Holographic data storage

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Holographic data storage is a potential technology in the area of high-capacity data storage. While 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 records information throughout the volume of the medium and is capable of recording multiple images in the same area utilizing light at different angles.

Additionally, whereas magnetic and optical data storage records information a bit at a time in a linear fashion, 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.[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, or more, 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.

Reading data

The stored data is read through the reproduction of the same reference beam used to create 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.[2]

Longevity

Holographic data storage can provide companies a method to preserve and archive information. The write-once, read many (

CD – have largely lived up to the original longevity claims (where reputable media makes are used) and have proved to be more reliable shorter-term data carriers than the floppy disk and DAT media they displaced.[2]

Terms used

Sensitivity refers to the extent of

modulation produced per unit of exposure. Diffraction efficiency is proportional to the square of the index modulation
times the effective thickness.

The dynamic range determines how many holograms may be multiplexed in a single volume data.

Spatial light modulators (SLM) are pixelated input devices (liquid crystal panels), used to imprint the data to be stored on the object beam.

Technical aspects

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). Rewritable holographic storage can be achieved via the photorefractive effect in crystals:

When the information is to be retrieved or read out from the

hologram, only the reference beam is necessary. The beam is sent into the material in exactly the same way as when the hologram was written. As a result of the index changes in the material that were created during writing, the beam splits into two parts. One of these parts recreates the signal beam where the information is stored. Something like a CCD
camera can be used to convert this information into a more usable form.

Holograms can theoretically store one

nm
could store 30 gigabytes per cubic millimeter. In practice, the data density would be much lower, for at least four reasons:

  • The need to add
    error-correction
  • The need to accommodate imperfections or limitations in the optical system
  • Economic payoff (higher densities may cost disproportionately more to achieve)
  • Design technique limitations—a problem currently faced in magnetic Hard Drives wherein magnetic domain configuration prevents manufacture of disks that fully utilize the theoretical limits of the technology.

Despite those limitations, it is possible to optimize the storage capacity using all-optical signal processing techniques.[3]

Unlike current storage technologies that record and read one data bit at a time, holographic memory writes and reads data in parallel in a single flash of light.[4]

Two-color recording

Set up for holographic recording

For two-color holographic recording, the reference and signal beam fixed to a particular

illumination with the reference beam alone. Hence the readout beam with a longer wavelength would not be able to excite the recombined electrons
from the deep trap centers during readout, as they need the sensitizing light with shorter wavelength to erase them.

Usually, for two-color holographic recording, two different

conduction band
and then to recombine at the shallow traps nearer to the conduction band. The reference and signal beam would then be used to excite the electrons from the shallow traps back to the deep traps. The information would hence be stored in the deep traps. Reading would be done with the reference beam since the electrons can no longer be excited out of the deep traps by the long wavelength beam.

Effect of annealing

For a doubly doped lithium niobate (

annealing
conditions for the crystal samples. This optimum state generally occurs when 95–98% of the deep traps are filled. In a strongly oxidized sample holograms cannot be easily recorded and the diffraction efficiency is very low. This is because the shallow trap is completely empty and the deep trap is also almost devoid of electrons. In a highly reduced sample on the other hand, the deep traps are completely filled and the shallow traps are also partially filled. This results in very good sensitivity (fast recording) and high diffraction efficiency due to the availability of electrons in the shallow traps. However, during readout, all the deep traps get filled quickly and the resulting holograms reside in the shallow traps where they are totally erased by further readout. Hence after extensive readout the diffraction efficiency drops to zero and the hologram stored cannot be fixed.

Development and marketing

Developed from the pioneering work on holography in photorefractive media and holographic data storage of Gerard A. Alphonse, InPhase conducted public demonstrations of a prototype commercial storage device, at the National Association of Broadcasters 2005 (NAB) convention in Las Vegas, at the Maxell Corporation of America booth.

The three main companies involved in developing holographic memory, as of 2002, were InPhase and Polaroid spinoff Aprilis in the United States, and Optware in Japan.[5] Although holographic memory has been discussed since the 1960s,[6] and has been touted for near-term commercial application at least since 2001,[7] it has yet to convince critics that it can find a viable market.[8] As of 2002, planned holographic products did not aim to compete head to head with hard drives, but instead to find a market niche based on virtues such as speed of access.[5]

InPhase Technologies, after several announcements and subsequent delays in 2006 and 2007, announced that it would soon be introducing a flagship product. InPhase went out of business in February 2010 and had its assets seized by the state of Colorado for back taxes. The company had reportedly gone through $100 million but the lead investor was unable to raise more capital.[9][10] The assets and know-how of InPhase has been acquired by Apple who is thought to plan using it for augmented reality.[11]

During

Blu-ray
's 100 GB. It has been announced that hologram disks will be a post-Blu-ray storage device.

In April 2009,

Blu-ray Disc players.[12]

Video game market

Nintendo filed a Joint Research Agreement with InPhase for holographic storage in 2008.[13]

Nintendo is also mentioned in the patent as a joint applicant: "... disclosure is herein made that the claimed invention was made pursuant to a Joint Research Agreement as defined in 35 U.S.C. 103 (c)(3), that was in effect on or before the date the claimed invention was made, and as a result of activities undertaken within the scope of the Joint Research Agreement, by or on the behalf of Nintendo Co., and InPhase Technologies, Inc.".[14]

In fiction

In Star Wars, the Jedi use holocrons and holographic crystals to store data about their history.

In 2010: The Year We Make Contact, a tapeworm had to be employed to erase HAL's holographic memory as "chronological erasures would not work".

In

Robot and Frank
, Robot has a holographic memory which can be half erased but, will be in half the resolution.

See also

References

  1. ^ Ashley, J.; Bernal, M.-P; Burr, G. W.; Coufal, H.; Guenther, H.; Hoffnagle, J. A.; Jefferson, C. M.; Marcus, B.; MacFarlane, R. M.; Shelby, R. M.; Sincerbox, G. T. (May 2000). "Holographic Data Storage Technology". IBM Journal of Research and Development. 44 (3): 341–368.
    doi:10.1147/rd.443.0341. Archived from the original
    on 2000-08-17. Retrieved 2015-01-07.
  2. ^
    S2CID 41111380
    .
  3. ^ N. C. Pégard and J. W. Fleischer, "Optimizing holographic data storage using a fractional Fourier transform", Opt. Lett. 36, 2551–2553 (2011) [1]
  4. ^ "Maxell USA". 28 September 2007. Archived from the original on 28 September 2007. Retrieved 8 April 2018.
  5. ^ a b "Update: Aprilis Unveils Holographic Disk Media". 2002-10-08. Archived from the original on 2010-12-20. Retrieved 2007-11-05.
  6. ^ "Holographic-memory discs may put DVDs to shame". New Scientist. 2005-11-24. Archived from the original on 2005-12-03.
  7. ^ "Aprilis to Showcase Holographic Data Technology". 2001-09-18. Archived from the original on 2012-02-14. Retrieved 2007-11-05.
  8. ^ Sander Olson (2002-12-09). "Holographic storage isn't dead yet". Archived from the original on 2013-09-28. Retrieved 2013-09-24.
  9. ^ “InPhase delays Tapestry holographic storage solution to late 2009”. Engadget. November 3, 2008
  10. ^ “Holographic Storage Firm InPhase Technologies Shuts Down”. Television Broadcast. February 8, 2010
  11. ^ "Apple sees the (augmented) light, buys holo-glass tech startup". The Register. Retrieved August 30, 2018.
  12. ^ GE Unveils 500-GB, Holographic Disc Storage Technology Archived 2009-04-30 at the Wayback Machine. CRN. April 27, 2009
  13. ^ "Could Holography Cure Nintendo's Storage Space Blues? News". July 30, 2008.
  14. ^ Inphase Technologies, Inc. (Longmont, Colorado, US) and Nintendo Co., Ltd. (Kyoto, Japan) (2008-02-26). "Miniature Flexure Based Scanners For Angle Multiplexing Patent".{{cite web}}: CS1 maint: multiple names: authors list (link)
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