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10/01/91

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Fifty holograms in a fiber solve data traffic jam

STANFORD -- Anyone who's ever impatiently waited for a personal computer to open a document or spreadsheet is familiar with the bottleneck: It doesn't matter how much information the PC can handle, it still has to store and retrieve it one bit at a time. Even for the fastest computers, getting data in and out of stored memory is as slow as the spin of a disk.

Since the 1970s, computer scientists have envisioned storing that spreadsheet all at once, with laser holography. In a single flash of laser light, the image of a whole page would be stored as a hologram, 100 to 1,000 times faster than now.

Until recently, this idea was hampered by a problem with the large crystals used to store the holograms. When data is retrieved, scattered light mixes up information from more than one page at a time. Now Lambertus Hesselink, a Stanford University professor of electrical engineering and aeronautics/astronautics, has come up with a solution that allows laser optics to store up to 50 holograms in a single crystal rod smaller than a pin. The rod is too small for "crosstalk" between images.

Each hologram contains 100,000 to 1 million bits of data, stored in the rod -- also called an optical fiber -- using two beams of laser light. An object beam is bounced off the image to be recorded -- a spreadsheet, for example -- and then into the fiber. A reference beam crosses the object beam and records the image in the fiber as a pattern of electrons.

Each reference beam is encoded so that, bounced into the fiber again, it retrieves only the pattern for the particular page that it stored.

Thus 50 spreadsheet pages can share the same tiny space, and data can be retrieved from any one at the flash of a laser beam.

In 1988, Hesselink and Steve Redfield of Microelectronics and Computer Technology Corp. in Austin, Texas were the first to record photorefractive holograms in a fiber. They used optical fibers of strontium barium niobate (SBN), known as a good medium for holographic storage. Hesselink and his colleagues at Stanford's Center for Materials Research were the first to grow optical fibers from SBN.

Hesselink and Redfield have patented their optical storage method and are now working on a five-year, $22.5 million grant administered by the National Institute for Standards and Technology to develop the architecture of input/output devices to take advantage of the new technology.

The result of their efforts may be a new sort of cache memory for computers. A few thousand SBN rods, packed together into a plate the size of a personal computer's 5-1/4 inch disk drive, Hesselink said, could hold many gigabytes of cache memory - as much as the large multiple storage disks of a mainframe computer.

High-speed optical data storage would provide the equivalent of having the entire data base in instantly-available random access memory.

Though several groups in the United States and Japan are working to develop the technology, Hesselink said it will probably be five to 10 years before products reach the market. Some of the first applications are likely to be for large data base management systems, such as payrolls, and for image-based systems, such as high-definition television.

Eventually, Hesselink said, optical memory "could revolutionize the design of computers."

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