Static information storage and retrieval – Information masking – Transparency
Reexamination Certificate
1995-05-30
2003-08-19
Fears, Terrell W. (Department: 2824)
Static information storage and retrieval
Information masking
Transparency
C365S119000
Reexamination Certificate
active
06608774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns three-dimensional optical memory apparatus and memory media, and methods of using such apparatus and media. The present invention particularly concerns (i) three-dimensional volumes of an active, radiation-sensitive, medium that is selectively both alterable and interrogatable by use of at least two intersecting beams of radiation, thereby to form a radiation memory; (ii) the manner of using the intersecting radiation beams and the physical and/or chemical effects of such use; (iii) the construction of binary-stated informational memory stores, three-dimensional patterns, and/or three-dimensional displays based on these effects; (iv) the manner of selectively directing radiation beams to intersect within three-dimensional volumes for purposes of addressing selected domains within such volumes, particularly to serve as an addressable memory store; and (v) the manner of selectively impressing information on, or extracting information from, one or more intersecting beams of radiation in order that such information may be radiatively written to, or radiatively read from, a three-dimensional volume memory.
2. Background of the Invention
2.1 The General Requirement for Information Storage in Memories
The need for computerized data storage and processing has been increasing, in the past decade, at a high rate. In response to this need, semiconductor-based computer technology and architecture have greatly improved. However, barriers to further reducing the size and price of semiconductors may now be inhibiting development of even higher performance computers, and the more widespread use of high performance computers.
The major determinant of the size and price of high performance computers is the memory. The data storage requirements of new high performance computers, circa 1994, are very great, typically many gigabytes (10
12
bits). New and improved, compact, low cost, very high capacity memory devices are needed. These memory devices should be able to store many, many gigabytes of information, and would desirably randomly retrieve such information at the very fast random access speeds demanded by parallel computing.
An optical memory offers the possibility of packing binary-stated information into a storage medium at very high density, with each binary bit occupying a space only about one light wavelength in diameter. When practical limitations are taken into account this leads to a total capacity of about 10
11
bits for a reasonably-sized two-dimensional optical storage medium—the amount of information contained in about 3000 normal size books. A comparison of the optical memory to existing types of computer memories is contained in the following Table 1.
TABLE 1
MEMORY
ACCESS
TYPE
CAPACITY
TIME
COST
TAPE
10
10
bits
100
sec
10
−5
¢/bit
DISK
10
8
bits
300
msec
5 × 10
−2
¢/bit
DRUM
10
7
-10
8
bits
10
msec
10
−2
¢/bit
CORE
10
6
bits
1
&mgr;sec
2
¢/bit
SEMI-
10
5
bits
100
nsec
20
¢/bit
CONDUCTOR
OPTICAL
10
9
-10
12
bits
10
nsec
10
−3
-10
−4
¢/bit
The present invention will be seen to be embodied in an optical memory system. Any optical memory system, whether three-dimensional (3-D), four-dimensional (4-D), or otherwise, is based on light-induced changes in the optical, chemical and/or physical properties of materials.
2.2 Optical Recording Media, and the Use Thereof in Optical Memories
At the present two general types of optical recording media exist, namely phase recording media and amplitude recording media. Recording on the media of the first type is based on light-induced changes of the index of refraction (i.e., phase holograms). Recording on the media of the second type is based on photo-induced changes in the absorption coefficient (i.e., hole burning).
Volume information storage is a particularly attractive concept. In a two dimensional memory the theoretical storage density (proportional to 1/wavelength &lgr;
2
) is 1×10
11
bits/cm
2
for &lgr;=266 nm. However in a 3-D memory the theoretical storage density is 5×10
16
bits/cm
3
. Thus the advantages of 3-D data storage versus previous two dimensional information storage media become apparent.
Volume information storage has previously been implemented by holographic recording in phase recording media. Reference F. S. Chen, J. T. LaMacchia and D. B. Fraser,
Appl. Phys. Lett.,
13, 223 (1968); T. K. Gaylord,
Optical Spectra,
6, 25 (1972); and L. d'Auria, J. P. Huignard, C. Slezak and E. Spitz,
Appl. Opt.,
13, 808 (1974).
The present invention will be seen to implement volume writable-readable-erasable optical storage in a phase recording medium that is also, coincidentally, an amplitude recording medium. One early patent dealing with three-dimensional amplitude-recording optical storage is U.S. Ser. No. 3,508,208 for an OPTICAL ORGANIC MEMORY DEVICE to Duguay and Rentzepis, said Rentzepis being the selfsame inventor of the present invention. Duguay and Rentzepis disclose an optical memory device including a two-photon fluorescent medium which has been solidified (e.g., frozen or dispersed in a stable matrix, normally a polymer). Information is written into a selected region of the medium when a pair of picosecond pulses are made to be both (i) temporally coincident and (ii) spatially overlapping within the selected region. The temporally-coincident spatially-overlapping pulses create, by process of two-photon absorption, organic free radicals which store the information at an energy level intermediate between a fluorescent energy level and a ground state energy level. The free radicals store the desired information for but a short time, and until they recombine. The information may be read out by interrogating the medium with a second pair of coincident and overlapping picosecond pulses. In the case where the medium is frozen solid, interrogation may also be accomplished by directing a collimated infrared light beam into the selected region, thereby causing that region to liquefy and permitting its contained free radicals to undergo recombination. In each of the aforementioned cases, the interrogation beam causes the interrogated region to selectively fluoresce in accordance with the presence, or absence, or free radicals. The emitted radiation is sensed by an appropriate light detector as an indication of the informational contents of the interrogated region.
This early optical memory of Duguay and Rentzepis recognizes only that two-photon absorption should be used to produce excited states (e.g., singlet, doublet or triplet states) of an radiation-sensitive medium over the ground state of such medium. These excited states are metastable. For example, one preferred fluorescent medium is excitable from ground to a singlet state by process of two-photon absorption occurring in about 10
−15
second. The excited medium will remain in the singlet state for about 10
−8
second before fluorescing and assuming a metastable triplet state. This metastable state represents information storage. Alas, this metastable state will spontaneously decay to the ground state by fluorescence after about 1 second (depending on temperature). The memory is thus unstable to hold information for periods longer than about 1 second. It should be understood that the fluorescent medium of the Duguay and Rentzepis memory is at all times the identical molecular material, and simply assumes various excited energy states in response to irradiation.
Another previous optical system for accomplishing the volume storage of information, and for other purposes, is described in the related series of U.S. Pat. Nos. 4,078,229; 4,288,861; 4,333,165; 4,466,080; and 4,471,470 to Swainson, et al. and assigned to Formigraphic Engine Corporation. The Swainson, et al. patents are variously concerned with three-dimensional systems and media for optically producing three-dimensional inhomogeneity patterns. The optically-produced 3-D inhomogeneity patterns may exhibit (i) contro
Fears Terrell W.
Fuess & Davidenas
The Regents of the University of California
LandOfFree
Two-photon four-dimensional optical memory does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Two-photon four-dimensional optical memory, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two-photon four-dimensional optical memory will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074713