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What is HVD ?
Holographic Versatile Disc (HVD) is an optical disc technology which
would hold up to 3.9 terabytes (TB) of information .
An HVD is an advanced optical disk that’s presently in the development
stage. Polaroid scientist J van Heerden was the first to come up with
the idea for holographic three-dimensional storage in 1960.
Holographic memory systems have been around for decades. They offer
far more storage capacity than CDs and DVDs -- even "next-generation"
DVDs like Blu-ray -- and their transfer rates leave conventional discs in
the dust.
Basics of Holographic Disk
The first step in understanding holographic
disk is to understand what "holographic"
means. Holography is a method of recording
patterns of light to produce a threedimensional
object.
The recorded patterns of light are called a
hologram.
HVD Structure
Green writing/reading laser (532 nm)
Red positioning/addressing laser (650 nm)
Hologram (data)
Polycarbon layer
Photopolymeric layer (data-containing layer)
Distance layers
Dichotic layer (reflecting green light)
Aluminium reflective layer (reflecting red light)
Working Principle
HVD uses a technology called 'collinear holography,' in
which two laser rays, one is blue-green and another is red,
are collimated into a single beam..
The blue-green laser reads data encoded as laser
interference fringes from a holographic layer near the top
of the disc while the red laser is used as the reference
beam and to read servo information from a regular CDstyle
aluminium layer near the bottom.
Servo information is used to monitor the position of the
read head over the disc, similar to the head, track, and
sector information on a conventional hard disk drive.
HVD Write System
A simplified HVD system consists of the following
main components:
Blue or green laser (532-nm wavelength in the
test system)
Beam splitter/merger
Mirrors
Spatial light modulator (SLM)
CMOS sensor
Polymer recording medium
The process of writing information onto an
HVD begins with encoding the information
into binary data to be stored in the SLM.
These data are turned into ones and zeroes
represented as opaque or translucent areas
on a "page" -- this page is the image that the
information beam is going to pass through
HVD Read System
To read the data from an HVD, you need to
retrieve the light pattern stored in the
hologram.
In the HVD read system, the laser projects a
light beam onto the hologram -- a light beam
-- a light beam that is identical to the
reference beam.
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
crystal, based on the angle at which the reference beam strikes
it.
The key component of any holographic data storage system is
the angle at which the reference beam is fired at the crystal to
retrieve a page of data. It must match the original reference
beam angle exactly. A difference of just a thousandth of a
millimeter will result in failure to retrieve that page of data.
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 CMOS, which interprets
and forwards the digital information to a
computer.