Tags: MEMORY, HOLOGRAPHIC, HOLOGRAPHIC MEMORY,
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
HOLOGRAPHIC MEMORY
#1


.pdf   1452923658-holographicmemoryseminar.pdf (Size: 655.84 KB / Downloads: 3)



Abstract
This paper describes holographic data storage as a viable alternative to magnetic disk
data storage. Currently data access times are extremely slow for magnetic disks when
compared to the speed of execution of CPUs so that any improvement in data access
speeds will greatly increase the capabilities of computers, especially with large data and
multimedia files. Holographic memory is a technology that uses a three dimensional
medium to store data and it can access such data a page at a time instead of
sequentially, which leads to increases in storage density and access speed.
Holographic data storage systems are very close to becoming economically feasible.
Obstacles that limit holographic memory are hologram decay over time and with
repeated accesses, slow recording rates, and data transfer rates that need to be
increased. Photorefractive crystals and photopolymers have been used successfully in
experimental holographic data storage systems. Such systems exploit the optical
properties of these photosensitive materials along with the behavior of laser light when it
is used to record an image of an object. Holographic memory lies between main
memory and magnetic disk in regards to data access times, data transfer rates, and
data storage density.



INTRODUCTION
This paper describes holographic data storage as a viable alternative to magnetic disk data
storage. Currently data access times are extremely slow for magnetic disks when compared to
the speed of execution of CPUs so that any improvement in data access speeds will greatly
increase the capabilities of computers, especially with large data and multimedia files.
Holographic memory is a technology that uses a three dimensional medium to store data and it
can access such data a page at a time instead of sequentially, which leads to increases in
storage density and access speed. Holographic data storage systems are very close to
becoming economically feasible. Obstacles that limit holographic memory are hologram decay
over time and with repeated accesses, slow recording rates, and data transfer rates that need
to be increased. Photorefractive crystals and photopolymers have been used successfully in
experimental holographic data storage systems. Such systems exploit the optical properties of
these photosensitive materials along with the behavior of laser light when it is used to record
an image of an object. Holographic memory lies between main memory and magnetic disk in
regards to data access times, data transfer rates, and data storage density.
As processors and buses roughly double their data capacity every three years (Moore’s Law),
data storage has struggled to close the gap. CPUs can perform an instruction execution every
nanosecond, which is six orders of magnitude faster than a single magnetic disk access. Much
research has gone into finding hardware and software solutions to closing the time gap
between CPUs and data storage. Some of these advances include cache, pipelining,
optimizing compilers, and RAM.
As the computer evolves, so do the applications that computers are used for. Recently large
binary files containing sound or image data have become commonplace, greatly increasing the
need for high capacity data storage and data access. A new high capacity form of data storage
must be developed to handle these large files quickly and efficiently.
Holographic memory is a promising technology for data storage because it is a true three
dimensional storage system, data can be accessed an entire page at a time instead of
sequentially, and there are very few moving parts so that the limitations of mechanical motion
are minimized. Holographic memory uses a photosensitive material to record interference
patterns of a reference beam and a signal beam of coherent light, where the signal beam is
studymafia.org
reflected off of an object or it contains data in the form of light and dark areas [1]. The nature of
the photosensitive material is such that the recorded interference pattern can be reproduced
by applying a beam of light to the material that is identical to the reference beam. The resulting
light that is transmitted through the medium will take on the recorded interference pattern and
will be collected on a laser detector array that encompasses the entire surface of the
holographic medium. Many holograms can be recorded in the same space by changing the
angle or the wavelength of the incident light. An entire page of data is accessed in this way.
The three features of holographic memory that make it an attractive candidate to replace
magnetic storage devices are redundancy of stored data, parallelism, and multiplexing . Stored
data is redundant because of the nature of the interference pattern between the reference and
signal beams that is imprinted into the holographic medium. Since the interference pattern is a
plane wave front, the stored pattern is propagated throughout the entire volume of the
holographic medium, repeating at intervals. The data can be corrupted to a certain level before
information is lost so this is a very safe method of data storage. Also, the effect of lost data is
to lower the signal to noise ratio so that the amount of data that can be safely lost is dependent
on the desired signal to noise ratio. Stored holograms are massively parallel because the data
is recorded as an optical wave front that is retrieved as a single page in one access. Since light
is used to retrieve data and there are no moving parts in the detector array, data access time is
on the order of 10 ms and data transfer rate approaches 1.0 Gbytes/sec [2]. Multiplexing
allows many different patterns to be stored in the same crystal volume simply by changing the
angle at which the reference beam records the hologram.
Currently, holographic memory techniques are very close to becoming technologically and
economically feasible. The major obstacles to implementing holographic data storage are
recording rate, pixel sizes, laser output power, degradation of holograms during access,
temporal decay of holograms, and sensitivity of recording materials [3]. An angle multiplexed
holographic data storage system using a photorefractive crystal for a recording medium can
provide an access speed of 2.4 s, a recording rate of 31 kB/s and a readout rate of 10 GB/s,
which is between the typical values for DRAM and magnetic disk. At an estimated cost of
between $161 and $236 for a complete holographic memory system, this may become a
feasible alternative to magnetic disk in the near future.



HOLOGRAPHIC MEMORY vs. EXISTING MEMORY TECHNOLOGY
In the memory hierarchy, holographic memory lies somewhere between RAM and magnetic
storage in terms of data transfer rates, storage capacity, and data access times. The
theoretical limit of the number of pixels that can be stored using volume holography is V2/3/
2
where V is the volume of the recording medium and  is the wavelength of the reference
beam. For green light, the maximum theoretical storage capacity is 0.4 Gbits/cm2 for a page
size of 1 cm x 1 cm. Also, holographic memory has an access time near 2.4 s, a recording
rate of 31 kB/s, and a readout rate of 10 GB/s. Modern magnetic disks have data transfer rates
in the neighborhood of 5 to 20 MB/s [8]. Typical DRAM today has an access time close to 10 –
40 ns, and a recording rate of 10 GB/s.


Holographic memory has an access time somewhere between main memory and magnetic
disk, a data transfer rate that is an order of magnitude better than both main memory and
magnetic disk, and a storage capacity that is higher than both main memory and magnetic
disk. Certainly if the issues of hologram decay and interference are resolved, then holographic
memory could become a part of the memory hierarchy, or take the place of magnetic disk
much as magnetic disk has displaced magnetic tape for most applications.


HOLOGRAPHIC MEMORY
Wide possibilities in this case are provided by technology of optical recording, it's known as
holography: it allows high record density together with maximum data access speed. It's
achieved due to the fact that the holographic image (hologram) is coded in one big data block,
which is recorded at one access. And while reading this block is entirely extracted out of the
memory. For reading and recording of the blocks kept holographically on the light-sensitive
material (LiNbO3 is taken as the basic material) they use lasers. Theoretically, thousands of
such digital pages, which contain up to a million bits each, can be put into a device measuring
a bit of sugar. And theoretically they expect the data density to be 1 TBytes per cubic cm
(TBytes/cm3). In practice, the developers expect around 10 GBytes/cm3, what is rather
impressive when comparing with the current magnetic method that allows around several
MBytes/cm2 - and this without the mechanism itself. With such recording density an optical
layer which is approx 1 cm in width will keep around 1TBytes of data. And considering the fact
that such system doesn't have any moving parts, and pages are accessed parallel, you can
expect the device to be characterized with 1 GBytes/cm3 density and higher.


Exceptional possibilities of the topographic memory have interested many scientists of
universities and industrial research laboratories. This interest long time ago poured into two
research programs. The first of them is PRISM ( Photorefractive Information Storage Material),
which is targeted at searching of appropriate light-sensitive materials for storing holograms and
investigation of their memorizing properties. The second program is HDSS (Holographic Data
Storage System). Like PRISM, it includes fundamental investigations, and the same
companies participate there. While PRISM is aimed at searching the appropriate media for
storing holograms, HDSS is targeted at hardware development necessary for practical
realization of holographic storage systems.
How does a system of holographic memory operate? For this purpose we will consider a
device assembled by a task group from the Almaden Research Center.
At the first stage in this device a beam of cyan argon laser is divided into two components - a
reference and an object beam (the latter is a carrier of data). The object beam undergoes
defocusing in order it could entirely illumine the SLM (Spatial Light Modulator) which is an LCD
panel where a data page is displayed in the form of a matrix consisting of light and dark pixels
(binary data).
The both beams go into the light-sensitive crystal where they interact. So we get an
interference pattern which serve a base for a hologram and is recorded as a set of variations of
the refractive exponent and the reflection factor inside this crystal. When reading data the
crystal is illuminated with a reference beam, which interacts with the interference factor and
reproduces the recorded page in the image of "chess-board" of light and dark pixels (the
holograms converts the reference wave into the copy of the object one). After that, this image
is transferred into the matrix detector where the CCD (Charge-Coupled Device) serves a base.
While reading the data the reference beam must fall at the same angle at which the recording
was made; alteration of this angle mustn't exceed 1 degree. It allows obtaining high data
density: measuring the angle of the reference beam or its frequency you can record additional
pages of data in the same crystal.
However, additional holograms change properties of the material, and such changes mustn't
exceed the definite number. As a result, the images of holograms become dim, what can lead to data corruption when reading? This explains the limitation of the volume of the real memory
that belongs to this material. The dynamic area of the medium is defined by the number of
pages which can be virtually housed, that's why PRISM participants are investigating
limitations to the light sensitivity of substances.
The procedure in 3-dimensional holography which concludes in enclosure of several pages
with data into the same volume is called multiplexing. Traditionally the following multiplexing
methods are used: of angle of dip of the reference beam, of wavelength and phase; but
unfortunately they require complicated optical systems and thick (several mm) carriers what
makes them unfit for commercial use, at least in the sphere of data processing. But lately Bell
Labs have invented three new multiplexing methods: shift, aperture and correlative, which are
based on the usage of change in position of the carrier relative to the beams of light. The shift
and aperture multiplexing use a spherical reference beam, and the correlative uses a beam of
more complicated form. Besides, considering the fact that the correlative and shift multiplexing
enable mechanical moving elements, the access time will be the same as that of the usual
optical discs. Bell Labs managed to build an experimental carrier on the same LiNBO3 using
the technology of correlative multiplexing but this time with 226 GBytes per square inch.
Another problem standing on the way of development of holographic memory devices is a
search of the appropriate material. The most of the investigations in the sphere of holography
were carried out with usage of photoreactive materials (mainly the mentioned LiNBO3), but
they are not suitable for data recording especially for commercial use: they are expensive,
weak sensitive and have a limited dynamic range (frequency bandwidth). That's why they
developed a new class of photopolymer materials facing a good perspective in terms of
commercial use. Photopolymers are the substances where the light cause irreversible changes
expressed through fluctuation of the composition and density. The created material have a
longer life circle (in terms of storing data) and are resistant to temperature change, besides,
they have improved optical characteristics and are suitable for WORM (write-once/read many).
Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page
Tagged Pages: explain recording rate for holographic memory,

[-]
Quick Reply
Message
Type your reply to this message here.

Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Possibly Related Threads...
Thread Author Replies Views Last Post
  Paper based Memory cells ppt download computer science crazy 0 18 01-09-2016, 04:49 PM
Last Post: computer science crazy
  HOLOGRAPHIC MEMORY dhanabhagya 0 329 27-02-2016, 03:44 PM
Last Post: dhanabhagya
  HOLOGRAPHIC VERSATILE DISC A SEMINAR REPORT Computer Science Clay 20 247,388 20-06-2015, 04:51 PM
Last Post: anand021
  Holographic Versatile Disc presentation Abstract 0 173 04-06-2015, 03:51 PM
Last Post: presentation Abstract
  Bacterio-Rhodopsin Memory presentation Abstract 0 208 04-06-2015, 03:47 PM
Last Post: presentation Abstract
  Breaking the Memory Wall in MonetDB presentation Abstract 0 204 04-06-2015, 03:38 PM
Last Post: presentation Abstract
  Holographic Versatile Disc presentation Abstract 0 180 26-05-2015, 03:46 PM
Last Post: presentation Abstract
  Bacterio-Rhodopsin Memory presentation Abstract 0 309 26-05-2015, 03:31 PM
Last Post: presentation Abstract
  Dynamic Memory Allocation presentation Abstract 0 236 26-05-2015, 03:06 PM
Last Post: presentation Abstract
  Holographic Memory presentation Abstract 0 365 23-05-2015, 04:30 PM
Last Post: presentation Abstract