CA2179177A1 - Optical volume memory - Google Patents

Abstract

An optical memory material in-cludes a two-photon storage component which can be written from a first to a second state in response to WRITE
light mixed with a signal component which fluoresces by one-photon absorp-tion only at the written locations in re-sponse to READ light. The storage ma-terial may be a fulgide. The memory material may also include a frequency upconversion material to aid writing.
Writing is performed by a spatial light modulator (SLM) with a dynamic fo-cussing system for concentrating suffi-cient power at WRITE locations for non-linear two-photon absorption. Crosstalk is avoided during simultaneous writing in some embodiments, by spacing the in-dividual WRITE beans apart by an in-teger number of inter-beam spacings so that non-adjacent datels are written si-multaneonsly in a "paragraph", and the non-written areas are written at a differ-ent time with different paragraphs. The memory material may be translated rela-tive to the SLM to access different para-graghs or accessed by an electronically sparsed SLM. Reading uses a sheet of READ light traversing the pages of written material to cause the signal component to fluoresce, and imaging the fluorescent pattern onto a detector array. The memory material may be stacked in layers, spaced apart by light waveguides, for guiding the READ beam to the page to be read. In another embodiment, writing and erasure are performed by a modulated quasi-one-dimensional sheet of light, intersecting a second, unmodulated sheet of light at a column within the memory material.

Description

~179177 Wo 95116994 Pcr/uss4l14146 OPTICAL VOLUME MF~ RY
Field of the Tnvention This invention relates to rewriteable data memories, and more ~crer;~irAlly to memories into which data may be 5 written, and from which the recorded data may be read, by means of light, and in which the data is stored in the form of various states of the material of the memory.
Bac~ Luu,.l of the Invention Data storage memories are widely used in computers and l0 control systems of variou1, types. Computers and control pLU~-C60)~ ordinarily use electronic, ' access memories (RAMs) to aid in performing their processes.
Such electronic RANs have the adv~..Layt: of high operating qpeed, but their volume s1:orage density is relatively low, 15 and they are volatile, in that the data stored therein is lost when the system is deenergized. To save the data in a volatile RAN preparator~ to deenergization, the data is ordinarily transferred to a rewriteable pPrr-nPnt medium such as magnetic disc or ~1agnetic tape. Disc and tape 20 media are capable of storing large amou1tt~ of data, but have ~uL ,L.,..Lial initial access time requirements to initially access or locate the data, and also have data 1-rAnqfPr rates which are limited by the serial nature of the tape or the track on a disc. These different memory 25 types constitute a hierarchy which lacks fast access time, high storage capacity members.
Three~ -irn~l (3D) optical storage RAMs have been described, in which light beams address data Pl~
(datels, also known as voxlels) within the volume of the 30 memory material, for writi~tg data thereto, and for raading. An article entitled A~mlications of Photnrhl-om.
PolYmer Fil~q, by A. E. J. ~ilson, published at pp 232-238 of Volume 15 , 1984 issue of Phys . Technol ., printed in Ir- Ul~:L~ ~reland, describes PI~ULUUI.L- ir materials 35 generally, their applications to optical data recording, and also lists desirable a#pects of an erasable reusable optical recording medium, ~l~hich include (l) high sensitivity for writing and erasing, (2) high storage WO 9~/16994 2 1 7 ~ ~ 7 7 PCT/US94/14146 capacity in bits per cm2, (3) nondestructive readout, (4) lack of fatigue, which i8 the ability to be cycled repeatedly without losing its characteristics, (5) archival storage or persistence of more than 10 years, (6) 5 no requirement for developDent of the image, and (7) low cost and ease of fabrication. ~n:-~1An patent application

2,037,059, filed February 26, 1991 in the name of Daniels, and laid open August 27, 1992, describes a system using liquid cry6tals as the memory material, which are stained 10 with a dye. A slight electric field is applied across the memory. Writing is a~ h~d by a light beam, which heats the dye through which the beam passes, and the heat is transferred to the adjacent or c~nt;~-n--~ liquid crystal datels, to allow them to change state under the 15 influence of the electric field. In one ~ L of the Daniels memory, the heating is ~ hPd by multiple intersecting beams of light. Patent Cooperation Treaty (P) patent application W093/02454, filed in the name of Strickler, and laid open Ft:bL~ Ly 4, 1993, describes 20 dev~l 'i L of a three-~ jnn~l optical memory in which a fluolesc~.lL dye is the storage medium, but which is undesirable because of pho1 nhle~rh~n~, and also describes an; uv~d three-~ -inn~l optical memory in which changes in the refractive index of a photopolymer are used 25 for 8torage, and in which intersecting beams of light are used to detect i~ tie5 (regions o~ altered index of refraction) in the medium. An article entitled Three-n~- -,ional O~tical storaqe !Semorv. authored by D. A.
PaL~ r~ ulos et al., and p--hll~:h~l at pp 843-845 of the 30 August 25, 1989 issue of OE Reports, p~hl~h~d by SPIE, the Int~rn~t~nns~l Society for Optical Engineering, describes a three-~l;- inn~l optical memory based on volume storage in an amplitude ~ ,L ling medium, 5p~ fi~ y the phuL~ ir - l~c~le spiL~bel~Z~yL~n~
35 which in a I (spiropyran) state absorbs visible light by a ~, p~,~ Lu.. absorption process (simultaneous absorption of two visible-light photons, C~LL~ in~ to energy in the WO95~1699~ 21 7 9 ~ 7~ PCrNss4/l4l46

- 3 -ultraviolet or W range), and when excited takes on a II
(merocyanine) state. The I state may '`ULL~a~JUI~d to an unwritten (logic 0) state, so that writing involves application of ultraviolet-energy light to create a II
5 state in the datel region. The II state absorbs light in the green-red region of tl~e visible light ~e.;L,~, and emits red-shifted fluc,-esc~-,ce when excited with green lightO Thus, reading is ~ h~ by applying a beam of green light to the datel, and the red shift id~nti~
the written (logic 1) stat:e. The persistence of the II
state, however, ranges from a few minutes under ordinary conditions to a few weeks when cooled. An article entitled poten~;Alc of L~ hoto~l based 3-D oPtical memories for hicrh p~Lr~ lall~e co~Put;n~:, by llunter et al., p-lhliCh~d at pp 2058-2066 of Applied Optics, Vol. 29r No.14, 10 May 1990, also ~;~rllc~-- the use of spirobenzopyran. The text ~lectroniC Materi;~l~ From Silicon to Orqanics, edited by L.S.Miller et al., and Fl-hl;l:hDd by Plenum pllhl;F:h;
Corporation, 1991, ln~ at pp 471-483 a chapter entitled Pl.u~ cs of the Fu~l~re, authored by H.G.~eller, which notes that the main reason that organic ~hotoul.rl ; c materials have not been developed for -o-al applications is the problem of ratigue, and which describes the properties of fulgides and heliotropic -. An article entitled Two Photon ~rhree D;- -ional Memorv Hier7-rcl~v, by S. Esner et al., p~ ed at the July, 199;~ SPIE meeting at San Diego, describes the aLu.. ;~n--~l hierarchy of memories for use in . - D and p~ Cc~L~, and also de cribes ~ u~u-~
30 8~ ry storage (memory) 6yDtems which have the potential for mill ~ c~- on~3 hccess time and Tbit/sec data .D~e~ rates, in which spiLu~ell~u~Lc~n material in a 3-n~ l memory is writt:en by i nt~rs~rting beams of light, and in which an HCl _ ~ of the memory 35 material provides ~ stability of tl~e written form.
However, p ,~ "~ stability implies an inability to erase an~ re-write, or to overwrite.
. _ _ . _ _ _ _ _ _ _ _ _ _ _ _ 217~77 wo 95/16994 Pcr~ss4/14146 It should be noted that the aL,.,v. ; ~^nPd di~ferent colors of light are est~hl i~h-^d by their wavelengths, which range in the visible D~e. L.u., from about 400 to 700 nanometers (nm), and it is also noted that wavelength and 5 freyuency of light are inversely related by the velocity of ~Lu~ayc.tion of light (C). The velocity of light is constant within a particular medium, but di~ferent media e~thibit different values of C.
Improved memories are desired.
~ of the Invention A light-controlled memory stores data in the form of one of a plurality of states of a multipartite memory material. Each bit of data is stored at a data element (datel) location, which may be at the ~;urface of the 15 memory material, or which may be within the bulk material.
The memory material i5 a combination of a storage ^nt or material which changes state in L e:a~ ae to a WRITE light and a readout or signal ~ ~ or material which provides an indication of the state of the storage 20 material at its location. The storage may change state in L~~~u..ae to; p~.~LL~.. absorption of the WRITE light, and the signal ~ may respond by one-photon absorption of a READ light. The memory material may also include a h: ic generation or r-e~ue~ y up-25 conversion material which translates light wavelength forgenerating the WRITE light which i5 Ahe~rh~l by the storage -t ~ of the memory material. In a particular of the invention, the memory material ~ d^l:
~ mixture of a L ~:~u~1~Cy u~ ~ Laion material such as an 30 "u~ ..vtLaion" dye, a p~.oto~l.L. ~-- storage material, and ~ ~luu~c s~,~..L material such as a "signalD dye, which L. a~u..15 to the local state of the ad~acent Pl.~,LU.1.L, ~!
material. In a more particular: ~- o~ the invention, the signal dye fluo~ a upon ~ min~tion 35 only when the storage material is in a first state, and WO 95/16g94 ~ 1 7 9 1 7 7 PCT/USg4/14146 does not fluoresce, or fluoresces only weakly, when illuminated when the storage material is in a second state. An u~ _v-,v~ ion dye may be Coumarin 6. The storage material may be a fulgide. The :eluvLe:sc~:~lL signal 5 dye may be DODCI. An omhor?; L of the light-controlled memory includes a light modulator for modulating light beam(s~ for writing into, and, when desired, for erasing the memory material. The light modulator may be a spatial light modulator for modulating light beams to form a two-10 ~ inn~1 representation of the data. The spatial lightmodulator may be one-~ nA l ( l-D), quasi-one-ir,nolll (q-l-~), or t~o~ ion~1 (2-D). A lens sys~em foc~llqcpq the light onto the desired datel(s) at the ~urface of, or within, the memory material. A dynamic 15 lens system, which may in~:lude a zoom lens, may be used to focus on various pages of memory within the body of the memory material. In a particularly a~v~ e, q ';- L, foc~s;nq is n: 1 ;Chl~ by a lens system ;nrlll~;n~ a microlens arrny, for simulf~r~r~q1y nCcoc~qin~
20 plural, spaced-apart (spa~-sed) datels to reduce crosstalk.
A translation stage may p~ovide relative motion of the memory material and the l ~ ght beams . In another : ' _; , a light beam in the form of a sheet or highly elliptical beam is used t~ simul1 ~n~ouqly access large 25 numbers of datels.
Descri~tic~n of the Drawincrs FIGURE 1 is a ~ fi~cl pc~ Live or ;I LLic view of the optical memory bloc:k portion of ~n optical memory in accordance with an aspe.ct of the invention;
FIGURE 2a is a simplified p~ ,ecl ~ve or; ic view of a portion of the block of FIGURE 1, illustrating the concept of addressing a particular datel within the block by means of a focussed light beam for writing or erasure, and FIGURE 2b is similar, illufitrating addressing by means of v,~ m;n~tion (;n1-~rs~ct;n~ beams);

4 2 1 7 9 1 7 7 PCINS94/14146 FIGURE 3a is a simplified perspective or isometric Yiew of a portion of a memory block similar to that of FIG~E 1, with a laminated or layered-sheet co~ L,uution, FIGURE 3b illustrates an upper edge of the ::~LLUU~ULe of S FIGURE 3a with light sources in the form of optical fibers coupled to each layer of the :~LL~ ULè;
FIGURE 4 i8 a s; 1~ fied block diagram of a memory system according to the invention;
FIGURE 5 is a uLuss~ Lional elevation view of a 10 portion of the block of FIGURES 3a and 3b, illustrating overlap of adjacent ro.ussed beams;
FIGI~RE 6a i5 a sche~atic diagram of a datel addressing scheme which simul~An~o~ly ad-lLe~ es non-adjacent datels in a sparse manner, PIGURE 6b is a fron~al view of a 15 spatial light modulator alLa..yed for modulating a of sparse light beam array, and FIGURE 6c is a cross-sec~innA~ view of the set of light beams of the sparse light beam array ~L.-lace~ by the modulator of FIGI~RE 6b, after foc~ in~ by a lens array, which beam array i=
20 usable with the aLLar., L of FIGURE 6a;
FIGURE 7 is a ~,y -l~c Le~L~ LatiOn of a ph~.Lo~", i~ fulgide which may be used in a memory nccording to the invention;
FIGURE 8 is a schematic block diagram of an electronic 25 sparse addressing system;
FIGURES 9a-9e are frontal views of various spatial light modulators useful in the ~ LLal~ L of FIG~RE 8;
FIGURE lOa is a 8~ lif~ecl pe,~,~ecLive or ~- ic view of a memory block and a pair of ~L I l-nJ~ l WRITE
30 light ~elleLatU~D aiding in un~e~ ing another WO 9~;/16994 2 ~ i~ 9 ~ 7 7 PCT/US9411414f~
_ 7 _ L of the inventi on, FIGU~E lob i5 a perspective or i ~- ic view of the intersecting light beams within the memory block of FIGUPE lOa, and FIGURE lOc is a plan view of the block of FIG~IRE lOa, illustrating the

5 ;nt~rsert;n~ light beams;
FIGllRE ll is a simplified block diagram of another ~hoAi L of the invention similar to FIGURE 4, in which an optical memory block is adllL~ aaed in a tIuasi-one-d; -ionAl manner by crossed beams;
FIGURE 12a is a frontal view of a t~uasi-one-dimensional spatial light modulator useful in the C L.lr.y, L of FIGURE 11, FIGURE 12b L~Le5~1~L~ a cross-section of a focussed light beam array pattern responsive to the spatial light modulator of FIGURE 12a, and FIGURE
12c 1e:~LC:a~ S the result of e asi~g the pattern of FIGURE 12b in a horizontal direction.
Descrition of the Invention FIGURE 1 illustrates memory material according to the invention, in the form of a r e~ I A J l Ar block or parA l l ~l t r; rt~A~ lO with si~e5 or faces oriented parallel to X, Y and Z axes. As illu~trated, block 10 has its "front"
face 12 lying in the X-Y ]?lane. Front face 12 is OU~IUt~ lly divided into a 5120-by-5120 element grid, each stluare element of wh ich L.~ s~..Ls the smallest 25 storage element which is ; ~ Ll y addressable in the X-Y plane for storage of ~lata bits. Also as illustrated in FIGURE 1, bl ock 10 is tlivided parallel to the X-Y plane into 1000 "pages" Pl, P2, P3, . . . P999, P1000, each of ~hich Lt:~L.~ Ls the smal].est ir.u.~ Lll region in the Z
30 direction in which storag~- can occur. The i..LeLa-:uLion of the projection of each gri d element with each of pages 1-1000, where the hyphen le~L~ sc~Ls the word "LhLuuyll, l' defines a LC:U~ _---J--1 Ar nbox~ volum~ memory storage element (a datel), designated dt r j,, in which one bit of data may WOg~/16994 2 ~ 79 1 77 Pcrluss4ll4l46 be stored. While the datels of FIGURE 1 are identified by dash-line outlines, it should be emphasized that block 10 is a monolithic whole, without identifiable ;ntDrnAl boundaries; the datel locations arise due to the method of 5 addressing, described below in ..u..jul.uLion with FIGURES 2a and 2b. The lengths of X, Y and Z sides of block 10 are about one inch, one inch, and in the range between one and four inches, respectively. Naturally, the ~ inn- may be larger or Dmaller to increase or decreaDe the torage 10 capacity. In FIGURE 1, el~ d"~ d2,1,1 and d~ are illuDL.~.tad as being those datels in the first, second and third positions along the X axis, and d5~9 ~ ~ and d~20 ~ ~ are the last D1~ ~s along the X axis. A 5120-by-5120 grid ;n~ AD~: more than twenty-six million Dl Ls. Also illustrated in PIGURE 1 are datels d~ 21~ d~ 5~9 ~ and d1 51201' which lie along the Y axis, and datel5 d1,s120,2~
d1,512D,W9 and dl,5lzo,1000- Datels d51zo 1 z and d5120 ~ ~0O are also identified. Thus, one page of memory block 10 ha~
storage datels sllffir;Dnt for 5120 times 5120, or 26 20 Mbits. A memory block such as block 10 of FIGURE 1, with lOoO pages, would include 2.62 Y 101 datels, COLL~ ;n7~ at 8 bits/byte, to about 3.20 Gbytes of storage capacity. Block 10 of FIGURE 1 is made from an optical memory material, described below.
According to an aspect of the invention, the memory material ;nrll~ADQ a combination of a h: ;n generatiOn or u~ ._UllvèlDion material which translates light wavelength (rLCylle~ ), a storage or memory materi~l which changes state in L-_rlUllDe to the translated light, and a readout material which provides an ;nA;cat~on of the state of the storage material at it_ location. In a particular D~hO~9i of the invention, the memory material is a miYture which inrl~ D~ a rLel"ue~.cy u~ eLDion material such as an u~ cu~vcLDion dye, a p1~ù~u..l..l ~ storage 35 material, and a fluc,L.__e--L material such as a signal dye, which 1 eDyu..~s to the state o~ the local or ad~ acent _ _ _ _ _ _ _ _ Wo 95/16994 ~ 7 Pcrlus94/14146 _ g _ phuLu~ L~ i C material . ~'he active materials may be associated with a carriel- such as a polymer. In a more particular omhgrl; ~ of the invention, the signal dye fluoresces when ;llum;nAt:ed only when ~he storage material 5 is in a f irst state, and does not f luoresce, or f luo~ esces weakly, when ;llum;n~ted when the storage material is in a second state.
The storage L of the memory material is chosen to be a fulgide, for its thermal stability and relatively 10 long data retention. me fulgide changes state in L6Dy~..De to ultraviolet (W) or visible light. The lack of fluuLesc~ ce of the fulgide is L,veL. - by mixing it ~ith a fluuLeD~llL signal dye material, which, upon being al.lL~ssed for reading, fluc,L-_ces only when the fulgide is 15 in a particular state, and not when the ~ulgide is in another state. The fulgide can have t . pl.ùto~ absorption when exposed to high intensity light, and is otherwise transparent. Usually, two photon absorption peaks at a particular wavelength, which may not match the operating 20 wavelength of a high speed 5patial light modulator, described below. This mismatch can li~it the overall writing eff;~iPn~~y. The u~ ,..ve:~:.ion dye is added to ~)V~:LI or ameliorate this limitation. The Ul, _UI-VeL~ion dye has Pffin;Pn~ two photon absorption at the operating 25 ~avelength of the high sp~ed spatial light modulator, and re-emits at a wavelength region which is very ~ iPnt for ~ VeL Ling fulgide fr~m one state to ~nother, as from a color state to a bleach state. The addition to the up-conversion dye can thus ellhance the overall writing 30 Pff~ic;Pnry and leads to r~-duced writlng energy. Preferred u~ LDion materials a~-e tho5e based on 3e._~",,.1 ~ i C
generation or ~ _ pl-oLu-, absorption-induced flh.,Le__c"~ ~.
F~.~ueh..y conversion dyes based on t . p1,~Lc,,, absorption-induced fluuL6:~c~ .e, such a~ Coumarin 6, can 35 be used to convert infrar~!d light in the 820 to 960 nm WO95/16994 2 1 7 ~ ~ 7 7 - lo - PCT/US94/14146 regime to visible light in the 550 nm range. The mixture of such a dye with a fulgide allows data writing to be n~ hPd by irradiating the material with infrared light, whereby the dye .,~..veL La the infrared light to 5 visible light, to thereby locally write the storage ~ of the memory material.
A first example of a memory material according to the invention includes the phuLo~ ic fulgide _ ' E-Adamantylidene [l-(2~5-dimethyl-3-furyl) ethylidene~
10 ~ rr;nic! anhydride, sym~lirllly illustrated in FIGURE 7, mixed with fregue~ .Vt:L:~ion dye in the form of the abvv. Lioned Coumarin 6 (CAS No. 38215-36-O, a Rodak optical product sl~rPl i~cl by Eastman Fine Ch~-mir~
Eastman Rodak Co., Ru~;l-eaLer, NY 14650), and with a signal 15 (READ) dye in the form of 3,3 -diethyl~rY~ v~!arine iodide (DODCI), in the preferred proportions described below. The miYture is prepared by dispersal in a carrier of polyvinylbutyral. In an eYperiment, a 35-1~m-thick film of the dispersed material was applied to a glass slide, 20 dried, and eYposed to UV radiation at 366 nm, which changed the photo_l-L i c material from the colorless form to the colored form. The resulting material, when exposed to a fouua~ed 920 nm laser beam, de~ sed in color intensity in the eYposed area, and resulted in an increase 25 in intensity of the light emitted in the 600 to 700 nm range when later eYcited by a light at 395 nm. When the eYposed area was ~ min~ted with light at 366 nm, the written spot was erased, and the emitted light in the 600 to 700 nm range as a result of illumin~tion at 395 nm 30 decreased.
The proportions of the ingredients of the mixture o~
the first example, as p~--e,.L_~es of the total weight of the ~uL,L~ inrlU~nr, the polymer carrier, range from .001% ~o 10% of the ~I,vLv..l-~_ ir , t,~ with 2.8%
35 preferred, o. OOOOlS to lS of the freguency u~ _~",v~ aion WO95/16994 ~ 7~ PCr/uss4ll4l46 \ - 11 -dye, with 0.496 preferred,, and 10-59c ~o 3% of the signal dye -nt, with 0.8% pre~erred.
A second example of zl memory materia~ is as described above for the first example, substituting 5 polymethylmethacry-late p~lymer for the polyvinylbutyral.
A third example of a memory material is as described above for the first example, substituting polyvinyl acetate for the polyviny].butyral.
A fourth example of a memory material is as described 10 zlbove for the first exa~lE~le, substituting urethane acrylate ultraviolet (W)-curable polyner for the polyvinylbutyral .
A fifth eYample of a memory material is as described above for the first example, substituting W-curable epoxy 15 polymer for the polyviny]butyral.
A sixth example of a memory material is as described above for the first examE~le, substituting 1-t2,5-dimethyl-3-furyl)ethylidene(isopropylidene) ~ rcin;r anhydride $or the photo~l, i c ~ .
A ~eventh example of a memory material is as described above for the first example, substituting 2,3-bist2,4,5-1-r; ' ' yl-3-thienyl) mal~ic anhydride :~or the ~ L,, l r, c An eighth example cf a memory material is as described above for the first exzlmple, substituting cis-1,2-dicyano-1,2-bis(2,4,5-tr;-- yl-3-thienyl)ethene for the p}~ tO-,llL ~
A ninth example of a memory material is as described zlbove for the first example, sub~t;t~t;n~ 1,2-dicyano-_ _ _ _ , . _ . _ _ . , . . _ _ _ _ WO 95/16994 2 1 7 ~ ~ ~ 7 PCTNS94114146 1,2bis(2-methylbenzo~hioFhPnp-3-yl)ethene for the photochromic L-A tenth example of a memory material is as describedabove for the first example, substituting 2,3-bis(1,2-5 dimethyl-3-indolyl)maleic anhydride for the photo~l,L, ic-~.
An eleventh example of a memory material is a~:
described above for the first example, substituting 8-hydroxyl-1, 3 6 pyL,..~risulfonic acid ~or the Coumarin-6 10 -, L, A twelfth example of a memory material is as described above for the first example, substituting Nile Red dye (CAS No. 7385-67-3 from Aldrich catalog #29,839-5) for ~he DODCI ~ . L .
A thirteenth example Or a memory material is as described above for the first example, substituting Pyridine-1 dye (Nodak CAS No. 87004-02-2, also known as LDS-722) for the DODCI ~.
A fourteenth example of a memory material is as 20 described above for the first example, substituting Pyridine-2 dye, available rrOm Exciton, also known as IDS-722, rOr the DODCI i .
A fifteenth example of a memory material is as described above for the first example, substituting 4-25 (dicyano methylene)-2-methyl-6-(p-dimethylamino styryl)-4 H-pyran for the DODCI L.
A sixteenth example of a memory material is ns described above for the fir5t exnmple, ~ubstituting 2~4-(4--dimethyl:~m;nnphPnyl)-l~3--b~ Pnyl]--3--Wo 95/16994 2 ~ 7 ~ PCT/USg4/14146 ethylbenzo~hiA7ol ium p-tl~luenesulfonate for the WDCI
L.
A seventeenth exampl~3 of a memory material is as described above for the first example, substituting 1,1',3,3,3',3' ' thy!L-4,4',5,5'-dibenzo-2, 2 ', indotricarbocyanine perchlorate for the DODCI
, An eighteenth example of a memory material was prepared with a slice of lithium iodate (LiIO3) crystal, 10 cut to Pf~!iontly doubl~ the fretauency of a 920 nm laser beam. A thin film was placed on the crystal. The film was of polyvinylbutyral ~ n~ ~in;~ the phuLo. l,L, ic E-Adamantylidene~ tl-(2,5-dimethyl-3-furyl) ethylidene] sl~r~;nic anhydride (the sa~e photochromic _ as in the first example) in the colored state, in a mixture with the fluo~sc:~s..L signal dye Pyridene-l.
E~ DULC: of the crystal and the 1:hin film to an intense f~ 6ed 920 nm laser beam resul1:ed in generation of 460 nm light from the LiIO~ f:Llm at the fGuuDsed sites, which 20 changed the colored form of the photo~ , i c to its colorless form at only those sites, and which resulted, when read by ~ ODUL~ to a beam of light at 395 nm, in omi~:~irn of light signal at 620-650 nm from the Pyridene-l _ ~ of tLIe memory materlal.
A n~r-t~ Ll~ example l~f a memory material is as described above for the e ighteenth example, substituting potassium dil-y-lLu~ phos3~hate (KDP) or polymethyl methacrylate (PMMA) doped with 2-methyl-4-nitroanylene (PlNA), or polymethyl ylate (PM~a) doped with para-nitro~ni 1 ono (p-NA) for t~le LiIO3 material . The potassium dil~ydLu~ll phosphate may })e crystalline.

Wo 95/16994 2 i 7 ~ t 7 7 PC~;~USg4/14146 A twentieth example of a memory material i nr~ lPc a lithium iodate crystal as described above in conjunction with the eighteenth example, substituting any of the memory materials of examples one through seventeen for the 5 thin film of example eighteen, with the sole difference that the memory material of the thin film uses E-Adamantylidene [1-(2,5-dimethyl-3-furyl) ethylidene]
in;~ anhydride and Pyridene-l.
A twenty-first example of a memory material is as 10 described in any of the eYamples above, in which the frequency conversion material is a gecond h i c generating polymer, such as polymethyl methacrylate (P~A~
doped with a material having a high second order nnnl inP:~r hyperpolarizability, such as 2-methyl-4 nitroanilene 15 (MNA), which, after doping, is poled by an electric field to align the nnnl ;ne;~r moieties.
While the examples given above describe various individual compositions for each function of frequency conversion, memory, and si~n:~ll in-J~ mixtures of the 20 abuv i t~nP~l compositions may be used to perform any or all of the fl7n-t;gnc.
Several approaches have been u- u~Gsed in the afuL Lioned Hunter et al. and Esner articles based on two photon absorption ~Lucesses. One is to write, read, 25 and erase a two-~;- -inn~l array simul~nPo~ly all through two-photon absorption of short (less than about 10 nsec duration) laser pulses. Such methods can provide high storage density, but have the dis~dva,,Lage that they require high laser power for reading, writing and erasing.
30 The data transfer rate is limited by the average laser power available. According to an aspect of the invention, WO 95116994 2 1 ~ 9 1 7 7 PCr/uss4114146 the data transfer rates are increased by reducing the average power, which in turn is ~ hPd by relying upon u1.~ pho~on absorption for reading. The power for reading is low enough so that it can be provided by a S conti~uuUs ~. ve (CW), as opposed to pulsed, source, but of course it will be re~o~n; 7ecl that the READ light source may Ibe turned ûN and OFF as required to perform the function. According to l~nother aspect of the invention, the page to be read is e~ h~ hPd by control of, or 10 reducing the size of, thla memory region ill-~m;n~ted by the READ source. This is po~:~ih~e~ because the use of one-photon reading increases the read sensitivity so much, by comparison with L . pl..lL~ reading, that less written inaterial is required to produce a useful READ signal.
15 This in turn reduces the amount of memory material which must be written, and thel-efore reduces the total ~IRITE
energy required. The rPr~l~c~inn of WRITE energy in turn allows longer WRITE pulses to be y~..eL~Lad by the WRITE
laser (or other source), or possibly even conti..uuu3 ~._v~
20 operation. A further ad~ a~1L._~ of the reduced amount of memory material which must be written is that f ewer l~ c~ q of the storage material must change state during any one store/erase cycl~, and if the storage material is subject to fatigue, the mnl ec~ available at any one 25 datel site will last for a large- number of cycles.
FIGURE 2a show6 a si li fi~d block diagram of a portion of block lO of FIGlJRE l, illustrating one datel, designated cl , fro~n which identi~ication the datel may be reco~n; 7A - ag beiny F ' ~ near the center of 30 block lO. In FIGURE 2a, a lens illu~LLaLed ~Ig a cylindrical object 20 foc~ c~ a beam 22 of collimated light to for~ a u~ v- L~ing beam 24, which is rc,uuDsed at datel ~ . Accordillg to an aspect of the invention, ~he energy density of the f~uu~ ad beam is insurficient to 35 result in ~ . phoLu~- absorption in the material at any datel through which the beam passes, except at the f ocal Wo95/16994 2 1 7q t ~7 PCT/US94/14146 point in datel A 7~nn . Thu5, a datel located within the body of block 10 of FIGURE 1 may be addressed without affecting adjacent datels. The dimensions of a single datel in the x and y directions are estAhl i ~h~d by the 5 intensity of the fc~u~sed light beam, by the optical spatial resolution, and possibly by the granularity of the memory material.
FIGURE 2b similarly illustrates datel ~' , minAted by two il.Le~e~Ling beams of light from two 10 lasers 26 and 28, which produce orthngrmAl beams of light 261 and 281, respectively. Lasers 26 and 28 each include mirrors and partially-transparent mirrors, as known, which essentially focus the light to form collimated beams 261 and 281. Neither of light beams 26 and 28 alone has 15 sufficient energy density to write the datel, but toget~er they have sllff~ci~nt energy density at the intersection of beams 26 and 28, which intersection occurs within datel A 5 . Thus, a particular datel within the bulk of memory block 10 of FIGIJRE 1 can be aa~lL. ased by different 20 lllllminAtion ~ILL , L~, to the ~Y~ inn of other datels, and achieve the required energy density for writing without additional focllc~ng. The beams can also be used for reading, or erasing, if desired. For reading, one of the beams of FIGURE 2b, such as beam 281, is used, 2~ and as it LL~.vc.~-es the line of datels ;nrluAinq datel ~A , it causes those datels which are in the excited state to fluoresce at long wavelength (about 600 to 700 nm), which fluuLe~c~ e can be d~t~ct~d to identify the current state of the bit stored in the datel. It should 30 be noted that as the beam di; ' beco~es greater, or the spatial r~nlutinn lesser (larger spot), that the minimum A ~ - in~l that a particular datel may have without crosstalk becomes larger, so that larger beam di_meters or poorer spatial r~oltltinn reduces the effective data 3~ capacity of a particular memory block. It should also be Wo 95~16994 2 g ~ 9 1 i~ i~ PCT/US94/14146 noted that the two beams of light illustrated in FIGURE 2b may be at different frequencies.
Reading of written datels may be at liqhD~ by m;n:~ting the cube with a sheet of light, the plane of 5 which is orl ht~gon 1l to the direction of WRITE beam 20 of FIGURE 2a. A sheet or f,an-shaped READ beam may be generated by an l~n~ ~hic lens such as a cylindrical lens. The sheet of light may LLaYeL:~e block lO of FIGURE
l from top to bottom, pa~allel to the X-Y plane. In order lO to read datels of only o~le page without reading datels of adjoining pages, the read beam must be tightly foc~qqed in the Z direction over the one-inch by one-inch area of a page, i.e. it must have ~1 focal depth of one inch.
However, the size of the focal spot of a lens is directly 15 related to the focal depl:h, and a large focal depth nDc eqs:-rily results in a large focal spot. This large focal spot, when reading over a large focal depth, requires that the datels be relatively widely spaced in the Z direction, in order to avoid crosstalk among 20 adjacent pixels. For a ~ocal depth of one inch, the READ
optics will have a focal spot di~ of about llO ~Lm, and this becomes the limit on the mini~um page t hir~nDss.
The ~; ~ i nll in the Z direction of a typical datel, such as ~atel d256 2s61 500 Of FIGIJRES 2a and 2b, thus needs 25 to be larger than, or equal to, 1the larger of the focal depth of the writing/erasure optics or tlle focal rl;5 of the reading optics, in order to avoid crosstalk in writing, erasure, or reading. For an optics to write a 5 ~m spot d i , the focal depth for ~riting is less than 30 20 ~m. As irnC-d above, a reading optics with one-inch focal depth has focal (~ o~ llO ,um. l~eL~r.,Le the smallest page size that can be used for such a system is 110 ~m. Memory block lO must be about four inches long in the z direction to: ' Le lO00 pages. For a .. ~.~L.~l~L

~79177 18- --size memory block, the limitation set by the focal depth thus limits the volume memory density.
one method to reduce the r?i- inn of the datel d2561.
- 2561 ~00 in the Z direction, so that a one-inch-long memory 5 block can Al -'-te lOOO pages, is to use a laminar ~L~U~:~UL~ which includes multiple waveguide layers.
FIGURE 3a illustrates a corner of a memory block 36 similar in function to block lO of FIGURE 1, but differing in that its .;~.",,~ u~ ~ion is laminar, consisting of 10 laminated layers. In FIGr~RE 3a, block 36 inAl~ a plurality of glass plates or lamina 3Z, such as 321~ 322, 32~, ..., each of which has deposited thereon a layer of memory material, according to an aspect of the invention.
Thus, glass sheet 321 su~u.~s a layer 301 of memory 15 material, glass sheet 322 ~u~ s a layer 32 of memory material, glass sheet 32~ "U~ L~:i a layer 3O3 of memory material, and memory material layer 3 04 is supported on a sheet of glass which is not illustrated in FIGURE 3a.
Spacer layers, described below, may also be provided. The 20 "back" surface of each sheet of glass 32 is j u~a~osed with the "front" surface of the layer of memory material of the neYt higher page of memory, s~a. ated therefrom by inactive "spacer" layers 311, 312, 315... with relatively low indeY of refraction. This c~"~LLu~Lion creates a 25 laminar ~ al~, consisting essentially of alternating layers of glass and active material. Each layer of memory material in the aLL_, L of FIGURE 3a constitutes one page of memory block 36. The aLL_r, of memory block 36 o~ FIG~RE 3a has internal boundaries ~ n1nAJ each 30 individual page, unlike the ~ILL___, of memory block lO
of FIGURES l, 2a and 2b, but block 36 has no ir3~nt;~;Ahle boundaries in the X and Y directions within a page. In order to F ' te one ~ such pages within a one-inch s~{uare block, each glass-plus - y- ial layer 35 (and spacer layers, if used) mu5t have a ~ hirl~n~Rfi not ~YAIA~e~inAJ one mil lO.OOl inch). Writing is ~ l;Rh~d WO 95116994 2 ~ 7 ~ ~ ~ 7 PCTrUSs4/14146 in the laminar structure in a manner 6imilar to that described in conjunction with FIGURES 2a and 2b, and the focussed WRITE beam forms a spot which easily fits within the one-mil page ~h; rlrnr~'C8.
Reading, and possibl~ erasure, is i~ l l chr rl in the aLL~,, of FIGURE 3a by applying tlle sheet of light to the top of one of the glass layers 32. If an A~ iC
lens is used to focus a ~eam of light onto the edge of each sheet of glass, the spot size can be very small in lO the Z direction, because the len_ needs to focus only onto the edge of the glass, arld the depth of focus which is reguired approaches zero. Each sheet of glass has an index of refraction greater than that of the adjacent memory material, and therefore tends to act as a light 15 waveguide. Light coupledi into the upper edge of a sheet of glass, such as sheet 32z of FIGURE 3a, will be trapped in sheet 322 by what may ]be conceived of as multiple rPfl~rt jr nc at the interfaces between glass sheet 322 and the adjoining layers 30z ~nd 31~, and will ~a~c.te toward 20 the bottom of the glass sheet.
FIGURE 3b ill~ .LLl,tes a portion of an upper edge of block 36 of FIGURE 3a, illustrating another way to couple light into the top of each glass layer 32. FIGURE 3b shows a plurality of optical fiber6 40 terminating on an 25 edge of each glass fiheet 32. For example, a set of four optical fibers 401~ 401b, 401C~ and 401d terminates on glass clheet 32~, and another se1: of optical fibers 4O2,~ 42b~ and 42c terminates on glass sheet 322. Each set of optical fibers may originate from an in~QrPn~t~nt source, as for 30 eYample optical fibers 40t., 40~b~ 40~c, ~nd 40~d may all originate from a single star coupler (a multiple-port optical power divider), driven by light from a single controllable source, whille optical fibers 42-~ 42b~ and 42c originate from a different star coupler, driven by a 35 sep.. L.. Le, ~nr~ Lly cl~ntrolled, light sourcQ.

wo 9511699~ pcrluss~/l4l46 217q~77 20- --In a light waveguide, the ele~ L-, Lic fields which carry the light energy are prinrirAlly constrained within the dielectric medium, but an "~vcli~ac~ L" portion of the fields lie outside the waveguide, and can couple to the 5 memory medium. The light which is coupled to the upper edges of glass sheets 32 in FIGURE 3b proceeds downward through the glass sheets, reflecting from the sides as a result of dirre.e..~i~s between the coefficient of refraction of the glass and the coPff~ciPnt of refraction of the adjacent material, but co~rl ing some of the light energy into the memory material, as suggested by arrows 38. READ light may be applied to one sheet of glass, such as glass sheet 322, for exciting those datels of memory material of adjacent sheet 30z which are in the written state, and for causing them to fluoresce.
To avoid having READ light applied to a glass sheet, such as sheet 322 of FIGURE 3b, ;llllminAtP the me_ory material associated with an ad~ acent sheet which is not ;nton-lPd to be read, such as sheet 303 of memory material, each layer of memory material 30 underlies a layer 31 of spacer material, such as layer of polymer or other material with an index of refraction lower than that o~
the glass. Thus, layer 301 of memory material of FIG~RE 3a underlies a spacer layer 311, layer 30z of memory material (FIGURES 3a and 3b) llnAPrl; P~l a spacer layer 312, and layer 303 of memory material underlies a spacer layer 313. Wh~n eAch glass sheet 321~ 32z, 323...with i~s deposited layers o~ memory material 301~ 32~ 303...and 5pacer 311, 312, 313. ..are stacked together or J ~l Al.~c~,?, each glass sheet 30 32 i8 in each case (except the last layer) j ~ )5P~ with a spacer layer 31. The spacer layers interact with the relatively high index of ~-r- _Lion of the glass layers in a fashion well known to those fAm;l;nr with ~iPlPrtric waveguides, to limit the reading/erasure light to ;ntPrnrt 35 with only one memory layer. Because the ~ cc- l- light intensities decay ~ inlly inside the layers 313 and WO 95/16994 2 ~ 7 9 ~ 7 7 PCT/US94114146 32 away from the interfaces, the intensity of the ele..LL~- yl.~l jr fields decay in the sp~cer layers 31 to a - level below the intensil:y recJuired to produce a significant READ signal~ while having sufficient amplitude S within the active memory material to produce fluule~c~ e.
As a result, the light },Lu~a~ating in any glass sheet 30 as illustrated in FIGURl~ 3b reaches only its associated layer 30 of memory mate~-ial, and is preferentially rejected by the adjacenl: spacer layers 31. In this 10 fashion, each layer of glass of the laminar block 36 of FIGURES 3a and 3b, and i~ts adjacent memory material, may be ;nrl~-r-~nrl~ntly 1111lmirt~ted with light for any purpose.
In a particular: _; L, light applied in this manner is used for reading, bec:ause all the latels associated 15 with (adjacent to~ a pa~ ticular layer of glass may be addLaDDed simult~n~o~ by light applied along the edge of the block as described in ~iu~ju~ Lion with FIGURE 3b, and a sol Pc t~l one of those datels may be simul~npo~~~ly illllm;rl:~ted by a fo~ or collimated light beam as 20 described in cu..j u~ ion with FIGURES 2a and 2b, to thereby ; 1 1 l~m; n~te the ~ t~ one datel with a maximum intensity of light, andor with light of different colors.
Ideally, the diLreL-:--ce between tlle coefficients of refraction of the glass and the spacer layers would be 25 about 0. 01, which would ~;UL.LC:D~JU~d with a reflection of the WRITE beam at each layer of the laminar LLU~;LULa of magnitude 10-4, ~.h~Leu~u~ the loss of the WRITE beam traversing 1000 layers would be about 0.1. In a p~rticular experimental: ; ~ of a laminated block 30 with glasg gheets 140 ~m thick, and having co~ff;r;c-nt of refraction rl ~ 1.515, and with the co~ff1~ n~ of refraction of the memory material according to the first example being ~=1. 47, certain datels were written. Llght was then ~Lu~ated as a "sheet" through a glass sheet of 35 a page of memory, genernlly as described above. The emitted light from written datels was oL~vad as flu~Le.~ e in the 600 to 700 nm range at the datel Wo 9~/16994 ~ 1 7 ~ 1 7 7 PCT~Sg4114146 location while looking in the Z direction through the material .
FIGURE 4 is a ~i 1 i fi~d block diagram of a memory System according to the invention, in which the memory is 5 a laminated block similar to memory block 36 of FIGURES 3a and 3b, and is identified by the same designation. The memory material is the composition described above in conjunction with example 1, with the above described preferred relative amounts of the three active -- tc~.
10 In FIGURE 4, a light source such as ~ laser 410 applies an infrared WRITE beam at 920 nm to a beam ~YrAn~l~r 412, which expands the beam to produce an ~ h led, collimated light beam 414. ~ Pd light beam 414 is passed through a polarizing filter 416 to polarize the light in the 15 direction illustratet by arrow 418. From filter 416, the WRITE beam enters a polarized beam splitter 420, and i5 reflected to the left, and through a quarter-wave plate 424 for polarization rotation, to a spatial light modulator (SLM) 426. Modulator 426 i n~ C as many 20 controlled modulation pixels as there are datels in a page of memory 36, if an entire page is to be written simult An~o~l~ly, or a lesser number ~-~p~n~l;n~ on the selected array size of data to be stored simult~n~ ly.
If the ~-1 etPd array size is smaller than the size of a 25 page, defined here as a 5120 Y 5120 size, the sDlerted size is termed a "~ala~-a~h". For example, a paragraph can have a size of 512 x 512, in which case a page will contain 100 pa~a~La~ as described in more detail below.
A preferred spatial light 1 Ator is a 2D GaAs SLM with 30 a high-speed ~ u--~,a of 100 M~lz or greater; a preferred modulator is described in cnr~n~l;ng patent application SN
08/109,550, filed August 20, 1993 in the name of Worchesky ~t al. The pixels of modulator 426 which UULLC:D~Unli to datels of memory 36 which are to be written are set for 35 r~flectjon of light, and those pixels which cu...: ~u-~d to datels which are not to be written are set for absorption.

WO95/16994 `2 ~ 79 J ~ PCr/USs4/14146 The modulator is contr~lled, for example, by the write control portion of a _ 437 or processor with which the memory arL-r, L of FIGURE 4 ic associated. Thus, the WRITE beam as reflected from SI~ 426 is spatially 5 modulated to ~;uLLea~u..~l to the relative spatial locations of the datels of memory~ 3 6 which are to be written on one p~Lt~ylLa~1~ or page. Th~ modulated WRITE light beam 428 is reflected from SLM 426, back through c~uaL Ler __ve plate 424 to lete its polarization rotation, and through 10 polarized beam splitter 420. From beam splitter 420, WRITE light beam 428 passes through dichroic (rLe~lutl~ y-censitive~ mirrors 430 and 432 to a dynamic foc~1eci system illustrated as a block 434. Dynamic foc~l~ccin~
system 434, under the control of an address control block 438 responsive to LeL 437, rci- uDses the WRITE beam at an image plane t-ninri~l~nt with one page of memory 36.
The fo-;ussed WRITE beam is illustrated as 436 in FIGURE 4.
Thus, each piYel of the WRITE beam i8 8imull 5'nPol'cly focussed on its respective datel in the memory material, 20 and all the datels in the particular paragraph or page are written simult:~n~o~lcl y. me material of memory 36 is transparent to the 920 1nm light, so the light can be fouu,,~ed at any page wi~hin the block.
The bright 920 nm s~?ots fo~ ~ ecl within the datels of 25 a particular page of memory 36 by ~oc~ Fin~ system 434 of FIGURE 4 are smaller than the tl; inn~ of the datels, so crosstalk among adj acen1: datels is not ~Tec ted due to the f o~ -~ed spot. Another tyl?e of crosstalk is described below in .;u..ju,.~ Lion wi~h FIGURE 5. At the focus, each of 30 the bright spots reaches an intencity s11f~ici~nt1 y great so that instead o~ beincl LL~ L-.-L, the Coumarin 6 dye absorbs the light by L, p~uLu-- absorl?tion, and re-radiates visible light i n the 500 to 550 nm range. The reradiated light is ~hsr~hed locally, within the cnnf;n~c 3~ of the datel, by the pl.~,Lc- l-L i~ fulgide material, which ~U..~I~L Ls to its colored state. Thus, the writing wo 95/16994 2 1 7 9 1 7 7 Pcrluss4ll4l46 operation changes the state of the photou~ material, in effect changing it from a logic "0" to a logic "1" at the particular datel. As mentioned, all the datels of a page can be written simultAneo~cl y to any pattern of ones 5 and zeroes. In the written state, the photochromic material continues to be transparent to the 920 nm radiation, so the writing of one page does not prevent pages more remote from focussing system 434 ("behind" the written page as viewed from the light source~ from being 10 written.
While crosstalk among adjacent datels due to the focussed spot is not expected, there is another potential source of crosstalk. FIG~JRE 5 illustrates a portion of a laminated memory block, similar to that of FIGURE 3a, 15 together with simultAnec~l~cly oc~uLLing WRITE beams at 920 nm, such as those described in u--jull~Lion with FIGURE 4.
In FIGURE 5, three mutually adjacent datels are being written by light ~ocu~ed at spots 510a, 510b, and 510c in memory layer 3 03 . The spots are smaller than the 20 ~ ~innC of the datels in which they occur, so no crosstalk occurs among the datels of layer 303. The light beams associated with f~cu -e;l spots 510a, 510b and 510c are indicated by their outl in~C~ and are designated 512a, 512b and 512c, respectively. While the focus of each beam 25 512 at 920 nm causes the power density at its ~;~LL ~l ~;ng rc,.iu~.led spot 510 to rise to a level at which the desired nrnl ;nC-~r e~fect of L pl-uLoll absorption and 550 nm r~ At; ~n to occur, the power density also rises in adjacent memory layer 30z due to the 30 overlap of the beam. Beams 512a, 512b and 512c do not overlap between the focal plane 514f and another plane 5141. Beams 512a and 512b overlap, an~ beams 512b and 512c overlap, between planes 5141 and 5142, and all three be ms overlap to the left of plane 5142. The power density at 35 any ~Lù6~ ee_Lion of a beam 512 decreases in proportion to the square of the distance of the ~Lu~s-s~ Lion from the Wo 95/16994 ' 7 Pcrluss4/l4l46 focal point 510, so th~ power density of the beams at large distances from focal point 510 is PYr~PrtP~l to be very low. Near the focal point, however, the overlap of adjacent beams may result in achieving sufficient power 5 density for; ~ L~rl~ absorption, with the result that crosstalk may occur am~ng datels of adjacent pages. If beams 512 of FIGURE S are 920 nm WRITE beams, writing may undesirably occur at ~ ~JLL~ ;n~ datels of pages of memory other than the clesired page.
According to another aspect of the invention, a sparse light pattern is used, to move the beam overlap locations to such a large distance from the focal points that the power densities of the beams are too low to affect the memory material except at the focal points. This is 15 ~,, liChPd by writin~ mutually adjacent datels only during different writing intervals, 30 that beams are never simul~ npnllcly rC)~ c~p~l on mutually adjacent datels of one page. As a resu~lt, the beam overlap is moved to a more remote location. This may be uu,d6:L~l ood by referring 20 to FIGI~RE 5, and ;r-ginin~ that beam 512b is eliminated, so that only beams 512a and 512c are present, focussed on semi-adjacent spots 510a and 510c, respectively. In such a ciL~u.w~ ce, the first beam overlap would be the overlap occurring at plane 5142, more distant from focal 25 plane 514f than plane 5141. Ac a result of the increased distance of the first beam overlap from the focal plane with sparse beams, the power density at the overlap is cj~n;f;t~rr~ntly reduced, thereby reducing the l;kPl;hnod of _ ~d interaction and the resulting undesired 30 crosstalk. By P~Pncic~n of the above method, simultaneous beams might be rc~.ur,rie-l only on spot~ s.:~c.L~ted by two, five, ten or more datels, thereby moving the light beam overlaps to very large ~istances from the focal plane, at which distances the bea~ power densitie~ are so low that, 35 even ~rhen overlapped, the beams cannot cau~e an WO 9~/16994 2 1 7 9 ~ 7 7 PCTIUS94/141~16 interaction with the memory material so as to create crosstalk .
According to a further aspect of the invention, the sparse light pattern is used in ~u~jull~Lion with physical S translation of the memory block relative to the light beams, to thereby allow all datels to be ~ s~cl by a NRITE beam. FIGURE 6a illustrates an aLL~ L of sparse beams interacting with a memory block. In FIGURE
6a, elements ~_CJLL~ ;n~ to those of FIGURE 4 are 10 designated by like reference numerals. In FIG~lRE 6a, WRITE beam 428 consists of spaced-apart beams 623a, 628b,..., 628n, generated by a spatial light modulator, such as modulator 426 of FIGURE 4, having an active region pattern such as that illustrated in FIGU~E 6b. In FIGURE
15 6b, the active modulating regions are illustrated as hatched regions 624, spaced from each other by A~
regions 626. Thus, only non-adjoining modulated beams 628a, 628b,..., 628n (FIGURE 6c) are ~L~,-lu~ ed. ûf course, the active regions 624 illustrated in FIGURE 6b may be 20 spaced apart by two, three, five, ten or more inactive regions"l~r~n~limJ upon how sparse the beams are to be.
Non-ad~acent modulated beams 628a, 628b,..., 628n of WRITE
beam 428 of FIGURE 6a are applied to a microlens array 610, which focuses at a focal plane 612. WRITE beam 428 25 of FIGURE 6a i5 ~ LLe ~ed by spatial light modulator 426 of FIGURE 4. The pattern is f6~;u :sed by a 2-D microlens array 610 of FIGURE 6a. Each lens or lenfilet of microlens array 610 has a .1i t~-r matching the pixel size of SL~I
426 of FIGI~RE 4. me fG.iu~ed 5pot size is smaller than 30 the size of a lens element of microlen5 array 610.
Therefore, a pattern is created at a plane 612 which CGLL~E~Jllds with that shown in FIGURE 6c with the bright spots 690, if any, which are y~.~eL~ted by the current state of modulator 426, appearing at the centers of the 35 el ~ Ls of an "invisible" lattice designated 698 . me side of one cell of the lattice equals the size of one W0 95116994 ~ ~ 7 ~ ~ 7 7 PCrlUss4/l4l46 element of the microlens array. Any bright spot 690 in the lattice will be separated from another bright spot in both x and y directions by at least the ~ r of a microlens element. A ~ocussing relay lens 614 couples the S sparse beamg to an ele_--uu~Lic or r- '~ ic:~l zoom lens 616, which ultimately ad~usts the focal depth of the beams within memory block 10, 36 but causes the beams to diverge. The same pattern of light and dark focal spots is then reimaged inside the memory block by lens 618. The 10 size of the imaged focal spots within the memory material is selected to be about 1/2 of the datel tl; - - ion in the X, Y, and Z directions. At the focal plane, imaged bright spots, if any, are separated from other spots by a multiple of the datel 3; ~innC in both the x and y 15 directions. The multiple can be one, afi suggested by FIGURES 6b and 6c, or the multiple can be two, three, ten or more, rl~pontl;n~ how sparse the beams are ~ci~nprl.
Thus, no adjacent datel will be written 5imU11 Anoou~S~y.
As so far described, writing may be r I i ch~c~ at sparse 20 locations at any page within the memory. If spatial light modulator 426 of FIGURE 4 is a 5120 x 5120 array, to ULL~iLJUlld with the datlal locations illustrated in FIGURF
1, but the modulator aclaive surface is sparse by a factor of, for example, ten, 5~ that the active portion is 512 x 25 512 ~ , the active 512 x 512 portion is termed a paragraph, as described above, and there would be, in the case of the example, 102 - 100 paL~.~L~ylls per page. Access to the dirferent PA ~ 9~J~ locations is achieved by a - 5~niC~l X-Y tranglation stage 622, coupled to memory 30 block 10, 36, which translatesl by an integer number of datels, to bring different P~SLC~LC~ 5 of memory block 10, 3 6 under the sparse bezlm ( interstitial writing) . The tl;CplA ~ in x or y direction may be 5 ~Lm per steps for 10 steps in each directi.on. Use of a pi~o~l ectrically 35 driven translation stag~! can re5ult ia ~ less than 30 ,usec access time between paLc,~ hs. Thus, all portions of the memory can be written, by s~-lec1 ;n~ the c-~Lv~Liate WO95/16994 2 1 7 9 1 7 7 PCT/USg4/14146 paragraphs by translation by means of stage 622. As an alternative to translation stage 622, the interstitial writing can be achieved by tilting a transparent 2 mm parallel plate 620 in a step of about 0.2- around the x, 5 y, or both axes to provide x or y motion of the focussed beams, or to rllqrlAce the image to any desired interstitial location.
Reading is ~ ~ 1 i ch~-l by applying a "sheet" o~ light to the glass sheet associated with one layer or page of 10 memory 36 of FIGTlRE 4, under the control of address block 438, which is ultimately under control of the memory read-write portion of the associated computer. In FIGURE 4, a read beam 400 at about 400 nm is applied to an acoustooptic (AO) device illu~LL~Led as a block 442, 15 together with additional control signals, if nP~-P~ y, for g~ nnim~ the read beam from page to page of the memory, and the resulting beam is spread along the upper edge of the glass sheet of the a~Iu~Liate page by a spreading deYice illustrated as a cylindrical lens 444 for 20 creating a highly elliptical beam, the major axis o~ which is parallel to one of the glass layers of the memory, for being coupled thereinto. r~--rl ~ ng of read light could also be ~ qh~d by a system of optical fibers and star couplers as described in cu.ljun~Lion with FIGURES 3a 25 and 3b. While the memory material ha~ a moderate absorption ~;r-~S~ e3~ Lion at 400 nm, the trAncp~rent glass guiding layer carries the read light deep into the cube as described in ~ -jul.~Lion with FIGURE 3b. ~he 400 nm light is ~hq-rhPtl by the DODCI ~ L of the memory material, 30 which fluoresces at a wavelength longer than 615 nm only from locations at which the logic one state is stored, and not from locations at which a logic zero state i8 stored.
Thus, a region adjacent to the glass sheet ~1U~Le:~CC3 to provide an indication o~ the state of the memory material.
35 Because of the ~vP,._~_e.-L decay of the 3g5 nm read beam light in the memory material and in the spacer, paqes of Wo9~/16994 2 ~ 79 ~ PCT/USg4/14146 memory remote from the sheet of glass associated with the page being read do not receive sufficient light to fluoresce. The fluoreccing signal dye material produces light at a wavelength longer than 615 nm, to which the 5 memory material is ~Lc.,,~ ~ar~,.L. The fluc,Ler ~el. e of the DODCI or other signal dye at or near the focal plane is picked up by focussing system 434, and formed into a collimated beam 448, wh ich passes through dichroic mirror 432, and reflects from dichroic mirror 430, to direct the lO collimated light beam through an array of pinholes onto an output array 450 of phc~toclat~rt~-s. The array of pinholes has a sparse pattern tc~ match the format of the light array created at the plane 612 of FIGURE 6a. More particularly, each pinhole is located at the center of a 15 cell of the invisible sparse lattice. The ~ i Pr of Qach pinhole is much s~ ~ ler tllan the size of the cuLL~ nq cell. The col l ecta~ light beam will form an image at the plane where the pinhn~a-: locate. Only those passing through the p~nhrl~s will are reimaged by the 20 pinho~es, to produce a diverging beam ~rom each pinhole which is i 11 llmi n:lt~Pd by the sparse pattern. The diverging beam from each pinhole il-LeLue~L:, a phuLod~:Lector in the plane of the array of plloto~et.ectors. Array 450 inr]llAac one location or pixel for each datel of one paL~l~L~l~h or 25 page of memory 36. Light beam 448 is sensed by array 450, and only those piYels respond which are a6sociated with fluorescing ones of the datels of memory 36, which means that the piYels of ~ a~ array 450 which respond are those which receive fluores~e,lL light rrOm datels of 30 memory 36 at which a logic one was stored. Since datels of memory 3 6 at which a logic zero was stored do not fluoresce when il l-~min~ted by a read beam, those pixels of 5~ - array 450 which ~ r L~ to the zero-storing datels do not respond. mus, the pattern of ones and 35 zeroes stored in one p~L JLcl~h of one page of memory ~6 is replicated on deL~ ~ol array 450 when the whole ~Lc~yL~pl or page is ~-d-l-e-secl by a read beam. Array 450 may be, _ _ _ _ _ _ _ _ _ _ . _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Wo 95/16994 2 t 7 ~ t i~ 7 Pcr/uss4/14146 for example, a CCD pll~ s~ r array, well known in the television art. The image-~e ~.es~-.L~tive signals may be read in a conventional manner with a parallel output signal bus, and coupled to a utilization ~ L~,L4s such as 5 a computer.
As - i ~.n~l above, the use of one-photon absorption signal dye, such as DODCI, for reading, reduces the power requirements Of the READ light source or laser, and because the one p1.~,Lc~-l material is more ~f l~ nt in 10 producing fluL)Le~- eslce, reduces the amount of memory material which must be written in order to produce a c~-~n;hl ~ READ 5ignal . The reduced requirement for written material also reduces the power requirements of the WRITE and ERASE light source5. AEI analysis of system 15 power requirements of 2-D read, write and erase systems which use _ plluLu.. absorption ~Luces~a_ eYclusively ~u~y~i~,Ls that such systems require high power, short-pulse lasers for reading, whereas the systems of the invention require f:i~n;f;ci~ntly less laser power, which may be ZO available from a CW laser. Also, the inventive systems appear to require about u~.~ tt:--LI- the pulsed power for writing and erasure, and one-third the reading power. The reduced power requirement5 of the 5y5tem according to the invention at least allows a greater pulse repetition rate 25 for reading and writing by comparison with exclusively-L..v pl-.oL~-. absorption~ so that an; ~ of data LLC~ reI rate by a factor of lO is An~ic;r~lte~.
As ;nnod~ one of the i-lv~--Lc-~. s of the use of fulgides as memory materials is that they are relatively 30 stable, and can r-;nti~in the written 5~ate for ye~rs at room ~ Lu.e. However, erasure may often be desired in ordinary operation of a data memory. In the of FIGURE 4, erasure is ~ h~ by applying an intense beam Of light at 710 nm to the datels 35 to be erased. More sr~c;fic~lly, the ~ L~ selects _ _ _ _ _ Wo 95/16994 2 ~ 7 ~ PCTIUS94/14146 those datels which are to be erased at each page or current paragraph of tlle current paragraph or page, if lrplir~hle, of memory. For each page (or paragraph thereof), those piYels of a spatial light modulator 460 5 UULL- -.L~ i nrJ to the datels to be erased in the current paragraph or page are set to a reflective condition. A
collimated, , l ~ted ERASE light beam, illustrated as 462, is applied through a polarizing filter 463, and the polarized light reflect:s from a polarized beam splitter 10 464, and passes throug~l a quarter-wa~e plate, generally as described above in relation to the W;RI~E beam. Portions of the ERASE beam arri~,~ing at spatial light modulator 460 are reflected, and the reflected portions, . .LL~ nrJ
to the datels to be erased, pass once again through the 15 quarter wave plate, and through beam splitter 466, to form a modulated ERASE beam designated 470. ERASE beam 470 is reflected by mirror 472, and by dichroic mirror 432, to pass through fo~ ccin~ system 434. The memory material is tr~nCFr.~rent to the 710 nm light, so it can reach any 20 location within block 3 6 . The photo~l.L~ t of the memory material absorbs the focussed 710 nm light at the f ocal plane through a two-photon process, and switches to its ground state. '~hus, the memory material can be erased. Those datels of memory which lie within one page 25 of memory, and which are to be erased, can be erased simult~nD~ cly.
It may be rlr~cirAhl~ to operate the memory ~ILL~, ' without An i rz~ l translation of the memory block or the light beam source. In FIGURE 8, a source of data 810 ~L..du~es parallel data to be stored, together with clock 30 and timing signals, which are applied to a one-of-four mul~ Yer 812. One-of-foUr mult;~ Y~r 812 accepts the PArA11~1 data to be stored, and routes the first set of data (one ~ L~L h) to a spatial light modulator (SLM) 826a. Light modulator 326a is associated with a polarized 35 beam splitter 420a and ~ ~UrlL L~L-W_V~: plate 824a for modulating an ~ lAtled collimated, polarized WRITE beam Wo 95116994 2 1 7 ~ ~ 7 7 PCr/Uss4/l4~46 814a, to produce a modulated output beam 828a. ~IGURE 9a illustrates a portion of the face of spatial light modulator 826a, identifying the active ~l~ Ls by the numeral "1". Each active element modulates one bit of the 5 data to be stored. The row and column locations of the active el~ Ls are identified by roman numerals and capital letters, respectively. As illustrated, the active Ls of SLM 826a are IA, IE, IIC, IIIA, IIIE, IVC...
The other elements of S~N 826a are absorptive, and do not 10 modulate the beam. One-of-foUr multiplexer 812 routes the second set of data from source 810 of FIGURE 8 to an SI~
826b, which is associated with a polarized beam splitter 420b, and a quarter-wave plate 824b for modulating an lated WRITE beam 814b, to produce a modulated output 15 light beam 828b. FIGURE gb illustrates a portion of the face of SLN 826b, . u,, _l lin~ to the portion of SL~ 826a illu~Lr ~ted in FIGURE 9a, with the active Pl ~
designated by the numeral "2". The third and fourth sets of data from source of data 812 of FIGURE 8 are routed to Z0 SLMs 826c and 826d, which are associated with quarter-wave plates 824c and d and polarized beam splitters 420c and 420d as described above, for modulating beams 814c and 814d, respectively. The ~ ocl elements are absorptive. FIGURES gc and 9d Le~l e~el-L by the numerals 25 "3" and "4", respectively, the active ~ L:j of the illu~-LL~,ted portion of the faces of SLMs 826c and 826d, respectively.
As illustrated in FIGURES 9a-9d, no numeral is ad~acent a like numeral, so at any one time, the 30 modulation is sparse. Referring to FIGURE 8, a mirror 840 reflects modulated light beam 828a toward half-silvered mirror 842a, where liqht beam 828a would combine ~ith beam 828b, if both existed simult~n~-o~qly. The "two" beams proceed toward half-silvered mirror 842b, where they 35 "c in~ with beam 828c. All the beams are '~ ino~
to~eth~r by half-mirror 842c. When properly aligned so ~ ~793 77 Wo 95/16994 i Pcr/uss4l14146 that the ~1 ~s are in registry, the beams generated by the various active elements are inte -~eL2~ed~ as illustrated in FIGURE 9e. The inteL.,~eL~,ed beams are applied through a dynamiic focus aLL_, L 434 similar to 5 tbiat described above, for focllccin~ into memory block lO
or 3 6 . To reduce loss, polarized beam combiners could be used instead of half-silvered mirrors.
In operation of the arr~~ ~ of FIGURE 8, the combined WRITE beam is seguentially modulated by the 10 patterns of FIGURES 9a, 9b, 9c and 9d. Therefore, the ru. u~bed light beams within the memory block are at all times spaced apart, but writing to the various locations of dl~ferent paL- ~L~ S is a~ h~l without physical translation of the memory block.
If tbie combination ~f a plurality of modulators as illu,.~L~ted in FIGURE 8 is insufficient in combination to write one entire page o~ memory, as for example if each of the four SL~s 726a-d is a 502 x 502 modulator, and a page as 5020 x 5020 datels, the electronic sparse writing 20 scheme may be used in combination with a translation aiLLG1~y ~, with the a~lv~ a~e of reducing the number of translations per unit time, and increacing the minimum step size.
The a~Lc.l, of ~our discrete SLMs arranged as in 25 FIGURE 8 may be viewed as a single SLII, in which all e] ~ are active as iLn FIG~lRE 9e, but in which the data is applied to different sets (sets l, 2, 3 4) of the ~1 , and the other ~1 ~ g remain in their absorptive state. Thus, a simple large SI~ may be used, 30 in which all Pl ' ~4 a~ e active, but which are seq~nl-i~lly enabled in a sparse manner, as suggested by FIGURE 9e. When a larg~ number of inactive modulator 5 Sey liL~l~e the active -1 ~ , a very large number of poccihle sparsing ~.lL~...s exist.

Wo 95116994 ~ 1 7 q ~ 7 7 Pcr/Uss4/l4l46 FIGURE lOa is a simplified p-~ e~ l ive or ir ' ic view useful in PYr~l A i n i n~ another : - ' i L of the invention. In FIGURE lOa, a block 10 of optical memory material, which may be a block using the fulgide and 5 signal dye compositions described above, but without the u~- u~V~ iOn dye, is associated with a first WRITE light projector lolo, which includes a source of light 1012, a beam QYpAndpl- 1014, if nPCP~Ary, and a cylindrical lens 1016 for shaping the oYrAn~lPCl light into a thin sheet of 10 light or "fan" shaped beam 1018, elongated in the Y
direction, which; ln~c on face 12 of memory block 10.
The plane of sheet beam 1018 is rArAl 1 Pl to the YZ plane.
A second WRITE light projector 1020 inrl~ Q~ a source 1022 of light, a beam Q-~AnA-~- if nDc~ y, and a cylindrical lens 1026, for shaping the light from source 1022 into a thin fan beam 1026, elongated in the Y direction, impinging upon block lo at a face ortho~nAl to ~ace 12.
The sheet of light beam 1026 lies parallel to the XY
plane. Fan beams 1018 and 1026 ~ntP~ s~rt within the block 20 along a vertically ~ rosPcl (parallel to the Y axis) line or column, illustrated as 1030 in FIGURE lOb and in the top view of FIGURE lOc. With the dLL , L of FIGURES
lOa, lOb, and lOc, a vertical column of memory material may be written simul~AnQ~ 21y, with the transverse 25 d 1 - ' ~ nc of the column being estAhl; ~hP~ by the fl1 inn~:: of the i l Pr je~ Lion of the beams. The two fan beams will tend to have relatively large LLc---n~-. Le or lateral d i ~ n~ near the cylindrical lens by which they ~re focussed, and also far from the focal point, as 30 sUggested by the shape of beams 1018 and 1026 in FIGURES
lOb and lOc, with a narrow or rc,~;u:",ed region (a waist) at moderate distances from the cylindrical lens. The two beams are made to il.L~:L~e-.L at a locat~-~n such as 1030 near the focus of the beams, to reduce the size of the 35 column of datels which is ultimately written at the beam ~n~QrSPrti~n. The beam intQ~sPCti~n will have finite but writing does not take place at any WO 95/16994 2 J 7 9 ~ 7 7 PCr/USs4/l4l46 location within the memory block, except at the intersection, because that is the only location at which the beam intensity is high enough to cause the nr-nl inP;~r interactions which result in writing. The memory material S may be a; . ~I.oL~.. absorbing material, such as those described above. The two beams may ~e at different rL~ iPC, such as 1300 nm and at 890 nm, for writing to the ab~ Lioned fulgide materials, but the LLæ lU~ riPc may of course be sPl et t~od for the particular material 10 being used.
As so far described, the A~ of FIGURES lOa, lOb, and lOc is capable of writing only to a narrow cylindrical volume (1030 of FIGURES lOb and lOc) vertically ~;crnaP~3 (pa~allel to the Y axis) in the memory 15 material. If, however, light source 1012 of FIGURE lOa includes a modulator, illdividual datels may be simult~nPollcly written into a particular column.
r ; ~;n~ that the me~ory material contains no internal boundaries, it is usefu3L to identify locations by their 20 column, and by the "flot~r" or "story" in that column. If, for example, WRITE light source 1012 of FIGT~RE lOa ;nl-lu~ac a column light modulator, such as a vertical 1 X
1024 pixel array, with c~ne pixel above another, as many as 1024 pixels could be si~lult~nP~IlRly written at different 25 vertically rl; cr~aP~ stot ies in column volume 1030 of FIGURES lOb and lOc. ~21ch story, in that instance, would contain one datel. Thu~, a "~a-c,g-~l-" as described in ...,..ju~.. ~ion with the ~r~_, ' of FIGURE 4 CULLC:~U~S, in the ~ of FIG~RE lOa, to a colulgn. The lateral 30 rl~- ir~nC of the column~ are P~P~-t~PCl to be sllffi-~iPntly large 50 that writing single datels into each story would be wasteful of useful memory material.
According to another~ aspect of the invention, light Cource 1012 of FIGIJRE lOa ; n~ pc a two-~ nAl 35 column modulator, such as an 8 X 1024 modulator. While it wo 95/16994 ~ 7 7 9 ~ 7 7 PCT/USg4/14146 is actually a two-fl; innAl modulator, its ~ ~~;nn~:
are 50 much like a column that it may be considered to be quasi-One-~li -jnnAl (q-1-D). Thus, tilis d~L~ may be termed "q-1-D." FIG~RE 11 is a Ri ,lifiP~ block diagram S of a memory system according to the q-1-D d~L~..Ci~, and is generally similar to FIGURE 4. In FIGI~RE 11, element$
cuLL--l,.. ling to those of FIGURE 4 are designated by like reference numerals in the 1100 series rather than the 400 series. In FIGURE 11, an ~ - lAted WRITE light source 1110 at 890 nm is applied to a l-D or line beam PYpAn~lP~
1112, which generates I - ~ 1 Ated l-D W~ITE beam 1114 . A
polarizer 1116 polarizes beam 1114 in the direction of aL.. --~7 1118, and the resulting polarized beam is reflected by polarized beam splitter 1120, to form beam 1122. Beam 1122 is applied through a quarter-wav-e plate 1124 for polarization rotation, and is applied to a q-l-D
(8 X 1024 pixel) spatial light modulator 1126, to which the information to be written to the memory cube is also applied from _ L~L 1137. The spatial light modulator 20 lies parallel to line beam 1122, and the piYels are modulated by the information, to produce a l-D WRITE beam, modulated by rPfl ecti nn o~ the associated pixels of the SLM. The modulated beam passes through quarter-wave plate 1124 to let~P its polarization rotation, emerging as a 25 beam 1128. Beam 1128 passes through beam splitter 1120, and through mirrors 1132 and 1148, and through a foc~ ; n~
system 1134 which mdy include a zoom lens controlled by address manager 1138. From foc~ n~ system 1134, the modulated l-D beam passes through an acousto-optic device 30 controlled by address manager 1138, for being d~flectP~ to cause beam 1128 to LL~ L--e the column to be written, and the ~fl~Pcf~9 modulated beam 1136 is L~ f6~;u~sed by a lens system 1190 as a sheet within cube 10. Lens system 1190 in effect adjusts the focus of beam 1136 to place the 35 waist of the beam near the desired in~ ct{nn column 1030 within the cube. However, the modulated 890 nm WRITE

W095/16994 2 1 7~ ~ ~7 PCT~Sg4/14146 beam 1136 does not have the intensity at any location within cube 10 to write datels.
At the same time that modulated beam 1136 is applied to cube 10, a second , - 1 Ated sheet WRITE beam 1146 at 5 13Q~ nm is applied fro~ an u~L~ cJ~ Al direction, as generally described in conjunction witll FIGURES lOa, lOb, and lOc. Beam 1146 of FIGllRE 11 originates as beam 1101 from a source (not illustrated in FIGURE 11), is rPflPct~cl from dichroic mirror 1196, and passes through dichroic 10 mirror 1198 to a dynamic focussing system 1194 and ~_uus~Lou~Lic device 1142, both controlled by address manager 1138, which adjust the focus of beam 1146 to place the waist of beam near the desired intersection point within the cube. Beam 1146 alone also lacks sufficient 15 energy to cause writing, but at the intersection column 1030, the i"~Cl energies are sl~1'f~iPnt to write at the bright spots resulting from the reflective pixels of spatial light modulator 1126. Tl - lAted WRITE beam 1146 may be viewed as "sensitizingN a plane of memory material, 20 so that writing may be ~ hP~i in the sensitized plane by the bright spol~s of i--Le.~e. Ling modulated WRITE
beam 1128.
The sparsing of the beams described in c u..j u..-_Lion with FIGURES 5, 6a and 6b is for the purpose of prevention 25 of writing to pages of 1 he memory material which are closer to and farther from the WRITE beam source (adjacent pages in the Z directiol~) than the page to which data is to be written. The pn~sihil 1ty of writing to such adjacent pages, in turn, arose from tlle high power density 30 of the WRITE beam, and from the pn~ ility of overlapping of the beams of adjacent: datel~ being written. In the of FIG~RES lala, lOb, lOc, and 11, the pncq~hil1ty of croggtalk to adjacent pages does not exist, because neither of the two in~PrseC~i in~ beams alone has 35 enough power density to write, and, so long as the waist WO 95/16994 2 1 7 ~ 1 7 7 Pcr/uss4ll4l46 region of, 1 ~ted sheet WRITE beam 1146 is sufficiently small in the intersection region, it "sensitizes" only one page, and there is no possibility of writing to pages which are adj acent in the Z direction .
5 ~ e~ Lly, the modulated liRITE beams need not be sparse in the X direction. However, crosstalk between datels can take place in the Y direction, because the - = l Ated WRITE beam sensitizes an area, rather than a line, in the XY plane. Therefore, the WRITE beam must be sparse in the 10 y directiOn.
FIGURE 12a is a view of a portion of 8 X 1024 spatial light modulator array 1126 of FIGURE 11, in which there are eight pixels horizontally, and 1024 pixels vertically.
Shaded pixels, such as piYels 1210, are absorptive, and 15 modulate the write light beam with a "dark" spot of zero intensity (no writing~, while the l~n~ d pixels, such as pixels 1212, ~e~fLesel~L reflective pixels which produce bright spots when the beams are ~ 6ed. FIGURE 12b is an illustration of the bright spots (if any exist as a 20 result of the information being modulated) of the "invisible lattice", which occur at a focal plane in the optical system of FIGURE 11 ~.uLL- lf- lin~ to plane 612 of FIGURE 6. In FIG~RE 12b, dots 1210 2 e~re~e~L the bright spots, which coLL~D~,u.-d with reflective pixels 1214 of 25 FIGI~RE 12a. FIG~lRE 12c illuDL-ates the result of passing the light pattern of FIGIJRE 12b through cylindrical lens 1190, which results in ~ Dion of the pattern of FIGURE 12b in the direction of arrows 1200 o~ FIGURE 12b, i. e. reduces the X ~1; inn without reducing the Y
30 ~lir inn In FIGURE 12c, all the spots 1222 are ~e~LeDe..Led as bright spots for ease of understanding.
The eight spots 1222 of each horizontal row are closer in the X or horizontal direction than in FIGURE
12b, but not closer in the Y or vertical direction. This 35 i8 the definition of a beam array which is sparsed in the vertical direction. Thus, the beam ~ludu~ ed by WRITE

217ql77 WO 95/16994 PCTiU~94/l4l46 light source 1110 of FIGURE 11 is made into a ~uasi-line beam by f~ Pr 1112, the beam is modulated, and the modulated beam is again passed through a cylindrical lens to reduce it to the final q-l-D for~, thereby aL 1 i~h;n,J the spar~ing in the vertical direction, as i n~ in uu~j u~ ion with FIGURE 12a, 12b and 12c .
Erasing is aL 1 ;ChPf~l in the arL_, of FIGURE
11 in generally the sa~e manner as writing. In FIG~lRE 11, an erasure beam 1162 al: 710 nm i8 applied through a 10 polarizer 1164, and th~- pûlarized beam is r~fl e~ t~ 1 by a polarized beam splitter 1166, through a quarter-wave plate to an erase spatial light modulator similar to SI~l 1126, which receives information from a source (not illua-r ~It~d) relating to the datels to be erased. The modulated ERASE
15 beam, L.:~L~:se--ted as 1170. is reflected by a mirror 1172 and by dichroic mirror 1132, and then follows the same path as that described for the I 1 ~ted WRITE beam through fof~ nfJ system 1134, acoust~optopif- device 1188, and lens system 1190. Thus, a sheet ERASE beam modulated 20 with the datels to be erased i5 applied to memory cube 10, at a power level insufficient to erase. At the same time, a second, ~ lAted ERASE be,~m 1186 is r~fl~ tf~l by dichroic mirror 1196, alrld follows the same path ~ LL
as ~he l~ted READ beam 1100, through focussing 25 system 1194, a-,-,uDLu~-ic device 1142, and lens system 1192, into cube 10. Th~ modulated and ~ tf~-l ERASE
beams i ~ f~ L in a co]Lu~n, with bright spots at the locations to be erased, much as described in ~,..ju..uLion with the READ function. Alternatively, if entire columns 30 are to be erased simul~n~ou~ly, erasure beam 1162 can be Applied directly to mirI-Or 1172, without passing through SLM 1160.
Reading is ~ hfJ~fl in the aL- , of FIG~lRE
11 in a manner generally similar to that described in 35 _~,..; u.. Lion with FIGURE 4, in that a planar light beam is ,,, , , . .,,,,,, _, ,, _,, _, , , _,,, . , , _, . ,, , ,, _, , _ _ _ _ _ WO95/16994 2 ~ 7 9 i 7~ PCT/US94114146 ~ 40 ~
passed through the block of mQmOry material, to cause one-photon absorption by the signal ~ ' of the memory material. In FIGURE 11, a READ light beam 1100 at 395 nm from a source (not illustrated) is applied through S dichroic mirrors 1196 and 1198 ~ and thereafter the READ
light beam follows the same path as the above described erasure beam 1186r being cG,.~.~LLe~ to a sheet or fan b~am with a narrow waist, such as that described in cu..Ju..u~ion with FIGURES lOb and lOc, near the region to be read. The 10 sheet READ beam is deflected by an ac~ uDLou~Lic device 1192 to the ~Lu~r iate Z position to intercept the column to be read. In the region ~ min~ted by READ beam 1100 within cube 10, the signal dye associated with datels in a written state fluur~sces. The flu.,L._Je~.~.e of a 8~1 ect~
15 q-l-D column is imaged by lens system 1190, a..uuDLou~Lic device 1189~ and ~o~ Rcing system 1134~ to form a read information beam 1148 ~ which is coupled to an output array 1150 of d~t~cto~s by dichroic mirrors 1130 and 1132.
Dei ~ctnr array 1150 L~'i~V~dS to the information light by 20 producing parallel signals Lc~L~s~..Ling the state of each of the datels of g-l-D column 1030 which has been read.
Crosstalk is avoided during reading because of the narrow waist of READ beam 1100 within the cube, whereby the memory material tends to respond at only one page, and by 25 the narrow depth of focus of f~-c~ in~ system 1134~ AO
device 1189 ~ and lens system 1190 .
Since the positions of the be~m i~ Lions 1030 within cube 10 of FIGURE 11 are esf ~hl i Ch~d by beam fl~ri inn provided by ac.,uDLDu~Lic devices 1142 and 1189 ~0 physical translation of the cube relative to thQ beam-forming DL~u~;LuL~ such as that described in c~..j~.uLion with FIGURE 4 ~ is 1 _ y .
Other - ' 'i of the inventio~ will be d~aL.:~L to those skilled in the art. For eYample, a plurality of 35 light sources such as laser diodes or LEDs may be coupled WO 95/16994 2 ~ 7 9 ~ 7 7 PCll[~S9d/14146 to the upper edges of gilass sheets 32 of block 36 of FIGURE 3b instead of using optical fibers 40. While the memory material has been described as being dissolved in a polymer which is then 501 i rl; f; ~1, there is no theoretical 5 necessity for the active memory material to be in the solid form; it could as easily be dissolved in a fluid such as a liquid which is contained in a LL~ ,~aLe.,t ca~ l Ar LLU.i~ULe~ in which each cell constitutes a datel. Thus, when the material is a fluid, a "slab"
10 requires a restraining ~uulld-Ly. While -- ~n;cAl translation of the memory block relative to the beams has been described in conju~lction with FIGURES 6a and 6b, the light beams themselves can be translated by translating their effective source l-elative to the memory block, or 15 both could be translatecl. While a pc~ yL~ /page system has been described, there is no requirement in principle that pages be subdivided. Instead of using a reflective spatial light modulator together with a polarized b~A~er3 itter~ as described, a WRITE laser array with 20 individually controllable drivers could be used. While the sparse addressing scheme has been described as being for the WRITE function, it may be used, if desired, for either or both of READ and ERASE f~lnrt; ~nC . While the light sources have been described as being lasers, other 25 light sources with equivalent ~-h~rAct~ristics may be used.
The signal dye, if used in the memory material, may respond when associated ~ither with written or unwritten storage ~ of the memory material. The addressing ArrA-, according t~ the invention may be used with 30 memory r-t~r;Al~ accordillg to the invention or with other memory materials, and meD10ry materials according to the invention may be used wit:h other addre~sing aLL_ ~

Claims (62)

1. An optical memory material, comprising:
a storage, component which coneverts from a first state to a second state in response to two-photon absorption of WRITE light; and a signal component which responds to one-photon absorption only at locations at which said storage component is in one of said first and second states, and not in the other one of said first and second states.

2. A material according to claim 1, wherein said signal component responds by fluorescing.

3. A material according to claim 1, wherein said signal component responds only at locations at which said storage component is in said second state.

4. A material according to claim 1, wherein said storage component is a fulgide.

5. A material according to claim 4, wherein said storage component consists essentially of one of (a) E-Adamantylidene [1-(2,5 dimethyl-3-furyl) ethylidene]
succinic anhydride, (b) 1-(2,5-dimethyl-3-furyl) ethylidene (isopropylidene) succinic anhydride, (c) 2,3-bis (2, 4, 5-trimethyl-3-thienyl) maleic anhydride, (d) cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethene, (e) 1,2-dicyano-1,2bis(2-methylbenzothiophene-3-yl)ethene, (f) 2, 3-bis (1, 2 -dimethyl-3 -indolyl) maleic anhydride, and (g) mixtures thereof.

6. A material according to claim 1, wherein said signal component consists essentially of one of (a) 3,3 -diethyloxadicarbocyanine iodide , (b) Nile red dye, (c) Pyridine-1, (d) Pyridine-2, (e) 4-(dicyano methylene)-2-methyl-6-(p-dimethylamino styryl)-4 H-pyran, (f) 2[4-(4-dimethylaminophenyl)-1, 3 -butadienyl]-3-ethylbenzothiazolium p-toluenesulfonate, (g) 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2, 2', indotricarbocyanine perchlorate, and (h) mixtures thereof.

7. A material according to claim 1, further comprising an associated apparatus together forming a system, said associated apparatus comprising:
means for concentrating writing light onto at least a portion of said material, for causing said multistate storage material to absorb said photons of light by two-photon absorption, for changing said storage component from said first state to said second state: and means for irradiating at least a portion of said active materials with reading light, for causing said signal component to respond, except at those locations at which said storage component is in said one of said first and second states.

8. A system according to claim 7, wherein said means for concentrating comprises one of focussing means and crossed beam means.

9. A memory material according to claim 1, comprising:
a frequency upconversion component which, upon receipt of a beam of light, converts at least a portion of said beam of light to a higher frequency by two-photon absorption, to thereby generate at least a portion of said WRITE light.

10. An optical memory arrangement responsive to light, comprising an active material including:
a frequency conversion material responsive to writing light (920 nm), for generating frequency-converted light (550 nm);

a multistate storage material, for changing from a first state to a second state in response to the presence of light including said frequency-converted light having a predetermined net intensity; and a signal dye material enabled for fluorescing (615 nm) in the presence of a reading light (395 nm) when the associated portion of said storage material is in said first state, and being inhibited from fluorescing when said associated portion of said storage material is in said second state.

11. An arrangement according to Claim 10, wherein said storage material is a fulgide.

12. An arrangement according to Claim 10, wherein said signal dye material is DODCI.

13. An arrangement according to Claim 10, wherein said frequency conversion material is a dye.

14. An optical memory arrangement according to Claim 10, further comprising associated apparatus, together constituting a system, said apparatus comprising:
means (410, 416, 420, 424, 426, 434) for focussing said writing light (920 nm) onto at least a portion of said active material, for causing said frequency conversion material to absorb energy of said writing light at a first frequency (920) and to reradiate said frequency-converted light at a second frequency (512 nm) higher than said first frequency, for thereby causing said multistate storage material to absorb said frequency-converted light for changing from said first state to said second state: and means (400, 442, 444) for irradiating at least a portion of said active materials with said reading light (446) at a third frequency (395 nm), for causing said signal dye material to fluoresce significantly at a fourth frequency (615 nm), except at those locations at which said storage material is in said first state.

15. An optical system according to Claim 14, wherein said apparatus further comprises:
erasing means (460, 462, 464, 466, 468, 472, 432, 434) for irradiating at least a portion of said active material with erase light at a fifth frequency (710 nm), for causing said multistate storage material to absorb energy of light at said fifth frequency and to change from said second state to said first state.

16. An optical memory arrangement according to Claim 10, wherein said active material is in solid form.

17. An optical memory arrangement according to claim 16, wherein said active material is dispersed in a polymer.

18. An optical memory arrangement according to Claim 10, wherein said storage material consists essentially of one of (a) E-Adamantylidene [1-(2,5-dimethyl-3-furyl) ethylidene] succinic anhydride, (b) 1-(2,5-dimethyl-3-furyl) ethylidene isopropylidene) succinic anhydride, (c) 2,3-bis(2,4,5-trimethyl-3-thienyl) maleic anhydride, (d) cis-1, 2-dicyano-1, 2-bis (2, 4, 5-trimethyl-3-thienyl ) ethene, (e) 1, 2-dicyano-1, 2bis (2-methylbenzothiophene-3-yl)ethene, (f) 2, 3-bis (1, 2-dimethyl-3-indolyl)maleic anhydride, and (g) mixtures thereof.

19. An optical memory arrangment according to Claim 10, wherein said signal dye material consists essentially of one of (a) 3,3 -diethyloxadicarbocyanine iodide, (b) ? dye, (c) Pyridine-1, (d) Pyridine-2, (e) 4-? methylene)-2-methyl-6-(p-dimethylamino styryl)-4 H-pyran, (f) 2[4-(4-dimethylaminophenyl)-1,3-butadienyl]-3-ethylbenzothiazolium p-toluenesulfonate, (g) 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2, 2', indotricarbocyanine perchlorate, and (h) mixtures thereof.

20. An optical memory arrangement according to Claim 10 wherein said frequency conversion material consists essentially of one of (a) Coumarin-6 dye, (b) 8-hydroxyl-1,3 6-pyrenetrisulfonic acid, (c) Nile red dye, (d) KDP, (e) PMMA doped with 2-methyl-4-nitroanilene, (f) PMMA
doped with para-nitroanilene, and (g) mixtures thereof.

21. An arrangement according to Claim 10, wherein said frequency conversion material is an electrically-poled polymer.

22. An arrangement according to claim 21, wherein said electrically-poled polymer comprises polymethyl methacrylate doped with a material having a high second order nonlinear hyperpolarizability.

23. An arrangement according to claim 22, wherein said material having a high second order nonlinear hyperpolarizability comprises 2-methyl-4 nitroanilene.

24. An arrangement according to Claim 10 wherein said frequency conversion material is crystalline.

25. An arrangement according to Claim 24, wherein said frequency conversion material is one of potassium dihydrogen phosphate and lithium iodate.

26. A memory, comprising:
a slab (10, 30) of material comprising a mixture of first, second and third compositions, said first composition absorbing energy of light centered at a first frequency (920 nm) by way of a multiple-photon absorption process, and reradiating said energy at a second frequency (512 nm) higher than said first frequency (920 nm), said second composition absorbing energy of light centered at said second frequency, and changing from a first state to a second state in response to said absorption of light at said second frequency, said second composition also absorbing light centered at a third frequency (710 nm) by way of a multiple-photon absorption process, and changing from said second state to said first state in response to said absorption of energy of light at said third frequency, said third composition responding to light at a fourth frequency (395 nm) by reradiating light at a fifth frequency (615 nm) only when the adjoining portion of said second composition is in said second (Logic 1) state, said third composition not responding to said light at said fourth frequency when said adjoining portion of said second composition is in said first state (logic 0);
means (410, 412, 416, 420, 424, 426, 430, 432, 434) for focussing light at said first frequency onto a portion of said slab, for causing said first composition to absorb energy of said light at said first frequency (920), and to reradiate said energy at said second frequency higher than said first frequency, and for causing said second composition to absorb energy of light at said second frequency, and to change from said first state to said second state, whereby said portion or said slab is written to said second state in response to said light of said first frequency; and means (400, 442, 444) for irradiating at least said portion of said slab with light at said fourth frequency, for causing said third composition to reradiate at all locations irradiated by said light at said fourth frequency, except those locations at which said first composition is in said first state, whereby said portion of said slab is read.

27. A memory according to Claim 26, further comprising:
means (460, 462, 464, 466, 470, 472, 432, 434) for irradiating at least said portion of said slab with light at said third frequency, for causing said second composition to absorb energy of said light at said third frequency, and to change from said second state to said first state, whereby said portion of said slab is erased to said first state in response to said light of said third frequency.

28. A memory according to Claim 26, in which said slab (10, 30) is in the form of a layer (30) laminated with a support (32), to form a lamina.

29. A memory according to Claim 27, in which said slab (10, 30) is in the form of a layer (30) laminated with a layer of a transparent substrate (32), to form a lamina.

30. A memory according to Claim 29, comprising a plurality of said lamina stacked together to form a laminated structure of alternating layers of said transparent substrate and said slab of mixture.

31. A memory according to Claim 30, wherein at least one of said means for irradiating comprises means (40;
400, 442, 444) coupled to an edge of at least one of said transparent substrates (32) for simultaneously coupling light to locations along said edge.

32. A memory according to Claim 31, wherein said means coupled to an edge comprises an elongated optical transmission path (40, 446).
.ang.

33. A memory according to Claim 32, wherein said elongated transmission path comprises an optical fiber (40).

34. A memory according to Claim 31, wherein the index of refraction of said transparent substrate is greater than the index of refraction of said slab of mixture.

35. A memory according to Claim 30, wherein each of said lamina further comprises a further layer (31) on a side of said slab remote from said transparent substrate, which further layer has an index of refraction less than that of said transparent substrate.

36. A memory according to Claim 26, wherein said means for focussing light at said first frequency (920 nm) comprises:
means (410) for generating a collimated beam of unmodulated light (414) at said first frequency.

37. A memory according to Claim 36, wherein said means (410) for generating a collimated beam (414) comprises a laser.

38. A memory according to Claim 36, further comprising:
spatial light modulation means (426) coupled to a source of data (437) and to said collimated beam of ted light (414), for modulating portions of said unmodulated light, to thereby form reflected modulated beamlets (428); and dynamic focussing means (434) coupled to said spatial light modulation means (426), for focussing said modulated beamlets (428) at a focal plane (510a) within said slab.

39. A memory according to Claim 38, wherein said dynamic focussing means (434) comprises a array (610).

40. A memory according to Claim 38, wherein said dynamic focussing means (434) comprises a zoom lens which is one of mechanical and electrooptic.

41. A memory according to Claim 38, wherein said beamlets are sparse, and further comprising:
translation means (622) coupled for selectively generating motion of said slab relative to said beamlets for thereby accessing different paragraphs of said slab.

42. A memory according to Claim 38, wherein said spatial light modulation means (426) comprises:
polarizing means (416) coupled for receiving said collimated beam (414) of unmodulated light, for polarizing said beam in a first direction (418) to form an unmodulated beam (422) of a first polarization;
polarized reflective means (420) coupled for reflecting said, unmodulated beam of a first polarization toward said spatial light modulation means (426), for generating said modulated beamlets (428);
polarization rotation means (424) coupled to said spatial light modulation means (426), for causing said reflected modulated beamlets (428) to have a second polarization, orthogonal to said first polarization, whereby said reflected modulated beamlets (428) pass through said polarized reflective means (420).

43. A memory according to Claim 26, wherein said second composition includes of one of (a) E-Adamantylidene [1-(2,5-dimethyl-3-furyl) ethylidene] succinic anhydride, (b) 1-(2,5-dimethyl-3-furyl) ethylidene isopropylidene) succinic anhydride, (c) 2,3-bis(2,4,5-trimethyl-3-thienyl) maleic anhydride, (d) cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethene, (e) 1,2-dicyano-1,2bis(2-methylbenzothiophene-3-yl)ethene, (f) 2,3-bis(1,2-dimethyl-3-indolyl)maleic anhydride, and (g) mixtures thereof.

44. A memory according to Claim 43, wherein said first composition consists essentially of one of (a) Coumarin-6 dye, (b) 8-hydroxyl-1,3 6-pyrenetrisulfonic acid, (c) Nile red dye, and (d) mixtures thereof.

45. A memory according to Claim 43, wherein said third composition consists essentially of one of (a) 3, 3'-diethyloxadicarbocyanine iodide, (b) Nile red dye, (c) Pyridine-1, (d) Pyridine-2, (e) 4-(dicyano methylene)-2-methyl-6-(p-dimethylamino styryl)-4 H-pyran, (f) 2[4-(4-dimethylaminophenyl)-1, 3-butadienyl]-3-ethylbenzothiazolium p-toluenesulfonate, (g) 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2,2',indotricarbocyanine perchlorate, and (h) mixtures thereof.

46. A memory according to Claim 26, wherein said mixture of first, second and third compositions is contained in a solid carrier.

47. A memory according to Claim 46, wherein said solid carrier is a polymer.

48. A memory according to Claim 47, wherein said polymer consists of one of (a) polyvinylbutyral, (b) polyvinyl acetate, (c) urethane acrylate, and (d) UV-curable epoxy.

49. An optical memory arrangement, comprising:
a slab of memory material;
memory addressing means optically coupled to said memory material, said memory addressing means including:
(a) light modulating means for modulating a plurality of light beamlets; (b) means for coupling said light beamlets as an array of spaced-apart beamlets directed toward said sheet of memory material, said beamlets being spaced apart sufficiently so that, at the locations at which said beamlets fall upon said sheet to define datels of memory, each of said datels is spaced apart from the others of said datels by an amount of said memory material corresponding to an integer multiple, including the integer one, of the dimensions of said datels, whereby not all datels of said sheet of memory material can be addressed simultaneously; and translation means coupled to one of said sheet of memory material and said memory addressing means, for translating said sheet of memory material relative to said memory addressing means by an integer multiple of said dimensions of said datels, whereby substantially all of said datels of said sheet of memory material can be addressed.

50. An arrangement according to claim 49, wherein said light modulating means comprises a spatial light modulator including a plurality of active pixels.

51. An arrangement according to claim 50, wherein said active pixels have equal dimensions and are spaced apart by an integer number, which may include the integer one, of said dimensions of said pixels.

52. An arrangement according to claim 51, wherein said pixels are reflective in one state of modulation and absorptive in another state of modulation, and further comprising:
beam splitting means coupled to said spatial light modulator for coupling unmodulated light to said pixels, and for coupling modulated beamlets from said pixels.

53. An arrangement according to claim 49, wherein said means for coupling beamlets comprises:
a lens array for focussing said beamlets at a plane;
and a lens for imaging said plane at a plane associated with said memory material.

54. An arrangement according to claim 53 , wherein:
said light modulation means comprises a plurality of active pixels, wherein said active pixels have equal dimensions, and are spaced apart by an integer number, which may include the integer one, of said dimensions of said pixels, and further wherein:
said lens array includes a plurality of lenslets, the transverse dimensions of which are substantially equal to the dimensions of said pixels of said spatial light modulator.

55. An arrangement according to claim 54, wherein said lenslets are spaced apart by said integer multiple of said dimensions of said pixels.

56. An arrangement according to claim 54, wherein said means for coupling beamlets comprises a zoom lens coupled to said lens array.

57. An optical memory arrangement according to claim 49, wherein said memory material comprises:
a multistate storage material, for changing from a first state to a second stage in respond to the presence of light having a predetermined net intensity; and a signal dye material enabled for fluorescing (615 nm) in the presence of a reading light (395 nm) when the associated portion of said storage material is in said first state, and being inhibited from fluorescing when said associated portion of said storage material is in said second state.

58. An arrangement according to claim 57, further comprising:

a frequency conversion material responsive to writing light, for generating as a frequency-converted light said light of a predetermined net intensity.

59. An arrangement according to claim 57, wherein said storage material is a two-photon absorption material.

60. An arrangement according to claim 59, wherein said storage material is a fulgide.

61. An arrangement according to claim 57, wherein said storage material is a two-photon absorption material, and said signal dye is a single-photon absorption dye.

62. An arrangement according to claim 60, wherein said signal dye is DODCI.