The present invention relates to a method of data/information storage, retrieval and to a related storage medium.
Optical or holographic data storage has been extensively studied, industrially and commercially exploited for the last three decades. There are many known techniques for data storage closely linked to the development of computers such as magnetic memory devices. Optical based data storage systems offer considerable capacity, especially when the information is holographically coded. For further information see e.g. “Holographic Data Storage Coufal H.J. Psaltis D., Sincerbox G. T. (Eds.), Springer Berlin, 2000”, and “Curtis K., Holographic Data Storage, Wiley, 2010” and references therein.
The very first commercially successful optical based data storage technology comprises the Compact Disc (CD), followed by well known media such as DVD, BD, SACD, etc. wherein binary data is written in a form of laterally collocated single tracks of lands and pits. Such tracks then relate to the binary code, thus determining bit “0, 1” information. The information is laser written and subsequently retrieved by reflecting the light beam from the pertinent lands and pits. Further, a specific data storage laser written technology is commercialized by LaserCard, California.
The principal goal of any data storage system is to encompass as much information/data on the smallest possible area or into the smallest volume. Thus the current state of the art approaches a capacity of hundreds GB per inch squared. When considering 3D recording the theoretical limit is to comprise 1 bit per cube size in the order of the wavelength of the writing beam. In general, research is focused on increasing the capacity of the disc/media up to 1 TB, or towards increasing the transfer (upload/download) speed. Holographic data storage breaks through the physical limitations of standard storage technologies by going beyond two-dimensional layered approaches in order to write in three dimensions, rather in two dimensions in several levels. All known techniques such as those above, however, handle bit-wise signals, such that binary scales are used for the data storage. So far, no prior art has proposed high density analogue signals data storage or, say, multi-level binary systems such as base-16 systems.
A holographic system for a discrete kind of data storage and play-back, thus data reconstruction or reading, where the data is recorded in a form of a diffractive grating, is described in (Mikaelyan, Soy. J. Quantum Elecron. 17 (5), May 1987, pp. 680). This paper teaches a technique similar to a standard CD writer, where the binary spots are positioned on a spiral. Each data-dot comprises grating grooves and so when reading the data, the light beam is diffracted to a pertinent, but constant angle.
However, such known systems, apparatus and methods exhibit limitations and disadvantages with regard in particular to the quality and capacity of data/information storage and retrieval and the controlled limitation thereof in particular.
According to a first aspect of the present invention there is provided recording method comprising the steps of modulating a first light beam for recording purposes; directing a second light beam to interfere with the said first light beam to produce an interference pattern in the region of a recording medium; forming an optical device in the said medium responsive to the said interference pattern and wherein optical characteristics of the said optical device are varied responsive to variations in the said interference pattern.
The efficiency and accuracy of data/information recording/retrieval is advantageously improved by way of the invention was also exhibiting markedly improved copy-protect characteristics.
Preferably, the first and second light beams can comprise coherent light such as for example laser light.
The said first beam is preferably modulated by a light modulator, and, in one aspect, a method can include splitting the said first light beam prior to the said modulation step. Of course, as an alternative, the method can include splitting the beam after modulation.
The method is not limited as to the number of beams that can be modulated and so, in one arrangement, at least two parts of the split beam can be modulated.
Presently, a variable optical characteristic of the said structure can comprise at least one of period, pitch, profile shape and/or high or modulation and orientation of the grating structure.
The method can then include the step of causing the said optical characteristic to vary in at least one of a substantially continuous, stepwise and/or discrete manner in the direction of relative movement between the interference and/or holographic pattern and the recording medium.
In particular, the method can include forming the optical characteristic as a track in the recording medium.
In one embodiment, the invention can involve forming discrete optical devices aligned in the direction of relative movement between the interference pattern and the recording medium or otherwise spatial relation.
In one configuration, there can be provided a plurality of differing optical devices within a common discrete region or arranged in a continuous region.
As will be appreciated, the method can comprise an analogue recording method and/or a digital recording method.
The method can comprise an optical recording method.
According to another aspect of the present invention, there is provided a recording method for multilevel digital recording including the step of recording a multiple variety of optical devices within a recording medium wherein each of the multiple variety of optical structures exhibits a differing optical characteristic.
In this aspect, the said optical devices comprise at least one of holographic and/or diffractive structures.
According to yet another aspect of the present invention, there is provided an optical recording method including a step of holographically recording a visual representation of part of a signal within a recording medium.
Presently, such a further method includes the step of creating an image of the said part of the signal.
In this manner, the invention can then include repeating the display and recording steps for a sequence of adjacent parts of the said signal.
According to still another aspect of the present invention, there is provided an optical playback method for retrieving a recording produced by way of a method outlined above, including the step of directing a light beam to a recording medium comprising an optical device; moving the optical device relative to the light beam so as to introduce regions of the optical device with differing optical characteristics to the light beam; and detecting changes in characteristic of light retrieved from the different regions of optical structure during the said relative movement.
As will be appreciated, the method can including the step of retrieving the recorded signal from the said detected changes.
Also, the playback method can comprise an audio signal playback method.
Further, the playback method can detect changes in the characteristic of the light as analog or digital changes.
Of course, the invention can also provide for an optical recording head including means for producing a first modulated light beam, a second light beam, and arranged to allow for interference between the beams and for optical recording according to a method as defined above.
Likewise, the invention can also provide for an optical playback head including means for producing a light beam or impinging on the recording medium and arranged to operate in accordance with a method as defined above.
Yet another aspect of the present invention can comprise a data carrier having data recorded thereon according to the method such as that defined above.
Thus, the preservation can provide for a data carrier arranged for use with a light beam and including an optical device arrangement having different regions including different optical characteristics.
Preferably, the data carrier can have regions that are continuous and contiguous, and also wherein the optical device can comprise a continually varying holographic or diffractive structure.
As already will be appreciated a particular aspect of the invention relates to the change of characteristics of a modulated light beam in time and leads to a spatial or position change of characteristics of diffractive structure created by the interference of the light beam with other beams. The structure originated as described above is then recorded and this forms a record of the information (data storage). Movement of the (light) beam over the recorded structure causes a change of a position, direction, intensity or other characteristics of the diffracted or reflected beam, and this can be further detected in time
The invention relates to data or any physically defined information storage. The data/information can be of analogue or advanced binary data nature, preferably of base-N system alphabets, where N>2 (e.g. hexadecimal alphabet). The recording of analogue and/or discrete signals, their storage, as well as further play-back, is all encompassed within the scope of the present invention.
Methods embodying the invention can provide data storage at very dense data/information capacity while maintaining a very high quality of the information nearly incomparable with standard digital data storage techniques. Unauthorized copying and/or undesired multiplication will be markedly more difficult in comparison to the current art and related standard ways of copying and production of carrier media.
The principal aspect outlined above is as follows. A signal or data structure is encoded into a specific diffractive structure. For example, the well known two (or multiple) beam interference experiment can be used for recording of such data, where at least one arm of the beam is modulated in a way linked to the input signal. The signals can be also recorded via any known technique of Holographic Data Storage (HDS), see (Curtis book) or any method being able to produce and record the interference pattern. As an advanced way of recording, any of physical properties of light such as polarization, wavelength, quantum states, modes can be exploited to assist with recording desired information.
As will therefore be appreciated the invention relates to systems in which the signal can be recorded in the form of specific diffractive structures, preferably diffractive gratings, holograms and so on. Similarly, the reading, or data retrieval, exploits the spatial distribution of diffracted light. Thus, the diffracted light direction and/or its intensity can serve to represent the desired information. This can advantageously be used for the recording/reading of analogue audio or video signal, but has no limitations for the data or any form of information recording of the discrete (binary or even multilevel alphabet, such as hexadecimal one and so on) signals. The invention can be further extended for a variety of combination of analogue and discrete signals.
The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which:
a and b illustrate well-known gramophone technology;
a and b illustrate the principles behind interference patterns and related diffractive structures;
a-e illustrate various differing forms of grating structure/patterns according to embodiments of the present invention;
a and b are schematic sensations of further details of playback arrangements according to embodiments of the present invention;
a and b illustrate a multi-pixel picture frame structure employed within an embodiment of the present invention;
a, b and c are straight aspects of the present invention within a multi-media arrangement;
a-d illustrate different examples of grating structures/configurations according to embodiments of the present invention;
Turning first to
A detailed description of the concept behind an embodiment of the invention employing well-known diffraction phenomena is shown in
A particular example of a recording apparatus and procedure is schematically depicted in
More simplified schematics for the case of the sound recording are shown in
Examples of the reading/recording relate to changes in diffraction/holographic properties and are linked to the change of the signal. This can comprise:
As should be appreciated, 1D-2D signals can be recorded, and volume holographic multiplexing advantageously used. For 1D signals can be in the form of data streams and analogue sound.
Turning now to
In so far as the information is recorded as diffractive elements the copying and multiplication of the data/information proves prohibitively complex. The median could be similar to the standard CD when provided in the form of relief holograms/DOE; or light assisted copied in the case of volume holograms.
Another important embodiment of the method is the fact that although copying and mass reproduction of such elements can be industrially performed, it would be nearly impossible to copy the data carries by means of standard tools such as equivalent to a CD burner. This leads to a near absolute protection for unwanted and undesired copying of the data stored.
In general, the present invention represents an improvement over any digital signal recording procedure having regard to signal-accuracy. A simple inspection shows that the dynamics of the analogue signal can reach about 100 dB level. This should be emphasised that the method disclosed offers analogue signal storage with the same quality of the known approached of the digital methods. However the continuous signal is principally exceeding possibilities of, for example digital CD sound systems, as the signal reconstruction is any additional sampling free. More importantly, the presented invention offers essentially better signal/noise as well as interchannel crosstalk ratio.
This can also be used in medicinal applications or so, where the signal is recorded in the original form, without any digital processing, hence most probably perturbation. If the signal, like heart-beat echo (EKG or EEG for brain activities) is recorded with dynamics close to 100 dB, the signal can be post-processed with very high accuracy, offering a yield of desired information and so on.
With regard to the recording and reading devices—in theory, any of the previously mentioned approaches can be used. A preferred recording head structure/function is illustrated with reference to
Another example of a recording device can be achieved via a direct modulation of the laser, that can yield laser wavelength changes proportional to the signal at the input, thus to be stored. Further techniques could be used, like the so called array waveguide grating approach (AWG) or any of antennae phased array arrangements yielding the interference spot being at one place.
A possibility of a 2D detection signal opens a broad area for usage for movie pictures storage, most likely in high quality (100 dB dynamics).
Another important application of the method described is the introduction of more flexibility into discrete (binary) data recording. Actually, one can record either more dense data information on a specific area/volume or, more importantly, the data can be written in a form of multilevel or in more than binary system, such as the hexadecimal system and so on. With the above-mentioned possible dynamics of the system, only the resolution of the detector will the limiting factor and the data storage using this technique could lead to in general N-base digital alphabets, where N can be quite a high number. The use of the hexadecimal alphabet would require four times less space for recording the same information comparing standard binary approach. Further, the multilevel binary approach may offer a substantially increased density of the data. Taking into account that very advanced techniques of the auto data corrections are widely used, this approach offers a dramatic improvement of the digital data storage.
Turning now to
Laser wavelength multiplexing and/or volume multilevel recording can be advantageously used for this approach. Such techniques have been studied extensively and more details are found in the Psaltis and Curtis references noted above. The hologram/diffractive structure can be recorded in a form of a surface gratin or, volume grating etc. Any known materials and approaches can be used for this technique with no principal limitations.
Next,
If for some applications, the signal from the diffrative structure might be considered rather weak, and comprising a broad spectrum of spatial frequencies, and that the principal maximum of the diffraction order will be rather broad, an extra Diffractive Optical Element (DOE) such as a grating of preferably shorter period than the shortest period of the diffractive signal structure, can be included into the optical path. This can cause splitting of the signal into two or more identical signals, or the DOE can be of a more advanced nature such as an aperiodic grating (see Veldkamp, Appl. Opt. 1982, p. 3209), that can spatially modulate the profile of the light to enhance detection and as is illustrated in relation to
Finally,
The principal technique behind a main embodiment of the invention can be summarized briefly in the following. We actually consider a basic wave optics two beam interference experiment, where two beams interfere under a given angle (see
The present invention can advantageously consider this method exploited in the following way. Principally, either beam (i.e. at least one, or more or all in the case of the multibeam inteference) can be modulated. Modulation means a change of some physical properties of the beam. However the most common way of modulation of the beam(s) would be a change of the angle of the beam with respect to the other beam(s) or to the substrate, where the interference pattern is to be recorded. Desired change of the angle is linked the variations of the input signal/information. So, it could be a binary/discrete change of the angle in the case of the digital data. More importantly, and considering an analogue signal such as sound, the angle between the interfering beams will fully depend on the variation of the harmonic signals. This can be seen from
A short mathematical inspection shows, that exploiting a standard acousto-optical deflector would guarantee a dynamic range of the stored signal with 100 dB. For such value, it is necessary to distinguish five orders difference between the weakest and the strongest signals. Considering an arrangement of the writing head as depicted on
In yet further detail, it should be appreciated that the method of the interference assisted recording can originate relief micro-changes, density changes or change of the refractive index. The materials used are, for example, photoresists, polymers (polymers can use photochanges of can be ablated by the laser beam), waxes, photosensitive density-changing materials, photopolymers. Substrates can comprise materials such as glasses, polycarbonates of similar thermoplastics, metals, all variants as nominated above, but comprising a conductive layer(s). Anti-reflex and/or anti-scratch coatings can be provided on the top of the disk/tape/media.
Industrial multiplication of the master copy can be achieved through a (micro)relief embossing, either at different refractive indices interface or at a metallic interface. Further, the multiplication can be done via contact-less or rather optical copying, such as relief or density of refractive index changes. A relief-type microstructure can be further multiplied by conventional techniques like CD, DVD etc, embossing/casting, or the optical reproduction. Density-media changes can be multiplied via optical copying of two different media/carrier densities, analogously at the density/refractive indices changes. Also optical-mechanical multiplication, i.e. transforming density/relief by optical means and further mechanical copying can be provided. Further, they carrier with refractive index changes can be copied optically (two different indices), multiplied optically (refractive index change with density variation) or copied from a photopolymer to a relief structure.
The record of the signal/data can be located on the surface, embedded within or covered by a protecting layer—but all presented as a single layer. However, multi-layer and multi-layer with continuous changes, recording methods can readily be employed. The tracking paths for the beam can be arranged in the plane of the record, or above or below as appropriate.
Number | Date | Country | Kind |
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1015892.1 | Sep 2010 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP11/66547 | 9/22/2011 | WO | 00 | 6/6/2013 |