Peptide packs in holographic data.

Holography can do more than make pretty pictures. It can cram thousands of pages of information into a tiny volume of light-sensitive material, a storage density that far surpasses the capacity of traditional computer drives and CD-ROMs.

Now, researchers have improved one such material so that it records holographic data encoded in light-interference patterns in less than 1 second. This is 350 times the recording speed of earlier versions of the material.

Rolf H. Berg, Soren Hvilsted, and P.S. Ramanujam of the Riso National Laboratory in Roskilde, Denmark, first designed such compounds 3 years ago. They consist of short protein molecules, or peptides, with azobenzene dye molecules attached.

The original azobenzene peptides appeared promising, but "one of the major drawbacks was the response time," says Bernard Kippelen of the University of Arizona's Optical Sciences Center in Tucson. It took several minutes for films of the peptides to record a hologram--too slow for practical applications.

A new version of the peptide synthesized by Palle H. Rasmussen of Riso and the original group has azobenzene attached to the amino acid proline. That amino acid gives the peptide a more rigid polymer backbone, which allows the dye molecules to react to light in a more coordinated way, says Berg. This improves the speed at which the material records and reads out information.

The team reported its findings May 11 in the online version of the JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Films of a two-unit peptide made up of copies of the dye azobenzene (orange) attached to proline amino acids (blue) can be used as a medium for storing data holographically.

Conventional magnetic disks store data in bits on the surface. In holograms, however, blocks of information are distributed throughout the material's volume (SN: 8/20/94, p. 127).

Because a page of data is recorded like a single snapshot, it can be read all at once. "This gives an extremely fast data rate--as much as 1 gigabit per second," says Glenn T. Sincerbox, director of Arizona's Optical Data Storage Center. In contrast, information on a magnetic disk is retrieved bit by bit by spinning the disk. "The only ways to get higher data rates are to spin it faster or put the bits closer together," he explains.

Although azobenzene peptides are among several promising potential holographic materials, many issues must be resolved before they can become practical for data storage. The film would have to be at least 1 millimeter thick to store the desired amount of data. So far, the researchers have tested only 13-micrometer-thick films. The Riso group's peptide can store 25 megabits of data in 1 square millimeter.

Also, the team used a green laser to record data and a red beam to retrieve them because the color difference protects information from corruption during readout. A practical, compact device would have to operate with a single wavelength of light. Kippelen says that his group is studying other types of light-sensitive polymers to find ways to accomplish this. "Some of these concepts could be extended to peptidelike materials," he notes.

Holographic storage will have to progress quickly to compete with existing technologies. "Traditional magnetic storage is advancing so fast that the window for holography is shrinking," says Kippelen. However, Sincerbox says that holographic storage applications might make their debut within a year.