3-D OPTICAL DATA STORAGE TECHNOLOGY * *ABSTRACT 3D optical agents storage is the totality fond to any shape of optical agents storage in which instruction can be commemorative and/or learn delay three sizeal conversion (as opposed to the two sizeal conversion afforded, for in, by CD). Vulgar optical agents storage resources, such as the CD and DVD treasury agents as a train of impercipient notes on an interior demeanor of a disc.
In classify to growth storage cleverness, it is unwell-acquainted for discs to tarry two or roll further of these agents laminas, but their reckon is sevetrust poor past the harangueing laser interacts delay entire lamina that it passes through on the way to and from the harangueed lamina. These interactions amountr tumult that periods the technology to almost 10 laminas. 3D optical agents storage directs entrap this consequence by using harangueing directs wnear singly the specifically harangueed voxel (volumetric pixel) interacts really delay the harangueing inadequate.
This necessarily complicates nonstraight agents learning and fitness directs, in subject-matter non straight optics. 3D optical agents storage is barkred to (and competes delay) holographic agents storage. Traditional ins of holographic storage do not harangue in the third size, and are for-this-reason not strictly "3D", but further of-late 3D holographic storage has been realized by the use of microholograms. Layer-selection multilamina technology (wnear a multilamina disc has laminas that can be keep-apartially activated e. g. electrically) is too air-tight barkred. This newfangledness has the unwell-acquainted to arattribute terabyte-roll body storage on DVD-sized disks.
Data annalsing and learnend are completed by centreing lasers delayin the moderation. However, beproducer of the quantitytric disposition of the agents composition, the laser inadequate must tour through other agents subject-matters precedently it stretches the subject-matter wnear learning or annalsing is desired. Therefore, some bark of nonlinearity is insist-upond to secure that these other agents subject-matters do not interfere delay the harangueing of the desired subject-matter. 1. Overview: Vulgar optical agents storage resources, such as the CD and DVD treasury agents as a train of impercipient notes on an interior demeanor of a disc. In classify to growth storage cleverness, it is unwell-acquainted for discs to tarry two or roll further f these agents laminas, but their reckon is sevetrust poor past the harangueing laser interacts delay entire lamina that it passes through on the way to and from the harangueed lamina. These interactions amountr tumult that periods the technology to almost 10 laminas. 3D optical agents storage directs entrap this consequence by using harangueing directs wnear singly the specifically harangueed voxel (volumetric pixel) interacts really delay the harangueing inadequate. This necessarily complicates nonstraight agents learning and fitness directs, in subject-matter nonstraight optics. 3D optical agents storage is barkred to (and competes delay) holographic agents storage.
Traditional ins of holographic storage do not harangue in the third size, and are for-this-reason not strictly "3D", but further of-late 3D holographic storage has been realized by the use of microholograms. Layer-selection multilamina technology (wnear a multilamina disc has laminas that can be keep-apartially activated e. g. electrically) is too air-tight barkred. Schematic fittingice of a cross-section through a 3D optical storage disc (yellow) convulgar a agents way (orange-flame notes). Four agents laminas are seen, delay the laser vulgarly harangueing the third from the top.
The laser passes through the primary two laminas and singly interacts delay the third, past near the inadequate is at a elevated eagerness. As an in, a prototypical 3D optical agents storage apsharp-end may use a disk that looks plenteous affect a self-evident DVD. The disc contains sundry laminas of instruction, each at a opposed profoundness in the resources and each consisting of a DVD-affect contortion way. In classify to annals instruction on the disc a laser is brought to a centre at a subject-matter profoundness in the resources that corresponds to a subject-matter instruction lamina. When the laser is acetous on it amountrs a photochemical modify in the resources.
As the disc spins and the learn/transcribe mind moves convulgar a radius, the lamina is written fitting as a DVD-R is written. The profoundness of the centre may then be modifyd and another completely opposed lamina of instruction written. The absence betwixt laminas may be 5 to 100 micrometers, allowing >100 laminas of instruction to be treasuryd on a solely disc. In classify to learn the agents end (in this in), a concordant course is used save this age instead of causing a photochemical modify in the resources the laser amountrs fluorescence. This is completed e. g. by using a inferior laser agency or a opposed laser triumphlength.
The eagerness or triumphprotrrenewal of the fluorescence is opposed depending on whether the resources has been written at that subject-matter, and so by measuring the emitted inadequate the agents is learn. It should be famous that the size of indivisible chromophore monads or photobountiful perversion centers is plenteous fineer than the size of the laser centre (which is solid by the diffrforce period). The inadequate for-this-reason haranguees a enlightened reckon (maybe roll 109) of monads at any one age, so the moderation acts as a congruous body rather than a matrix compositiond by the positions of chromophores. 2. History:
The origins of the opportunity end end to the 1950s, when Yehuda Hirshberg polite-behaved-mannered-acquainted the photochromic spiropyrans and suggested their use in agents storage.  In the 1970s, Valeri Barachevskii demonstrated that this photochromism could be concocted by two-photon stimulus, and finally at the end of the 1980s Peter T. Rentzepis showed that this could bring to three-dimensional agents storage.  This proof-of-concept apsharp-end stimulated a brawny traffic of elaboration and result, and in the forthcoming decades sundry academic and retail groups keep completemented on 3D optical agents storage results and technologies.
Most of the polite-behaved-mannered-acquainted appoints are fixed to some size on the contriveer ideas of Rentzepis. A broad attribute of natural phenomena for agents learning and annalsing keep been investigated, enlightened reckons of chemical appoints for the moderation keep been polite-behaved-mannered-acquainted and evaluated, and brawny completement has been carried out in solving the problems associated delay the optical appoints insist-upond for the learning and annalsing of agents. Currently, opposed groups survive completementing on solutions delay diversified rolls of result and curiosity-behalf in retailization. *3. Processes for creating written agents*:
Data annalsing in a 3D optical storage moderation insist-upons that a modify select attribute in the moderation upon stimulus. This modify is generally a photochemical reforce of some manner, although other possibilities endure. Chemical reactions that keep been investigated embrace photoisomerizations, photodecompositions and photobleaching, and polymerization preface. Most investigated keep been photochromic compounds, which embrace azobenzenes, spiropyrans, stilbenes, fulgides and diarylethenes. If the photochemical modify is alterable, then rewritable agents storage may be completed, at fineest n maxim. Also, multiroll annalsing, wnear agents is written in ‘grayscale’ rather than as ‘on’ and ‘off’ illustriouss, is technically practicable. 3. 1 Fitness by non*-*vibratory multiphoton aridity Although tnear are sundry nonstraight optical phenomena, singly multiphoton aridity is worthy of injecting into the resources the expressive temper insist-upond to electronically intensify molecular symbol and amountr chemical reactions. Two-photon aridity is the strongest multiphoton absorbance by far, but stationary it is a very destructible lion, bringing to low resources sensitivity.
Therefore, plenteous elaboration has been directed at providing chromophores delay elevated two-photon aridity cross-sections. Two photon aridity (TPA) is the concomitant aridity of two photons of selfselfconcordant or opposed frequencies in classify to intensify a monad from one naradmonish (usually the agent narrate) to a elevateder temper electronic narrate. The temper estrangement betwixt the complicated inferior and loftier narrates of the monad is correspondent to the sum of the energies of the two photons. Two-photon aridity is a cooperate-classify coursees opposed classifys of bulk destructibleer than straight aridity.
It differs from straight aridity in that the agency of aridity depends on the balance of the inadequate eagerness, thus it is a nonstraight optical course Fitness by 2-photon aridity can be completed by centreing the fitness laser on the subject-matter wnear the photochemical fitness course is insist-upond. The triumphprotrrenewal of the fitness laser is clarified such that it is not straightly exhausted by the moderation, and for-this-reason it does not interact delay the moderation save at the focal subject-matter. At the focal subject-matter 2-photon aridity befits expressive, beproducer it is a nonstraight course relative on the balance of the laser fluence.
Writing by 2-photon aridity can too be completed by the force of two lasers in contemporaneousness. This direct is typically used to complete the convulgar fitness of instruction at once. One laser passes through the resources, defining a continuity or flatten. The coopeadmonish laser is then directed at the subject-matters on that continuity or flatten that fitness is desired. The contemporaneousness of the lasers at these subject-matters intensifyd 2-photon aridity, bringing to fitness photochemistry. 3. 2 Fitness by sequential multiphoton aridity Another adit to fit resources sensitivity has been to inure vibratory wo-photon aridity (too public as "1+1" or "sequential" 2-photon absorbance). Nonvibratory two-photon aridity (as is generally used) is destructible past in classify for stimulus to select attribute, the two curiosity-behalfing photons must get at the chromophore at almost precisely the selfselfconcordant age. This is beproducer the chromophore is feeble to interact delay a solely photon nondescript. However, if the chromophore has an temper roll identical to the (weak) aridity of one photon then this may be used as a strideping stone, allowing further insubservience in the pretense age of photons and for-this-reason a plenteous elevateder sensitivity.
However, this adit results in a forfeiture of nonlinearity compared to nonvibratory 2-photon absorbance (past each 1-photon aridity stride is essentially straight), and for-this-reason betrays compromising the 3D conversion of the appoint. 3. 3 Microholography In microholography, centreed gleams of inadequate are used to annals submicrometre-sized holograms in a photorefrbountiful esthetic, usually by the use of colstraight gleams. The fitness course may use the selfselfconcordant barks of resources that are used in other types of holographic agents storage, and may use 2-photon coursees to shape the holograms. . 4 Grounds annalsing during manufacturing Grounds may too be inventd in the manufacturing of the resources, as is the subject delay most optical disc shapeats for retail agents classification. In this subject, the user cannot transcribe to the disc - it is a ROM shapeat. Grounds may be written by a nonstraight optical direct, but in this subject the use of very elevated agency lasers is desirable so resources sensitivity befits near of an consequence. The dishonorable of discs containing agents molded or printed into their 3D composition has too been demonstrated.
For in, a disc containing agents in 3D may be affected by sandwiching coincidently a enlightened reckon of wafer-thin discs, each of which is molded or printed delay a solely lamina of instruction. The resulting ROM disc can then be learn using a 3D learning direct. 3. 5 Other adites to fitness Other techniques for fitness agents in three-dimensions keep too been examined, including: Persistent *spectral** **cavity enduring* (PSHB), which too allows the possibility of shadowy multiplexing to growth agents dullness. However, PSHB resources vulgarly insist-upons exceedingly low temperatures to be maintained in classify to escape agents forfeiture. Void* shapeation, wnear indiscernible bubbles are prefaced into a resources by elevated eagerness laser irradiation.  Chromophore poling, wnear the laser-inherent reorientation of chromophores in the resources composition brings to learnable modifys. *4. Processes for learning agents*: The learning of agents from 3D optical memories has been carried out in sundry opposed ways. Timeliness some of these trust on the nonlinearity of the inadequate-matter interforce to conquer 3D conversion, others use directs that spatially defecate the resources's straight repartee.
Reading directs embrace: Two photon aridity (resulting in either aridity or fluorescence). This direct is essentially two-photon-microscopy. Straight stimulus of fluorescence delay confocal balancethrow. This direct is essentially confocal laser scanning microscopy. It offers stimulus delay plenteous inferior laser agencys than does two-photon absorbance, but has some unwell-acquainted problems beproducer the harangueing inadequate interacts delay sundry other agents subject-matters in abstracted to the one substance harangueed. Measurement of fine estrangements in the refrbountiful refutation betwixt the two agents narrates.
This direct usually inures a exposure contrariety microscope or confocal cogitation microscope. No aridity of inadequate is expedient, so tnear is no betray of damaging agents eraliness learning, but the insist-upond refrbountiful refutation opponent in the disc may period the dullness (i. e. reckon of agents laminas) that the resources can stretch due to the accumulated haphazard triumphfront errors that waste the centreed discoloration kind. Coopeadmonish harmonic progeny has been demonstrated as a direct to learn agents written into a poled polymer matrix.
Optical closeness tomography has too been demonstrated as a convulgar learning direct. *5. Resources *design: The bountiful keep-akeep-apart of 3D optical storage resources is usually an constitutional polymer either doped or grafted delay the photochemically bountiful symbol. Alternatively, crystalcontinuity and sol-gel esthetics keep been used. 5. 1 Resources shape constituent Resources for 3D optical agents storage keep been suggested in opposed shape constituents: Disc. A disc resources offers a gradation from CD/DVD, and allows learning and fitness to be carried out by the polite-behaved-mannered-acquainted spinning disc direct. Card.
A security card shape constituent resources is attrbountiful from the subject-matter of sight of portability and vacation, but would be of a inferior cleverness than a disc. Crystal, Cube or Sphere. Opposed experience myth transcribers keep suggested fine solids that treasury bodyive totals of instruction, and at fineest in maxim this could be completed delay 3D optical agents storage. 5. 2 Resources manufacturing The simplest direct of manufacturing - the molding of a disk in one concern - is a possibility for some appoints. A further frequent-sided direct of resources manufacturing is for the resources to be affected lamina by lamina.
This is insist-upond if the agents is to be naturally inventd during manipulation. However, lamina-by-lamina deciphering scarcity not moderation the sandwiching of sundry laminas coincidently. Another choice is to invent the moderation in a shape twin-fellow to a roll of obstinate tape. *6. Propel sketch*: A propel sketched to learn and transcribe to 3D optical agents storage resources may keep a lot in low delay CD/DVD propels, subject-matterly if the shape constituent and agents composition of the resources is concordant to that of CD or DVD. However, tnear are a reckon of distinguished estrangements that must be selectn into totality when sketching such a propel, including: Laser.
Particularly when 2-photon aridity is economized, elevated-powered lasers may be insist-upond that can be brawny, enigmatical to cautious, and embarrass insurance concerns. Existing optical propels economize consistent triumph diode lasers unobstructed at 780 nm, 658 nm, or 405 nm. 3D optical storage propels may insist-upon solid-naradmonish lasers or pulsed lasers, and opposed ins use triumphlengths abundantly profitable by these technologies, such as 532 nm (green). These enlightenedr lasers can be enigmatical to blend into the learn/transcribe mind of the optical propel.
Variable round imbecility amendment. Beproducer the apsharp-end must harangue opposed profoundnesss in the moderation, and at opposed profoundnesss the round imbecility inherent in the triumphfront is opposed, a direct is insist-upond to dynamically totality for these estrangements. Sundry unwell-acquainted directs endure that embrace optical elements that swap in and out of the optical footpath, emotional elements, adaptive optics, and immersion lenses. Optical appoint. In sundry ins of 3D optical agents storage appoints, opposed triumphlengths (colors) of inadequate are used (e. g. eading laser, fitness laser, illustrious; rarely roll two lasers are insist-upond fitting for fitness). Therefore, as polite-behaved-mannered-mannered as coping delay the elevated laser agency and alterable round imbecility, the optical apsharp-end must be-mixed and opposed these opposed perversions of inadequate as insist-upond. Detection. In DVD propels, the illustrious concocted from the disc is a cogitation of the harangueing laser gleam, and is for-this-reason very fervent. For 3D optical storage so-far, the illustrious must be generated delayin the lilliputian quantity that is harangueed, and for-this-reason it is plenteous destructibleer than the laser inadequate.
In abstracted, fluorescence is radiated in all directions from the harangueed subject-matter, so specific inadequate assemblage optics must be used to maximize the illustrious. Grounds waying. Once they are signed convulgar the z-axis, indivisible laminas of DVD-affect agents may be accessed and wayed in concordant ways to DVD discs. The possibility of using convulgar or page-fixed harangueing has too been demonstrated. This allows plenteous faster agents give admonishs, but insist-upons the abstractedal frequent-sidedity of spatial inadequate modulators, illustrious imaging, further agencyful lasers, and further frequent-sided agents handling. *7.
Development consequences*: Despite the elevatedly attrbountiful disposition of 3D optical agents storage, the result of retail results has selectn a expressive protrrenewal of age. This results from poor financial ending in the opportunity, as polite-behaved-mannered-mannered as technical consequences, including: Noxious learning. Past twain the learning and the fitness of agents are carried out delay laser gleams, tnear is a unwell-acquainted for the learning course to amountr a fine total of fitness. In this subject, the repeated learning of agents may rolltually attend to cancel it (this too happens in exposure modify esthetics used in some DVDs).
This consequence has been harangueed by sundry adites, such as the use of opposed aridity bands for each course (lection and fitness), or the use of a learning direct that does not complicate the aridity of temper. Thermodynamic uprightness. Sundry chemical reactions that answer not to select attribute in circumstance happen very unwillingly. In abstracted, sundry reactions that answer to keep happened can unwillingly contrariety themselves. Past most 3D resources are fixed on chemical reactions, tnear is for-this-reason a betray that either the spoken subject-matters gain unwillingly befit written or that the written subject-matters gain unwillingly accrue to substance spoken.
This consequence is subject-matterly earnest for the spiropyrans, but brawny elaboration was conducted to confront further steady chromophores for 3D memories. Resources sensitivity. 2-photon aridity is a destructible lion, and for-this-reason elevated agency lasers are usually insist-upond to amount it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to complete stimulus, but these instruments are not homogeneous for use in consumer results. *8. Academic result*: Plenteous of the result of 3D optical agents storage has been carried out in universities.
The groups that keep arranged estimable input embrace: Peter T. Rentzepis was the creator of this opportunity, and has of-late polite-behaved-mannered-acquainted esthetics bountiful from noxious learnout. *Watt W. Webb* co polite-behaved-mannered-acquainted the two-photon microscope in Bell Labs, and showed 3D annalsing on photorefrbountiful resources. Masahiro Irie polite-behaved-mannered-acquainted the diarylethene rise of photochromic esthetics.  Yoshimasa Kawata, *Satoshi Kawata* and Zouheir Sekkat keep polite-behaved-mannered-acquainted and completemented on opposed optical agents manipulation appoints, in subject-matter involving poled polymer appoints. 14] Kevin C Belopportunity is amplifying photochemical appoints for 3D optical agents storage by the use of clash temper give betwixt monads, and too amplifys elevated 2-photon cross-section esthetics. Seth Marder produced plenteous of the existing completement amplifying close adites to the molecular sketch of elevated 2-photon cross-section chromophores. Tom Milster has made sundry contributions to the speculation of 3D optical agents storage. Robert McLeod has examined the use of microholograms for 3D optical agents storage. Min Gu has examined confocal learnout and directs for its augmentation. 9 Retail result*: In abstracted to the academic elaboration, opposed companies keep been set up to retailize 3D optical agents storage and some enlightened corporations keep too shown an curiosity-behalf in the technology. However, it is not yet disencumbered whether the technology gain incessantly succeed to noteet in the closeness of two-of-a-trade from other quarters such as callous propels, glitter storage, holographic storage and internet-fixed storage. Examples of 3D optical agents storage resources. Top row - Written Call/Recall resources; Mempile resources. Middle row - FMD; D-Data DMD and propel. Bottom row - Landauer resources; Microholas resources in force.
Call/Recall was founded in 1987 on the foundation of Peter Rentzepis' elaboration. Using 2-photon annalsing (at 25 Mbit/s delay 6. 5 ps, 7 nJ, 532 nm pulses), 1-photon learnout (delay 635 nm), and a elevated NA (1. 0) immersion lens, they keep treasuryd 1 TB as 200 laminas in a 1. 2 mm dull disk.  They aim to amelioadmonish cleverness to >5 TB and agents admonishs to up to 250 Mbit/s delayin a year, by amplifying new esthetics as polite-behaved-mannered-mannered as elevated-powered pulsed sky sky sky blue laser diodes. Mempile are amplifying a retail apsharp-end delay the spectry TeraDisc. In March 2007, they demonstrated the annalsing and learnend of 100 laminas of instruction on a 0. mm dull disc, as polite-behaved-mannered-mannered as low crosstalk, elevated sensitivity, and thermodynamic uprightness.  They design to acquit a red-laser 0. 6-1. 0 TB consumer result in 2010, and keep a roadmap to a 5 TB sky blue-laser result.  *Constellation 3D* polite-behaved-mannered-acquainted the Fluorescent Multilamina Disc at the end of the 1990s, which was a ROM disk, manipulationd lamina by lamina. The fraternity failed in 2002, but the psychological peculiarity (IP) was adventitious by D-Data Inc. who are attempting to preface it as the Digital Multilamina Disk (DMD).
Storex Technologies has been set up to amplify 3D resources fixed on fluorescent photosensitive glasses and glass-ceramic esthetics. The technology derives from the patents of the Romanian student Eugen Pavel, who is too the instituter and CEO of the fraternity. Primary results, 40 nm notes commemorative into 3D implicit laminas opposedd by 700 nm, were presented in October 2009 at the ISOM2009 meeting. Landauer inc. are amplifying a resources fixed on vibratory 2-photon aridity in a sapphire solely crystal substrate. In May 2007, they showed the annalsing of 20 laminas of agents using 2 nJ of laser temper (405 nm) for each note.
The learning admonish is poor to 10 Mbit/s beproducer of the fluorescence era. Colossal Storage aim to amplify a 3D holographic optical storage technology fixed on photon inherent electric opportunity poling using a far UV laser to conquer enlightened amelioratements balance vulgar agents cleverness and give admonishs, but as yet they keep not presented any tentative elaboration or feasibility examine. Microholas operates out of the University of Berlin, lower the bringership of Prof Susanna Orlic, and has completed the annalsing of up to 75 laminas of microholographic agents, opposedd by 4. micrometres, and suggesting a agents dullness of 10 GB per lamina.  3DCD Technology Pty. Ltd. is a university spin-off set up to amplify 3D optical storage technology fixed on esthetics signed by Daniel Day and Min Gu. Opposed enlightened technology companies such as Fuji, Ricoh and Matsushita keep applied for patents on 2-photon-responsive esthetics for applications including 3D optical agents storage, so-far they keep not fond any symptom that they are amplifying generous agents storage solutions.