Holographic Memory

HOLOGRAPHIC MEMORY

Mass Storage is generally defined as a means of preserving computer generated information for subsequent use or retrieval.

Computer Storage

Random Access

Serial Access

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What will be the next logical step in computer storage ?

Parallel Access

Parallel Access Is The Ability To Put Information In Any Form, And Take It Out At The Same Rate. In Other Technologies, We Get One Bit Stream At A Time. Higher Bandwidth Is The Result.

Holographic memory is a three-dimensional data storage system that can store information at high density inside the crystal or photopolymer.It is a memory that can store information in the form of holographic image (hologram).Like other media, holographic media is divided into write once (where the storage medium undergoes some irreversible change), and rewritable media (where the change is reversible).

What is Holographic Memory?

Using holograms as memory storage was first proposed by Pieter Heerden in the 1960s. During the early 1970s, a group of scientists from TRCA laboratories succeeded in storing 500 holograms using an iron doped litium niobate crystal. Moreover, they were also able to store five hundred fifty high-resolution hologram images using a material made up of light sensitive polymer. The high cost of the materials needed for this type of technology as well as the rise of magnetic and optical drives shelved the project in the end.

History

Working Principle

In holographic data storage, an entire page of information is stored at once as an optical interference pattern within a thick, photosensitive optical material. This is done by intersecting two coherent laser beams within the storage material. The first, called the object beam, contains the information to be stored; the second, called the reference beam, is a simple light wave. When the two combine in an optical storage medium, they change the chemical or physical construction of that medium and so store the data. If the storage medium is then illuminated with the reference beam again, the object data beam is produced.

Laser

Spatial Light Modulator (SLM)

Multiplexing agent

Storage Medium

Charge Coupled Device (CCD)

HDS Components

Laser

Blue-green argon laser which is split into two beams, a reference beam and an object beam.

The interference pattern created by these two beams forms the hologram.

Spatial Light Modulator

SLM is a 1024 * 1024 array of light or dark squares. This array represents the data to be stored, and is usually implemented by a set of pixels on an LCD.

An SLM can usually 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, shift multiplexing and angular multiplexing

Shift Multiplexing uses a rotating disk to vary the angle of the laser beam, and so access a different view of the hologram.

Angular multiplexing uses mirrors to change the angle at which the laser strikes the crystal.

Storage Medium

Two storage mediums are,

Lithium-niobate crystals

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 so read the information from the hologram.

The matrix construction of the CCD allows it to read all 1Mb of the data at once.

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

Recording data

Reading data

HVD is an advanced optical disk that’s presently in the development stage. It can transfer data at the rate of 1 Gigabit per second. The technology permits over 10 kilobits of data to be written and read in parallel with a single flash. The disk will store 1 terabyte (TB) of data on a single optical disk.

Holographic Versatile Disc

1. Green writing/reading laser (532 nm)2. Red positioning/addressing laser (650 nm)3. Hologram (data)4. Polycarbon layer5. Photopolymeric layer (data-containing layer)6. Distance layers7. Dichroic layer (reflecting green light)8. Aluminium reflective layer (reflecting red light)9. Transparent baseP. PIT

Holographic Versatile Disc structure

  DVD BLU-RAY HVD

Capacity 9.4 GB 50GB 300 GB (max 3.9 TB)

Laser wave length

650 nm 405 nm 407 nm

Disc diameter 120 mm 120 mm 120 mm

Read/write speed

11.08 Mbps 36 Mbps 1 Gbps

Comparison With Other Storage DevicesComparison With Other Storage Devices

Entire page of data can be retrieved quickly and at one time.

Offers storage of 1 TB of data.

It offers high density storage.

Its transfer rate is so high that a person can easily load the required data.

Resistance to damage

ADVANTAGE

Tapestry 300r holographic storage

Developed by InPhase Technologies

Holographic Data Storage disk will be the next technological revolution.

The page access of data that holographic memory creates will provide a window into next generation computing by adding another dimension to stored data.

The large cost of high-tech optical equipment would make small-scale systems implemented with holographic memory impractical.

Conclusion

Francis Sajay K P