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					International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME
                                  TECHNOLOGY (IJCET)
ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online)
Volume 4, Issue 6, November - December (2013), pp. 232-239
Journal Impact Factor (2013): 6.1302 (Calculated by GISI)                      ©IAEME

                         3-D HOLOGRAPHIC DATA STORAGE

                                  D.Sai Anuhya,      Smriti Agrawal
        Department of Information Technology, JB Institute of Engineering and Technology,
                                       Hyderabad, India


        In response to the rapidly changing face of computing and demand for physically smaller,
greater capacity and high bandwidth storage devices, the holographic memory came into existence.
Holographic data storage using volume holograms offers high density and fast readout. It can store
1Tb-4Tb of information on a sugar cube sized crystal. That means a single holographic device can
replace more than thousands of CD’s. This paper provides description about the principle of
holography along with the comparisons observed between the conventional optical disks and the
holographic disks. Further, it investigates on what is making holographic devices still unfamiliar and
summarizes applications of computer systems wherein holography can be used.


        Computing technology is ever fast emerging. Ever since the IC (Integrated Circuits) was
developed, the number of transistors that engineers can pack on a chip has increased at a phenomenal
rate. ICs are made by the Photolithography process in which the patterns of metal or chemically
treated silicon are layered one on top of another, on to a die of silicon. Building even smaller chip
features requires using light sources with even shorter wavelength. That means designers had to
move from visible light, to ultraviolet light, and finally to the X-Rays territory. But using the X rays
for the photolithographic introduces a new set of problems. For example the issue of having a
reliable X ray source, the X rays cannot be focused with optical lenses and therefore the mask, which
produces the required pattern on the silicon, must be the size of the features themselves and
furthermore the materials opaque to light are not necessarily opaque to X rays. In the case of optical
disks, the wavelength of the light used limits the distance between the bits. It is estimated that in the
next five or ten years we will reach the limiting density for storing data on magnetic disks [1, 2, 3].
There is currently much research into other methods of memory and storage.

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME

        The capacities of today's mass storage devices cannot satisfy the demands of new processes
which will be developed in near future. Storage capacities are very competitive with magnetic or
optical disk, and the media volumetric storage density is significantly greater since it is a 3-D storage


Optical data storage techniques are categorized in three basic groups.

The symbol ‘•’ that precedes a technique indicates a method that is already in use to produce
commercial products.

   1. Surface or 2D recording [3, 4]

   a. • CD/DVD—Data are stored in reflective pits and scanned with a focused laser. Disks are
      easily replicated from a master.
   b. • CD-Recordable—Reflective pits are thermally recorded by focused laser. This type is
      usually lower density than read-only versions. Researchers have proposed blue lasers and
      “electron-trapping” materials to achieve density improvements.
   c. • Magneto-optic disks—Spots are recorded with a combination of magnetic field and
      focused laser.
   d. Near-field optical recording—Higher 2D density than with conventional surface recording
      is achieved by placing a small light source close to the disk. Light throughput and readout
      speed are issues.
   e. Optical tape—Parallel optical I/O has the advantages of magnetic tape without the long-term
      interaction between tape layers wound on the spool. Flexible photosensitive media is an

   2. Volumetric recording [5, 6, 7]

   a. Holographic—Data are stored in interference fringes with massively parallel I/O. Suitable
      recording material is still needed.
   b. Spectral hole burning—This technique addresses a small subset of molecules throughout
      the media by using a tunable narrowband laser. Alternatively, all subsets are addressed with
      ultra short laser pulses. It may add a fourth storage dimension to holography but requires
      cryogenic temperatures and materials development.

   3. Bit-by-bit 3D recording [7, 8]

   a. • Sparsely layered disks—The focus of the CD laser is changed to hit interior layers. DVD
      standard already includes two layers per side.
   b. Densely layered disks—A tightly focused beam is used to write small marks in a continuous
      or layered material; read with con-focal (depth-ranging) microscope.
   c. 2-photon—Two beams of different wavelengths mark writes, then read in parallel using
      fluorescence. Material sensitivity is an issue.

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME


        Holographic memory is a three-dimensional data storage system that can store information at
high density inside the crystal or photopolymer. It stores information in the form of holographic
images. Holographic memory serves as a high-capacity data storage challenging the current
domination of the magnetic and conventional optical data storage. Magnetic and optical data storage
devices rely on individual bits being stored as distinct magnetic or optical changes on the surface of
the recording medium. Holographic data storage overcomes this limitation by recording information
throughout the volume of the medium and is capable of recording multiple images in the same area
utilizing light at different angles.
        Holographic media like other media are available in both the forms, namely, write once
where the storage medium undergoes irresistible change, and rewritable media where change is
reversible [5, 16, 17, 19].
        Traditionally, magnetic and optical data storage records information a bit at a time in a linear
fashion, which leads to poor bit transfer rate. However, holographic storage is capable of recording
and reading millions of bits in parallel, enabling data transfer rates greater than those attained by
traditional optical storage.
        The holographic storage has additional advantage of being compact. It has the potential of
storing up to 1 terabyte or one thousand gigabytes of data in a crystal of the size of a sugar cube. It is
being researched and slated as the storage device that will replace hard drives and DVDs in the
future [8, 9, 10].


        Holographic memory is very promising because it not only offers greater capacity, but the
access speeds are very fast because there are few moving parts and no contact is required [1].
Photographic holograms are made by recording interference patterns of a reference beam of light and
a signal beam of light reflected off an object. Photosensitive material holds this interference pattern,
and the image can be reproduced by applying an identical beam of light to the reference beam onto
the photosensitive material. Many variations of the object can be recorded on a single plate of
material by changing the angle or the wavelength of the incident light. This is illustrated in the
figure 1. Each frame of an animation is stored by varying the angle of the incident light. Prototypes
developed by Lucent and IBM differ slightly, but most holographic data storage systems (HDSS) are
based on the same concept [1, 8, 11, 12, 13].

                Figure 1: Storing information in a holographic data storage system [1]

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME

            Figure 2: Retrieval of information from a holographic data storage system [1]

The basic components that are needed to construct an holographic data storage systems HDSS are:
   • Blue-green argon laser
   • Beam splitters to spilt the laser beam
   • Mirrors to direct the laser beams
   • LCD panel (spatial light modulator)
   • Lenses to focus the laser beams
   • Lithium-niobate crystal or photopolymer
   • Charge-coupled device (CCD) camera

        When the blue-green argon laser is fired, a beam splitter creates two beams (refer Figure 1).
One beam, called the object or signal beam, will go straight, bounce off one mirror and travel
through a spatial-light modulator (SLM). An SLM is a liquid crystal display (LCD) that shows
pages of raw binary data as clear and dark boxes. The information from the page of binary code is
carried by the signal beam around to the light-sensitive lithium-niobate crystal. Some systems use a
photopolymer in place of the crystal. A second beam, called the reference beam, shoots out the side
of the beam splitter and takes a separate path to the crystal. When the two beams meet, the
interference pattern that is created stores the data carried by the signal beam in a specific area in the
crystal -- the data is stored as a hologram.

    1. Recording data
        Holographic data storage contains information using an optical interference pattern within a
thick, photosensitive optical material. Light from a single laser beam is divided into two separate
optical patterns of dark and light pixels. By adjusting the reference beam angle, wavelength, or
media position, a multitude of holograms (theoretically, several thousand) can be stored on a single
volume [1].

    2. Reading data
        The stored data is read through the reproduction of the same reference beam used to create
the hologram. The reference beam’s light is focused on the photosensitive material, illuminating the
appropriate interference pattern, the light diffracts on the interference pattern, and projects the
pattern onto a detector. The detector is capable of reading the data in parallel, over one million bits at
once, resulting in the fast data transfer rate. Files on the holographic drive can be accessed in less
than 0.2 seconds [14, 20, 21, 23].

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME

        An advantage of a holographic memory system is that an entire page of data can be retrieved
quickly and at one time. In order to retrieve and reconstruct the holographic page of data stored in
the crystal, the reference beam is shined into the crystal at exactly the same angle at which it entered
to store that page of data. Each page of data is stored in a different area of the crysta based on the
angle at which the reference beam strikes it. During reconstruction, the beam will be diffracted by
the crystal to allow the recreation of the original page that was stored. This reconstructed page is then
projected onto the charge-coupled device (CCD) camera, which interprets and forwards the digital
information to a computer. The key component of any holographic data storage system is the angle at
which the second reference beam is fired at the crystal to retrieve a page of data. It must match the
original reference beam angle exactly.
        Early holographic data storage devices will have capacities of 125 GB and transfer rates of
about 40 MB per second. Eventually, these devices could have storage capacities of 1 TB and data
rates of more than 1 GB per second, fast enough to transfer an entire DVD movie in 30 seconds [1].

    3. Longitivity
        Holographic data storage can provide companies a method to preserve and archive
                         once,            (        )
information. The write-once, read many (WORM) approach to data storage would ensure content
security, preventing the information from being overwritten or modified. Manufacturers believe this
technology can provide safe storage for content without degradation for more than 50 years, far
exceeding current data storage options. Counterpoints to this claim are that the evolution of data
reader technology has – in the last couple of decades – changed every ten years. If this trend
                                                                    50 100
continues, it therefore follows that being able to store data for 50–100 years on one format is
irrelevant, because you would migrate the data to a new format after only ten years [4 15].


This section summarizes some of the facts illustrate the impact of holographic memories.

   •   It has been estimated that all the books in the U.S. Library of Congress, could be stored on
       six (6) HVD's.
   •   The pictures of every landmass on Earth (Google Earth for example) can be stored on two (2)
   •   With MPEG4 ASP encoding, a HVD can hold between 4,600 to 11,900 hours of video,
       which is enough for non-stop playing for a year.

                             Figure 3: Conventional and Holographic [5]

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME


        In conventional optical disc, the data is burned onto the surface one bit at a time. It gets stores
at a rate of 1 bit/pulse. As bit per bit is saved onto it, the space in between the data is left unused.
This makes wastage of the space to a larger extent. But when it comes to Holographic optical disc or
Holographic Versatile Disc (HVD) the data is stored as a page data and it is generally recorded into
the volumetric recording layer. It can store at a rate of 60,000 bits/pulse when Spatial Laser
Modulator (SLM) is passed onto it. This is illustrated in the figure 3.
        With three-dimensional recording and parallel data readout, holographic memories can
outperform existing optical storage techniques. In contrast to the currently available storage
strategies, holographic mass memory simultaneously offers high data capacity and short data access
time (Storage capacity of about 1TB/cc and data transfer rate of 1 billion bits/second).
        The capacity of DVD is generally of 9.4 GB and of BLU-RAY disc is of 50GB. But the
capacity of HVD ranges from 300 GB to 3.9 TB. Scientists are planning to push future storage
densities of optical mass storage over 40,000 Terabits/ [10]. When it comes to read/write speed
DVD is said to have 11.08 Mbps, BLU-RAY of 36 Mbps but that of HVD is 1Gbps [5]. This is
summarized in the figure 4.
        Holographic data storage has the unique ability to locate similar features stored within a
crystal instantly. A data pattern projected into a crystal from the top searches thousands of stored
holograms in parallel. The holograms diffract the incoming light out of the side of the crystal, with
the brightest outgoing beams identifying the address of the data that most closely resemble the input
pattern. This parallel search capability is an inherent property of holographic data storage and allows
a database to be searched by content.

                          Figure 4: Comparison between storage devices [5]

        But still each and every development has some defects with it. They are not limitations
regarding technical aspect but it is mostly regarding the cost. The manufacturing cost of HDV is very
high and there is a lack of availability of resources which are needed to produce HDV. However, all
the holograms appear dimmer because their patterns must share the material's finite dynamic range.
In other words, the additional holograms alter a material that can support only a fixed become so dim
that noise creeps into the read-out operation, thus limiting the material's storage capacity. But then
when Blu-ray was introduced in 2006, a 25-gigabyte disc cost nearly $1 a gigabyte. It is about half
the cost now. Overtime, the overall cost of holographic data storage should decrease to an acceptable
amount. So, even the HDV’s price can go down as time passes [10].

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME

        A difficulty with the HDV technology had been the destructive readout. The re-illuminated
reference beam used to retrieve the recorded information, also excites the donor electrons and
disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the
recording. In the past, this has limited the number of reads that can be made before the signal-to -
noise ratio becomes too low. Moreover, writes in the same fashion can degrade previous writes in the
same region of the medium. This restricts the ability to use the three-dimensional capacity of a
photorefractive for recording angle-multiplexed holograms. You would be unable to locate the data if
there’s an error of even a thousandth of an inch.


        There are many possible applications of holographic memory. Holographic memory systems
can potentially provide the high speed transfers and large volumes of future computer system. One
possible application is data mining. Data mining is the processes of finding patterns in large amounts
of data. Data mining is used greatly in large databases which hold possible patterns which can’t be
distinguished by human eyes due to the vast amount of data. Some current computer system
implement data mining, but the mass amount of storage required is pushing the limits of current data
storage systems.
        Another possible application of holographic memory is in petaflop computing. A petaflop is a
thousand trillion floating point operations per second. The fast access extremely large amounts of
data provided by holographic memory could be utilized in petaflop architecture. Optical storage such
as holographic memory provides a viable solution to the extreme amount of data which is required
for a petaflop computing [12, 16, 17, 18, 19, 20].
        Experts also note the possible introduction of "hybrid" holographic media. Just as magnetic
hard drives are starting to incorporate significant quantities of flash or Ram within the disc, near-
term holographic storage media may add some amount of flash memory in the cartridge to provide a
degree of re-write ability until a suitable rewritable media is developed and productized [15, 23, 24].


        The holographic disk will be the next technological revolution and its future is very
promising. Recent research has demonstrated that holographic storage systems with desirable
properties can be engineered. The next step is to build these systems at costs competitive with those
of existing technologies and to optimize the storage media. It will most likely be used in next
generation supercomputers where cost is not as much of an issue. The page access of data that HDSS
creates will provide a window into next generation computing by adding another dimension to stored
data. Finding holograms in personal computers might be a bit longer off, however. As there is a
limitation of more cost but as time goes on this magnetic memory device will be cheaper as that was
in the case of BLU-RAY.


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 [3]   M. Imlau, M. Fally, G. W. Burr, and G. T. Sincerbox, "Holography and optical
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International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 4, Issue 6, November - December (2013), © IAEME

 [4]    G. W. Burr, "Holographic storage,'' Encyclopedia of Optical Engineering, ed., R. B. Johnson
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