Patent Application
20070242592
This invention relates to a 3-dimensional optical data storage and retrieval system.
The following publications are referred to in the present description:
The computerized era has raised the need to provide reliable means for storing large amounts of data. Ever-growing amounts of information are nowadays stored in personal and commercial computers, and with progress of technology, this demand will surely grow. One approach to fulfill such a need is to use optical methods for the storage of data, since an optical memory makes it feasible to pack information as binary digits at very high density. Furthermore, the stored information could be maintained undamaged for long periods of time, with no apparent loss of information.
U.S. Pat. No. 5,592,462 (Beldock) describes a three dimensional system for optical data storage and retrieval. According to this publication, incorporated herein as a reference, the data is stored and retrieved by irradiating the storage medium with two interfering light beams. The use of two light beams allows the definition of the particular portion of the volume being written or read at every instance.
U.S. Pat. No. 5,268,862 (Rentzepis) describes an active medium for use in a system of the kind describe by Beldock. The medium makes use of two forms of a spirobenzopyran derivative to represent the two binary digits. However, the memory is maintained at a temperature lower than room temperature, typically at −78° C. Thus writing, storing the written information and reading is done at this low temperature. Raising the temperature will erase the entire stored information, as the active isomer is stable at room temperature for only 150 seconds. The maintenance of such a memory is expensive and cannot be used commercially.
There is thus a need for a low-cost, stable and efficient optical memory.
According to one aspect, the present invention provides a three-dimensional memory apparatus comprising an active medium, said active medium being capable of changing from a first to a second isomeric form in a multiphoton process; said memory apparatus being characterized in that said active medium comprises diarylalkene derivatives, substituted at least on the double bond. Preferably, one of said first and second isomeric forms is a cis form and the other one is a trans form.
The active medium of the present invention may be embedded in a supporting matrix, which may be a polymer, and the active medium is chemically bound thereto. In this respect the active medium itself may be a monomer that can be polymerized or co-polymerized to obtain the desired polymer three dimensional memory apparatus. In case the active medium is bound to a polymer, the active medium being capable of changing from a first isomeric form to another isomeric form in a multiphoton process. Hence an active medium according to the present invention should be understood as a plurality of molecules or active groups of polymers confined within a given volume that are capable of changing their states from one isomeric form to another wherein an isomeric state represents information.
The invention is further directed to a three-dimensional optical data carrier. This is an optical data carrier in the form of a solid disk comprising an active medium as defined above which is a removable object in the sense that it can be taken out and inserted upon desire in an appropriate three dimensional memory apparatus. The active medium of he optical data carrier may be embedded in a supporting matrix or chemically bound thereto such as being bound to a polymeric supporting matrix.
The information stored by the apparatus of the present invention is stored as a series of data units represented by the different isomeric forms residues. According to one embodiment, the data units are binary digits, and each portion of the active medium comprised in the volume represents a 0 or a 1. In this case, there is set a high concentration residue threshold and a low concentration residue threshold of the isomeric forms of the active medium. Volume portions having a concentration above the high ratio threshold represent 1 digit, while portions having a concentration below the low ratio threshold represent the other digit. For example, a volume portion having 70% or less active medium of the first isomeric form may represent 0, while a volume portion having 20% or less of active medium of the same isomeric form may represent 1. Alternatively, the data representation is analog, and each concentration represents a predefined data unit. Generally, the control of the different forms in a volume portion enables also other data encoding schemes that are well known in the art
Diarylalkene derivatives according to the present invention are of the general formula Ar1C(R1)═C(R2)Ar2, wherein R1 and R2 are not hydrogen and wherein Ar1 and Ar2 are optionally substituted aryl groups. In particular, R1 and R2 are electron acceptors which may be selected from pyridinium and ammonium salts, alkenyl or alkynyl groups, azobenzenes, nitrites, halides, carboxylic acids, derivatives thereof or their esters or nitro compounds. The substituents on the Ar1 and Ar2 are electron donors which may be selected from alkyls, alkoxy groups, ethers and thioethers, alcohols, thiols and their salts, amines, biphenyls, and heteroaromatics.
The three-dimensional memory apparatus according to the present invention may comprise a monolithic bulk (plate) or a single thin layer of active medium where the thickness allows only one data unit to be inscribed. The thickness of such a layer is determined by factors such as focusing and signal collection from such a layer. Typical focus size is less than 10 microns. Production capabilities also dictate the layer thickness which is typically less than 50 microns, however can be also lower than 10 microns. A plurality of such thin layers of active medium as defined above where more than one data unit of information may be recorded and differentiated may also be produced. The active medium is capable of changing from a first to a second isomeric form in a multiphoton process. Such a three-dimensional memory apparatus is characterized in that its active medium comprises diarylalkene derivatives. In case the diarylalkene derivatives are bound to a polymer then the active medium is capable of changing from a first to another isomeric form in a multiphoton process.
Preferably, the apparatus according to the invention further comprises means for reading the data units from the isomeric forms of the active medium in different portions of said active medium.
Preferably, the isomeric form of a specific portion of the active medium is to be controlled (in the writing process) and determined (in the reading process) by directing towards the portion a light beam that interacts therein.
According to another of its aspects, the invention provides a method of producing a three-dimensional pattern of different response to multiphoton interaction
The invention is further directed to a method of producing a three-dimensional pattern of different response to multiphoton interaction:
According to yet another aspect, the present invention is directed to a method of identifying the isomeric form residue of an active medium in a portion of a three-dimensional pattern producible in a method as described above. The method comprising directing to said portion of the pattern a light beam causing predominantly in said portion fluorescence, reading the intensity of the produced fluorescence, wherein said fluorescence being substantially different in intensity in one isomeric form than the other, and thereby identifying the isomeric form residue of the active medium in said portion.
According to yet another aspect, the present invention is directed to a method of identifying the isomeric form residue of an active medium comprising diarylalkenes in a portion of a three-dimensional pattern producible in a method as mentioned above, the method comprises directing to said portion of the pattern a light beam causing predominantly in said portion multiphoton interaction, and reading the intensity of the produced interaction
In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
As mentioned the present invention concerns a three-dimensional memory apparatus whose active medium is comprised of a diarylalkene derivative that is capable of changing from a first to a second isomeric form in a multiphoton process. Diarylalkene derivatives according to the present invention are of the general formula Ar1C(R1)═C(R2)Ar2, wherein Ar1 and Ar2 which could be the same or different, are independently substituted or non-substituted aryl groups. If they are substituted, they are preferably substituted with electron donors. Non limiting examples of electron donors are alkyls, alkoxy groups, ethers and thioethers, alcohols, thiols and their salts, amines, biphenyls, and heteroaromatics. R1 and R2 which are the same or different, are not hydrogen, and are preferable electron acceptors. Non limiting examples of electron acceptors are pyridinium and ammonium salts, alkenyl or alkynyl groups, azobenzenes, nitriles, halides, carboxylic acids, derivatives thereof or their esters or nitro compounds. More specifically, R1 and R2 are nitriles, C1-8β-carboxylic acids or their esters, 2-hydroxyC1-8alkyl, 2-fluoroxyC1-8 alkyl, 2-nitroC1-8alkyl, 2-cyanoC1-8alkyl or a nitro group. Most preferably the substituents on the aryl rings are C1-4 lower alkyls or O—C1-4 alkyls and the R1 and R2 are chosen from cyano. The use of such diarylalkene, derivatives or mixtures thereof allows the memory apparatus of the invention to be fully operative in room temperature, due to the great thermal stability of each of their isomeric forms. The two isomeric states of the diarylalkene are stable for long periods of time, and essentially no spontaneous thermally induced inter-conversion of one isomeric form to the other occurs. This stability further enables the memory apparatus to be of a kind that may be written and read many times, e.g. it may be a rewritable memory as well as a WORM (=Write Once Read Many).
The compound of formula (III) is a diarylalkene having electron acceptors on the double bond and electron donors substituents on the two aryl groups, that serves as an active medium. The compound of formula (II) is an example of a compound of the active medium which already comprises a part rendering the compound a monomer. It is a diarylalkene having electron acceptors on the double bond and electron donors substituents on the two aryl groups, that serves as an active medium. It is further bound through a spacer to a polymerizable group turning the active medium into a monomer that can be polymerized into a polymer. Turning to
The cis and trans isomers of the compound of formula (II) were found to be stable to visible light and I.R. irradiation and further to isomerizes by bi-photon process. As may be seen in
The optical data carrier apparatus is linearly transparent to the multiphoton interacting light; hence such interaction does not interfere with recording or retrieving of information. It should be understood that as indicated by quantum selection rules, the linear optical reaction of the first and second isomeric forms to irradiation is different than their multi-photonic interaction with irradiation, e.g. by exposing the medium to irradiation suitable for bi-photonic interaction one obtains interactions which are not achievable with single photon interaction. Thus the multiphoton process according to the present invention may be two-photon excitation and subsequent fluorescence or it may be a different form of non-linear interaction such as one of the family of four wave mixing interaction or different forms of Raman scattering detection. The concentration of the isomeric forms in a given volume portion represents a data unit. Hence according to the present invention one may utilize the 3D optical memory to record a 3D mark in the volume and retrieve it. Once the method of recording such marks and retrieving information about their isomeric form is given, there are numerous techniques to encode data which are well known in the art. Turning to
The alternative beams 21a and 21b are combined into one beam by a non-polarizing beam splitter 14 and directed into the focusing system. In a first embodiment the focusing lens is a standard DVD lens (NA=0.65) which is SA corrected for approximately 100 microns around the depth of 0.6 mm. In a second embodiment a lens system that is both chromatically corrected and corrected for spherical aberrations is used. Such for example is the Olympus LCPlanFI lens. If additional requirements are applied such as the control of the distance between the foci of different wavelengths and low weight then a lens system disclosed in PCT/IL03/00803 may be used. It should be noted that according to the present invention one may record a mark and continuously obtain a signal in a 3D optical disk in a many pulse sequence or only record a mark with a one pulse (Examples 5 and 6, respectively). The energy in the reading performed with the reading performed with the continuous recording (many pulse sequence—Example 5) is different than the energy in the recording without reading (one pulse—Example 6) clearly demonstrating that there are two threshold energies.
Data recording is a non linear process performed with one beam. The process is a multi-photon process of absorbance of photons having a first energy threshold. In a preferred embodiment, data retrieval (reading the recorded data) is also a two photon process done with one beam.
In a preferred embodiment of the invention, the isomeric forms of the active medium have a substantially different absorption coefficient for absorbing energy of second threshold energy, thus allowing the retrieval of the information in a manner similar to its preferred manner of writing, described below.
The substituents on the various double bonds determine in part the I.R spectrum and the Raman scattering pattern of each of the possible isomeric forms of the active medium. The I.R. spectra and the Raman scattering of the substituents will be significantly different in each of the different isomeric forms of the diarylalkene derivatives (bound or non-bound to the polymer). The Raman scattering may be detected by Coherence Anti-Stocks Raman Spectroscopy (CARS), by Raman Induced Kerr Effect Spectroscopy (RIKES) or a variation thereof.
Pure trans-4-bromostilbene diethylacetate was dissolved in acetonitrile and irradiated with a mercury lamp having a Hg filter. The U.V. spectrum displayed in
Pure trans-stilbene dipropanol was dissolved in acetonitrile and irradiated with a mercury lamp having a Hg filter. The U.V. spectrum displayed in
trans-stilbene diethylacetate was dissolved in acetonitrile and irradiated with a mercury lamp having a Hg filter. The displayed U.V. spectrum (
Manufacturing of a 3-dimensional memory apparatus comprising as the active medium a compound of formula (II). A mixture of methyl methacrylate, (89.03% w/w), an radical initiator 2,2′-azobis(isobutyronitrile) (0.97% w/w) and a compound of formula (III, n=3) (10.0% w/w) are stirred at 65° C. for 60 minutes where the polymerization is initiated. The mixture is then filtered, degassed and filled into a mold. Polymerization continues at 65° C. for 24 hours after which a translucent monolithic bulk is obtained. The bulk is a polymer that comprises photoactive pendant groups that are highly susceptible to interaction with light.
Recording a mark and obtaining a signal with many pulses in a 3D optical disk.
An acrylate based disk having as its active medium 10% weight of a compound of formula II was used.
Recording a mark with one pulse in a 3D optical disk. An acrylate based disk having as its active medium 10% weight of a compound of formula II was used.
The signal from the mark is lower than the signal from the surrounding volume. The modulation depth of the recorded mark formally is defined as
where Pmax is the signal from space (pointed out by the dotted line) and Pmin is the signal from a mark (pointed by a circle). The modulation of recorded mark in this example is about 8%.
| Number | Date | Country | Kind |
|---|---|---|---|
| 135309 | Mar 2000 | IL | national |
This application is a continuation in part of U.S. application Ser. No. 10/240,420 dated Mar. 28, 2001 and continuation in part of U.S. application Ser. No. 10/505,109 dated Feb. 20, 2003 wherein these two applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10240420 | Jun 2003 | US |
| Child | 11285210 | Nov 2005 | US |
| Parent | 10505109 | May 2005 | US |
| Child | 10240420 | Jun 2003 | US |
