the illumination. The storage medium is provided with illumination means, and further comprises control means connected to the illuminating means, and further - optionally - includes detector means connected to the control means, the detector means having at least one detector element for distinguishing between two states of the storage medium.

According to the invention, a, the illumination means comprises at least three light sources radiating in different directions, the light of each light source reaching any memory cell, b, at least the wavelength and/or the intensity of the light emanating from the illumination means may be varied, and c, the light sources can be controlled such that the light of all light sources simultaneously illuminates and/or reads at least one memory cell.

In a preferred embodiment, the detector means comprises at least three detector elements being sensitive in different directions, and where the detectors are controlled such that each detector element simultaneously reads one memory cell. It is also foreseen that the light sources comprise laser diodes or one/two-dimensional laser diode matrices, and similarly the detectors comprise photo-diodes or one/two- dimensional photo-diode matrices, preferably CCD-detectors.

It is especially advantageous if the storage medium comprises bacteriorhodopsin, or a material with fluorescent, luminescent or phosphorescent properties.

Further, it is suggested that the storage medium is in solution in a transparent fluid or gel. and the fluid or gel is stored in a closed tank. In this case the tank advantageously comprises transparent walls, and the walls are provided with bandpass filters.

Instead of light sources radiating or receiving on a large surface, it is also suggested to make the light sources and/or detectors to be tiltable around at least one axis, or to be translatable in at least one direction.

It is especially advantageous if the switchable optical property of the storage medium is the colour (absorption- or reflection spectrum) and/or the absorption (intensity) and/or fluorescence and/or luminescence and/or phosphorescence and/or Raman-spectrum.

In a further preferred embodiment different materials are used as storage medium, which luminescence or phosphorescence or fluorescence in different colours. This possibility is especially suggested for applications as a three-dimensional display. In this manner coloured images may be produced.

For the reading of storage materials like bacteriorhodopsin it is suggested to comprise in the apparatus a buffer memory connected to the control means, for storing the momentaiy states of the memory cells of the storage medium. The original state of the memory cell is restored after the readout according to the value or values stored in the buffer memory.

Brief Description of Drawings By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawing, in which

Fig. 1 is a schematic diagram of the apparatus according to the invention for the realisation of the method according to the invention, Fig. 2. is a schematic diagram of the storage medium, the illumination means and the detector means of the apparatus of Fig. 1 , Figs. 3a-c are illustrating several, non-limiting examples of the embodiments of the illuminating means of the apparatus of Fig. 1,

Fig. 4. is a schematic cross section of the illuminating means in a further embodiment of the three-dimensional storage medium of the invention, and Fig. 5. is a perspective view of a three-dimensional display of the invention.

Best Mode for Carrying out the Invention

Fig. 1. is a schematic diagram of the apparatus 1 according to the invention for the implementation of the method according to the invention. The apparatus 1 comprises a three-dimensional storage medium 2, which is positioned between an illumination means 5 and optionally a detector means 6. As will be shown later, the role of the detector means 6 may be performed by the eyes of the viewer. The storage medium 2 is divided into several memory cells 3 (see also Fig. 2.) An optical property of the storage medium 2 may be switched between at least two stable states with illumination. The switching between the states may be controlled by the duration and/or intensity and/or wavelength of the illumination. The switched property of the storage medium 2 may be the colour (the absorption or reflection spectrum), the absorption (intensity) and/or fluorescence and/or Raman-spectrum, or any other property which may be detected by optical means.

The illumination means 5 and the detector means 6 are connected to a control means 7, which in turn is connected to a buffer memory 8, a working memory 10 and an interface 9. The detector means 6 allows the distinction between the two states of the storage medium 2, e. g. by detecting the intensity of the light falling on the detector means from the memory cells 3 of the storage medium 2. The control means 7 controls the operation of the illumination means 5 according to a method that will be explained below, and further the control means 7 receives and evaluates the signals of the detector means 6, and thereby reads the data stored in the storage medium 2. The data are stored in the working memory 10 and/or in the buffer memory 8, and transmitted towards external systems via the interface 9. Fig. 2 shows a preferred embodiment of the storage medium 2, the illumination means 5 and the detector means 6 in the apparatus 1 of Fig. 1., and at the same time illustrates the working principle of the three-dimensional data storage method according to the invention. In the method an optical storage medium 2 is used. which is cube-formed in the shown embodiment. The storage medium 2 is covered on three sides with the illumination means 5 and on three sides with the detector means 6. The structure of the detector means 6 and the illumination means 5 are explained in Figs. 3a-c and Fig. 4. Memory cells 3 are formed in the storage medium 2, which allow the storage of a bit or an analogue value. The division of the storage medium 2 into memory cells is only a theoretical division, a real physical division of the storage medium is not necessary, but is not excluded either in theory. The storage medium 2 is an optical material, which, on one hand, is transparent at least on the wavelength of the illumination means 5, and on the other hand, may be switched by illumination between two stable states. The switching between the states of the storage medium is controlled by the controlling or adjusting of the duration and/or intensity and/or the wavelength of the illuminating light. In the shown embodiment, the storage medium 2 consists mainly of bacteriorhodopsin. which is kept in a solution in a fluid or gel, in a tank (not shown), the walls of which are transparent on the illuminating wavelength. The solution or the gel is at least so much transparent, so that the light of the illumination means 5 is able to penetrate it with an intensity that may be detected by the detector means 6, independent of the momentary state of the memory cells (see further below).

The detector means 5 are constructed so that at least the wavelength and/or the intensity and/or duration of the emitted light beams 4 may be varied. E. g. it is foreseen that the illumination means 5 radiates optionally green or red light. In the preferred embodiment of Fig. 2, the illumination means 5 comprises the laser blocks L(x.y). L(x,z) and L(y,z). The laser blocks comprise several semiconductor lasers 15 arranged beside each other in a two-dimensional matrix. Similarly, the detector means 6 comprises the detector blocks D(x,y), D(x,z) and D(y,z), which in turn comprise several semiconductor photo-detectors 16 arranged beside each other in a two-dimensional matrix. In practice, the detector blocks D(x,y), D(x,z) and D(y,z) are each a made of a single CCD-detector.

The laser blocks L(x,y), L(x,z) and L(y,z) of the illumination means 5 radiate in different directions, in this case along the X,Y,Z co-ordinates. The laser blocks L(x,y), L(x,z) and L(y,z) are arranged in such a manner that each laser 15 of each laser block illuminates one row of memory cells 3.

The single lasers 15 of the laser blocks are controlled in a manner so that one laser from each laser block may simultaneously illuminate a memory cell. On Fig 2 it is the memory cell 3ijk, which is simultaneously illuminated by the lasers 15ij, 15ik, and 15jk.

It must be noted that the method of the invention works also well if one or more of the illuminating light beams is substituted by an electron beam or similar directed energy beam. The only requirement is that the exciting energy beam is capable to excite the storage medium, and that it is appropriately concentrated and positioned so as not to excite the neighbouring memory cells. It is preferred to use light beams, however, since the generation of concentrated and directed electron beams or other types of directed radiation requires presently very bulky and complicated equipment. Light sources, on the contrary, are small and cost-effective.

Similarly, the detector means 6 comprise three detector elements, in this case the detector blocks D(x,y), D(x,z) and D(y,z), which are sensitive in three different directions. The single detectors 16 of the detector blocks D(x,y), D(x,z) and D(y,z) are constructed such that each detector 16 reads simultaneously one row of memory cells 3, and the detectors 16 are basically insensitive in the other directions. E. g. the detector 16jk receives only the light coming from the direction of the laser 15jk, i. e. the detector 16jk reads only those memory cells 3, which are positioned along the light beam 4 emitted by the laser 15jk. For this purpose the individual detectors 16 and/or the lasers 15, or the complete detector blocks D(x,y), D(x,z) and D(y,z) and laser blocks L(x,y), L(x,z) and L(y,z) are provided with the appropriate means (not shown), e. g. with collimating optics.

The method for the storage of data according to the invention is performed as follows:

A memory cell 3 in the three-dimensional storage medium 2 is illuminated simultaneously from at least three directions by at least three light beams 4, emitted by the illumination means 5. Thereby one memory cell 3 will be at the crossing point of the three light beams 4. In Fig. 2 it is the memory cell 3ijk, with the co- ordinates (i,j,k). During illumination, the illumination intensity and the wavelength of the light beams 4 will be set such that the total intensity of the three light beams will reach or surpass the threshold of the switching within the memory cell 3ijk, so a switching into the selected state will be effected only within the memory cell 3ijk. On the other hand, the illuminating intensity and the wavelength is kept so low, so that by simultaneously illumination by no more than two light beams, the switching threshold between the states is not reached in any memory cell 3 of the storage medium 2. Thereby the undesired switching of any other memory cell 3 outside of the memory cell 3ijk is avoided. In this manner the writing of data into the storage medium 2 is possible. Each memory cell 3 may represent a bit. and the values of the bit - 1 or 0 - may be represented by the two states of the storage medium.

The exact intensities of the light beams 4 satisfying these conditions are easily calculated.

Let us assume, that the switching takes place if the intensity of the excitation surpasses the threshold value A. The intensity of the light emitted from a laser 15 is denoted LI, and after the passing through (in the worst case) the total length of the storage medium 2, the intensity is L2 = k x L 1 , where k < 1 , due to the absorption in the storage medium 2.

In this case the following is valid: 2 LK A < 3 L2 = 3 k Ll (I) from which it follows that

2/3 < k (II)

That is, the intensity LI of a laser 15 must be somewhat below the half of intensity of the switching threshold A, and not more than a third of the intensity LI may be lost by absorption in the storage medium 2.

If these conditions are met, than the switching will always take place in the crossing point of the three light beams, because the switching threshold will always be reached in the memory cell 3 concerned, independent from the position of the memory cell being close to one or more laser 15 or being further away, maybe completely on the other side of the storage medium 2. At the same time it is ensured that at the crossing point of no more than two light beams the switching threshold is not reached in any memory cell 3 of the storage medium 2, also independent from the position of the memory cell. With other words, it does not matter whether the memory cell concerned is close to one or more lasers 15, or positioned further away.

The satisfying of these conditions also allows the simultaneous writing or reading of all memory cells along a surface within the storage medium 2. E. g. by switching on all the lasers 15 of the laser block L(x,z) along the line (i,l)-(i,n) and by switching on all the lasers 15 of the laser block L(x,y) along the line (i,l)-(i,n), the complete plane F (i,y,z) will be simultaneously illuminated, and by the controlled switching of certain lasers 15 of the laser block L(y,z) each memory cell 3 on the plane F(i,y,z) may be switched into the desired state.

The readout of the data is effected by determining the actual or momentary state of the individual memory cells 3. The direct illumination of memory cells and the determination of their state would be possible only for those memory cells, that are situated along the outer planes of the storage medium. The momentary state of those memory cells that are situated inside the storage medium, can not be determined directly, because firstly the illuminating light beams, secondly, the light beams emitted from the selected memory cell must penetrate other memory cells being in a randomly varying state. Therefore, it can not be determined, by which memory cell 3 the light emanating from the surface of the storage medium 2 have been influenced, and therefore the state of the selected cell can not be determined directly.

According to the invention, it is suggested to solve the above problem with the following method: During readout of data, a selected memory cell is illuminated with light beams with different intensities and/or wavelengths and/or duration of illumination according to the light necessary for switching between the states, and the switching (or the absence of switching) during the illumination is detected. The momentary state of the memory cell is determined from the coincidence of the switching with the illumination having appropriate intensity and/or wavelength and/or duration.

E.g. if the switching into the first state needs red light, and the switching into the second state needs green light, than the selected memory cells is illuminated from three sides first with red light, and subsequently with green light. The intensity of the penetrated light is measured, and the switching is determined during the illumination. E. g. if the memory cell is in the first state at start, than the switching will take place during the illumination with green light. The switching may be detected by a small drop or jump in intensity. On the contrary, if the memory cell is in the second state at start, than the switching will take place during the illumination with red light, and this switching may also be determined by measuring the intensity. In this way it may be determined in which state the memory cell was in. With other words, the momentary state of the memory cell is determined from the coincidence of the switching with the illumination having appropriate intensity and/or wavelength and/or duration. In this case, the intensity of the light beams will be controlled very similarly to the writing procedure, that is the intensity will surpass the switching threshold only in the selected memory cells. The original state of the memory cells 3 may also be determined from the absence of switching during illumination. In this case the illumination with a duration and/or intensity and or wavelength corresponding to the other state may be left out completely, and thereby the readout will be faster.

After determining the actual state of a memory cell in such a manner, this actual state must be restored, because after this reading method obviously all memoiy cells will be in the same state, namely in the state which was switched with the last illumination. Therefore, it is suggested that after determining the momentary state of the memory cells, this state is stored, and the state of the concerned memory cell is restored according to this stored state, which in turn corresponds to the original state. The determined state, i. e. the corresponding bit value is stored in the buffer memory 8. After finishing the reading process, the values of stored in the buffer memory 8 are retrieved by the control means 7, and the original state of the memory cells is restored according to these values.

According to the invention, by using fluorescing, phosphorescing or luminescing (hereafter referred to a fluorescing) storage materials in the storage medium, further possibilities arise. Such a material for a fluorescent memory is principally homogenous and transparent, at least on the wavelengths of the excitation and the fluorescence, so that after the writing to the storage medium, it is still possible to excite and to switch, and to read the memory cells inside the storage medium. In this manner such a memory is readable and writable in three dimensions.

The intensities necessary for the fluorescence are established in the crossing point, from the sum of the intensities of the light beams 4 along the X, Y, an Z axis. The excited molecules in the crossing point emit a fluorescent light with a wavelength differing from the wavelength of the exciting light. By controlling the duration and/or intensity and/or wavelength of the irradiation, the fluorescing molecule can act as a chemical sensor, and lose its fluorescing properties. Thereby two states may be defined, e. g. by defining the first state as the fluorescing state, and the second state as the non-fluorescing state. Alternatively, the Raman-spectrum may be altered by a suitable chemical reaction, and the states may be defined according to the properties of the Raman-spectrum.

Obviously, such a fluorescent storage medium offers several advantages. Firstly, the states of the memory cells may be determined directly, by the direct detection of the fluorescence emitted from the individual memory cells, or the absence thereof. Secondly, the detectors may be provided with appropriate band filters, which filter out the exciting beams, and transmits the fluorescence only. In this manner the sensitivity of the detectors may be improved.

Theoretically it is also possible to detect the fluorescence with a single detector for the whole storage medium 2, instead of a directed detector matrix, but this would mean that all memory cells would have to be read one after the other (serially), and the readout rate would be very low. However, this could be partly compensated by using multiple storage medium units within one storage apparatus, and addressing the units in a parallel fashion. If only a single large-area detector is applied in one viewing direction, the construction of a single storage medium unit is simpler, and it is feasible to use 32, 64 or 128 small storage medium volumes, e.g. each in the form of a small cube with the size of approx. 2 mm x 2mm x 2 mm. With highlv integrated optical write and readout elements, the size of a complete storage medium unit could be smaller than one cubic centimetre.

Figs. 3a-c show alternative embodiments of the illumination means 5. From the above it is clear that the illumination means 5 need not necessarily comprise lasers. The task of the illumination means 5 is only to provide on or more light beams 4, with which each memory cell 3 of the storage medium may be reached, and where the geometry of the light beams is formed so that the effective beam diameter is not larger than the diameter of a memory cell. This latter condition is necessary, so that in the crossing point of the light beams always one memory cell is illuminated only. Most advantageously, the illumination means 5 provides three light bundles perpendicular to each other, and several parallel light beams constitute a bundle. The light beams should be switched on and off independently modulated from each other. It is a further condition, that the wavelength and/or the intensity and/or the duration of the illumination may be varied, so that at least two states of the memory cells may be switched accordingly.

Fig. 3a shows an optical system 20, as an example only, which produces the desired light bundles, consisting of the light beams 4. The light source of the optical system 20 is a lamp 21, e. g. a high-power gas discharge lamp. The light emitted from the lamp 21 is collected by the collimating optics 22, and transformed into a parallel light bundle. From this bundle individual light beams 4 are separated with the help of an aperture system 23, and transmitted through the LCD-matrix switch 24. The single light beams 4 can be switched on and off individually by the LCD-matrix switch 24. Instead of the lamp 21 a single high-power laser may be used as well, the light of which is transformed into a wide beam with known means. Fig 3b. shows a similar, alternative optical system 30, where instead of the LCD- matrix switch 24 a so-called SLM 35 (Spatial Light Modulator) is used. The SLM 35 consists of microscopic mirrors arranged in a matrix, where the mirrors may be tilted with a few grades, and thereby the light falling on the mirror may be directed in a certain direction or away therefrom. Thus the single light beams 4 can be switched on and off independently from each other.

As mentioned previously, the light beams 4 need not be parallel with each other under any circumstances. Even the creation of a light bundle, i. e. several simultaneously active light beams is not necessary. The only condition for the proper functioning of the method according to the invention is that the illumination means 5 creates at least three light beams crossing each other in the same point, and that the crossing point of these light beams may be positioned in any memory cell 3. Fig 3c shows further solutions, where the illumination means only provides one light beam 4 in at least one direction, and these light beams 4 arrive at the memory cells through different means. In one direction the light beams 4 are created with a light source 41 , and with a tiltable mirror 42 directed towards the different memory cells of the storage medium 2. In the other directions the light source 44 provides the necessary collimated light beam 4, and the light source 44 is translated along a rail device 45 with the help of a stepping drive 43. The light source is preferably made of a laser block, which in turn contains a row of semiconductor lasers, so that a complete plane may be illuminated within the storage medium. Theoretically, only one laser is also sufficient, if suitable positioning means are present, which is able to translate the light source 44 so that all memory cells 3 may be reached.

Figs. 3a-c show the positioning of the light beams 4 only in one dimension, but positioning in two dimensions is also obvious. Of course, the solutions shown may be combined freely with each other.

W en using bacteriorhodopsin, it is required to illuminate the storage medium 2 with light having different wavelengths. In this case the wavelength of the light sources must be variable. Discharge lamps have a relatively broad spectrum, from which the desired wavelengths, - e. g. 500-650 nm for switching into the first state, and 200-400 nm for switching into the second state - may be selected by known means, e. g. by a prism or grid. A further possibility is the use of tuneable die lasers. Another possibility is the use of a semi-transparent mirror 27, as shown in Fig. 3c. In this case the light source 41 provides e. g. red light, while a second light source 47 provides UV or blue light, and the two beams are combined by the mirror 27. This may be effected by providing on the mirror 27 a band filter, which is transparent in red, but reflecting in UV or blue.

Fig. 4 shows an especially advantageous embodiment of the illumination means 5 and the detector means 6. Only one dimension is shown again, but the application in two or three dimensions is equally obvious. In this case the storage medium 2 is enclosed from two sides with the laser blocks LI and L2. The laser blocks LI and L2 comprise one or several rows of semiconductor lasers 35 and 35'. The laser blocks LI and L2 operate on two different wavelengths, which are necessary for the switching between the states of the storage medium, e. g. the semiconductor lasers 35 operate in the red, while the semiconductor lasers 35' operate in the green or blue wavelength range. Each laser 35 and 35' is provided with its own collimating optics 36. The collimating optics 36 transforms the divergent beams of the lasers 35 and 35' into essentially collimated light beams 4. The laser blocks LI and L2 are positioned relative to each other in such a manner that the light beams of the individual lasers 35 and 35' mutually fall into the exit aperture of the opposing lasers 35' and 35. In this manner the laser blocks LI and L2 mutually function as detector means for the other laser block. While the lasers of one laser block are switched on with a normal power sufficient for reading or writing, the lasers of the other laser block are operating with a very low power, which is barely enough to reach the lasing threshold. In this state the semiconductor laser is very sensitive towards external light entering its aperture. The driving voltage of the semiconductor laser varies in the function of the entering light. With other words, in this configuration the semiconductor lasers may act as detectors, so in this case there is provided an integrated illumination and detector means, which is very compact, and produces at the same time the light beams 4 on two wavelengths. It is also ensured that the detectors are sensitive only in certain directions, namely in the direction towards the opposing semiconductor laser. Thereby the parallel readout and writing of several memory cells 3 is possible, which, in a given case, may be situated beside each other.

Fig. 5 shows a further possible application of the three-dimensional storage medium 2, and at the same time serves as the principal scheme of an alternative method of three-dimensional data storage according to the invention. In this case the storage medium is enclosed in the apparatus 1 in solution in a transparent fluid or gel. The fluid or gel is contained in a closed tank 51. The tank 51 is provided with transparent walls 52, and is covered on three sides with two-dimensional laser blocks L(x,y), L(x,z) and L(y,z). The walls 52 opposite to the laser blocks L(x,y), L(x,z) and L(y.z) are provided with the bandpass filters 53. For simplicity, the storage medium 2 is shown again as cube-formed, and surrounded on three sides with an illumination means 5. Here the illumination means 5 consist of the laser blocks L(xy), L(x,z) and L(y,z). The bandpass filters 53 are opposite to the laser blocks. The bandpass filters filter out the light in the UV-range, and transmit the light in the visible range.

In this embodiment a material with fluorescent, luminescent or phosphorescent (in short, fluorescent) properties are used, and the readout of a memory cell is effected by detecting the luminescence, fluorescence or phosphorescence. The detection of the fluorescence may be done with known means, e. g. with detector units shown in Fig. 3a-c. But the specific advantage of this system is the possibility to detect the fluorescence with naked eyes. In this case, of course, the bandpass filters 53 should be transparent on the wavelength of the fluorescence, but should be blocking on the wavelength of the laser blocks L(x,y), L(x,z) and L(y,z), which operate in the UV or lower blue ranges.

If, as shown in Fig. 5., a transparent storage medium 2 is used, the storage medium 2 may be applied as a three-dimensional display. This is illustrated with the object 54. which appear to be a three-dimensional real object within the storage medium 2. In this case the memory cells of the storage medium 2 are utilised as image pixels, and it is not the data content of the memory cell, which is important, but the position and the colour of the memory cells. If the light beams used for the activation (switching) of the memory cells are in the UV range, than these beams may be filtered out by the bandpass filters 53. and will not disturb the viewing of the image within the display. As mentioned above, the bandpass filter 53 is transparent in the visible wavelength range, and therefore the fluorescence must also appear in the visible range. In this manner the viewer can sense the object 54 as a real three- dimensional object. If the post-luminescence of the storage medium, i. e. that of the image pixels is sufficiently short, than the images may change quickly, without the need to quickly switch the pixels on and off . The new image is simply created by the illumination means, and the old image disappears automatically, just like with an ordinary TV-screen. This solution allows a simpler construction of the control means 7.

It is also foreseen to use several materials fluorescing in different colours. The different colour components may be switched with different properties of the material, so an independent switching of the colour components is possible. In this manner the three-dimensional display may be realised as a colour display.

The three-dimensional display can also be realised with the use of materials without fluorescent properties. Here, too, is sufficient if the storage medium 2 may be switched between at least two states, and at least one state is accompanied by a visible change in comparison to the other state or states. In this case the images within the three-dimensional display must be deleted before a new image is formed. However, it is advantageous if the storage medium remains completely transparent in at least a part of the visible range, and in the second state turns absorbing or reflecting, that is turns visible. Preferably, the storage medium remains also transparent on the excitation (switching) wavelengths.

E. g. a promising storage material is LiNbO_?. In this material a small, local change of the refractive index may be induced, and consequently detected. This change of the refractive index remains stable for a longer period of time.

Further possible materials are photonic crystals or so-called nanocrystals, e.g. CdS and CdSe, which may also act as fluorescent materials. These nanocrystals may be mixed in a liquid or gel solution or fixed in a solid binder material.

Further, it is also possible to use simpler diode lasers in the illuminating beam sources. In that case it is foreseen to utilise optical waveguide effects within an appropriately dimensioned lattice structure, instead of the more traditional focusing optics, and thereby directing the light beam to a selected memory cell within the storage medium. It must be noted that the memory cells 3 may store not only binary data. It is also possible to store an analogue value by controlling the intensity and/or beam diameter. The number of the participating (switched or excited) molecules within a memory cell is a statistical quantity. Therefore, the memory cells may store an analogue value in the three-dimensional space. In a given case this analogue value may be stored more advantageously than a digital value, the storing of which may require several hundred memory cells. There are certain applications, e. g. the speech recognition, and generally the area of the so-called associative storage, where the precision of the stored values is less important, but at the same time the storage of large amounts of data is required. In these applications a large capacity analogue memory could be especially advantageous. Optionally, the precision of the readout of an analogue value could be improved by calculating and considering the absorption of the light between the concerned memory cell and the detector, when the light entering the detector means is evaluated.

Claims

Claims:

1. Method for three-dimensional storage of data, including writing and reading of data, using a three-dimensional storage medium, which can be switched between

5 two stable states by physical excitation, and where the switching between the states of the storage medium is controlled by controlling the duration and/or the intensity and/or the wavelength of the excitation, and where the writing of the data is effected by switching to a predetermined state within predetermined memory cells of the storage medium, and where the readout of data is effected by detecting the l o momentary state of the storage medium within predetermined memory cells, characterised by that during writing into the three-dimensional storage medium a memory cell is subjected to excitation with at least three directed and concentrated energy beams from at least three directions, so that a memory cell is positioned in the crossing

15 point of the three energy beams, and where the intensity and/or duration and/or wavelength of the illumination is determined such, that through simultaneous excitation by two energy beams the switching threshold between the states is not reached in any memory cell of the storage medium, while through simultaneous excitation by at least three energy beams the switching threshold is surpassed in any 0 memory cell.

2. Method according to claim 1. characterised by using electron and/or electromagnetic beams, preferably light beams as the exciting energy beams.

5 3. Method according to claim 1 or 2, characterised by using bacteriorhodopsin as storage medium.

4. Method according to any of the claims 1 to 3, characterised by performing the excitation from three directions, where the directions are independent from each 0 other.

5. Method according to any of the claims 1 to 4, characterised by performing the excitation from perpendicular directions.

6. Method according to any of the claims 1 to 5, characterised by parallel translation of the exciting energy beams.

7. Method according to any of the claims 4 to 6, characterised by using materials with fluorescent, luminescent or phosphorescent properties, and where the readout of a memory cell is effected by detecting the fluorescence, luminescence or phosphorescence.

8. Method according to any of the claims 1 to 7, characterised by storing an analogue value by controlling the intensity and/or duration and/or beam diameter of the excitation.

9. Method according to any of the claims 1 to 8, characterised by using a transparent (translucent) storage medium, and using the storage medium as three-dimensional display device.

10. Method according to any of the claims 1 to 9, characterised by using invisible light beams in the UV range.

11. Method according to any of the claims 1 to 10, characterised by detecting the light emanating from a memory cell during the readout of data.

12. Method according to any of the claims 1 to 11, characterised by exciting a memory cell during readout of the data from that memory cell with energy beams with different intensities and/or wavelengths and/or duration of excitation according to the energy amount necessary for switching between the states, and detecting the switching during the excitation, and determining the momentary state of the memory cell from the coincidence of the switching with the excitation having appropriate intensity and/or wavelength and/or duration.

13. Method according to claim 12, characterised by storing the state of a memory cell after detecting the momentary state of that cell, and resetting the state of that cell according to the stored state.

14. Method according to any one of claims 1 to 13, characterised by using multiple storage media addressed in a parallel manner.

15. Apparatus for three-dimensional storage of data, particularly for the implementation of the method according to claim 1, having a three-dimensional optical storage medium divided into several memory cells, where an optical properly of the storage medium may be switched by illumination between at least two stable states, and where the switching between the states is controlled by controlling the duration and/or the intensity and/or the wavelength of the illumination, where the storage medium is having illumination means, and further comprises control means connected to the illuminating means, characterised by that a, the illumination means comprises at least three light sources radiating in different directions, the light of each light source reaching any memory cell, and b, at least the wavelength and/or the intensity and/or the light emanating from the illumination means may be varied, and where c, the light sources can be controlled such that the light of all light sources simultaneously illuminates and/or reads at least one memory cell.

16. Apparatus according to claim 15, characterised by comprising control means connected to a detector means having at least one detector element, said detector element being capable of distinguishing between two states of the storage medium.

17. Apparatus according to claim 15 or 16, characterised by that the detector means comprises at least three detector elements being sensitive in different directions, and where the detectors are controlled such that each detector element simultaneously reads one memory cell.

18. Apparatus according to any of the claim 15 to 17, characterised by that the light sources comprise laser diodes or one/two-dimensional laser diode matrices.

19. Apparatus according to any of the claim 15 to 18, characterised by that the detectors comprise photo-diodes or one/two-dimensional photo-diode matrices. preferably CCD-detectors.

20. Apparatus according to any of the claim 15 to 19, characterised by that the storage medium comprises bacteriorhodopsin, or a material with fluorescent. luminescent or phosphorescent properties.

21. Apparatus according to claim 15, characterised by that the storage medium comprises a material with fluorescent, luminescent or phosphorescent properties.

22. Apparatus according to claim 21 , characterised by that the storage medium is made of transparent (translucent) material, and the light sources operate in the UV range.

23. Apparatus according to claim 21 or 22, characterised by that the storage medium is in solution in a transparent fluid or gel, and the fluid or gel is stored in a closed tank.

24. Apparatus according to any of the claims 21 to 23, characterised by that the tank comprises transparent walls, and the walls are provided with bandpass filters.

25. Apparatus according to any of the claims 15 to 24, characterised by that the light sources and/or detectors are provided with collimating optics.

26. Apparatus according to any of the claims 15 to 25, characterised by that the light sources and/or detectors can be tilted around at least one axis.

27. Apparatus according to any of the claims 13 to 26, characterised by that the light sources and/or detectors can be translated in at least one direction.

28. Apparatus according to any of the claims 15 to 27, characterised by that the switchable optical property of the storage medium is the colour (absorption- or reflection spectrum) and/or the absorption (intensity) and/or fluorescence and/or luminescence and/or phosphorescence and/or Raman-spectrum.

29. Apparatus according to any of the claims 21 to 28, characterised by that different materials are used as storage medium, which are luminescing or phosphorescing or fluorescing in different colours.

30. Apparatus according to any of the claims 15 to 29, characterised by comprising a buffer memory connected to the control means, for storing the momentary states of the memory cells of the storage medium.

31. Apparatus according to any of the claims 15 to 30, characterised by comprising multiple storage media units that are addressable in a parallel manner.