Holographic data Storage

Presented By:Zara Mudassir

C.S.E – 4Roll No.: 1000112236

An Overview

Devices that use light to store and read have been the backbone of data storage for almost three decades.

CDs revolutionized data storage in 1980s followed by an improved version of CDs, DVD, around 1997.

CDs and DVDs are the primary storage media for music, software, personal computing and video.

An Overview(contd.)

A CD can hold approximately 783 megabytes of data whereas a double-sided, double-layered DVD can hold up to 15.9GB of data.

Background

Although conventional storage mediums meet today's storage needs, storage technologies have to evolve to keep pace with increasing consumer demands.

Today’s user requires such storage media thatprovides faster data access ,huge storage capacitybut in a small package. To achieve this, scientistsare now working on a new optical storage method called “Holographic Memory”.

Polaroid scientist Pieter J. vanHeerden first proposed the idea of holographic storage in the 1960s.

The Defence Advanced Research Projects Agency (DARPA) and high-tech giants IBM and Lucent's Bell Labs have led the resurgence of holographic memory development.

Introduction

Holographic Data Storage is an advanced data storage concept that stores information in the form of holographic images.

Holographic Data Storage is a volumetric approach of storing data.

An HDSS can store 1-4 TB of data on a sugar-cube sized crystal.

Introduction (contd.)

The technology uses holograms which are created when a light from a single laser beam is split into two beams.

What is Holographic Data Storage?

Uses a reference beam and a data beam to create an interference pattern.

While writing : The intersection of the two beams causes

a change, which is then stored. While reading:

Action of the reference beam and interference pattern is used to recreate the data beam.

Prototypes of HVD:

Components of a HDSS

Blue-green argon laser Beam splitters Mirrors LCD panel Lenses Lithium-niobate crystal or

photopolymer Charge-coupled device(CCD) camera

Laser

• Blue-green argon laser is split into two beams.

• One is known as the object or signal beam, and the other as the reference beam.

• Interference pattern created by these two beams creates hologram.

Spatial Light Modulator(SLM)

• SLM is a 1024 * 1024 array of light or dark squares.

• The array represents the data to be stored, and is usually implemented by a set of pixels on an LCD.

• An SLM can be refreshed at rates of about 1000 frames per second.

Multiplexing Agent

• It is used to allow the laser beam to access different pages in the hologram.

• Two types of multiplexing is used- shift and angular multiplexing.

• Shift multiplexing uses a rotating disc to vary the angle of laser beam so as to access a different view of the hologram, used in reading data.

• Angular multiplexing uses mirrors to change the angle at which the laser strikes the crystal, used in recording data.

Storage Medium

• There are mainly two storage mediums used:• Lithium-niobate crystal, and• Photopolymer.

Charge-Coupled Device (CCD)

• CCD is an array of sensors which corresponds to the pixels on the SLM.

• The CCD is used to read the interference pattern from the reference beam, and also to read the information from the hologram.

• The matrix construction of the CCD allows it to read1Mb data at once.

• Typical CCD dimensions are one square centimeter, and typical access rates are 1000 frames / second, or 1 Gigabit / second.

Working of an HDSS:

When the blue-green argon laser is fired, a beam splitters creates two beams.

The object or signal beam travels straight and bounces off one mirror and travels straight through SLM(Spatial-Light Modulator).

The signal beam passes through a SLM, that stores pages of raw binary data.

The information from the page is carried by the signal beam to light-sensitive lithium-niobate crystal.

the reference beam shoots out the side of beam splitters and takes a separate path to the crystal.

When the two beams meet ,the interference pattern created stores the data in a specific area in the crystal.

HDS contains information using an optical interference pattern within a thick, photosensitive optical material.

Light from a single 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 can be stored on a single volume.

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.

What is a Hologram?

¤ The word Hologram is derived from a Greek word “holos” meaning whole and “gram” meaning message.

¤ A hologram contains the information about size, shape, brightness and contrast of object being recorded.

¤ It is a 3-D image formed by the interference of light beams from a laser or other coherent light source.

Classification of Hologram

Amplitude and phase modulation holograms

Volume holograms Transmission and reflection holograms

Advantages of Holographic Data Storage

Increased storage capacity Increase read/write speed due to

parallel access. Longer storage life Security

Drawbacks of Holographic Data Storage

The challenge is to find the right recording material-a photosensitive substance that is both stable and cheap enough to use commercially.

Problems with parallel recording. Cross-talk noise, as it is known, causes

faint images all of the files recorded to be called up even when only one is being accessed.

Spatial light modulators in a low cost system.

Holographic recording is also very data sensitive. You have to keep the data streaming. It’s not appropriate for partial recordings.

Conclusion

The future of holographic memory is very promising. The holographic storage provide high data density. It can easily store 1000GB of data in a small cubic centimeter crystal reducing the cost on the other hand. It may offer high data transfer rate.

But even then the holographic way of storing data is still at the base stage and it may take another couple of years for this technique to hit desktop with a real life data storage solution.

However this technology itself is dazzling and aims to light up the desktop experienences.