Holographic storage, once a pipe dream, will be headed to the open market soon. A company called hVault has plans to turn the high-tech concept into reality this year. Holographic storage systems will initially target those that have lots of data to store. Those that need to store analog video information will most likely be among the first. This will be the entertainment industry and its backlog of old movies, the military that has an abundance of satellite images needing to be saved, and the health care industry with millions of diagnostic images. This will be especially true for those who access that data routinely and need it quickly.
In most cases, holographic storage is a write once, read many times (WORM) data archival technique. Unlike other types of storage, holographic storage uses a photosensitive medium similar in concept to film to store three dimensional (3D) images that represent data. Analog film appears to have a shelf life of nearly 100 years and should not be too different from holographic storage. Magnetic storage, like tape and hard disks, are said to last maybe 2 to 3 years and therefore need reduplication for continued storage. The other problem with tape is that it is serial access, so it can take a while to find and transfer information from tape storage. I was surprised to learn that even CDs and DVDs are expected to last only 3 to 5 years (according to the National Archives).
Currently, hVault claims that its system’s shelf life is at least 50 years and with 1/100th the power needs of disc arrays. It also has fewer environmental requirements since the media is impervious to magnetic fields, dust and dirt, heat and cold, static electricity, humidity, and water. Finally, due to the way data is stored (in holograms), tampering and data thievery become less of a threat than in 2D systems. All this means that total cost of ownership (TCO) is 100 times less than conventional magnetic or optical long-term storage systems.
Tape and hard drives are magnetic media. Optical discs bounce lasers off little pits burned into the DVD or CD and are mostly surface storage—limiting the total space that is available for storage. Holographic storage, on the other hand, uses a photosensitive medium—again, much like photographic film—to store 3D images or holograms that represent data at different depths into the crystal or photopolymer storage media.
Storing data via holograms has been around for a while, although just in the laboratory. When first attempted in the 1960s, the argon gas laser that was used was 6 feet long. Liquid crystal displays (LCDs) were not in production until ~1968, and the charge-coupled device (CCD) camera or the image capture ability and small size was not around until just over a decade ago.
Now, the component parts are getting to be commodities, making miniaturization of a holographic data storage system (HDSS) possible and available. Also, during that time semiconductors continued to get cheaper, and with the advancement of magnetic storage it helped to keep holography in the lab. It was not until recently that the component parts became cost-effective and readily available, which are most likely the main reasons for its resurgence.
How Does it Work?
To generate a hologram, a beam of coherent, monochromatic light (laser) is split into two beams. One part, called the signal beam, is directed onto an object and reflected onto a high-resolution photographic plate. The other part, the reference beam, is shined directly onto the photographic plate. It is the interference pattern of the two light beams that is recorded on the plate as a hologram. When the developed plate or holographic image is illuminated from behind in the exact same angle and direction as the original reference beam, it projects a 3D image of the original object in space. By shifting your perspective to different angles, you will see other sides of the 3D image.
It is much the same case in an HDSS. To record or write to the HDSS, a coherent beam, such as a blue-green argon laser, is first split into the two beams that are needed—the signal beam and the reference beam (figure 1). The signal beam passes through the spatial light modulator (SLM), which is an LCD picking up the ones and zeros as encoded on the liquid crystals by blocking or allowing light to pass through. The signal beam is then directed onto the photosensitive polymer or lithium niobate crystal along with the reference beam, and the resulting interference pattern is recorded. This physically changes the medium, and the data hologram is quite happily stored there for conservatively 50 years, probably longer.
To retrieve or read the data, the reference beam is aimed at the storage medium at exactly the same angle and intensity to reproduce the hologram. A CCD is mounted behind the storage medium and takes a picture capturing the data. Therefore, transfer rates are very high—a million bits in parallel, and all at once! hVault says it will soon be at 1GB transfer rates.
Holographic storage is expected to be able to store a substantial amount of data—four gigabits per cubic millimeter of the storage medium. Depending on the thickness and quality of the storage medium, and the capability of the laser, thousands of individual holograms can be stored, stacked on top of one another. It is all dependent on the angle and wavelength of the reference beam. hVault advertises that it can replace petabyte (PB) storage clusters and can access any data in the system in less than 10 seconds. Four gigabits per cubic millimeter equates to around 2.5 terabits per square inch—more than twice denser than Seagate’s heat-assisted magnetic recording—or HAMR—hard drive technology.
Today’s total storage media is made up of tape (~44%), hard disc drives (~39%), optical discs (~17%), and solid state (~0.2%, mostly in digital cameras). In the “2011 Digital Storage for Media and Entertainment Report,” published by Coughlin Associates, Atascadero, Calif, analysts predicted that between 2011 and 2016 the media and entertainment industry will see about a 5.6x growth in storage capacity shipments per year—from 11,248 PBs to a mind-boggling 62,736 PB of extra needed space! I think we will see the need for holographic storage ride along with this growth wave, leading to cheaper HDSS for all of us. After all, I have some nice spreadsheets that should be stored for 100 years—don’t you?
Jeff Kabachinski, MS-T, BS-ETE, MCNE, has more than 20 years of experience as an organizational development and training professional. He is the director of technical development for Aramark Healthcare Technologies in Charlotte, NC. For more information, contact .