BACKGROUND OF THE INVENTION Field of the Invention This invention relates to methods of data recording and retrieval on WORM (write-once-read-many) or WER (write-erase-read) optical disks and cards nd the like. More particularly, it relates to two-or three-dimensional luminescent optical data carriers wherein information is recorded by means of polarized radiation and retrieved by measuring the polarization state of the luminescent, data carrying, radiation.

Description of the Prior Art Existing optical memory systems utilize 2D information carriers having, as a rule, one or two information layers. In the majority of earlier technical solutions in the field of optical memory, registration of changes in intensity of reflected laser radiation in local microregions (pits) of the information layer was proposed. Said changes could be a consequence of interference effects on the relief of optical discs of CD or DVD ROM-type, hole burning in thin metal or semi-metal films, organic dye bleaching, variation of reflection coefficient in phase-change systems, etc.

Three-dimensional, for instance, multilayer, optical storage systems provide a sufficiently high data storage capacity. However, this imposes specific limitations on and requirements to the design and features of the optical

information carrier, ways of data recording and reading, especially in the depth of the multilayer carrier.

In reflection-mode storage systems, every information layer of the multilayer optical information carrier should possess partly reflective coating. This leads to reduction in the intensity of both recording and reading and reflected (information carrier) laser beams when they pass through the carrier to designated information layer and back to the receiver.

Besides, as said laser beams are coherent, they can be subject to considerable diffraction and interference distortions on fragments (pits and grooves) of the information layers on their way.

In view of the above, luminescent multilayer optical information carriers with luminescent reading are preferable, as they are free of partly reflective coatings on the surface of information layers. Diffraction and interference distortion in this case will be much less due to the non-coherent nature of luminescent radiation, its longer wavelength in comparison with the reading laser wavelength, and transparency and homogeneity (similar refractive indices of different layers) of the optical data carrier in reference to the reading and luminescent radiations. Thus, luminescent multilayer data carriers have some advantages over identical reflective ones.

Optical storage systems based on incoherence of luminescent (fluorescent, phosphorescent) information signals have twice as high spatial resolution as compared to coherent laser ones (Wilson T., Shepard C."Theory and Practice of Scanning Optical Microscopy", Academic Press, London, 1984).

Therefore, theoretically the use of incoherent optical radiation in the multilayer optical memory can result in an eight-fold increase of the recording density and consequently of its information capacity.

The most optimal mode for data recording and retrieval in luminescent multilayer information carriers is cooperative two-photon absorption by non-

luminescing dye precursors and/or luminescing products of photochemical reaction via an intermediate virtual level.

Said data reading/writing mode generally enables local information registration as luminescing marks (pits)-analogs of information pits in conventional reflective CD-or DVD-ROM-in the volume of information medium. In this case, reading by luminescence ensures the highest signal-to-noise ratio in contrast to the absorption method.

Practical implementation of this method today is, however, hindered by the large size of femtosecond laser radiation sources requisite for said recording and the extremely low sensitivity of the photoluminescent media themselves. The latter is primarily due to the extremely low magnitudes of two-photon absorption cross-section for currently known photosensitive materials.

That same reason precludes application of 1-10 mW small-size semiconductor lasers for two-photon data recording.

The conventional one-photon mode for recording information luminescent mark (pit) in the volume of the medium (either continuous or multilayer) is accompanied by variations of luminescent properties throughout the recording beam's passing via the medium. This can result in occurrence of noises and degradation of contrast at reading.

Besides, in the case of high-speed (tens and hundreds of megabit/s) one- photon information recording using today's commercially available continuous diode lasers with an output of 10-40 mW, the recording pulse energy will be low and hence the concentration of molecules capable to luminesce in the recorded pit will be also low. It can be comparable with or even lower than the total number of luminescing impurity or photoproduct molecules randomly generated while the 3-D recording medium was stored in the dark. All the above along with random exposure of the photoreceiver to extraneous radiation, could lead to occurrence of noise and degradation of contrast in reading, as in terms of intensity the

luminescent reading signal will be comparable with or even much lower than the luminescent background in the same spectral band.

The object of the present invention is to eliminate the above-mentioned drawbacks, i. e. to improve effective sensitivity through reduced energy consumption at the stage of recording by using anisotropic photosensitive substances in the recording medium, polarized radiation at the stage of recording and registration of the state of luminescent radiation polarization at the stage of data retrieval.

SUMMARY OF THE INVENTION A method for data writing and reading in two-and three-dimensional luminescent information carriers for WORM or WER optical disks and cards et al is proposed. In said method, polarization-sensitive photoluminescent materials are used as media for optical data carriers in order to improve effective sensitivity of the medium in data recording, to increase the velocity of recording itself and to raise the signal-to-noise ratio in data reading.

Another subject of the proposed invention is the choice of photosensitive components for polarization-sensitive luminescent materials from those classes of compounds that demonstrate strong absorption and/or luminescence anisotropy in the original and/or photoinduced states.

One more subject of the proposed invention is consecutive bit-by-bit or page-by- page recording of information by polarized radiation both in one-and two-photon absorption regimes.

Further, the subject of the proposed invention is the method for data retrieval wherein the detecting signal defining the fact of presence or absence of information pit in a designated microregion of the optical recording medium is the fact of presence or absence of anisotropy of the luminescent response in a given information pit's local microregion. In this case, the size of the luminescent

response is virtually of no importance and is defined only by energy potentialities (photosensitivity) of the photodetective devices used for reading.

Further, the subject of the proposed invention is data reading both in one- and two-photon absorption regimes.

The degree of polarization of the luminescent signal is determined by means of optical diagram including a modulator that rotates the polarization plane of the reading radiation and a photoreceiver that subsequently performs photoelectric separation of the variable temporary component in the luminescent signal ; said component is indicative of the presence or absence of the information pit in given microregion of the recording medium.

In the case of two-photon absorption, luminescence anisotropy can be detected by means of two photoreceivers with subsequent comparing the intensities of two orthogonally polarized components of the luminescent signal.

The next subject of the proposed invention is bit-by-bit or page-by-page mode of data retrieval.

The attached figures and examples illustrating this invention will make more demonstrative the specific features and advantages of the proposed method for data recording/retrieval on the proposed polarization-sensitive photoluminescent materials.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation of the simplest variant of polarization data recording/retrieval on polarization-sensitive photoluminescent material.

Fig. 2 is a schematic representation of molecular ordering_ (a) and the absorption spectrum (b) of the polarization-sensitive photoluminescent material in the original state.

Fig. 3 is a schematic representation of molecular ordering (a) and the absorption spectrum (b) of the polarization-sensitive photoluminescent material following polarization recording.

Fig. 4 is a schematic representation of molecular ordering (a) and the luminescence spectrum (b) of the polarization-sensitive photoluminescent material in data retrieval.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS At the present time, the properties of polarized luminescence in two-or three- dimensional optical storage systems are not utilized.

At the same time, in laser optics polarized information encoding has great opportunities as compared to amplitude methods. In the case of polarized encoding, information is carried by the state of polarization rather than by the phase and polarization. For example, in the case of analog encoding of the angle of rotation of the polarization vector azimuth for linear polarized light relative to selected direction, the signal's magnitude is encoded.

The techniques for polarization optical encoding and polarization optical storage are not so well developed as corresponding amplitude methods.

In the present invention, a new principle is proposed for data recording/retrieval in WORM and WER two-or three-dimensional luminescent optical storage like optical disks and cards et al.

In said 2D or 3D luminescent optical storage it is proposed to utilize polarization-sensitive photoluminescent materials as photosensitive materials; said polarization-sensitive photoluminescent materials exhibit an effect of photoinduced anisotropy (absorption dichroism and polarized luminescence) under the action of polarized or even non-polarized but directed radiation absorbed by said materials.

As photosensitive components in such media, we used anisotropic compounds undergoing nonreversible or reversible (photochromic) photochemical reactions resulting in a spatially oriented molecular ensemble of photoproducts which are likewise capable of anisotropic absorption and luminescence.

As photochromic compounds generating anisotropic luminescent photoproducts, there can be used chemicals from classes of polycyclic aromatic compounds such as endopyroxides, aromatic acenes and derivatives thereof (for instance, anthracenes, naphthacenes, pentacenes, hexacenes), spiropyrane derivatives of the indoline series, acrylmethanes and diarylethylenes, stilbenes, thioindigoid dyes, compounds with intermolecular hydrogen bond, etc.

As nonreversible photosensitive compounds capable of nonreversible photochemical generation of anisotropic luminescent substances, there can be used for instance derivatives of furyl chromone, oxadiazole, bases of xanthene dyes, coumarin derivatives and some other compounds.

The polarization-sensitive layers are solid polymer solutions with uniformly distributed at the molecular level photosensitive anisotropic substances capable of generating anisotropic photoproducts with polarized luminescence. In some cases, the polymer binder may be just as well absent.

The three-dimensional luminescent information carrier can represent either a multitude of polarization-sensitive layers separated by layers transparent to recording, reading and luminescent radiations or a homogeneous polymer block with uniformly distributed anisotropic photosensitive substances.

Information is recorded by means of polarized radiation in both conventional one-photon absorption mode and two-quantum (cascade) or two- photon (cooperative) absorption mode.

In the general case of the cascade two-quantum writing technique, just like the one-photon method utilizing two independent radiation sources with different

wavelengths, is based on real consecutive absorption of light quanta initially from the ground level then from the excited (singlet or triplet) one.

In the case of cooperative two-photon technique, writing is generally performed also by two independent sources of different wavelengths, with the light quantum energy of each of them separately leading to no changes in the medium. If the sum of two quantum energies, however, is resonant with certain frequency of two-photon absorption of the anisotropic photosensitive center, said center can switch to a virtual state with subsequent photochemical restructuring and generating anisotropically luminescing photoproduct. Information is retrieved through detecting the presence or absence of luminescence anisotropy at one-or two-photon absorption of the reading radiation.

In compliance with the proposed invention, data are recorded bit by bit or page by page.

The radiation propagation directions of two said independent sources can be either collinear or at an angle to each other. In the former case, their polarization vectors should be parallel, in the latter case their polarization vectors should be predominantly perpendicular to the plane defined by their propagation directions. The most acceptable is a two-photon recording by one linearly polarized beam.

The photoinduced anisotropy in the polarization layer can be induced by both nonpolarized and polarized radiation. In doing so, the optical axis of the induced anisotropy is determined by the propagation direction of activated radiation.

Data reading is also possible in both bit-by-bit and page-by-page modes using the CCD camera.

Another variant of polarization data recording on a luminescent carrier in compliance with the present invention is sensitized polarization recording. In this case, as one-or two-photon-absorber, anisotropic compounds are used for anisotropic transfer of the absorbed light quantum energy onto the photosensitive

anisotropic compound to yield an anisotropically luminescing photoproduct as a result of photochemical reaction.

The invention can be illustrated by several optical media and methods of polarization data recording/reading in one-photon, two-quantum (cascade) or two-photon (cooperative) absorption.

The invention can be exemplified by the one-photon principle of polarization recording and polarization reading of information on a polarization- sensitive photoluminescent carrier. In compliance with the proposed invention, as basic components in such a carrier there can be used nonreversible photosensitive or photochromic compounds exhibiting strong absorption anisotropy in the original state and strong absorption and luminescence anisotropy the photoinduced state.

It is known that the property of optical anisotropy is characteristic of the majority of substances of both natural and synthetic origin. Individual molecules are as a rule anisotropic, i. e. they possess their own absorption and radiation oscillators that in most cases can be considered linear. Probability of light absorption s by such molecules is # = #E#2 ##og#2Cos2# (1) where E is the vector of the light wave field intensity, Dog is the vector of the transfer dipole moment at absorption; 0 is the angle between them.

Luminescence of molecules is also anisotropic to a greater or lesser extent. It is this feature that underlies the proposed method for optical information recording/writing on polarization-sensitive photoluminescent materials. Said method is as follows.

An originally isotropic layer of photoluminescent material with randomly (isotropically) ordered photosensitive molecules (A) (luminescing dye precursors) NAx(x,y) = NA y(x,y) = NA = Const (2) and molecules of luminescing dopants Ndopx (x, y) = Ndop y(x,y) = Ndop = Const (3) are initially exposed to linearly polarized radiation of intensity Iwrite x*x,y) carrying information about the pit recorded.

Here NA x,y(x,y) and Ndop x,y(x,y) are volumetric concentrations of photosensitive molecules (A) and molecules of luminescent dopants, respectively, predominantly oriented along axes X, Y of the orthogonal coordinate system, said axes lying in the plane of the photosensitive material. It is assumed that polarization vector E of recording radiation twrite x (x, y) incident along axis Z is parallel to axis X.

In this case, according to expression (1) only those molecules (A) are predominantly excited and enter into a photochemical reaction for which the direction of absorption oscillator uog approaches one of vector E of writing radiation Iwrite x(x,y)# The concentration distribution NB (x, y) of luminescent molecules (B) resulting from the photochemical reaction also has a predominant orientation : NB x (x,y) = NA#KAx#Iwrite x(x,y) and NB y(x,y) = NA#KA y#Iwrite x(x,y)

where coefficients KA x and KA y are functions of anisotropic properties (absorption probability (1)) and the quantum yield in the photochemical reaction of original molecules (A).

Thus, the whole set of molecules capable of luminescing under the action of reading radiation can be presented as composed of two parts: totally random (in terms of orientation) molecules of dopants Ndop and predominantly ordered (in accord with the orientation of polarization vector of recording radiation irrite x of photoproduct molecules (B) Na (x, y) carrying information about the recorded pits.

While the concentration of the former is constant on the surface of the layer and is independent of the writing radiation energy, the concentration of the latter is unambiguously related to said radiation energy. The higher is the local surface writing radiation energy, the higher is the concentration of molecules (B) and, consequently, the higher is the local orientation anisotropy of the layer at reading (NB x(x,y) > NB y(x,y)).

At the stage of reproduction of the recorded information, the photoluminescent material is exposed to reading, for instance nonpolarized, radiation ! read. it is absorbed by molecules (B) and dopants; as a result their luminescence is excited. The light radiated by the exposed recording medium will be partially polarized in microregions containing information marks (pits). Said light can be presented as a sum of the nonpolarized radiation of the randomly oriented ensemble of luminescent dopant molecules Ifl dop x(x,y) = Ifl dop y(x,y) = 1/2 Idop = Kdop#Ndop#Iread and partially polarized luminescence of molecules (B) forming the image of the information mark (pit) tf)pit x (x, y) = Ks x'N B x (x, y)'tread (7)

and tf) pit y (x, y) = KB y-N B y (x, y)' ! read (8) where constants KB x, KB y and Kdop characterize luminescent capability of molecules (B) and the dopant, and Iread is the reading radiation intensity.

The total luminescence intensity of components polarized along the axes and at some point (X, Y) of the information mark will be Ifl pit x(x,y) = Kdop#Ndop#Iread + KBx#NB x(x,y)#Iread and Ifl pit y(x,y) = Kdop#Ndop#Iread + KBy#NB y(x,y)#Iread.

Their difference is tf)pit x(x,y) - Ifl pit y(x,y) = (KBx#NB x(x,y) - KB y#NB y(x,y)#Iread Thus, the information about the recorded mark in the proposed method is represented as a difference of intensities of components polarized along axes X and Y independent of the intensity of the background.

To measure said difference, partially polarized luminescent radiation from the exposed photoluminescent medium is transmitted for instance via a polarizer rotating at angular velocity. The light intensity behind the polarizer at each moment of time t is defined by the expression fl pit(x,y,t)=Ifl pit x(x,y)#Cos2(#t)+ Ifl pit y(x,y)#Sin2(#t)= Ifl pit x(x,y) + Ifl pit y(x,y))/2+ If,pit x(x,y) - Ifl pit y(x,y))/2#Cos(2#t)=Const+(KBx#NB x(x,y) - KBy#NB y(x,y))#Iread#Cos(2#t).

The augend, representing a sum of the useful weak signal and strong background, is independent of time, while the addend carrying only information

about the luminescent mark (pit) recorded in the medium is modulated in time t with frequency 2a3.

The light signals are then converted by the photoreceiver to electrical followed by separation of the variable component (information signal) from photoelectrically recorded signal using conventional radioelectrical procedures; said variable component's magnitude can be hundred or thousand times less than the constant (background) component.

Fig. 1 gives a schematic illustration of a simples embodiment of the proposed polarization method for data recording and reading on a luminescent optical card. The reading principle is based on the described above rotating polarizer method.

The device has optical card 1 with luminescent multilayer information carrier 2, source of recording radiation 5 and source of reading radiation 8, lens elements 6,9 and 13, photoreceiver 16, permanent polarizer 3, rotating polarizer 14, dichroic filters 10 and 12, spectral filter 15, polarizer rotation control unit 18 and frequency selective filter 17.

Said device operates as follows.

At the stage of data recording, radiation 4 of recorder 5 is polarized by polarizer 3 followed by focusing said radiation 4 by optical system 6 on one of the information layers of luminescent carrier 2.

After the information has been written, the scanner (not shown in Fig. 1) reads the information bit by bit on card 1 by means of nonpolarized radiation 7 from source 8. Radiation 7 is focused in the preset microregion of one. of the layers of carrier 2 by means of optical system 9 via dichroic mirrors 10 and 12.

Luminescent radiation 11 from the pit being read off is directed to photoreceiver 16 by means of dichroic mirror 12 via tens system 13 and light filter 15.

The magnitude of anisotropy of the luminescent signal is modulated in compliance with the information written in the medium. Due to the rotation of

polarizer 14, a time-fluctuated light flux is incident on photoreceiver 16. Using frequency-selective filter 17, a 2ca variable component is separated from said flux ; the amplitude of said component is modulated in compliance with the information written on carrier 2.

In the experiment, a photochromic material representing a solid 5% by weight) solution of 1,3,3-trimethyl-61,8-dinitrospiro (indo ! ine-2, 2'- [2H-1]- benzopyrane) in polystyrene as luminescent polarization-sensitive material. The layer thickness was about 1 micron.

Said material is isotropic in the original state but is transparent in the visible spectral range and intensively absorbs radiation with the wavelength of the order of 385 nm dying in violet with maximum absorption at 545 nm. The died form luminesces in red (about 580 nm).

A nitrogen laser with the wavelength of 337.1 nm was used as a source of recording polarized radiation. Prior to data recording, the material specimen had been exposed to nonpolarized radiation for 2 seconds; said procedure was equivalent to generation in the polarization-sensitive layer of molecules of luminescent dopant with spectral characteristics identical to characteristics of molecules generating luminescent information marks (pits).

Thereafter, information was written and read by both conventional method (by measuring the luminescence intensity of the information signal) and the proposed method. It was established that a significantly lower energy of recording radiation is required for data recording by polarized radiation and data reading by measuring the state of polarization of the information-carrying luminescent radiation in contrast to the conventional reading/writing technique. Also, the information signal contrast was better in the proposed method.

Figs. 2-4 schematically represent the principle of sensitized two-photon polarization recording and polarization reading of information on a photochromic carrier.

Figs. 2a-4a schematically represent relative ordering of sensitizer molecules (1), photochromic molecules in original form A (2), as well as molecules of the dopant (3) and randomly generated molecules in form B (4) and photochromic molecules in form B carrying information (5) in the volume of the recording medium (6) in the original state (Fig. 2a), for data recording by polarized radiation with polarization vector E in the absorption band of sensitizer (1) (Fig. 3a) and for one-photon reading by polarized radiation in the absorption band of photochromic molecules in form B (Fig. 4a). Figs. 2b-4b show absorption and luminescence spectra corresponding to said ordering.

It can be seen that in the original state all molecules have a random space orientation (Fig. 2a) and their absorption spectra are isotropic (Fig. 2b). When this isotropic assemblage of anisotropic particles is exposed to polarized radiation E, there occurs two-photon excitation of molecules (1) through consecutive two-step excitation, for example, via intermediate resonance first singlet-excited state. As a result, in the microregion of the recorded information pit an anisotropically oriented ensemble of excited molecules of the dye- sensitizer (1) is generated with a highly pronounced luminescence anisotropy (provided the recorded layer is free of photochromic molecules). The reason for the highly pronounced radiation anisotropy lies in that the second anisotropic excitation Si-S2 selects excited oscillators by direction not from the chaos as the first anisotropic excitation but from certain primary anisotropy already created by the primary anisotropic excitation So-Si.

For one-photon linearly polarized excitation, the limiting degree of polarization P of luminescence of the isotropic recording layer is P = T4, white for two-photon excitation P = 2/3. Here P = (la-ll)/(1 + Il), where 10, 1 denotes

intensity of the component polarized parallel or perpendicular to the electrical vector of recording (exciting) radiation.

With the availability of photochromic component (2) in the recording layer, the luminescence of dye (1) is switched off and anisotropic dipole-dipole energy transfer from the donor (dye (1)) to acceptor (2) (photochromic compound in form A) takes place followed by a photochemical conversion of colorless form A to died form B.

According to the mechanism described in the Foerster theory, the efficiency of said energy transfer depends not only on the extent of overlapping of the luminescence bands of dye (1) and the absorption of photochromic compound A and the distance between them, but on the relative orientation of their dipole moments. As a result, the ensemble of excited photochromic molecules in form A and hence subsequently generated died photochromic molecules in form B will be anisotropic and their luminescence will be polarized (Fig. 4b). The molecular ordering of the dopant remains random (Fig. 3a).

Consequently, the absorption spectra of photochromic molecules in form A and photoproducts of form B generated under the action of polarized recording radiation will exhibit dichroism while the absorption spectrum of dopant molecules will remain isotropic (Fig. 3b). Thus the whole assemblage of molecules situated at the location of the information mark (pit) that are capable of luminescing under the action of reading radiation can be divided into two parts: totally random (isotropic in terms of orientation) molecules of dopants and predominantly ordered (in accord with the orientation of polarization vector E of the recording radiation) information carrying molecules of the photoproduct (Fig. 4b). The magnitude of luminescence intensity itself, for all practical purposes, is of no importance and is restricted by the threshold sensitivity of the photoreceiver. Said photoreceiver allows registration of information pits; the intensity of said pits can

be not only comparable with but lower than the intensity of the background radiation. This improves the reliability of reading.

As distinct from the conventional data reproduction technique, wherein the fact of the presence or absence of an information pit in the specified local microregion of the carrier is qualitatively detected by the presence or absence of luminescence proper, in the proposed method as a detected signal is used the presence or absence of the anisotropic property in the luminescent signal at absorption of the reading radiation by molecules of the photoproduct in the local microregion of the information pit (Fig. 3b).

Reading can be performed by means of one-or two-photon absorption.

In the former case, the degree of polarization of the luminescent signal is determined by means of an optical diagram including a modulator that rotates the polarization plane of the reading radiation and a photoreceiver that subsequently performs photoelectric separation in the luminescent signal of the variable component with a double rotation frequency of the polarization vector of the reading radiation. Said component is indicative of the presence or absence of the information pit in the specified microregion of the information medium. In this case, the constant component of the background luminescence of dopant molecules is cut off enabling registration of information pits wherein the intensity of luminescence can be considerably lower than the background radiation. This allows one to reduce the power requirements of the recorder, to raise the effective photosensitivity of the actual recording medium, as well as to diminish the erasing effect of reading radiation through decreasing the intensity thereof.

Polarization reading permits reduction in noise and improvement of the contrast of the information pit.

One-photon polarization retrieval enables page-by-page reading using the CCD camera.

In the case of two-photon absorption, luminescence anisotropy can be detected by means of two photoreceivers with subsequent comparing the

intensities of two orthogonally polarized components of the luminescent signal.

The further advantage of polarization data writing and reading is lower requirements to selecting and cleaning of substrates used for fabrication of the recording medium, as well as film-forming components, photosensitive and other compounds, as the proposed method allows a significant reduction in the harmful impact of luminescent molecules of dopants and external exposures.

One-photon information reading can be carried out by the same source of radiation as in writing provided the source's wavelength is within the absorption spectral region of the died form of a photochromic or photochemically irreversible compound.

The polarization luminescent method owing to its very high sensitivity can be applied up to the concentration of luminescent substances in the layer of the order of 0.001%. At the same time, the concentration of photosensitive molecules in known luminescent information carriers is generally 0.1-5 wt %. To convert them into luminescent photoproducts the power requirements will be about 0.05- 1 J/cm2 or about 5 10-1°-10-8 J/pit (for the pit diameter of about 1 micron).

Consequently, the use of the proposed polarization-sensitive photoluminescent materials and polarization methods for data reading/writing can permit a reduction in concentration of anisotropic photosensitive components in each information layer of the fluorescent multilayer information carrier. The result will be a lower absorption factor in individual information layers and consequently a possibility of increasing their total number in the multilayer information carrier.

In the above examples we have shown preferred embodiments of the present invention. However, other embodiments differing, for instance, in the choice of composition for the polarization-sensitive material and modes of polarization data reading and writing are possible as well. They can complement the above- mentioned list of embodiments rather than restrict the scope of claim to priority of

the proposed application for the discovery in compliance with the following claims.