Tech Primer

Holographic Versatile Disk (HVD)

What is a Holographic Versatile Disk?

An HVD is an advanced optical disk that’s presently in the development stage. Polaroid scientist J van Heerden was the first to come up with the idea for holographic three-dimensional storage in 1960. An HVD would be a successor to today’s Blu-ray and HD-DVD technologies. 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.

What’s the technology used in an HVD?

The technology behind these disks is called collinear holography wherein two lasers, one red and the other blue or green, are used. The red laser reads servo information from normal or regular CDs. The servo information is used to monitor the position of the read head over the disk. The blue or green laser reads data encoded as laser interference fringes from the holographic layer. A Dichroic Mirror layer between holographic data and servo data reflects the blue or green laser while allowing the red laser to pass through.

More than a dozen companies including Konica Minolta and Fuji Photo Film have come together to form the HVD alliance to provide a forum for testing and technical discussions, and to design and manufacture HVDs.

Are there any problems with conventional holographic memories?

Some of the problems of conventional holographic memories are:

• There is no precise standard for holographic recording media
• Lack of interchangeability between holographic recording devices and recording media
• Holographic recording media requires flatness of the order of the optical wavelength which makes it hard to mass-produce
• Production of holographic media requires investment in new equipment.

What’s the concept behind collinear holographic memories?

The concepts of collinear holographic memories are:

• To increase the recording capacity, thick volume-recording media is used
• A batch of two-dimensional page data is recorded and reconstructed as a hologram to improve transfer rates
• The optical disk is pre-formatted with addresses and optical servo information
• The beam for the optical servo is utilised to provide backward compatibility with the existing CDs or DVDs.

What are the components needed to construct an HVD reader?

A blue-green argon laser, beam splitters to spilt the laser beams, mirrors to direct the laser beams, LCD panels (spatial light modulator), lenses to focus the laser beams, lithium-niobate crystals or photopolymers, and charge-coupled device (CCD) cameras.

For more information see
www.optware.co.jp/english/what_040823.htm

—Garima Grover
grover_garima@hotmail.com