holographic storage

holographic storage

An optical technology that records data as digital holograms. DVD-sized holographic discs that hold terabytes of data are expected to become a consumer medium in the 2014-2015 time frame. Although research in this area dates back to the 1960s, the first commercial product was InPhase's Tapestry drive in 2010 (see Tapestry). Holographic discs may look like DVD or Blu-ray discs, but the technology is dramatically different.

Two Lasers Write the Hologram
The first laser (data laser) is beamed through a matrix of LCD shutters, called a "spatial light modulator," into an optical region. The shutters are opened and closed based on the binary pattern of the matrix of data being stored. For example, using a matrix of 1,200 bits on each side, the "data page" would hold one 1.44 megabits.

The second laser (reference laser) is angled into and intersects the data laser at the optical site. If the angle or frequency of the reference laser is changed, another hologram can be written into that same area, overlapping and filling the same three-dimensional volume as the first hologram. In fact, as hard as it is to imagine, each bit occupies the full volume of the material.

Theoretically, thousands of holographic data pages can be written into the same optical space; however, the first commercial drive writes 330 overlapping holograms.

One Laser Reads the Hologram
The page is read by directing just the reference laser back into the hologram. The light is diffracted into a copy of the binary data that is sensed by a matrix of CCD sensors. See micro-holographic, PRISM, HVD and optical disc.

The Spatial Light Modulator

In this example, cylinders are used as the optical region. LCD shutters open and close to create a binary pattern of typically a million bits. The data laser is beamed through the modulator and intersects with the reference beam, creating a unique interference pattern.

Create an Interference Pattern

The combination of data and reference lasers create the unique interference pattern, which is the hologram stored in the optical material. To read back the binary pattern, only the reference laser is used to output the data.

An Early Prototype

In this holographic storage prototype from IBM's Almaden labs, the green laser beams are directed through lenses to the optical storage unit. The bottom magnification of the storage area shows the intersection where the hologram is created. The red arrow is the reference laser; the blue is the data laser. (Images courtesy of IBM Almaden Research Center.)

---

holographic storage [¦häl·ə‚graf·ik ′stȯr·ij]

(communications)

A form of data storage in which bits of information are distributed throughout the storage volume and recorded interferometrically, rather than being stored at discrete locations in the medium.