Patent Application
20050084801
The present invention generally relates to a photonics data memory. In particular, the present invention relates to a storage material for use in the photonics data memory and a process for making said storage material. And in particular, the present invention relates to apparatuses for recording/reading information to/from the photonics data memory.
The large storage capacities and relative low costs of CD-ROMS and DVDs have created an even greater demand for still larger and cheaper optical storage media. Holographic memories have been proposed to supersede the optical disc as a high-capacity digital storage medium. The high density and speed of the holographic memory comes from three-dimensional recording and from the simultaneous readout of an entire packet of data at one time. The principal advantages of holographic memory are a higher information density (1011 bits or more), a short random access time (˜100 microseconds and less), and a high information transmission rate (109 bit/sec).
In holographic recording, a light beam from a coherent monochromatic source (e.g., a laser) is split into a reference beam and an object beam. The object beam is passed through a spatial light modulator (SLM) and then into a storage medium. The SLM forms a matrix of shutters that represents a packet of binary data. The object beam passes through the SLM which acts to modulate the object beam with the binary information being displayed on the SLM. The modulated object beam is then directed to one point on the storage medium by an addressing mechanism where it intersects with the reference beam to create a hologram representing the packet of data.
An optical system consisting of lenses and mirrors is used to precisely direct the optical beam encoded with the packet of data to the particular addressed area of the storage medium. Optimum use of the capacity of a thick storage medium is realized by spatial and angular multiplexing. In spatial multiplexing, a set of packets is stored in the storage medium shaped into a plane as an array of spatially separated and regularly arranged subholograms by varying the beam direction in the x-axis and y-axis of the plane. Each subhologram is formed at a point in the storage medium with the rectangular coordinates representing the respective packet address as recorded in the storage medium. in angular multiplexing, recording is carried out by keeping the x- and y-coordinates the same while changing the irradiation angle of the reference beam in the storage medium. By repeatedly incrementing the irradiation angle, a plurality of packets of information is recorded as a set of subholograms at the same x- and y-spatial location.
A volume (thick) hologram requires a thick storage medium, typically a three-dimensional body made up of a material sensitive to a spatial distribution of light energy produced by interference of a coherent light beam and reference light beam. A hologram may be recorded in a medium as a variation of absorption or phase or both. The storage material must respond to incident light patterns causing a change in its optical properties. In a volume hologram, a large number of packets of data can be superimposed, so that every packet of data can be reconstructed without distortion. A volume (thick) hologram may be regarded as a superposition of three dimensional gratings recorded in the depth of the emulsion each satisfying the Bragg law (i.e., a volume phase grating). The grating planes in a volume hologram produce change in refraction and/or absorption.
Several materials have been considered as storage material for optical storage systems because of inherent advantages. These advantages include a self-developing capability, dry processing, good stability, thick emulsion, high sensitivity, and nonvolatile storage. These materials also have demonstrated disadvantages which will be discussed below.
Photorefractive crystals such as those formed, for example, by lithium niobate (LiNbO3) have been used for recording volume phase holograms in real-time. Data in the form of holograms have been successfully stored in these crystals. The storage mechanism consisting in redistributing the photoelectrons in the crystal when variations in the intensity of the laser beam cause the modifications in the local refractive index at each point in the crystal. The photorefractive materials contain localized centers with trapped electrons that can be excited into the conduction band by the action of light. When this material is exposed to an interference pattern, the electric charges from interference maxima drift and/or diffuse and are (trapped) collected at the interference minima. The space charge pattern creates a strong spatially periodic field. This field deforms the crystal by the Pockels effect and causes a refractive index modulation producing a hologram.
However, these photorefractive crystals have a number of drawbacks. First, there is a very low tolerance in terms of localizing the read beam. This is because, given the crystalline nature of the solid employed, the addressing of the desired data tolerates an angular deviation with respect to the angular value in question of only about a few milliradians, requiring in fact the use of a read device of very high precision, resulting in a prohibitively large increase in the fabrication cost. This low tolerance also comes up against a technological availability problem. At the present time no system is capable of combining, simultaneously, precise angular control with rapid angular control. Either such a system is precise but not rapid, or it is rapid but not precise. Moreover, the energy needed to record data in such a material is of the order of 1 watt/cm2 In addition, recording a packet in the conventional format requires an area of about 1 cm2 which, moreover, has to be doubled with a depth of the material of at least 1 cm, therefore resulting in a medium of relatively large dimensions. Moreover and above all, these materials have an unacceptable defect, namely that reading the data stored in the material results in erasure of the data, something which, as is readily appreciated, is in complete conflict with the desired objective of serving as a storage medium. In order to overcome this major problem, a novel, non-destructive, method of reading has in fact been proposed, which makes use both of an electric field and a beam of polarized light. In this way, the holograms require more energy to erase the data than to store the data. However, this technique requires an apparatus which is more complicated to employ and is also not conducive to rapid access to the information stored. Recent progress made In the field of photorefractive systems has not adequately solved these basic problems. Physical limitations of a theoretical nature remain, so that it is not conceivable to overcome these problems in the near future. Finally, the difficulties encountered in growing the crystals preclude any reproducibility with economically viable scale-up costs.
Photopolymer materials are also capable of forming memories based on optical diffraction. The technology employed relies on the polymerization of photosensitive monomers under the action of a laser beam carrying the hologram to be stored. The concentration gradient of the photosensitive species which results from the polymerized pattern causes the unpolymerized photosensitive species to diffuse and generates a pattern which converts the original optical interference into a modulation of the refractive index. Analyzing this index modulation by means of a suitable read beam allows the information stored to be retrieved.
While it is true that these materials allow relatively large amounts of data to be stored, they have the drawback of being quite unstable over time. This instability can vary depending on their exposure to light, and especially to UV radiation. Even in the absence of light, the stored data is liable to disappear. Physicochemical processes have been developed in order to increase the stability of the stored information. But these prove to be not very satisfactory in so far as in all cases they significantly increase the noise, to above the permissible levels.
Moreover, the photopolymers introduce a reduction in the thickness of the material of about 7 to 10%, resulting in a change in the Bragg angle when retrieving or reading. This change must be compensated for either by modifying the geometry of the read system or by modifying the wavelength of the read beam. This notion of Bragg angle results from the multiplexing, that is to say from the storage of several holograms in the same volume. To do this, the angle of incidence of the reference laser beam is modified during the phase of storing the information within the medium. This reference laser beam interferes coherently with the laser beam carrying the information to be stored, and conventionally called the object beam, so as to form the interference pattern or hologram, which will be stored in the medium due to the perturbation in the refractive index. Thus, each hologram is stored at a unique angle of the reference beam. The separation between the various holograms stored within the same volume relies on the coherent nature of the hologram, in order to allow its retrieval in phase within the said volume only for a defined angle value. Retrieving the stored information therefore requires the use of a read beam whose characteristics correspond to those employed for writing or for storage (wavelength, angle of incidence and position within the storage material). This read beam induces diffraction due to perturbation in the refractive index corresponding to the characteristics of the beam, thereby creating the stored modulated beam. Thus, the great importance of the variation in the Bragg angle for correctly and rapidly retrieving the stored information is recognized.
Also developed, in parallel with the above two technologies, has been the technology called PHB (Photochemical Holes Burning). This technology relies on the use of quantum effects. More precisely, this technology consists in creating a novel absorption profile for a material exposed to the action of a light source. This excitation is different depending on the species present in the material, which have different absorption lines from that of the main channel. If this burning is of sufficient duration, the burning of the holes is said to be persistent. Materials having this characteristic are amorphous solids (polymers, inorganic glasses, xerogels) doped with organic molecules. Ion-doped crystals may also develop these characteristics.
The “hole burning” effect is generated in principle when the material is cooled. This phenomenon is accentuated at temperatures equal to or below that of liquid helium (4.2 K). In this case, the homogeneous absorption line is very narrow and the disorder of the amorphous medium gives absorption lines dispersed over a wide band, called the inhomogeneous absorption band. The medium thus behaves as a photosensitive medium whose spectral sensitivity depends on the wavelength of the inhomogeneous absorption band. The material can then record data: it can be used for spectral hole burning holography. The light source used is a dye laser for recording at several wavelengths in a doped amorphous material. During the recording operation, the material is placed under a high voltage in a cryostat. The inherent difficulty with this technology for multiplexed data storage resides in the need to maintain a low temperature throughout the recording operation. Another difficulty is how to control the wavelengths of the dye laser very accurately. Consequently, this type of technology is not conceivable in the immediate future for storage of diffractive memories.
Thus, the materials discussed above have disadvantages when used as a holographic storage media. In addition to avoiding the above disadvantages, it is desirable to develop a storage material which has a high diffraction efficiency and a low cross-talk.
Diffraction efficiency is a storage medium parameter meaning the ratio of the light of the read beam used for data packet reconstruction to the total light of the read beam incident on the hologram. Thus, a material with a high diffraction efficiency will use less power for each read operation which retrieves a packet.
Crosstalk occurs during retrieval of the stored data, resulting in the desired data and neighboring data being retrieved simultaneously. The interfering patterns from the neighboring data significantly affects the quality of the information sought. This crosstalk problem depends directly on the angular bandwidth of each hologram, that is to say on the mid-height width of the maximum diffraction efficiency as a function of the angle of incidence, and also defined as being the angular band within which the angle of the incident reference beam can vary without reducing the quality of the information contained in a packet read out.
Once an adequate storage material is found for the storage of holographic information, the material is shaped into a storage medium (e.g. square matrix, cube, disc) and corresponding apparatuses subsequently developed for recording information onto and reading information from the material. The apparatuses are designed to take advantages of the properties of the material. For example, a storage material may permit faster access of information or require less precision in the positioning of the beam which still maintaining crosstalk within an expectable tolerance. A control mechanism typically under computer control drives the optical beams during both the record phase and the write phase to rapidly focus the optical beams accurately at a specific point location and angle with respect to the storage medium. It presents a significant challenge to a designer of a holographic storage system to design a mechanism for accurately positioning of the beam within the required tolerances, especially of the angle of the beam.
In view of the foregoing, it is an object of the present invention to provide a photonics data storage system using a material making it possible both to considerably increase the memory capacity and, in parallel, to optimize the address speed, that is to say to limit the time for access to the stored information sought.
It is another objective of the present invention to develop a polypeptide material for the recording and storage of information by interferometric coding with a reference laser beam.
It is another objective of the present invention to develop a polypeptide material in which information is capable of being stored by an interference pattern using spatial and angular multiplexing.
It is another object of the present invention to develop a polypeptide material having minimum crosstalk in which information is capable of being stored by an interference pattern via angular multiplexing.
It is another object of the present invention to develop a polypeptide material in which information is capable of being stored by an interference pattern via angular multiplexing with a high diffraction efficiency.
It is a further object of the present invention to provide software for accurately positioning the angle of the read beam in a polypeptide material.
It is still another object of the present invention to provide a photonics data storage system with transformational nodes within an optical path to direct the read beam onto the storage medium within a precision which takes into consideration the nature of the storage material.
Other objects and advantages will become apparent from the following disclosure.
In order to achieve the above-mentioned objectives, there is a photonics data storage system wherein data is encoded in a storage medium by an interferometric process. The recording medium is made up of a polypeptide material based on or derived from a collagen, such as pork skin collagen, chicken leg (bone) collagen, and the like, The polypeptide material comprises a gel of chromium-doped collagen based polypeptide, in which alpha and beta chains are predominately present in portions such that the alpha/beta chains weight ration is greater than 1.
In a further aspect of the present invention, the alpha/beta chains weight ration is between about 1.2 and about 2.1.
In yet another aspect of the present invention, the chromium doping is carried out by adding a chromium VI salt in an aqueous solution to the polypeptide solution in an amount of about 5 to about 10% by weight of dry polypeptide, preferably about 10%. A 5% addition of chromium VI salt gives a chromium loading of about 100 mg per 100 ml of polypeptide solution (5% polypeptide).
In still a further aspect of the present invention, the average molecular weight of the polypeptide starting material is between about 120,000 and about 150,000 Daltons, preferably about 120,000 Daltons.
According to another aspect of the present invention, the viscosity of the polypeptide gel is between about three and about four centipoise, preferably about 3.5 centipoise, under Standard Conditions.
In still further aspect of the present invention, the polypeptide can be doped or treated with a hardening (tanning, curing) agent. Hardening is preferred.
In still a further aspect of the present invention, the hardening agent comprises a water-soluble chromium III salt, if hardened before exposure, or alum if hardened during development.
In accordance with another aspect of the present invention, the collagen based polypeptide, or polypeptide derived from collagen, is doped or treated with a surfactant, such as a fluorinated surfactant or fluorocarbon surfactant.
In still another aspect of the present invention, a polypeptide material is produced for the purpose of making a storage medium. A polypeptide, normally in dry powder form, of biological origin, such as collagen, is solvated in water, preferably deionized water, for a period of about two to about ten hours at room temperature to form at least a partial polypeptide solution. During the salvation, the polypeptide swells. The solution is then heated to between about 40 and about 60 degrees Celsius until the polypeptide is completely dissolved. The polypeptide solution is then doped with Cr VI (a chromium +6 salt), and optionally with a surfactant and/or hardening agent. Thereafter the solution is maintained at a temperature between about 55 and about 60 degrees Celsius for a period of about 15 to about 60 minutes. The solution is then filtered. The solution thus obtained can be stored for future use or deposited as a coating or layer on a glass or plastic substrate. When stored for future use, the solution is stored under refrigerated conditions in the dark. The solution thus deposited is then chilled and dried to yield a polypeptide gel storage medium. The above steps, commencing with doping with Cr VI are carried out in the dark—red inactinic light can be used. The completed storage medium are stored at cold temperatures, around zero degrees Celsius, in the dark, to maintain their photosensitivity.
In yet another aspect of the present invention, prior to depositing the solution on the substrate, the substrate can be, and preferably is, provided with a thin hydrophilic adhesive layer to give better bonding between the polypeptide gel and the substrate. The adhesive layer is sandwiched between the substrate and the polypeptide gel layer.
In accordance with another aspect of the present invention, the polypeptide solution is deposited on the glass or plastic substrate. Glass substrates can be coated by gravitational coating. Plastic substrates are preferably plated by extrusion coating or the Doctor blade method. Film substrates can be plated with the Meyer bar coating method or roll dipping.
In still another aspect of the present invention, the polypeptide solution is molded between two sheets, such as glass and/or plastic sheets. One of the sheets can be metal, ceramic or stone, having a planar, smooth polished surface. The polypeptide solution is spread between the sheets and an internal surface, i.e. facing surface, of one the sheets is pretreated with a hydrophobic film or coating to prevent the polypeptide solution from adhering to the treated planar, smooth polished surface. The polypeptide solution adheres to the other sheet, a clear, transparent sheet. The final thickness of the storage or recording medium is defined by the spacing between the sheets which can be controlled by shims placed between the two sheets.
In still a further aspect of the present invention, the exposed recording medium is developed, i.e. fixed or fixed/hardened, dehydrated and dried. A transparent plate or sheet is glued to the top surface of the developed recording medium to protect the recorded medium from moisture and abrasion. Alternatively, the top or exposed surface of the developed recording medium can be protected with a layer or coating of varnish. Preferably the protective plate or varnish has a refractive index close to that of polypeptide. The varnish must bind to the exposed surface of the doped polypeptide and must be inert so as not to react with the polypeptide layer. In addition, the protective plate or varnish must be optically transparent to the wavelength of light used when reading the exposed, recorded recording medium. The varnish can be coated or deposited as a monolayer or can be applied as a multilayer as long as it does not disturb the optical signal during reading. Preferably the varnish is hydrophobic, not hydrophilic, and is not water-soluble.
The exposed recording medium is developed in a fixer solution at a temperature of between about 20 and about 22 degrees Celsius. Optionally the exposed recording medium can be hardened before the development. Preferably, if hardening has not been carried out before, the fixing and hardening are carried out together. We have found that a combination treatment with Kodak brand fixer and Kodak brand hardener yields reproducible results and excellent recorded medium. The exposed recording medium is placed in a solution of fixer, or of fixer and hardener, for about 4 to about 10 minutes. The recording medium turns color from orange brown to a colorless or very light green colored plate during development. The hardening step is important because the hardening operation can make the developed plate physically more stable from the influences of humidity and temperature.
Normally, the polypeptide only has to be hardened once, either following doping with Cr VI or just prior to or with fixing. Preferably the polypeptide is hardened during the fixing step.
The treated plate, fixed and optionally hardened is washed in a water bath[s] and dehydrated with a water miscible inert low boiling point organic solvent, such as methanol, ethanol, isopropanol, acetone, or the like. Preferably the dehydration is carried out incrementally using drier and drier solvent, such as with four sequential aqueous baths of 25% alcohol, 50% alcohol, 75% alcohol, and finally 100% alcohol. The dehydration is preferably done with agitation. The dehydration only a takes a few minutes in each alcohol bath with agitation. After dehydration, the exposed, hardened, fixed, washed recording medium, i.e. the recorded medium, is dried at an elevated temperature to remove the organic solvent to yield the polypeptide gel recording medium mounted on a substrate, such as a plate, sheet or film. The drying step can be carried out in a vacuum.
In another aspect of the present invention, digital information is stored in a storage medium, alternately referred to as a storage medium, made up of a polypeptide material. A reference light beam and an object light beam intersect in the polypeptide material forming an interference pattern which is stored throughout the entire thickness of the storage medium. The storage medium forms a volume phase grating in which the interference pattern is formed.
In a further aspect of the present invention, the polypeptide material is in the form of a flat sheet defined by rectangular co-ordinates (X,Y). A packet of digital information modulated onto the object light beam is encoded as a subhologram at a point of a plane of the flat sheet.
In yet another aspect of the present invention, the variation of the angular direction of the reference light beam is accomplished by variable spacing of from one to four degrees.
In still another aspect of the present invention, the storage medium is shaped in the form of a flat sheet defined by rectangular coordinates (X,Y) of a plane of the flat sheet. At least fifteen discrete variations are made in an angular direction of the reference light beam for coding a wavefront of the object light beam.
According to another aspect of the present invention, there is a system having a storage medium made up of a polypeptide material having stored therein digital information as a plurality of packets stored throughout the entire thickness of the storage medium. A read light beam is configured to address at least one of the packets in the storage medium.
In yet another aspect of the present invention. The read beam is directed and shaped by one or more transformation nodes located in an optical path of the read beam to one of a plurality of points defining a matrix on the storage medium as determined by one or more initial storage conditions and one or more operating parameters.
In still another aspect of the present invention, the initial storage conditions include the size of the matrix, the number of points of the matrix, and the physical characteristics of the polypeptide material. The physical characteristics of the polypeptide material include a selection of constitutive molecules and results from a process for preparing the polypeptide material. The process for preparing the polypeptide material determines a wavelength sensitivity of the polypeptide material and includes a coating method. The physical characteristics of the polypeptide material are determinable by a recording process. The recording process is defined by at least one of the following parameters: wavelength, temperature, humidity, and the physical characteristics of a substrate of the polypeptide material. The physical characteristics of the polypeptide material further include a post exposure process. The post exposure process is defined by factors such as the physical characteristic of baths and physical parameters such as temperature and humidity.
In yet another aspect of the present invention, the operating parameters includes the desired time needed to access the storage medium, the type of activators used, the level of miniaturization, and the level of resolution.
In a further aspect of the present invention, the nodes consist of dynamic devices. The dynamic devices are selected from a group comprising mirrors, micro mirrors associated with a rotating component, acoustooptic components, diffraction gratings associated with liquid crystals, Kerr cells and Pockels cells. The positioning in space of the dynamic devices and the control of their orientation are managed by software.
In yet another aspect of the present invention, components are positioned at the nodes for deflecting the read beam. The components comprise two acoustooptic devices which diffract, in a known manner, the read beam in an angular direction according to the frequency of ultrasonic waves applied. The components further comprise a diffraction grating located downstream with respect to the acoustooptic devices and oriented in such a way that a beam emerging from the acoustooptic devices strikes the active face of the grating at a first angle being optimized so that a diffracted beam emerges at a second grazing angle. The components further comprise at least one dynamic angular deflection device located downstream with respect to the grating directing the beam emerging from the grating onto the storage medium.
Further objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to a preferred embodiment (s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.
In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only.
A photonics data storage system according to the present invention is described comprising a recording (storage) material, a data recording/storage apparatus for recording information on this storage material, and an addressing/data reading apparatus for reading the recorded information from this storage material. The photonics data storage system overcomes the limitations of the previous holographic systems discussed in the prior art.
The Material
A holography system according to the present invention is described comprising a recording medium (also referred to as a photonics data storage medium, recording material, data storage material, volume holographic memory, data storage recording medium, storage material and polypeptide recording material), a data recording/storage apparatus for recording information on the recording material and an addressing/data reading apparatus for reading the recorded information from the recording material.
Referring to
All the above steps from the point of adding ammonium dichromate to the polypeptide solution through the development is done in the dark or, at most, in red inactinic light. Exposure to actinic radiation or light prior to development or during or after doping with ammonium dichromate exposes the recording medium and destroys its ability to record data.
The Polypeptide Material
The polypeptide material for use as a recording medium, according to the present invention comprises a solution of chromium-doped collagen based polypeptide, in which solution the alpha and beta chains making up the polypeptide are predominantly present in proportions such that the alpha/beta ratio is greater than 1 and advantageously between about 1.2 and about 2.1. This polypeptide material of biological origin undergoes a preparatory treatment before being coated on a substrate. The recording medium is maintained and stored in an atmosphere at a defined temperature and at a defined relative humidity before use.
The polypeptide starting material, of average molecular weight between about 120,000 and about 150,000 Daltons, preferably about 120,000 Daltons, is obtained from a base material consisting of a collagen. A method of producing the polypeptide material for the recording or information medium according to the invention will now be described below in greater detail.
This process consists firstly in solvating and swelling a polypeptide of biological origin in water, preferably deionized water, for a period of about two to about ten hours at room temperature. The polypeptide is normally available as a dry powder. Polypeptides are selected that have the desired alpha chain to beta chain weight ratio, the average molecular weight, that can form gels of the desired gelling power and that have the desired viscosity as described above. The partial solution thus obtained is heated to a temperature of between about 40 and about 60° C., until the polypeptide has completely dissolved. The dopants are then added, especially the chromium VI salts. The aim is to completely dissolve these dopants or additives.
Collagen, Hydrolysis
Conventionally, when collagen is converted into a water soluble polypeptide, for example by alkaline or acid hydrolysis, denaturation occurs, resulting in the loss of the helical structure of the collagen. The collagen is produced from a number of animal sources, utilizing bones, hides, and tendons of animals. Depending upon the source of the collagen, the material characteristics of the resulting polypeptide will be slightly different because of the molecular makeup of the polypeptide from the collagen source. Even collagens from the same type of animals can vary depending upon the geographical habitat of the animal. In addition, manufacturing processes can induce differences in the resulting polypeptide.
Polypeptides produced from collagens are commercially available and are used in the food, drug, cosmetic and photographic film industries. The best results we have found to date come from polypeptides produced by the hydrolysis of pork skin collagen and poultry leg collagen. Such polypeptides are readily available because they are used in the cosmetic industry. Polypeptides have been acquired from several producers and used in the present invention with success. The polypeptide from pork skin collagen produced by the SKW Company located in South France which has an alpha chain to beta chain weight ratio of between about 1.2 and about 1.3 has been found to be very suitable. We have used polypeptides from chicken and turkey collagens having alpha to beta weight ratios of about 1.5 and from about 2.0 to about 2.1 produced by alkaline hydrolysis.
When it is available, polypeptides produced by genetic engineering using bacteria will probably produce a consistent and standard polypeptide that will eliminate most variances in the polypeptide. At the present time, this is not available in commercial quantities, although small batches have been made on the research scale. We have not tested these polypeptides. We found that commercial polypeptide based collagens, i.e. polypeptides derived from collagens, can also be found in the chemical catalogs of SIGMA MERCK KNOX NITTA KONICA, and CRODA COLLAIDS. We have not tested these polypeptides.
The molecules in collagen consist of amino acids linked by peptide bonds that are associated in a triple helix. The molecules of collagen from different sources differ by the amino acid sequence on the helix and the location of each amino acid on the helix. Amino acids can be repeated many times on the helix. The collagen molecule architecture is organized around a backbone. Every third carbone is occupied by a glycine. Amino acids that are most commonly found on the collagen molecule chain are glycine, proline, hydroxyproline, and alanine. Those are the most common amino acids, although many of the other amino acids are normally found on a collagen molecule.
Collagens are not pure materials as they have many other chemical constituents, including lipids and some minerals. Some of these impurities are carried over to the polypeptide following a hydrolysis and separation of the water soluble polypeptide. Minerals are normally present at less than 2% and usually less than 1% by weight in the polypeptide.
The Polypeptide, Hydrolysis
Although any collagen based polypeptide can be utilized in the present invention, we find that the polypeptides of high purity industrial grades collagens are the most suitable, especially the collagens of type I (type I collagens essentially come from mammalian sources), and the collagens from chicken and turkey.
About half the molecular weight will be between around 34,000 and 125,000 Daltons. See
Alpha and Beta Chains
Two basic polypeptide components are obtained during hydrolysis, called alpha and beta chains. Another component, the gamma chain, may also be obtained.
The alpha chain are components with an average molecular weight of about 95,000. The beta and gamma chains are components having respective average molecular weights of about 190,000 and about 285,000, the gamma component being similar to tropocollagen. The alpha chain is that portion of the polypeptide having a molecular weight of more than 70,000 Daltons and less than 125,000 Daltons. The beta chain is that portion of the polypeptide having a molecular weight of more than 125,000 Daltons but less than 230,000 Daltons. The gamma chain is that portion of the polypeptide that has a molecular weight of more than 230,000 Daltons but less than 340,000 Daltons. Other residual components may also be produced during hydrolysis.
According to one characteristic of the invention, the material used to prepare the recording medium or storage memory is based on a polypeptide in which the alpha/beta chain weight ratio is greater than 1 and advantageously between about 1.2 and about 2.1. It is shown in fact that, with such a ratio, the diffraction efficiency is increased, this quantity itself being defined as the ratio of the energy of the diffracted signal to the energy of the incident light. Although we have found that the weight ratio of the alpha and beta chains of greater than 1 is essential for the practice of the invention, we have also found that the high molecular weight constituents give the material its photonic sensitivity. We believe the reason for this is that during the gelation or gel formation, it is easier to gel from nonseparated polypeptide molecules (higher molecular weight constituents) that have a triple helix architecture than for a simple helix polypeptide molecules (lower molecular weight constituents) that have a simple helix, such as the alpha chain. By increasing the weight ratio of the alpha to beta chains, we achieve a lower diffraction efficiently.
If we change the origin of the collagen, for example switching from pork collagen to chicken or turkey collagen, we have a change of the optimal ratio for diffraction efficiency because the acid hydrolysis of pork skin gives a weight ratio of alpha to beta chains of 1.2 to 1.3, while acid hydrolysis of bones (chicken or turkey collagen), give an alpha to beta chain weight ratio of about 1.5. A different relationship with diffraction optimization exists also. Photonics parameters as light sensitivity depends on the choice of polypeptide molecule. The diffraction efficiency adjustment (related for instance to exposure time and photonics energy level used) will not be the same depending of the origin of the polypeptides molecules for instance it will different (slightly) between pork and chicken and turkey polypeptide.
During the acid hydrolysis of collagen, transverse bonding is not destroyed. So when alpha and beta chains are produced, gamma chains are also produced. In alkaline hydrolysis, covalent crosslinks between collagen chains are broken and more alpha chains can be produced than in acid hydrolysis. The relative percentages of the alpha, beta and gamma chains depends on the collagen and the specifics of the hydrolysis process which is controlled by the commercial manufacturer. There is a molecular weight distribution connection to the distribution of the alpha, beta and gamma chains. See
During commercial preparation of the polypeptide from collagen, the producer can exert some control over high molecular weight and low molecular weight components by removal by filtration, centrifuge separation, and differential separation by cooling the polypeptide aqueous solution. At the present time, it is not possible to produce a polypeptide comprising only the alpha, beta and gamma constituents. The hydrolysis temperature also has an effect on the distribution of the alpha, beta and gamma chains also. Lower temperature hydrolysis favor higher molecular weight fraction production, while higher temperature hydrolysis increases the lower molecular weight fractions and favors alpha chain production.
The Polypeptide Gel
The polypeptide material used according to the invention as a recording medium is in the form of a gel supported on a substrate. A polypeptide gel is a saturated form of soft material that follows the sol formation out of a liquid where water is a solvent and polypeptide is substrate. The gel can have impurities or defects. The defects can arise from the structure of the gel and the impurities can consist of foreign materials coming from the collagen. In the practice of the present invention, tolerance exists for both these criteria.
It has been demonstrated that the ability of the material to record and store, under the optimum conditions, the holograms representative of the data to be recorded depends on the quality of this gel. The viscosity and gelling power of the polypeptide influence the photosensitivity of the doped polypeptide. Thus, the viscosity and gelling power are critical for reaching optimal results of the present invention. The higher the viscosity and the gelling power of the polypeptide, the higher the energy exposure must be. The gel strength of this polypeptide gel may be defined by a quantity called the “bloom strength”. This quantity allows the number of hydrogen bonds per unit volume to be determined. It correlates directly with the polypeptide gelling power. Advantageously, the gel strength of the polypeptide lies between about 90 and about 300 bloom, and more specifically close to about 250 bloom, so as to obtain optimal recordings. The gel strength is determined by means of a gelometer, using a method according to an AFNOR NF V 59-001 or BSI BS 757 (1975) standard. The nature of the gel may also be determined by melting point, pH, impurities in the gel, molecular weight distribution, average molecular weight, and viscosity. The gel strength is measured before doping of the polypeptide with surfactant, Cr VI, hardener, plasticizer, and the like.
The viscosity of the polypeptide is also an important criterion in the present invention. The viscosity of the polypeptide constitutes a factor involved in the quality of the recording medium. The viscosity is directly related to the length of the molecular chains making up the polypeptide material. In our early investigation, we measured the viscosity of the polypeptide at between about 3 and about 4 centipoises. However, more recent results show that the viscosity is closer to around 3.5 centipoises measured by the Standard Method. The viscosity measurements were made in milliPascal seconds. Viscosity measurements were done at 60° C. with a 6.67% by weight polypeptide concentration in water. The time necessary for a 6.67% by weight polypeptide solution to flow through a capillary viscosimetric pipette by the Standard Method for the sampling and testing of gelatins was used (“Standard Method” herein). The viscosity measurements are prior to doping the polypeptide.
The polypeptide gel is formed by taking the polypeptide material, which commercially is normally in the form of solid flakes or powder, and mixing the polypeptide material in deionized water. The polypeptide is allowed to remain in the water for 2 to 10 hours. During this time, the polypeptide dry material absorbs the water and swells and forms at least a partial solution. The polypeptide is then heated to a temperature between about 40 and about 60° C. to form a polypeptide solution. The polypeptide solution is produced in concentrations from about 5% to about 10% by weight dry polypeptide. The polypeptide solution is then treated or doped with chromium VI ion as described below.
Polypeptide Doping Stage
As already mentioned, the polypeptide is doped with a chromium VI salt. The polypeptide is doped in solution with a soluble chromium VI salt solution containing 5 to about 20% by weight salt, preferably about 5 to 10% by weight salt, using water soluble salts such as ammonia dichromate, potassium dichromate, and the like. Pyridine dichromate can also be used. This is the most light sensitive of the dichromate salts, but its use decreases the shelf life of the recording medium. The dichromate salt solution is poured into the polypeptide solution (about 5% to about 10% by weight polypeptide) at a temperature from about 55 to about 60° C. The addition is a mass addition although incremental additions can also be used. The resulting doped solution is agitated, i.e. stirred. We have found stirring for 10 to 15 minutes to be sufficient. The chromium VI salt doping is done in the amount of about 5 to about 15% by weight of the dry polypeptide used, preferably about 10% by weight. The chromium VI salt doping can be done in amounts of less than 5% or in amounts in excess of 10%. When doped with the less than 5% by weight of the chromium VI salt, the doped polypeptide is not as actinic light sensitive as the polypeptides doped with a higher loading of the chromium VI salt. When doped with less than 5% by weight of the chromium VI salt, more photonic energy is required for recording than for polypeptides doped with from about 5 to about 10% by weight of the chromium VI salt. The polypeptide can be doped with up to 25 to 26% by weight of the chromium VI salt. However, at the higher loadings, surface crystallization of the doped polypeptide can occur. A loading of 25 or 26% chromium VI salt is not usable because polypeptides saturate chromium ion which renders the polypeptide virtually useless for recording for the present invention. A chromium VI ion concentration greater than 15% by weight of the polypeptide can result in saturation of the absorption of the light by the polypeptide layer. The consequence of this is the appearance of noise. Other chromium VI salt loadings may be possible, but we find that for a doped polypeptide coating on a recording medium of 30 microns in thickness, a doping of about 5 to about 15% of the chromium VI salt is quite suitable for the practice of the present invention. The final polypeptide doped solution will preferably have a concentration between about 100 and about 200 mg of chromium VI ion per 100 ml of 5% polypeptide solution to about 200 to about 400 mg of chromium VI ion per 100 mil of polypeptide solution. The Cr VI doping and all subsequent steps through development are done in the dark, although red inactinic light can be used. The Cr VI doped polypeptide is sensitive to actinic radiation or light.
It has been demonstrated that the latent image, that is to say the holographic data recorded in the polypeptide of the recording medium, is due to the intermolecular transfer of charges (electrons) from the polypeptide to the chromium VI (Cr +6), which undergoes a reduction reaction to chromium V (Cr +5). At the same time, the polypeptide is oxidized. During the development step which follows the recording step, the chromium V (Cr +5) is in turn reduced to chromium III (Cr +3), which is complexed by the polar groups of the peptide chains, forming stable bonds of a covalent nature. The chromium VI remaining unreduced in the constitutive matrix of the material is removed during fixing and washing steps with aqueous fixer and water, described in greater detail below.
Again according to another advantageous characteristic of the invention, the polypeptide doped solution used may also be hardened prior to or after the Cr VI doping by means of hardening agents, such as an aqueous chromium III solution employing a soluble Cr III salt in an amount of about 0.5% by weight of dry polypeptide. The hardening agents are intended to improve the mechanical integrity of the polypeptide. Hardening also effects the optical properties of the recording medium. The hardening product reacts with the ionized parts of the polypeptide molecule, creating covalent bonds and forming a three-dimensional network. Preferably hardening is done during fixing.
This hardening agent may consist of soluble chromium III salts or other soluble hardening agents for polypeptides such as metal ions comprising salts of aluminum, cobalt, iron, platinum, titanium, zirconium or the like, or with organic hardeners such as aldehydes (formaldehyde, glyoxal, glutaraldehyde, crotonic and succinicaldehyde, acroleine), aldehyde carboxylics (glyoxylics), polymeric aldehydes (para aldehyde), ketones (diacetyl, 3-hexene-2,5-dione, quinone), carboxylic and carbonic acid derivatives, sulfonate esters and sulfonyl halides, epoxides (butadiene dioxide, ethylene glycol diglycidic ether) aziridines, active olefins (divinyl sulfone, divinyl ketone triazines), isocyanates, carboiimides, polymeric hardeners, and the like. These other types of polypeptide hardeners have not been tested for this invention and the use of them may require some adjustments to the process with regard to concentrations of hardeners, time of treatment, temperature of treatment, and the like.
The polypeptide doped solution may be treated with a surfactant, such as a surfactant of the fluorocarbon type. The use of such a surfactant helps to reduce the surface tension of the polypeptide solution. Such a surfactant may have a formula of the semi-developed form below:
RF
in which RF denotes a stable fluorine-containing radical and X denotes a stabilizing or hydrophilic group. The surfactant improves the surface finish of the doped polypeptide layer and, at the same time, improves the coating of the latter onto a substrate, allowing it to be automated. The surfactant is a nonreactive material in the polypeptide solution that by reducing a tensile strength of the polypeptide solution provides for better coating. A 3M product: CF129 has been found quite suitable for use in the present invention. The composition of CF129 is reported to be the following: 51% potassium fluoroalkylcarboxylates, 31% water, 14% Z-Butoxyethariol, 4% ethylic alcohol. We have added sufficient surfactant to give a loading around 0.005% surfactant by weight for each 100 milliliters of the polypeptide solution. If the proper amount of surfactant is not added, the polypeptide coating or resulting layer may not glue or adhere to the substrate satisfactorily. We have found that the above amount of the 3M CF129 surfactant gives satisfactory results virtually every time. Other surfactants, such as, a surfactant that is soluble in the polypeptide solution and polypeptide gel, and that does adversely effect the exposure sensitivity of the recording medium or the quality of the stored data in the exposed and developed recording medium, can be used. A slight decrease in exposure sensitivity and quality of the stored data can be tolerated. Preferably the surfactant does not chemically react or bond with the chromium or other constituents of the polypeptide solutions and gel.
The way we conduct the doping process comprises, we first add the surfactant, then dope the polypeptide solution with the chromium VI aqueous solution, and finally add the hardener, when we harden at this stage. This order may not be crucial and it may be possible to have other orders of addition, but we have not investigated them.
A plasticizer of the glycerol type may also be added to the polypeptide solution. The plasticizer we use is a glycerol. The amount of glycerol must be controlled because its effects at low temperature (photonic data volume output is lowered and blurring can occur below 50° C.). We have added 5% by weight glycerol to the polypeptide solution. We have added it last following Cr VI doping or hardening, whichever is last. The order of addition may not be critical. We have successfully practiced the present invention without the use of glycerol or other plasticizer.
A plasticizer that is soluble in the polypeptide solution and polypeptide gel, and that does adversely effect the exposure sensitivity of the recording medium or the quality of the stored data in the exposed and developed recording medium can be used. A slight decrease in exposure sensitivity and quality of the stored data can be tolerated. Preferably the plasticizer does not chemically react or bond with the chromium or other constituents of the polypeptide solutions and gel.
The solution thus obtained following the addition, or treatment with, the dopant is then filtered and thermostated at a temperature between about 55° C. and about 60° C. for a period of about 15 to about 60 minutes for the purpose of eliminating the thermal memory of the polypeptide. As stated above, this is done in the absence of actinic light. The heated solution is then filtered. Filtering can be done with a Whatman filtering paper having 20 to 25 micrometers pores (filter no. 541). Gravity filtering has been found quite satisfactory although pressure filtration or vacuum filtration can also be employed if desire. The resulting filtered solution is then deposited on a substrate as described below.
The polypeptide is an organic material and can be an organic food for bacteria and fungi over a wide temperature range. It has been found that some bacteria rapidly attack polypeptides at temperatures between 50 and 60° C. Higher temperatures treatment are not desirable because of possible bacterial attack and possible hydrolysis of the polypeptide. Lower temperatures can be used, but temperatures of 40° C. or lower the sol gel transition point for polypeptides is reached which it makes it difficult to dissolve all the polypeptide in solution. Thus, temperatures close to 60° C. are preferred. However, to minimize bacterial attack at 60° C., it is preferred that the polypeptide solution only be maintained at this temperature for about 15 minutes at the most. It is believed that the Cr VI doping and Cr III hardening have antibacterial and antifungal properties. In our clean room, we have never noticed a bacteria attack at room temperature (20° C.) even after 3 days of storage. At higher temperature around 50° C. we have never noticed a bacteria problem.
We believe the 55 to 60° C. temperature is necessary for dissolving any last polypeptide aggregates that could have been formed at lower temperature, such as storing the doped solution in a refrigerator prior to coating. It is preferred not to store the polypeptide solution, but to go directly from swelling to the making of the polypeptide solution with the doping treatment and the coating step. It may even be better to start from the production of the polypeptide by hydrolysis and proceed all the way to the coating step.
The doped solution thus obtained is ready to be deposited, especially by coating, on a glass or plastic substrate. We have found that a polypeptide loading of about 5% by weight in the solution gives satisfactory deposition results. However, other loadings may be used, such as from about 3% to about 15% polypeptide solution.
However, prior to depositing the doped polypeptide solution on the substrate, the latter if polished glass plate or plastic plate or film it is advantageously coated with a thin layer of an adhesive, for example a hydrophilic adhesive in nature, so that the adhesive is sandwiched between the substrate and the polypeptide solution. As regards the glass substrate, this adhesive layer can consist of a solution comprising 0.5 g of gelatin and 1 ml of a 10% chromium alum solution in 100 ml of water. We have not found the adhesive coating necessary for float glass. However, adhesive coatings might be needed or desired for some glass plates, such as polished glass plates.
With regard to the plastic substrate, and especially polymethyl methacrylate (PMMA) and polycarbonate substrates, the adhesive can consist of a solution containing cellulose. More precisely, the cellulose is in the form of nitrated carboxymethylcellulose (NCMC). An adhesive solution comprises 1.5 parts by weight of methyl vinyl ether/maleic anhydride copolymer, 0.5 part by weight of NCMC and 98 parts by weight of 2-methoxyethanol has worked well. The surface of plastic plates or film can also be treated with oxygen plasma or chemical vapor disposition using plasma reactions to improve adhesion.
The use of such an adhesive layer promotes the attachment of the layer of polypeptide material to the substrate.
When a gravitational coating method is used, a suitable amount of the polypeptide solution is actually coated on the substrates; the final thickness of the coating following drying is dependent upon the concentration of the solution and the amount deposited.
We normally deposit about 6.5 ml of doped solution (5% polypeptide by weight) per 100 square centimeter of substrate surface to yield a coating or layer about 30 microns in thickness after drying.
A layer of the polypeptide recording medium solution may usefully be spread using conventional devices, such as a doctor knife, roll, nozzle, etc., or else by spinning. The polypeptide coating solution has a polypeptide loading between about 3% and about 15% by weight, preferably about 5%. The polypeptide is added in sufficient amount (a coating 650 to 700 microns in thickness to yield a layer of recording medium from about 30 to about 35 microns in thickness after drying). A 700 micron thickness for a 5% by weight polypeptide recording medium solution is satisfactory and yields a recording medium coating of about 33 microns in thickness after drying.
We believe enhanced recording capabilities could be achieved by having doped polypeptide layers approaching up to 500 microns in thickness after drying. Although layers in the 30 to 35 micron thickness range are easily obtainable, it has not been possible to obtain a homogenous coating having a thickness of up to 500 microns at the present time. In addition to the problem achieving a thick homogenous layer of the doped polypeptide on a substrate, there is also the problem of uniform drying and achieving uniform development of the “image” in a thick recording medium. Besides these two problems, a third problem arises from thick coating and that is the roughness of the exposed surface of the coating. With the coating in the 30 to 35 micron range in thickness, the surface of the coating, applied in a clean room, literally has the smoothness of a polished glass plate. Irregularities, roughness, physical defects in the substrate will reflect on the surface of the doped polypeptide. In order to obtain satisfactory results with regard to recording and reading of the recorded medium, the exposed surface of the doped polypeptide (which is protected with a transparent glass or plastic plate or varnish) must be smooth.
Alternatively, a molding operation may be carried out for thicker coatings, i.e. +35 microns. In this situation, the polypeptide solution according to the invention is deposited as a sandwich between two sheets or plates, such as two glass or plastic sheets or plates, or between a glass sheet or plate and a plastic sheet, or between a metal plate and a glass or plastic sheet or plate. One of the sheets being coated on the inner side of the sandwich with a hydrophobic coating or film, for example of the silane type, e.g. dichlorodimethysilane. For purposes of this invention, plates mean sheets and plates and sheets mean sheets and plates. The hydrophobic coating or film prevents the polypeptide solution and polypeptide gel from adhering to the sheet.
In this situation, the thickness of the final, dried coating is determined by the space or distance placed between the two faces of the sheets and by the concentration of the solution. The space or distance can be fixed by shims between the sheets. The shims can have a thickness of between about 500 and about 1000 microns.
After the polypeptide recording medium solution has been applied to the plate or sheet, the coated plate or sheet is chilled at a temperature below about 10° C. for a time of about two hours, such as on a chilled coating table, to form a gel. The plate or sheet bearing the polypeptide recording medium gel coating is detached from the coating table and dried. The chilling can be done by using a temperature regulated coating table in a temperature regulated surrounding. The drying is done in a dry atmospheric chamber. A drying temperature of about 10° C.±0.5° C. is employed. No vacuum is necessary, but a vacuum could be useful especially for thicker coatings. Vacuum drying also may be of benefit for hardened coatings. The sheet with the dried recording medium is stored at cool temperatures, such as between about 3 and 5° C. These same steps can be employed for the molded thick coatings.
The recording radiation on the recording medium according to the invention acts in the following manner.
As already mentioned, when the recording medium is exposed to light, the chromium VI ions are reduced to chromium V and chromium III ions. The latter react with the polypeptide chains and forms a covalent bond therewith. These bonds result in curing of the polypeptide, thus creating a hardness differential between the exposed regions and the unexposed regions of the recording medium. When the exposed recording medium is developed, there is a further reduction of the chromium V ions to a chromium III. The first reduction, the photoreaction reduction, is very fast. The second reduction, the development reduction, is slow. There is also a dark reaction that occurs slowly in the recording medium without light that reduces the chromium VI to chromium III. This latter reaction limits the shelf life of the recording medium. Thus, the recording medium is preferably stored in a refrigerator at a low temperature to maintain the photosensitivity. We have found that chilled (0° C.) stored recording medium kept its shelf life for more than a year. The recording medium can be stored as low as −18° C. if the recording medium is first desiccated to prevent ice formation. The recording medium is preferably stored in the dark and only exposed, if at all, to inactinic light or radiation until exposed and developed for recording purposes.
The hardness modulation creates a refractive index modulation during the “development” process. After exposing the recording medium of the invention to the recording radiation, the recording medium preferably undergoes a “development” step necessary for optimizing the optical properties of the hologram and stabilizing the exposed recording medium.
This “development” step essentially consists of treating the material in an aqueous fixer solution, a water bath[s], and then in dehydrating solutions. Thus, the irradiated or exposed material undergoes a treatment in aqueous fixer, during which the chromium +6 ions (Cr VI) that have not reacted are removed, and the chromium +5 ions (Cr V) are reduced to chromium +3 ions, leaving only chromium +3 ions (Cr III) linked to the polypeptide. After development, the exposed recording medium is stable to actinic radiation or light.
Conventional photographic (silver halide) fixers can be used. Kodak brand fixer 3000A has been found quite suitable. Before or during this “fixer” step, it is recommended to harden the hologram obtained, for example by a physicochemical process, for the purpose of optimizing the recording medium and its images' stability over time. The post photoexposure development/hardening can be carried out with conventional photographic fixers and tanning agents or hardening agents. Kodak brand tanning agent 3000B has been found quite suitable. If hardening is required after exposure, preferably the recording medium is fixed and hardened in a single step. Although hardening can be carried out during the doping stage, it is preferred to harden during fixing. One volume part of fixer is conveniently mixed with 3 volume parts of water to yield a 25% by volume fixer solution. The tanning agent or hardener is then added to this mixture at the ratio of 1 volume part hardener to 35 volume parts of the fixer solution. Other volume ratios can be utilized.
The fixing step, hardening step and fixer/hardening step are done at between about 20 and about 22° C. Temperatures outside this range can be employed but we have not tested them. We found that fixing and hardening at 28° C. made the bandwidth wider. The fixing or fixing/hardening is continued until all of the dichromate is removed (about 3 to about 10 minutes). The undeveloped recording medium is transparent and orange brown in color. Upon fixing or fixing/hardening, it becomes colorless, i.e. the orange brown coloration disappears. The fixing or fixing/hardening time is preferably between about 4 and about 10 minutes.
Other hardening agents, besides Kodak brand tanning agent 3000B, can be used. Each hardener would have to be tested to determine its effect on the exposed plate. Hardening can be measured in a number of ways including: melting point changes, scratch resistance of the polypeptide coating, resistance of the polypeptide coating to boiling, and the like. An estimated value of the most appropriate hardening can also result from the analysis of the swelling of the coating on the plate coming from the amount of water absorbed. Swelling of polypeptide layer is determined by measuring the change of weight between a water swollen doped polypeptide and the dry polypeptide. The swelling is expressed as percent increase in weight (W−Wo)/Wo %. Where Wo denotes the weight of the dry layer and W is that of the swelled layer. A polypeptide swellable up to about 300% is workable in the present invention; preferably the polypeptide is hardened so that swelling is between about 190 and about 210%. It is important to have good control of this hardening step for the final product. An infrared balance can also be used to determine degree of hardening.
If the hardness of the doped polypeptide is too low, there will be a high level of light scattering by the hologram. On the other hand, if the doped polypeptide's hardness is too high, the refractive index modulation is greatly reduced, which goes counter to the desired aim, since a possibility of multiplexing in the recording medium depends directly on this refractive index modulation.
This hardness depends on the preparation conditions of the material, such as the concentration of the hardening solution and the residence time in the hardening bath. The degree of hardening becomes more significant with increased amounts of light energy being used for the recording or exposure. The greater degree of hardening, the greater the decrease in the amount of swelling. Increased hardening also decreases the diffraction efficiency of the recording medium and shifts the Bragg angle.
Following the fixer and/or fixer/hardener treatment step, the recording medium is washed in a sequence of at least two water baths to remove the excess fixer and hardener, if present, from the recording medium. The washing step is conducted between a temperature of about 20 and about 22° C. Other temperatures can probably be used for washing, but we have not tested other wash temperatures. Each washing step takes between about 3 to about 4 minutes and is preferably conducted with agitation to enhance removing fixer and hardener, if any, from the recording medium. The washing can be extended beyond 4 minutes, but it is preferred to do for at least about 3 minutes. After the recording medium is washed, it is subject to a dehydrating step.
During the dehydrating step, alcohol or other water miscible low boiling organic solvent is used to remove water from the recording medium, giving a recording medium having high refractive index modulation corresponding to the interference fringes produced during the exposure.
This dehydrating step must be carried out gradually, so as to ensure uniformity over the entire thickness of the material, i.e. the curve of the diffraction efficiency is symmetric—inside the recording medium layer the fringe spacings are identical. The alcohol or other water miscible solvent absorbs the water and replaces the water.
The use of an alcohol bath makes it possible to remove the residual water from the polypeptide coating or layer. In order to meet the need for gradual removal of this water, it is proposed to immerse the material in four or five successive alcohol baths, containing, for example, 25%, 50%, 75% and 100% alcohol respectively, for respective times of about three minutes for the first two treatments and about five minutes for the last treatments. Preferably the recording medium is treated in two-100% alcohol baths in the last bath treatments. The dehydration is carried out at the same temperature as the fixing and hardening, namely between about 20 and about 22° C. Other bath temperatures can probably be used but we have not tested other temperatures.
Increased water bath temperatures and dehydrating bath temperatures renders the recording medium layer more sensitive to damage. If the temperature of the baths are increased, the degree of hardening of the polypeptide has to be increased. If the bath temperature is too high and the doped polypeptide has not been sufficiently hardened, the doped polypeptide will precipitate giving layer of the recording medium a milky aspect. This can interfere with the retrieval of information from the recording on the recording medium.
After the dehydration step is completed, the alcohol is removed from the recording medium by heating the plate in an oven at about 100° C. for about 1 hour. Other temperatures and heating times can probably be used. The temperature must be maintained below a limit temperature. This limit temperature is the one at which the polypeptide has a reconstruction. This reconstruction consists in polypeptide bond changes. These changes induce modifications of the photonic response of the polypeptide that will not have beyond this temperature the optimal characteristic for the recording. The alcohol removal step can be done under vacuum. Methanol, ethanol and isopropanol can be used with good effect. We found the best results were obtained with isopropanol. Methanol is not favored because of its toxicity. It appears that any low boiling inert, water miscible organic solvent can be used, such as acetone also. We prefer isopropanol because it is readily available and less toxic than methanol or acetone. Methanol vapors are very toxic. Although butanol can be used, we found it gave the recording medium small diffraction efficiency.
In the preferred embodiment, the polypeptide employed in making a recording media preferably has the low as possible amounts of lipids and unhydrolyzed proteins as well as dust and metals to ensure good optical quality. The average optical index of the polypeptides employed in the invention have been around 1.5. We have used polypeptides having optical indexes within the range of about 1.49 to about 1.52. Polypeptides having optical indexes outside this range can probably be used. The polypeptide material is clear and transparent. The optical density value of the polypeptide is significant but not critical. Low optical density is preferred. A change in the optical density will induce a modification of the diffraction efficiency. The optical density can be slightly different between the exposed plate and the developed plate. We have attempted to achieve an optical density as high as possible for the exposed image. We also attempt to achieve the greatest possible difference between the optical density of the unexposed regions compared to the optical density (OD) of the exposed regions of the plate.
After the recording medium has been dehydrated and dried, the exposed surface of the recording medium is protected. For recording medium mounted on glass plates or plastic plates, the exposed surface can be protected with a glass plate, clear transparent plastic plate, or with a varnish coating or layer. When the recording medium is deposited on a film, the exposed surface is protected with a coating or deposit of varnish. The protective plates are glued to the exposed surface of the recording medium. The glue and varnish can be UV cured. Protective plates and varnish protect the recording medium from physical damage to minimize the effect of changes in humidity.
The recording medium after the exposure development, etc., can be stored at room temperature or in a refrigerated environment. If stored in refrigerated environment, the recording medium is stored at a temperature above the freezing point of water and the crystallization point of the polypeptide, whichever is higher. When the recording medium is stored in nonrefrigerated conditions, it is stored at temperatures below the melting point of the polypeptide layer.
Ideally, the recordings are made under the same conditions that the recording medium is read. We have found that humidity of 45 to 50% at a temperature of about 21° C. quite satisfactory for recording and reading. In order to ensure reproducible results, after removing unexposed plate from the refrigerator, we maintain the plate at room temperature, i.e. the temperature at which the recording is to be done and at the same humidity as the recording medium exposed to during recording. During the recording step, recording medium should not be subject to temperature changes or humidity changes. Similarly, if the recorded recording medium is stored in refrigerated conditions, the recorded recording medium is allowed to stabilize at room temperature. The conditions of reading are preferably under the same conditions of humidity and temperature as used during the recording step.
The recorded recording medium with its protective plate or varnish is very stable and can be stored in actinic light or radiation and at room temperature without any ill effects. The recorded pate once protected can be stored for a very long time in a surrounding having a temperature ranging from 100° C. down to −20° C.
The protective glass or plastic plates are glued to the exposed surface of the recording medium employing a glue which will bond glass or plastic to the doped polypeptide. We have used a glue which has a refractive index of about 1.56. Preferably, the refractive index of the plate and glue are close to the refractive index of the doped polypeptide. Likewise, preferably the refractive index of the protective varnish is close to refractive index of the doped polypeptide. The plates are carefully glued to the exposed surface of the recording medium so that no air gaps or air bubbles form between the contact surface of the plate and the exposed surface of the doped polypeptide.
Recording Phase
The recording phase includes, inter alia, choosing the characteristics of the recording material, preparing the recording material, calculating parameters of the addressing system, and recording a light beam modulated with information onto the recording material.
Data Recording/Storage System
The display 6 comprises, for example, a liquid crystal display screen on which data is encoded in a two-dimensional pattern of transparent and opaque pixels. The data is input to the display 6 via a computer (not shown) or by other digital data or analog origins. The plurality of bits represented on the display screen of the display 6 as a two-dimensional pattern of transparent and opaque pixels is known as a data packet. The data packed displayed is derived from any source such as a computer program, the Internet, and so forth. In an Internet storage application, the packets displayed may be formatted similarly to the packets of the Internet.
The object beam 3 becomes modulated by the information to be recorded by means of reflection off of the display 6 (shown) or transmission through the display 6. The modulated object beam 3 then becomes reduced by means of a suitable lens 7 so that the point of convergence of the modulated object beam 3 lies slightly beyond storage material 8.
At the same time, the reference beam 4 undergoes various reflections off the set of mirrors 9, 10 at least one of which can rotate until the reference beam 4 comes to a series of mirrors 11 which are distributed linearly or along a circular arc and the orientation of which will modify the angle of incidence of the reference beam 4 with respect to the object beam 3, again in the region of the storage material 8. Thus, by this mechanism angular multiplexing is implemented. There is formed a diffracted optical image 8a (see
In order to be able to have information with the smallest possible dimensions for the purpose of storing it within the aforementioned storage material 8, lens 7 carries out a pseudo-Fourier transform of the object beam 3 that has undergone interference with the reference beam 4. A pseudo-optical Fourier transform is a Fourier transform for which the plane of formation of the Fourier transform has been shifted by 1 to 5% of the focal length of the lens that has generated this Fourier transform. Thus, on the exit side of this lens there is no longer the entire diffraction spectrum but only the central spot, making it possible in particular, by selecting the appropriate lens, to have a spot size of about 1 mm2. It may be shown that the information contained in this signal, coming from a pseudo-Fourier transform, is sufficient and in all cases representative of the information to be stored and subsequently retrieved.
In this case, a 1 mm2 image 8a is obtained by focusing the object beam 3 onto the storage medium 8 centered at its coordinate. Due to this interference between the two beams 3,4, a diffractive image 8a 1 mm2 in size is recorded in the storage material 8 centered at the coordinates of the matrix. Spatial multiplexing is carried out by sequentially changing the rectilinear coordinates. The object beam 3 focuses on the storage material 8 so that a separate image 8a is recorded at a unique position in the plane defined by its coordinates (x, y). This spatial multiplexing results in a 10 by 10 matrix of diffractive images 8a. Angle multiplexing is carried out by sequentially changing the angle of the reference beam 4 by means of mirrors 11. Angle multiplexing is used to create 15-20 packets of information 8b corresponding to 15 discrete variations of the angle of incidence of the reference beam. A data packet is reconstructed by shinning the reference beam 4 at the same angle and spatial location in which the data packed was recorded. The portion of the reference beam 4 diffracted by the storage material 8 forms the reconstruction, which is detected by a detector array of CCD camera 12. The storage material 8 is mechanically shifted in order to store data packets at different points by its coordinates (x, y).
Method for Positioning the Recording Beam
In angular multiplexing, two constraints must be determined. The first constraint is the location which must be determined with sufficient accuracy, in terms of the coordinates (X,Y) of the point of impact of the resulting interference between the object laser beam 3 and the reference laser beam 4 on the storage medium 8. The second constraint is the value of the angle of the reference beam with the plane of the storage medium 8 which must be determined within a predetermined precision. The tolerance within which the angle must be determined (i.e., the precision) depends on characteristics, e.g., the chemical and physical characteristics such as thickness, of the storage material used.
In order to manage these constraints, the present invention modifies the spatial positions of the laser beams, especially the reference laser beam 4, by the positioning of nodes, that is to say points of location of the various activating members involved in the construction of the writing device. The nodes are the points where the laser beam changes shape or direction. The location of these nodal points is determined from calculations carried out using software taking into account the geometrical constraints to which the write device is subject but also the characteristics of the material, e.g., chemical and physical characteristics such as thickness, within which the data will be stored.
In the following example, the number of points in the matrix of the storage medium 8 is 10×10, each point being capable of containing 15 to 20 packets. In other words, the initial conditions must firstly be defined, that is to say the base parameters, as a function of which not only the location but also the type of activators to be used will be determined. These initial conditions comprise the size of the matrix, the size of the elementary points in this matrix, the nature of the storage material and especially the choice of constitutive molecules, the process for preparing the material (e.g., wavelength sensitivity, coating method), the recording process (e.g., wavelength, temperature, humidity, nature of the substrate), and the post exposure process (e.g., nature of the baths and physical parameters: temperature, humidity).
It is also necessary to take into consideration the operating parameters consisting of: the desired time needed to access the stored information, the type of activators used, the level of miniaturization, and the level of resolution.
The level of miniaturization refers to the size of the addressing system. One embodiment, a “large” system, uses motor activated centimetric mirrors usable for high quality and rather slow recording with every mirror being in the range of a centimeter in size. Another possible embodiment, a “small” system, uses MEOMS (Microoptoelectronomechanical system) package addressing where the solid state mirrors have a surface of around 1 millimeter. The volume of all the addressing systems can range from a few liters to a few cubic millimeters. The complexity of the addressing system is transferable into a chip MEOMS or an association of several chips. A MEOMS is a solid state chip produced by micro lithography and includes micro mechanical electronics and photonics.
From these various items of data, it becomes possible to modify the dimensions of the system, especially with the objective of achieving greater miniaturization of both the recording apparatus and the reading apparatus. In fact, it becomes possible to maintain the predetermined focusing of the read beam, its positioning on the data-carrying matrix, the intensity of the read beam and the ranges of angles of incidence of the read beam at a defined point (X,Y) on the matrix. These ranges of the angles are themselves determined by the initial conditions.
The algorithms, embodied in the form of software, take into account the initial conditions in the case of a change of scale of the reading or recording device.
In step 51, a general-purpose interface bus (GPIB) is initialized. The GPIB bus (not shown) is installed in a computer (not shown) for managing the write phase. The connections between the output of the GPIB bus and the input of various components (see, e.g.,
In Action A, after checking all the connections, a reply representative of the operation of the components and of the processing of the control signals is sent to a microcomputer.
In step 52, an initial position in the x- and y-plane of the matrix 8 is determined. This step is intended to order all the axes (translation and rotation axes) to adopt the initial position. These positions correspond to the position of the storage sheet of the matrix 8, in such a way that the first point is recorded at the initially programmed point and that the first multiplexing angle is associated with this point.
In Action B, the recording conditions are normalized (e.g., control of vibration; checking that there are no errors in the program).
In step 53, the initial angle is determined. The reference beam adopts the prescribed initial multiplexing angle value, corresponding to the start of the angular multiplexing sequence, which will be set to the value of this initial angle.
In Action C, the actuators move to positions to direct the laser beam at the multiplexing angle value.
In step 54, a packet of data is sent from the computer to the display 6 (e.g., SLM or LCLV) where it is converted to an image. The data is shaped on the display according to constraints corresponding to optimization criteria such as those associated with image quality such as a maximum signal/noise ratio.
In Action D, the image of the packet of information is modulated onto the laser beam.
In step 55, a minimum delay time is determined. The minimum delay time is the minimum time needed to prevent the appearance of a noise level incompatible with quality criteria.
In action E, the reference beam 4 and the object beam 3 intersect in the storage material 8 to form an interference pattern.
In step 56, recording of a data packet occurs at a point defined by the multiplexing angle. The term “point” should be understood to mean a certain complex volume with a mean cross section of 1 mm2. The recording time depends on the mean power and on the wavelength of the laser source used and on the necessary degree of modulation to retrieve the data with an acceptable noise level. The degree of modulation depends on the degree of photosensitization of the material used for storing the data. The exposure time is obtained from response curves. These response curves represent the measure of diffraction efficiency of a holographic grating recorded in the photosensitive material.
In Action F, the angle is changed to record data at the same point in the matrix.
In step 57, the next angle is selected. There is a repetition of the 53-C-54-D-55-E-56-F procedure.
Step 58 represents the repetition loop wherein data is recorded for a plurality of angles at the same point of the matrix. The minimum number of angles corresponding to each multiplexed point in a plane is 15 and the maximum number is more than 20.
In Action G, after multiplexing over all the possible angles for the same point, the procedure passes to the next point by simply changing the (X, Y) position at the matrix.
In step 59, there is an incrementation of the position. Adjustment of the best density of points depending on the operating criteria. In the example described, the (X,Y) matrix spacing is 1 millimeter.
In action H, after having recorded a point in the matrix, the laser beam passes to the next line in this matrix and operations B to G are repeated.
Experiments have demonstrated that the number of multiplexing angles depends on various parameters, including, of course, the nature of the material, that is, the material's diffraction efficiency and ability to limit crosstalk effects.
Flow Chart for Write Phase
As shown in
At step 116 the chosen characteristic of the recording material refers to the chemical concentration. This concentration will play a part in determining the optimal level of photonic energy necessary for having an optimal diffraction efficiency. At step 117 for a given concentration range there is a related exposure time range. At step 118, the selected material thickness and chemical concentration will determine the optimal angles of multiplexing. At step 119 to obtain effectively the optimal result it is necessary, in the post processing, to use the appropriate bath with related time and temperature of processing. In step 120, after all of the preceding steps are done, these steps will result in an optimal data storage system operating for a specific angular multiplexing and matrix distribution of the multiplexed recorded points.
Material Tolerancing
The diffraction efficiency is measured by means of a photodiode 36, using the set-up described in
Our approach relies on the fact that the output packet light intensity is only varying slowly with addressing angle variation in a given range. That is to say that the signal remains roughly the same when an angular addressing error exist, for instance, as may be created by a dithering of the scanning system. This allows the use of a fast addressing device. A fast addressing device generally has an angular addressing error that is larger than a slower addressing device.
Angular tolerancing for the addressing device is evaluated by measuring the diffraction efficiency at different angles. To obtain this measurement, the storage plate to be tested is mounted on a rotating bench controlled by a computer. The input beam is referenced through the appropriate angular measuring system. The output intensity is automatically measured at different angles. The angular variation steps are {fraction (1/10)} of a degree.
By this method, it has been verified that for an error in angle of {fraction (2/10)} of degree, there is a variation of diffraction efficiency of less than 1%. This difference is not significant for having an effect on the signal quality level. This signal can be applied to a CCD camera that operate with a response accurate with an error of 1%.
This can be compared to other diffractive storage media, such as photorefractive crystal material where an angular multiplexing angle step is about for instance 0.001 degrees and where an angular error cannot be higher than the half of the angular spacing for instance 0.001/2 degrees. Above this last angular value significant noise occurs because there is crosstalk caused by several of the subholograms being read at the same time.
In the present invention, tolerancing can be controlled by an appropriate thickness selection, by index modulation, and adjustment in the chemical processing. So it is possible to obtain a material adapted to a given addressing specificity by molecule selection, and an adapted wet processing. A good formula to represent this possibility is:
q˜L/d
where q is the angular bandwith;
The reading phase includes extraction of the signal content from the storage material.
Node Addressing Design
The optical elements at node 2 focus the laser beam 15a onto node 3. The location of node 2 is calculated based on the positions of the other nodes in such a way that the beam's focal point lies on a point of node 3. Node 2 is not a dynamic node.
Node 3 is a dynamic node. The optical elements of node 3 route the laser beam 15a dynamically to node 4. The rotation of the laser beam 15a is around a static axis. The laser beam 15a will move following every step calculated out of the point separation (vertical spacing between points).
The location in space of node 4 is stable. Node 4 supports beam defocusing that is calculated in such a way that the beam emerging from the node will be collimated. This is a static node.
Node 5 rotates the laser beam around one axis that is located in such a way that the routing to node 6 will be possible. Node 5 is programmed for sending the laser beam 15a on the target 8 in such way the beam will always reach the node 6 after the node 5. Node 5 is a dynamic node.
Node 6 implements a dynamic angular position of the laser beam 15a. The beam 15a is rotated around an axis, and the rotation is synchronized with node 5 in such a way that the beam will always reach the matrix 8. The accuracy of the pointing will depend on the accuracy of the other nodes, 10−2 mm is normal.
Node 5 includes an actuator that angularly rotates the laser beam around one axis that is spatially located in such a way that the laser beam will reach node 6. Node 6 include an actuator that will angulary rotate the laser beam around an axis that is spatially located in such a way that the laser beam coming from node 5 will reach node 6. The laser beam output from node 6 will reach the matrix of points constituting the storage medium 8 with a selected angle and axis specific geometrical location. In the plane of the memory, every packet has a xy location on the memory plate and a specific angle of beam addressing. So the addressing is the result of the nodes positioning (spatial) and of the angular selection that is programmed out the recording x y position and multiplexing angles. As a result of the combination of the spatial location of nodes 5 and 6 and the rotation axis positioning and programmed actuators angle selection and positioning of mirrors with an appropriate programming and computer control, the packet will be addressed with the laser beam positioning on the point matrix of the memory plate 8 with the angle corresponding to the selected packet to be read.
The rotation angles and geometry in this nodal system is configured so that there is access to every data packet. Every packet is reached within less than 1 ms. using, for instance, micro galva actuated mirrors implemented in the nodes. After hitting the matrix 8, the beam 15a will deliver one packet of data. The resulting beam is focused by imaging lens 8b onto CCD camera 8c which has a number of pixels adapted to the desired resolution.
Apparatus for Control of the Read Beam
Computer 106 under the control of software 108 sends signals to the activators at one or more nodes. The software 108 receives information via a connection 105 from the activators 102.
The laser beam 15a is directed by the nodes onto the storage medium 8 and from there focused by imaging lens 8b onto CCD camera 8c which has a number of pixels adapted to the desired resolution. The digital output of CCD camera 8c is further processed by the computer 106.
Addressing-Read System
In
The addressing read apparatus 14 of
As shown in
Referring to
where
The focal lengths f16 and f18 must satisfy this relation and their choice depends on the size of laser source beam output. The distance between the lens 16 and the mirror 17 must be equal to f16 because the laser beam must be focussed on the mirror 17.
Optical element 17 (node 3) is static having one rotation axis that rotates around its horizontal axis.
The center of mirror 18 is located at a distance f18 from the center of mirror 17. The axis of symmetry of mirror 18 must be orthogonal to the rotation axis of mirror 17. The horizontal axis intersection must be on the laser focus point that is located on mirror 17.
The beam coming from mirror 18 is collimated having a diameter of 1 mm. The laser beam scans one column of memory device matrix 8 by rotation of mirror 17 around its horizontal axis.
During matrix recording, the vertical distance between two consecutive points is 1 mm. The rotating angle of mirror 17 can be calculated to scan any point in one column. The relation is:
To read all packets in one point, different angles combination implemented on mirror 19 and mirror 20 must be found. The main constraint here is to keep stable the spatial positions for mirror 19 and mirror 20. So, they have just one rotation possibility around the vertical axis.
The laser beam coming from mirror 18 will be reflected by mirror 19, then by mirror 20. This laser beam will hit one matrix point with a specific angle to read a specific packet. The mirror size implemented on mirror 19 must have at least 1 mm of width because the laser beam size is 1 mm. The vertical size of the mirror is 11 mm high so as to make it possible to read a column completely which contains 10 points (point size=1 mm2).
All laser beams coming from mirror 18 must be orthogonal to the vertical axis which is the rotating axis of mirror 19. The vertical rotating axis of mirror 20 must be parallel to mirror 19.
The mirror vertical size of mirror 20 is 11 mm. The mirror width must respect those conditions:
All these conditions must be satisfied respected and the distance between mirror 19, mirror 20 and the matrix 8 must be as small as possible.
To find an optimized size and position of the mirror 19, 20 and the matrix 8, simulations were done by using a CAD/CAM software package, e.g., Code V optical CAD/CAM Software from Optical Research Associates. The result of CAD/CAM optical simulations are respective positions of the mirrors 19, 20 and the matrix 8. The CAD/CAM simulations give also angles values combination for the mirrors 19, 20. These angle values correspond to multiplexing angle values used in matrix recording and the size of points number in matrix recording (10×10 points with at least 15 packets per point).
In an alternative form of the embodiment of the read device 14 of
In
Because of the relatively small angle of diffraction available at the exit of such an acoustooptic material 21, 22, a two-dimensionally blazed grating 23 is oriented so that the angle of incidence of the beam is such that the diffracted beam (of order 1 or −1, depending on the gratings used) exits the grating at an angle close to the grazing angle (the grazing angle being at 90° to the normal to the surface of the grating).
Thus, as shown in
Consequently it may be understood that, by varying the vibration frequency of the piezoelectric crystal associated with the acoustooptic component(s), it becomes possible to modify, very rapidly, the desired orientation of the grating within the rows and columns of the data-carrying matrix 8. The limiting factor then becomes the MEOMS or the micromirrors which act on the angle of incidence of the read beam at the matrix 8.
In light of the foregoing, many advantages of the present invention may be appreciated. Firstly, and taking into account the storage material used on the one hand and the recording and addressing procedure on the other, it becomes possible to very significantly increase the amount of information that can be stored in packets within an entity of relatively small physical size.
This result can also be obtained by using low-power read or recording devices, allowing the system to be miniaturized, in formats broadly compatible with that of the recording and storage devices known hitherto, or may even be greatly reduced in size compared with the latter.
Finally, because of the components used and because of the particular choice of storage material, access to the stored information can be carried out rapidly, without the need for devices which are expensive or difficult to use.
Software for Positioning the Read Beam
In angular multiplexing, the read beam is positioned in order to access a data packet contained at a defined point (X,Y) in the storage medium at the corresponding addressing angle. A scan is then made to retrieve the entire series of points making up a horizontal line in the medium along the OX axis. This process is repeated by incrementing the OY axis to scan a new line along the OX axis.
The read procedure is similar to the write procedure, in that they both use the same principle of nodal points. Thus, an activator or a member for shaping the read laser beam is placed at each node 102 of the system 100. The reading procedure is carried out with a greater degree of tolerance than the recording procedure. However, the laser source used for reading does not need to be as powerful as the laser source used for recording. Consequently, it is possible to use a very compact laser source of the solid-state type for the read process.
Read beam 15a is directed and shaped by one or more transformation nodes 102 located in an optical path of the read beam 15a to one of a plurality of points defining a matrix 8 on the storage medium as determined by one or more initial storage conditions and one or more operating parameters.
The initial storage conditions include the size of the matrix, the number of points of the matrix, and the physical characteristics of the polypeptide material. The physical characteristics of the polypeptide material include a selection of constitutive molecules and results from a process for preparing the polypeptide material. In the selection of a molecular arrangement, there are hundreds of thousands of molecules to choose from. Proteins to some extent can be considered to be polymers and are structured like monomers associated to each other.
The process for preparing the polypeptide material determines a wavelength sensitivity of the polypeptide material and includes a coating method. The physical characteristics of the polypeptide material are determinable by a recording process. The recording process is defined by at least one of the following parameters: light wavelength, temperature, humidity, and the physical characteristics of a substrate of the polypeptide material. The physical characteristics of the polypeptide material further include a post exposure process. The post exposure process is defined by factors such as the physical characteristic of baths and physical parameters such as temperature and humidity. The operating parameters include the desired time needed to access the storage medium, the type of activators used, the level of miniaturization, and the level of resolution.
The incident read laser beam 15a is modulated by means of one or more transformation activators 102 lying in the optical path of the beam. The activators 102 consist of dynamic devices typically consisting of mirrors or micromirrors associated with a dynamic component. They may also consist of acoustooptic components associated with a diffraction grating, or else Kerr or Pockels cells. One of the major difficulties confronting the present invention is how to position the dynamic devices in space and, as a corollary, how to control their orientation.
For this purpose, both for positioning and for orienting, software 108 has been developed in relation to the present invention for integrating a certain number of these items of data, among which are the constraints in terms of the nature of the wavefront and the size of the point of impact of the read beam.
The results of the computations performed by this software thus make it possible to accurately determine the positions of each of the activators 102. The activators 102 are divided into groups: the stationary components, consisting especially of the lenses, the parabolic mirror, the CCD camera for receiving the information read out and the laser source; and the moving components, and especially the mirrors or equivalent members.
According to one fundamental characteristic of the present invention, taking into account the material used, the tolerance necessary in terms of excitation or modulation of the read wavefront is relatively large. Thus, it becomes possible to use, as devices for activating the wavefront, systems already known for doing such and capable of achieving, at high speed, the desired modulation of the read beam wavefront and, as a corollary, of retrieving the desired data packet. For example, when the recording results from angular multiplexing, the angle of incidence of the read beam on the information medium at the point of defined coordinates (X,Y) may vary by a value within about one tenth of a degree, something which hitherto was not possible with storage and storage materials. This great tolerance means that the speed of access to the coded and stored information can be very significantly increased.
Calculation Positions of Transformation Nodes
In
An example is now given for the case where the transformation nodes 1-6 are the nodes of the read apparatus of
The simulation of the optimized positions for the transformation nodes (OBJ, STO, NODE5, NODE6, IMG) is entirely defined by the computed values of the spatial and angular coordinates. The spatial coordinates for a point on the (x, y, z) axis is defined in the computer program by the variables: XDE, YDE, and ZDE. A unique angular coordinate for a spatial point is given by the variables ADE, BDE and CDE.
According to the particular embodiment of the invention, the angular variation of the reference beam with respect to the normal to the plane formed by the storage material varies in steps of 2° between two extreme values lying between 10° and 38°. Thus, 15 angular directions corresponding to 15 possible ways of storing different images for a given (X,Y) position are used.
The energy used to store the information, and especially the energy needed for the reduction reaction affecting the chromium VI ions contained in the constitutive material, is relatively low and typically about a few millijoules/cm2. For such an energy, the write or recording time is also relatively short, typically about 10 milliseconds.
According to the particular embodiment described, when the laser beam has undergone a discrete variation in steps of 2° between the two above-defined extreme values, the plate supporting the storage material according to the invention undergoes a translation of 1 mm until coming to the adjacent write or recording area. The recording operation is repeated for this new position. The reference laser beam undergoes a new discrete variation in steps of 2° corresponding each time to writing a new packet into the storage material. At the end of an entire line in the material, the latter resumes its initial position by a suitable support plate system and, as a corollary, undergoes a height translation along OY in order to start the process of recording the next line along OX, and so on.
Flow Chart for Read Phase
As shown in
At step 215, the beam is then configured to read the information from the matrix 8 at a given multiplexing angle. The optics is adjusted so that the beam has a 1 mm size. The term “Laser beam reshape” means that the laser beam size fits as exactly as possible the size of one point. The laser beam intensity has to be as uniform as possible around a Gaussian profile.
At step 220, the address system is arranged as a group of activators that are spatially organized to directionally process the beam in such a way that a targeted point will be reached by the laser beam at a specific angle and with a satisfying geometrical accuracy.
At step 225, the dimensions of the address system are determined in order to minimize its size. For example, the size of the system could be medium using gaiva mirrors or small using MEOMS. The dimensions of the address system depends on the size of the directional beam processor. With MEOMS it will be miniaturized but it will be “laboratory size” with motor activated mirrors.
At step 230, the read beam is then directed to the storage medium 8 at a precise point and angle wherein it interacts with the matrix 8 to retrieve the information at that point and angle. After the processing steps the laser beam is going to hit the selected point in the XY plane with a selected angle at a given time.
At step 235 is concerned with the extraction of the signal content is extracted from the matrix memory.
At step 240, the storage medium is used in various applications, for example defense 241, networks 242, consumer products 243, and computers 244. The digital data will be packaged differently according to the targeted applications.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP01/09025 | 7/20/2001 | WO |
