Terabyte Disk Memp

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INTRODUCTION

The optical disc revolution started with CDs and then moved on to DVDs, and we're

in the midst of the next-gen battle between HD DVD and Blu-ray. Since the birth of

the CD 25 years ago, we've gone from 600MB to a whopping 50GB of storage

capacity on these little, convenient and versatile discs. But for those who desire more

space on a highly portable medium, newtechnologyfrom a company called Mempile

in Jerusalem promises to blow these limits away. The company claims that they can

store up to 1TB (1,000GB) on an optical disc with the same dimensionsonly

slightly thickerthan a regular DVD and will be able to store 5TB once the jump to

blue lasers is made. The 1TB disc is divided into 200 different layers, each

comprising 5GB of storage space. Unlike standard multilayer DVDs, the layers aren't

physically stacked and stuck together. The Mempile discs are solid and use a specially

developed variant of the polymer polymethyl methacrylate (PMMA)a mixture of

Perspex, Lucite, and Plexiglassknown as ePMMA. It's this polymer that gives the

discs a distinctive yellow color. When recording data to the disc, the laser focuses on

one of the virtual layers and, using a photochemical reaction, modifies only a part of

the plastic to represent a "1" or leaves it alone to represent a "0". This approach uses

three dimensions in the polymer to store data rather than the two dimensions used by

DVD. The technology is currently limited to WORM (write once, read many)

although the company hopes to have read/write drives available in the future.

OPTICAL MEDIA

Optical media - such as the compact disk (CD) - arestoragemedia that hold content

in digital form and that are written and read by a laser; these media include all the

various CD and DVD variations, as well as optical jukeboxes and autochangers.

Optical media have a number of advantages over magnetic media such as the floppy

disk. Optical disk capacity ranges up to 6 gigabytes; that's 6 billion bytes compared to

the 1.44 megabytes (MB) - 1,440,000 bytes - of the floppy. One optical disk holds

about the equivalent of 500 floppies worth of data. Durability is another feature of

optical media; they last up to seven times as long as traditional storage media.
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Optical media are used for storing digital sounds, images and data. There are three

main families:

The commercially issued, mass produced, CD family including the digitalaudio CD- both 12cm and the "single" 8cm disc - CD-ROM, CD-I and CD-V

and the analogue Video Disc.

Optical disks and tapes that can be recorded on once. Re-recordable disks.

Mass Produced Discs:-

The mass-produced discs of the CD family have the digital information in the form of

microscopic pits pressed into a polycarbonate base which is coated with a light

reflective layer. This reflective layer is usually of aluminium, but gold and silver are

also used. A transparent lacquer is then placed over the reflective surface to protect it.

This surface also carries any label information. As the data on members of the are

impressed, they cannot be altered or rewritten.

Because of the high costs to setup the production of a pressed disc, the discs are only

used when large numbers of copies are required (over about 100), for example,

encyclopaedia or sound recordings. The higher the number of discs issued, the lower

is the unit price. The storage capacity of a 12cm CD is about 650 MB or one hour of

audio. The average access time is about 300 ms with a double speed player, 250 ms

with quadruple speed and 130 ms with sextuple speed.

The first disc in the family to be developed was the 30cm analogue LV (Laser Vision)

Disc for video. This usually consisted of two discs stuck back-to-back to form a

double sided disc with one hour of video per side. A sub-format was developed which

could store up to 54000 still video images per side. The LV disc was the most

successful of several attempts to generate market acceptance but is expected to be

superseded by the DVD (Digital Versatile Disc or Digital Video Disc) that is being

launched in 1997.

The DVD is the same diameter as the CD (12cm) but, by using a laser with a shorter

wave length, the storage capacity of one layer is increased by a factor of seven to 4 7


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GB. Additionally, a dual layer structure will be possible, read by two different laser

wave lengths, thus doubling the capacity to 9 GB. In principle, by glueing two such

double layer disks together like the LV video disks, a total capacity of 18 GB can be

achieved. The disk is intended for the storage of data-reduced video-films or, like CD-ROMs, texts and multimedia data with, however, considerably higher storage

capacities.

Optical Tape:-

Optical tape is made by ICI and packaged in a cassette for use as a WORM format

data storage tape. The tape drives are made by EMASS in the USA and supplied in

Europe by GRAU Storage Systems. Kodak are about to launch a competing system.

The tape contains a dye layer which changes its state when a high power laser beam is

applied and can be read by a lower power laser - the same basic method as for CD-Rs.

Because the tape is a sequential carrier, the access time can be quite long. In

compensation, the storage capacity of one tape is considerably greater than a disc (up

to 100GB).

Rewritable Optical Media:-

In contrast to the preceding optical media, data on rewritable optical disks

("Erasable"), MagnetoOptical (M/O) and Phasechange, can be altered or deleted many

times. There are rewritable optical disks in the 5 25 inch format and, more

recently, in the 3 5 inch format. The most common still are the magnetooptical

discs, where a laser beam in the write mode heats the inner layer of the optical

disk and thus changes the polarity of a magnetic coating. The resulting

microscopic magnetic marks of different polarity can be read as a bit stream by a

lowenergy laser beam in the read mode. A more recent recording technology is the

Phasechange where the carrier layer is coated with a thin semimetal film, which can

be both in an amorphous and in a crystalline state. A laser beam in the write mode can


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change single spots to either an amorphous or a crystalline state so that, again, a

digital bit stream is created. The Phasechange may replace M/O in the future.

Rewritable optical disks have a short accesstime (600 milliseconds). The storage

capacity has steadily increased up to the current 2 6 GB.

The Stability of Optical Carriers:-

The main factors that affect the stability of carriers and the retrieval of information

can be summarised as:

Humidity and temperature. Mechanical deformation. Dust and dirt of all kinds.

For some carriers there are additional factors:

Light Stray magnetic fields.

Humidity is, as with other data carriers, a most dangerous factor. In the case of

optical media it has a hydrolytic action on components such as the protection layer of

CDs and a corrosive influence on all metal components including metallic reflective

layers. As a secondary effect, high humidity levels (above 65% RH) encourages the

growth of moulds and fungi which can obstruct the reading of optical information.

Temperature, as with all other data carriers, determines the speed of (deteriorating)

chemical reactions. More importantly, it is responsible fordimensional changes which

may be of concern, especially in the case of multi-layer media.

Mechanical integrity is of utmost, and underrated, importance. Even microscopic

scratches can hinder the reading laser beam, as do fingerprints and other foreign

matter. Mechanical bending of discs cause microscopic cracks which again divert the

laser. While the WORM and MO-disks developed as computer storage media are

housed in cartridges which only open when inserted into the respective players, the


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representatives of the CD-family must be handled with utmost care, keeping

mechanical integrity in mind.

Dust and dirt affects the proper reading of the recorded information. Cigarette smoke

will accumulate on the disk surfaces and may hide information. The CD-family is

again more exposed to this danger than those disks that are protected by cartridges.

Light may affect the dye layers used in recordable and erasable disks.

Stray magnetic fields must be kept away from magneto-optical disks.

3D OPTICAL DATA STORAGE3D optical data storage is the term given to any form of optical data storage in

which information can be recorded and/or read withthree dimensional resolution(as

opposed to the two dimensional resolution afforded, for example, by CD).

This innovation has the potential to provide terabyte-level mass storage on DVD-

sized disks. Data recording and readback are achieved by focusing lasers within the

medium. However, because of the volumetric nature of the data structure, the laser

light must travel through other data points before it reaches the point where reading or

recording is desired. Therefore, some kind of nonlinearity is required to ensure that

these other data points do not interfere with the addressing of the desired point.

No commercial product based on 3D optical data storage has yet arrived on the mass

market, although several companies are actively developing the technology andpredict that it will become available by 2010.

Current opticaldata storage media, such as the CD andDVDstore data as a series of

reflective marks on an internal surface of a disc. In order to increase storage capacity,

it is possible for discs to hold two or even more of these data layers, but their number

is severely limited since the addressing laser interacts with every layer that it passes

through on the way to and from the addressed layer. These interactions cause noise

that limits the technology to approximately 10 layers.3Doptical data storage methods
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circumvent this issue by using addressing methods where only the specifically

addressed voxel (volumetric pixel) interacts substantially with the addressing light.

This necessarily involves nonlinear data reading and writing methods, in particular

nonlinear optics.

3D optical data storage is related to (and competes with) holographic data storage.

Traditional examples of holographic storage do not address in the third dimension,

and are therefore not strictly "3D", but more recently 3D holographic storage has been

realized by the use of microholograms.Layer-selectionmultilayer technology (where a

multilayer disc has layers that can be individually activated e.g. electrically) is also

closely related.

Schematic representation of a cross-section through a 3D optical storage disc (yellow)

along a data track (orange marks). Four data layers are seen, with the laser currently

addressing the third from the top. The laser passes through the first two layers and

only interacts with the third, since here the light is at a high intensity.

As an example, a prototypical 3D optical data storage system may use a disk that

looks much like a transparent DVD. The disc contains many layers of information,

each at a different depth in the media and each consisting of a DVD-like spiral track.

In order to record information on the disc alaseris brought to afocusat a particular

depth in the media that corresponds to a particular information layer. When the laser

is turned on it causes a photochemical change in the media. As the disc spins and the

read/write head moves along a radius, the layer is written just as a DVD-R is written.

The depth of the focus may then be changed and another entirely different layer of

information written. The distance between layers may be 5 to 100 micrometers,

allowing >100 layers of information to be stored on a single disc.

In order to read the data back (in this example), a similar procedure is used except this

time instead of causing a photochemical change in the media the laser causes

fluorescence. This is achieved e.g. by using a lower laser power or a different laser

wavelength. The intensity or wavelength of the fluorescence is different depending on

whether the media has been written at that point, and so by measuring the emittedlight the data is read.
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It should be noted that the size of individual chromophore molecules or photoactive

color centers is much smaller than the size of the laser focus (which is determined by

the diffraction limit). The light therefore addresses a large number (possibly even 109)

of molecules at any one time, so the medium acts as a homogeneous mass rather thana matrix structured by the positions of chromophores.

Media form factor:-

Media for 3D optical data storage have been suggested in several form factors:

Disc. A disc media offers a progression from CD/DVD, and allows reading and

writing to be carried out by the familiar spinning disc method.

Card. A credit card form factor media is attractive from the point of view of

portability and convenience, but would be of a lower capacity than a disc.

Crystal or Cube. Several science fiction writers have suggested small solids that

store massive amounts of information, and at least in principle this could be achieved

with 3D optical data storage.

Drive design:-

A drive designed to read and write to 3D optical data storage media may have a lot in

common with CD/DVD drives, particularly if the form factor and data structure of the

media is similar to that of CD or DVD. However, there are a number of notable

differences that must be taken into account when designing such a drive, including:

Laser. Particularly when 2-photon absorption is utilized, high-powered lasers may be

required that can be bulky, difficult to cool, and pose safety concerns. Existing optical

drives utilizecontinuous wavediode lasers operating at 780 nm, 658 nm, or 405 nm.

3D optical storage drives may requiresolid-state lasersor pulsed lasers, and several

examples use wavelengths easily available by these technologies, such as 532 nm

(green). These larger lasers can be difficult to integrate into the read/write head of the

optical drive.
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Variable spherical aberration correction. Because the system must address

different depths in the medium, and at different depths the spherical aberration

induced in thewavefrontis different, a method is required to dynamically account for

these differences. Many possible methods exist that include optical elements thatswap in and out of the optical path, moving elements,adaptive optics, and immersion

lenses.

Optical system. In many examples of 3D optical data storage systems, several

wavelengths (colors) of light are used (e.g. reading laser, writing laser, signal;

sometimes even two lasers are required just for writing). Therefore, as well as coping

with the high laser power and variable spherical aberration, the optical system must

combine and separate these different colors of light as required.

Detection. In DVD drives, the signal produced from the disc is a reflection of the

addressing laser beam, and is therefore very intense. For 3D optical storage however,

the signal must be generated within the tiny volume that is addressed, and therefore it

is much weaker than the laser light. In addition, fluorescence is radiated in all

directions from the addressed point, so special light collection optics must be used to

maximize the signal.

Data tracking. Once they are identified along the z-axis, individual layers of DVD-

like data may be accessed and tracked in similar ways to DVD discs. The possibility

of using parallel or page-based addressing has also been demonstrated. This allows

much fasterdata transfer rates, but requires the additional complexity ofspatial light

modulators, signal imaging, more powerful lasers, and more complex data handling.

Development issues:-

Despite the highly attractive nature of 3D optical data storage, the development of

commercial products has taken a significant length of time. This is the result of the

limited financial backing that 3D optical storage ventures have received, as well as

technical issues including:

Destructive reading. Since both the reading and the writing of data are carried out

with laser beams, there is a potential for the reading process to cause a small amount
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of writing. In this case, the repeated reading of data may eventually serve to erase it

(this also happens in phase change materials used in some DVDs). This issue has been

addressed by many approaches, such as the use of different absorption bands for each

process (reading and writing), or the use of a reading method that does not involve theabsorption of energy.

Thermodynamic stability. Many chemical reactions that appear not to take place in

fact happen very slowly. In addition, many reactions that appear to have happened can

slowly reverse themselves. Since most 3D media is based on chemical reactions, there

is therefore a risk that either the unwritten points will slowly become written or that

the written points will slowly revert to being unwritten. This issue is particularly

serious for the spiropyrans, but extensive research was conducted to find more stable

chromophores for 3D memories.

Media sensitivity. As we have noted, 2-photon absorption is a weak phenomenon,

and therefore high power lasers are usually required to produce it. Researchers

typically use Ti-sapphire lasers or Nd:YAG lasers to achieve excitation, but these

instruments are not suitable for use in consumer products.
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HOW OPTICAL DISC WORKS?

CDs, DVDs, and the current HD media have a number of physical similarities. Each

uses a 1.2mm (4/100 inch) piece of clear polycarbonate plastic with microscopic

bumps arranged as a single, continuous, spiral track of data. Optical media requires a

player composed of a fast-spinning drive motor for spinning the media, a laser

(infrared, red, or blue, depending on the player and media), and a tracking mechanism

that moves the laser beam to follow the spiral track (with a resolution in the scale of

submicrons).

The function of the player is to focus the laser on the track of bumps. In a CD, the

laser beam passes through the polycarbonate layer of the media and is reflected off the

aluminum layer and hits an opto-electronic device that detects changes in light. Since

the bumps in the media reflect light differently than the rest of the layer, the opto-

electronic sensor detects that change in reflectivity and translates this difference into

digital information (zeros and ones).


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The main difference between the current types

of optical media is the size of the data track,

bumps and the wavelength of the laser used for

reading the data. In a CD, each track is about1.6 microns wide and each pit has a depth of

about 0.11 micron and a minimal length of

about 0.834 micron. A DVD shrinks this almost

by half with a 0.74 micron track and a pit

length of 0.4 (interestingly, the pit depth of a

DVD is a bit deeper at 0.12 micron). As we

already mentioned, the 650nm wavelength

(down from 780nm of a CD) allows the DVD

to read this extra information. HD media does even better with a pit length of about

0.2 for HD-DVD and 0.15 for Blu-ray.

Another important technical change is the size of the laser spot which had to be

reduced to read the ever smaller pits in the media. The original CD had a spot size of

about 1.6 microns, which shrunk to 1.1 microns on a DVDand even further in HD

(0.62 micron in HD-DVD and 0.48 micron in Blu-ray). Besides the size of the data

and reading apparatus, the datas location inside the media also changed over time.

While the original CD had only one layer located in the innermost part of the 1.2mm

thick polycarbonate plastic (fairly close to the label), in a DVD (and HD-DVD) the

data surface is located in the middle of the media. Blu-ray however is very different in

this respect, locating its data surface on the opposite side of the label. Although each

media type has a different location for its data surface, the overall volume taken up by

the data inside the media is very small and the majority of space could be consideredwasted.

Pits on a CD and DVD media


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So far we discussed read-only memory (ROM)

media. However CD-R/RW, DVD-R/RW and

similar HD media are in widespread use.

Unlike ROM media, which is made in one goby commercial pressing machines, R/RW

media use laser light to record the data onto the

disc. In write once media (R) the burner

turns the laser writer on and off according to

the way the ones and zeros should appear on

the disc. Some describe the operation of the

laser as darkening the material to encode a zero

and leaving it translucent to encode a one,

although a more accurate description might be to say that the laser changes the

volume of the disc in a specific location (filling the pit). A rewritable (RW) media

is more complicated as it is based on phase-change technology. The phase-change

element is a chemical compound made out of silver, antimony, tellurium, and indium

(other compounds exist as well, including organic dyes). When the compound is

heated above its melting temperature (about 600 degrees Celsius, or 1,112 degrees

Fahrenheit), it becomes a liquid; at its crystallization temperature (about 200 degrees

Celsius, or 392 degrees Fahrenheit) it turns into a solid. The crystalline form has less

volume, so it leaves the pits empty while the noncrystalline form has a larger

volume, so the pits are full. When the pits are full, there is constructive interference

between reflection from the pits and their surrounding which means more light is

reflected. When the pit is empty, there is a destructive interference, which means the

light is reflected in a lower quantity.


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In blank media, all of the material in the

writable area is in the crystalline form, so

light will shine through this layer to the

reflective metal above and bounce back tothe light sensor. In order to write

information on the disc, the burner uses its

write laser, which is more powerful and

can heat the compound to its melting

temperature. The melted spots have the

same function as the bumps on

conventional optical media. Nonreflective areas on the RW media indicate a zero,

while areas which remain reflective indicate a one (here as well, things are a bit more

complex in practice, and data on a disc is encoded as a series of lines having different

lengths similar to Morse code called Run Length Limited or RLL for short).

Since the days of the first CDs, optical media increased its capacity by 75 times (from

650 MB in a CD to 50 GB in dual-layer Blu-ray media). However the demand for

more storage space continues, and with ever larger hard drives now reaching

capacities of 1TB and beyond, an appropriate next-generation optical media is in the

making.

MEMPILE TECHNOLOGY

For years Ortal Alpert tried to stay ahead of the game buying the latest hard drives

and optical drives to store his ever growing library of data. In the mid 1990s, Alpert

came up with a novel idea for storing data, and he decided to start his own company.

Almost ten years later, Alperts dream lead to the creation of a new optical

technology, one with the potential to hold 20 times more data than the best existing

optical technology.

In late April 2007 the TFOT team visited the offices ofMempile, 20km Northwest of

Jerusalem, Israel. Mempile, the company created by Alpert and a few of hiscolleagues in 2000, is now in advanced stages of developing its revolutionary optical

Comparison of a CD, DVD and Blu-ray

(Credit: Matsushita Electric)
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technology, which we had a chance to see. When we first set our eyes on the see-

through yellowish disc we were a bit surprised. Was the choice of color the idea of the

PR department looking to draw attention to the new media, we inquired? The answer

we received took us straight into the heart of Mempile's technology and made usrealize that looks could very well be deceiving.

In a DVD or HD optical media, there are either one or two layers of data. Adding

more layers using existing technology would be expensivebut more importantly, it

would have to get around a very basic problem: its difficult to read information

embedded deep inside this kind of media. The current semireflective layers used to

store data on CD/DVD/HD-DVD/BD reduce the amount of light that reaches the deep

layers, making the amount of signal reflected from each layer smaller, after a few

layers the amount of light reflected becomes so small and so noisy that reading the

data becomes nearly impossible.

Overcoming this basic limitation of existing optical media is the goal Mempile set for

itself, and the way to achieve it is by completely changing that way optical media

worksstarting from the material of which it is made. Mempile developed a special

variant of the polymer polymethyl methacrylate (PMMA) known as ePMMA. Afterseveral years of trial and error, Mempile was able to develop this unique polymer,

which it claims is almost entirely transparent to the specific wavelength of the laser

used by its recorder/player. The yellowish color of the media is thus not a publicity

stunt but the result of the special properties of the material used by Mempile.

Using ePMMA, Mempile was able to create a media with about 200 virtual (i.e.,

created by the laser) layers, five microns apart, each containing approximately 5 GB

of data. Although current prototypes are still in the 600800GB per media range,

Mempile is convinced that further optimization will enable it to reach its goal of 1 TB

per 1.2mm disc in the very near future.

But using specially designed polymers is just half the story. In order to make a media

which could actually store all this data and effectively retrieve it, the old method of

reading and writing on optical media had to be abandoned. Instead of the pits and flat

surfaces representing zeros and ones, Mempile chose to implement a photochemical


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process, which happens when an ePMMA molecule is precisely illuminated by a red

laser of a specific a wavelength.

In order to be able to precisely illuminate

a specific molecule inside the disc,

Mempile uses what is known as nonlinear

optics. In linear optics the amount of light

which is absorbed by an object is directly

proportional to the amount of light used,

in nonlinear optics the amount of light

absorbed does not stand in direct

proportion to the amount usedinstead,

a small decrease in the amount of light

used will result in a dramatic decrease in the amount of light absorbed. The process

that Mempile uses to write and read data is called two-photon absorption and is

nonlinear in nature. When the laser beam is focused to a small radius on the disc, it is

very easy for the photons to excite the ePMMA molecules (chromophores), but whenthe radius of the beam increases even slightly, it becomes very improbable for two

photons to be absorbed by a chromophore, so no writing or reading can occur.

Nonlinear optics is required in this case because in a 200-layer disc, linear optics

would cause some of the light to be absorbed by the layers above the intended one

resulting in errors and loss of signal.

In order to read data Mempile uses laser at a specific power which excites the

chromophore in a particular layer of the disc. In order to record data, a stronger light

is used which creates a different chemical reaction in the molecule. Mempile told

TFOT that its technology can also be adapted to perform RW in the future, but market

demand for such a product does not seem to be huge.

According to Mempile their product should be very reliable, and different simulations

and acceleration tests showed data lifetime of about 50 years. Although Mempile is

currently planning to launch their first product using red laser (which is a more mature

Top right - DVD, bottom right - CD,

middle - Blu-ray,left - Mempile media
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technology), moving to blue laser further down the road will possibly allow the

technology to achieve up to 5 TB of data per disc.

There are currently several other companies

developing next-generation optical storage

technologies. TDK recently announced a 200GB

Blu-ray disc, which seems to be getting closer to

the limit of Blu-ray media technology. A different

path was taken by InPhase, which TFOT covered

in 2006. InPhase uses holographic technology to

record data on a special media currently

containing about 300 GB. InPhase is working on

increasing the capacity of its media and hopes to

reach 1.6 TB by early next decade. The current main market for InPhases technology

is professional users who are willing to pay extra for a fast and large backup storage

system. Mempile is looking toward both the professional market and the consumer

market and hopes to launch its first product early in the next decade.

Although this might seem like a long time to wait, there are some good reasons

behind this decision. Besides the fact that Mempile developed an entirely new

technology which is inherently different than that used by conventional CD/DVD/HD

media, and hence bound to take longer to develop, the current market doesnt seem

ripe for such a revolution. In a time when 25/50GB media are still just a small

percentage of the consumer market, bringing in 1 TB media doesnt make sense from

the point of view of most manufacturers. For that reason we shall probably see

Mempiles technology on the market just after HD media becomes mainstream.

However, when this transformation occurs, we shall reach a whole new stage in data

storage. The invention of the CD-ROM made the question of storing documents (and

to some extent images) irrelevant, as one disc could store more documents than most

people write in their entire lifetime. The DVD allowed for the first time saving full

movies (without the need for excessive compression). Only with the recentintroduction of HD media did it become possible for higher-resolution movies to be

InPhase holographic technology
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saved on one disc. When Mempiles technology reaches the market, it will make

storing all major data types irrelevant. A single TeraDisc will be able to store over

250,000 high resolution, high quality pictures or MP3s, over 115 DVD-quality

movies, and about 40 HD movies not to mention an unimaginable number ofdocuments. Mempile also sees its technology being used as a network-based backup

technology, allowing users to save data from a variety of devices, including desktops,

laptops, and digital video recorders (DVRs).

Although many people find it hard to imagine the need for such space on a single

disc, it is not inconceivable that by the time Mempiles technology reaches the

market, even higher-resolution video formats will start to appear, requiring hundreds

of Gigabytes per hour, on entirely new display technologies, such as holographic

displays, which could require even more storage space.

TERABYTE CONCEPT

When you compare them to this new disc from Mempile, they dont ha ve much of a

chance. The product is only a concept at this point, so its still quite unsure if and

when the disc will be available in mass production We have just started to get to know

blu-ray and HD DVD with pretty good storage capabilities.

Mempiles TeraDisc optical media solution will enablelow-cost, high-capacity

(>1 TeraByte) permanent storageon a DVD-size disc.

The TeraDisc is made of a material which is highly responsive to two-photon writing

and reading. This allows us to write anywhere in that we can focus a red laser onto the

disc, e.g. multiple layers. However, many other properties of the material have to be

optimized to allow this to work properly. Especially the written points, and written

layers have to remain transparent after writing, without which it would be very

difficult for the reading process to see the 200th layer through 199 written,

nontransparent layers.
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When a red laser is focused to a small spot inside the TeraDisc, we can choose if we

probe the state of this material (reading , low power) or alter it (writing at higher

power). This is very similar to the way a regular CDR works, except for the fact that

this is now done in 3D.

Archiving in consumer and enterprise markets where rich media content is

growing exponentially. Home storage needs are growing exponentially and we are

beginning to see 1TB hard-disk drives entering the home networking market. There

are no solutions for archiving personal content other than low-capacity optical media.

The TeraDisc fills this void. In enterprise markets, compliancy requirements are

increasing, compounded by high-resolution content being produced. Healthcare,

government, video surveillance, etc., are all searching for low-cost solutions that will

provide high data reliability over increasingly longer periods of time for rich media

content. Mempile believes that libraries of TeraDiscs will meet these archival needs.

TWO PHOTON CHEMISTRY

Two-photon microscopy (TPM) has come to occupy a prominent place in modern

biological research with its ability to resolve the three-dimensional distribution of

molecules deep inside living tissue. TPM can employ two different types of signals,

fluorescence and second harmonic generation, to image biological structures with

subcellular resolution. Two-photon excited fluorescence imaging is a powerful

technique with which to monitor the dynamic behavior of the chemical components of

tissues, whereas second harmonic imaging provides novel ways to study their spatial

organization. Using TPM, great strides have been made toward understanding the

metabolism, structure, signal transduction, and signal transmission in the eye. These

include the characterization of the spatial distribution, transport, and metabolism of

the endogenous retinoids, molecules essential for the detection of light, as well as the

elucidation of the architecture of the living cornea. In this review, we present and

discuss the current applications of TPM for the chemical and structural imaging of theeye. In addition, we address what we see as the future potential of TPM for eye


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research. This relatively new method of microscopy has been the subject of numerous

technical improvements in terms of the optics and indicators used, improvements that

should lead to more detailed biochemical characterizations of the eyes of live animals

and even to imaging of the human eye in vivo.

Writing by 2-photon absorption can be achieved by focusing the writing laser on the

point where the photochemical writing process is required. The wavelength of the

writing laser is chosen such that it is not linearly absorbed by the medium, and

therefore it does not interact with the medium except at the focal point. At the focal

point 2-photon absorption becomes significant, because it is a nonlinear process

dependant on the square of the laserfluence.

Writing by 2-photon absorption can also be achieved by the action of two lasers in

coincidence. This method is typically used to achieve the parallel writing of

information at once. One laser passes through the media, defining a line or plane. The

second laser is then directed at the points on that line or plane that writing is desired.

The coincidence of the lasers at these points excited 2-photon absorption, leading to

writing photochemistry.

Positioned to become the 2-photon optical storage standard, Mempile's TeraDisc

solution:

Fills a void in the fest-growing consumer market where no high-capacityarchiving solutions exist.

Leads to significant growth in removable archiving activity in enterprise,healthcare and public sector markets.

Provides significant advantages over existing optical storage offerings. Has the potential to dislodge alternative storage options from their

traditionally entrenched positions.

Has great synergy with rapidly increasing digital-content trends in the home,health, enterprise and government markets.

The demand for storage capacity is doubling on an annual basis. Driven by high

capacity applications, data proliferation, broadband web access, networked homes,

multi-channel access to digital information and - more than allubiquity, the need for
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a robust solution providing high capacity, reliable and user-friendly removable

archival storage at a reasonable price is becoming acute.

Existing optical storage technology is reaching its physical limitations with blue-laser

technologies expected to hit the 200GB barrier around 2010. Mempile is able to

record 1TB while providing truly random data access, creating a significant increase

in capacity at greatly reduced marginal costs.

BLU RAY DISC

Blu-ray Disc (also known as Blu-ray or BD) is anoptical disc storage media format.

Its main uses are high-definition video and data storage. The disc has the same

dimensions as a standardDVDor CD.

The name Blu-ray Disc is derived from the blue-violet laserused to read and write

this type of disc. Because of its shorterwavelength(405nm), substantially more datacan be stored on a Blu-ray Disc than on theDVDformat, which uses a red (650 nm)

laser. A dual layer Blu-ray Disc can store 50GB, almost six times the capacity of a

dual layer DVD.

Blu-ray Disc was developed by theBlu-ray Disc Association, a group of companies

representing consumer electronics, computer hardware, and motion picture

production. The standard is covered by several patents belonging to different

companies. As of March 2007, a joint licensing agreement for all the relevant patents

had not yet been finalized.

Competition from HD DVD:-

TheDVD Forum (which was chaired byToshiba) was deeply split over whether to go

with the more expensive blue lasers or not. In March 2002, the forum voted to
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approve a proposal endorsed by Warner Bros. and other motion picture studios that

involved compressing HD content onto dual-layer DVD-9 discs. In spite of this

decision, however, the DVD Forum's Steering Committee announced in April that it

was pursuing its own blue-laser high-definition solution. In August, Toshiba and NECannounced their competing standard Advanced Optical Disc. It was finally adopted by

the DVD Forum and renamedHD DVDthe next year, after being voted down twice

by Blu-ray Disc Association members, prompting the U.S. Department of Justice to

make preliminary investigations into the situation.

HD DVD had a head start in the high definition video market and Blu-ray Disc sales

were slow at first. The first Blu-ray Disc player was perceived as expensive and

buggy, and there were few titles available.This changed whenPlayStation 3launched,

since every PS3 unit also functioned as a Blu-ray Disc player. By January 2007, Blu-

ray discs had outsold HD DVDs, and during the first three quarters of 2007, BD

outsold HD DVDs by about two to one.

Some analysts believe that Sony's PlayStation 3 video game console played an

important role in the format war, believing it acted as acatalyst for Blu-ray Disc, as

the PlayStation 3 used a Blu-ray Disc drive as its primary information storagemedium. They also credited Sony's more thorough and influential marketing

campaign. More recently several studios have cited Blu-ray Disc's adoption of the

BD+ anti-copying system as the reason they supported Blu-ray Disc over HD DVD,

an opinion supported by Paul Kocher, Cryptography Research's president and chief

scientist.

Blu-ray Disc was locked in aformat warwithHD DVDuntil Blu-ray Disc's victory

on February 19, 2008. On that day, Toshiba the main driving force behind HD

DVDannounced it would no longer develop, manufacture and market HD DVD

players and recorders, leading almost all other HD DVD supporters to follow suit.

HD DVD
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DVD (also known as "Digital Versatile Disc" - see Etymology) is a popularoptical

disc storagemedia format. Its main uses are video anddatastorage. Most DVDs are

of the same dimensions as compact discs (CDs) but store more than six times as much

data.

Variations of the termDVD often describe the way data is stored on the discs: DVD-

ROM has data which can only be read and not written, DVD-RandDVD+Rcan be

written once and then functions as a DVD-ROM, and DVD-RAM,DVD-RW, or

DVD+RW holds data that can be erased and thus re-written multiple times. The

wavelength used by standard DVD lasers is 650 nm.

DVD-Video and DVD-Audio discs respectively refer to properly formatted and

structured video and audio content. Other types of DVDs, including those with video

content, may be referred to as DVD-Data discs. The term "DVD" is commonly

misused to refer to high definition optical disc formats in general, such as Blu-ray

DiscandHD DVD. As a result, the original DVD is sometimes called SD DVD (for

standard definition).

DVD capacity:-

Single layer capacity Dual/Double layer capacity

Physical size GB GiB GB GiB

12 cm, single sided 4.7 4.37 8.54 7.95

12 cm, double sided 9.4 8.74 17.08 15.90

8 cm, single sided 1.4 1.30 2.6 2.42

8 cm, double sided 2.8 2.61 5.2 4.84
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The 12 cm type is a standard DVD, and the 8 cm variety is known as a mini-DVD.

These are the same sizes as a standard CD and a mini-CD, respectively.

ADVANTAGES

1.A single TeraDisc will be able to store over 250,000 high resolution, high quality

pictures or MP3s, over 115 DVD-quality movies, and about 40 HD movies and

unimaginable number of documents.

2.Archiving in consumer and enterprise markets where rich media content is growing

exponentially.

3.Used as a network-based backup technology, allowing users to save data from a

variety of devices, including desktops, laptops, and digital video recorders (DVRs).

CONCLUSION
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While Blu-ray and HD DVD battle over the sub-100GB space and holographic

storage companies try to get things going around 300GB, a company called Mempile

is working to ship optical discs, the same size as standard DVDs and that will

ultimately contain a full terabyte of data.

The TeraDisk is a removable disk the size of a single DVD. It uses a new optical

technology that allows it to store 300GB more data than the blue-laser technologies

will be able to in 2010. Mempile uses a two-photon technology that allows it to record

in three-dimensions and write data to transparent virtual layers over the entire surface

of the disk. As many as 100 layers can be recorded and read.
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Terabyte Disk Memp